Bio

Clinical Focus


  • Pediatric Infectious Disease
  • Infectious Diseases, Pediatric

Academic Appointments


Professional Education


  • Fellowship:Stanford University School of Medicine (2004) CA
  • Residency:Stanford University School of Medicine (1999) CA
  • Internship:Stanford University School of Medicine (1998) CA
  • Board Certification: Pediatric Infectious Disease, American Board of Pediatrics (2005)
  • Medical Education:Stanford University School of Medicine (1997) CA

Research & Scholarship

Current Research and Scholarly Interests


My laboratory studies the strategies pathogens utilize to colonize and subvert the epithelial barrier. We have focused on the epithelial junctions as a target for bacterial pathogens, since the cell-cell junctions serve as both a barrier to infection and also a major control site for epithelial function. In particular, we are interested in how the gastric pathogen Helicobater pylori may cause cancer by interfering with cell signaling at the epithelial junctions. We are also studying how various bacteria cross and invade the epithelium. For example, we recently found that Listeria monocytogenes targets a specialized subset of cell-cell junctions at the tip of the intestinal villi to find its receptor for invasion. We are interested in determining whether this mode of gastrointestinal invasion of the epithelium is also used by other gastrointestinal pathogens.

Teaching

2013-14 Courses


Postdoctoral Advisees


Graduate and Fellowship Programs


Publications

Journal Articles


  • Iron deficiency accelerates Helicobacter pylori-induced carcinogenesis in rodents and humans JOURNAL OF CLINICAL INVESTIGATION Noto, J. M., Gaddy, J. A., Lee, J. Y., Piazuelo, M. B., Friedman, D. B., Colvin, D. C., Romero-Gallo, J., Suarez, G., Loh, J., Slaughter, J. C., Tan, S., Morgan, D. R., Wilson, K. T., Bravo, L. E., Correa, P., Cover, T. L., Amieva, M. R., Peek, R. M. 2013; 123 (1): 479-492

    Abstract

    Gastric adenocarcinoma is strongly associated with Helicobacter pylori infection; however, most infected persons never develop this malignancy. H. pylori strains harboring the cag pathogenicity island (cag+), which encodes CagA and a type IV secretion system (T4SS), induce more severe disease outcomes. H. pylori infection is also associated with iron deficiency, which similarly augments gastric cancer risk. To define the influence of iron deficiency on microbial virulence in gastric carcinogenesis, Mongolian gerbils were maintained on iron-depleted diets and infected with an oncogenic H. pylori cag+ strain. Iron depletion accelerated the development of H. pylori-induced premalignant and malignant lesions in a cagA-dependent manner. H. pylori strains harvested from iron-depleted gerbils or grown under iron-limiting conditions exhibited enhanced virulence and induction of inflammatory factors. Further, in a human population at high risk for gastric cancer, H. pylori strains isolated from patients with the lowest ferritin levels induced more robust proinflammatory responses compared with strains isolated from patients with the highest ferritin levels, irrespective of histologic status. These data demonstrate that iron deficiency enhances H. pylori virulence and represents a measurable biomarker to identify populations of infected persons at high risk for gastric cancer.

    View details for DOI 10.1172/JCI64373

    View details for Web of Science ID 000313598500049

    View details for PubMedID 23257361

  • ChePep Controls Helicobacter pylori Infection of the Gastric Glands and Chemotaxis in the Epsilonproteobacteria MBIO Howitt, M. R., Lee, J. Y., Lertsethtakarn, P., Vogelmann, R., Joubert, L., Ottemann, K. M., Amieva, M. R. 2011; 2 (4)

    Abstract

    Microbes use directed motility to colonize harsh and dynamic environments. We discovered that Helicobacter pylori strains establish bacterial colonies deep in the gastric glands and identified a novel protein, ChePep, necessary to colonize this niche. ChePep is preferentially localized to the flagellar pole. Although mutants lacking ChePep have normal flagellar ultrastructure and are motile, they have a slight defect in swarming ability. By tracking the movement of single bacteria, we found that ?ChePep mutants cannot control the rotation of their flagella and swim with abnormally frequent reversals. These mutants even sustain bursts of movement backwards with the flagella pulling the bacteria. Genetic analysis of the chemotaxis signaling pathway shows that ChePep regulates flagellar rotation through the chemotaxis system. By examining H. pylori within a microscopic pH gradient, we determined that ChePep is critical for regulating chemotactic behavior. The chePep gene is unique to the Epsilonproteobacteria but is found throughout this diverse group. We expressed ChePep from other members of the Epsilonproteobacteria, including the zoonotic pathogen Campylobacter jejuni and the deep sea hydrothermal vent inhabitant Caminibacter mediatlanticus, in H. pylori and found that ChePep is functionally conserved across this class. ChePep represents a new family of chemotaxis regulators unique to the Epsilonproteobacteria and illustrates the different strategies that microbes have evolved to control motility.Helicobacter pylori strains infect half of all humans worldwide and contribute to the development of peptic ulcers and gastric cancer. H. pylori cannot survive within the acidic lumen of the stomach and uses flagella to actively swim to and colonize the protective mucus and epithelium. The chemotaxis system allows H. pylori to navigate by regulating the rotation of its flagella. We identified a new protein, ChePep, which controls chemotaxis in H. pylori. ChePep mutants fail to colonize the gastric glands of mice and are completely outcompeted by normal H. pylori. Genes encoding ChePep are found only in the class Epsilonproteobacteria, which includes the human pathogen Campylobacter jejuni and environmental microbes like the deep-sea hydrothermal vent colonizer Caminibacter mediatlanticus, and we show that ChePep function is conserved in this class. Our study identifies a new colonization factor in H. pylori and also provides insight into the control and evolution of bacterial chemotaxis.

    View details for DOI 10.1128/mBio.00098-11

    View details for Web of Science ID 000296844000004

    View details for PubMedID 21791582

  • Helicobacter pylori Perturbs Iron Trafficking in the Epithelium to Grow on the Cell Surface PLOS PATHOGENS Tan, S., Noto, J. M., Romero-Gallo, J., Peek, R. M., Amieva, M. R. 2011; 7 (5)

    Abstract

    Helicobacter pylori (Hp) injects the CagA effector protein into host epithelial cells and induces growth factor-like signaling, perturbs cell-cell junctions, and alters host cell polarity. This enables Hp to grow as microcolonies adhered to the host cell surface even in conditions that do not support growth of free-swimming bacteria. We hypothesized that CagA alters host cell physiology to allow Hp to obtain specific nutrients from or across the epithelial barrier. Using a polarized epithelium model system, we find that isogenic ?cagA mutants are defective in cell surface microcolony formation, but exogenous addition of iron to the apical medium partially rescues this defect, suggesting that one of CagA's effects on host cells is to facilitate iron acquisition from the host. Hp adhered to the apical epithelial surface increase basolateral uptake of transferrin and induce its transcytosis in a CagA-dependent manner. Both CagA and VacA contribute to the perturbation of transferrin recycling, since VacA is involved in apical mislocalization of the transferrin receptor to sites of bacterial attachment. To determine if the transferrin recycling pathway is involved in Hp colonization of the cell surface, we silenced transferrin receptor expression during infection. This resulted in a reduced ability of Hp to colonize the polarized epithelium. To test whether CagA is important in promoting iron acquisition in vivo, we compared colonization of Hp in iron-replete vs. iron-deficient Mongolian gerbils. While wild type Hp and ?cagA mutants colonized iron-replete gerbils at similar levels, ?cagA mutants are markedly impaired in colonizing iron-deficient gerbils. Our study indicates that CagA and VacA act in concert to usurp the polarized process of host cell iron uptake, allowing Hp to use the cell surface as a replicative niche.

    View details for DOI 10.1371/journal.ppat.1002050

    View details for Web of Science ID 000291014000034

    View details for PubMedID 21589900

  • Listeria monocytogenes Internalin B Activates Junctional Endocytosis to Accelerate Intestinal Invasion PLOS PATHOGENS Pentecost, M., Kumaran, J., Ghosh, P., Amieva, M. R. 2010; 6 (5)

    Abstract

    Listeria monocytogenes (Lm) uses InlA to invade the tips of the intestinal villi, a location at which cell extrusion generates a transient defect in epithelial polarity that exposes the receptor for InlA, E-cadherin, on the cell surface. As the dying cell is removed from the epithelium, the surrounding cells reorganize to form a multicellular junction (MCJ) that Lm exploits to find its basolateral receptor and invade. By examining individual infected villi using 3D-confocal imaging, we uncovered a novel role for the second major invasin, InlB, during invasion of the intestine. We infected mice intragastrically with isogenic strains of Lm that express or lack InlB and that have a modified InlA capable of binding murine E-cadherin and found that Lm lacking InlB invade the same number of villi but have decreased numbers of bacteria within each infected villus tip. We studied the mechanism of InlB action at the MCJs of polarized MDCK monolayers and find that InlB does not act as an adhesin, but instead accelerates bacterial internalization after attachment. InlB locally activates its receptor, c-Met, and increases endocytosis of junctional components, including E-cadherin. We show that MCJs are naturally more endocytic than other sites of the apical membrane, that endocytosis and Lm invasion of MCJs depends on functional dynamin, and that c-Met activation by soluble InlB or hepatocyte growth factor (HGF) increases MCJ endocytosis. Also, in vivo, InlB applied through the intestinal lumen increases endocytosis at the villus tips. Our findings demonstrate a two-step mechanism of synergy between Lm's invasins: InlA provides the specificity of Lm adhesion to MCJs at the villus tips and InlB locally activates c-Met to accelerate junctional endocytosis and bacterial invasion of the intestine.

    View details for DOI 10.1371/journal.ppat.1000900

    View details for Web of Science ID 000278759900019

    View details for PubMedID 20485518

  • Helicobacter pylori Usurps Cell Polarity to Turn the Cell Surface into a Replicative Niche PLOS PATHOGENS Tan, S., Tompkins, L. S., Amieva, M. R. 2009; 5 (5)

    Abstract

    Helicobacter pylori (Hp) intimately interacts with the gastric epithelial surface and translocates the virulence factor CagA into host cells in a contact-dependent manner. To study how Hp benefits from interacting with the cell surface, we developed live-cell microscopy methods to follow the fate of individual bacteria on the cell surface and find that Hp is able to replicate and form microcolonies directly over the intercellular junctions. On polarized epithelia, Hp is able to grow directly on the apical cell surface in conditions that do not support the growth of free-swimming bacteria. In contrast, mutants in CagA delivery are defective in colonization of the apical cell surface. Hp perturbs the polarized epithelium in a highly localized manner, since wild-type Hp does not rescue the growth defect of the CagA-deficient mutants upon co-infection. CagA's ability to disrupt host cell polarity is a key factor in enabling colonization of the apical cell surface by Hp, as disruption of the atypical protein kinase C/Par1b polarity pathway leads to rescue of the mutant growth defect during apical infection, and CagA-deficient mutants are able to colonize the polarized epithelium when given access to the basolateral cell surface. Our study establishes the cell surface as a replicative niche and the importance of CagA and its effects on host cell polarity for this purpose.

    View details for DOI 10.1371/journal.ppat.1000407

    View details for Web of Science ID 000267085800051

    View details for PubMedID 19412339

  • Host-bacterial interactions in Helicobacter pylori infection GASTROENTEROLOGY Amieva, M. R., El-Omar, E. M. 2008; 134 (1): 306-323

    Abstract

    Helicobacter pylori are spiral-shaped gram-negative bacteria with polar flagella that live near the surface of the human gastric mucosa. They have evolved intricate mechanisms to avoid the bactericidal acid in the gastric lumen and to survive near, to attach to, and to communicate with the human gastric epithelium and host immune system. This interaction sometimes results in severe gastric pathology. H pylori infection is the strongest known risk factor for the development of gastroduodenal ulcers, with infection being present in 60%-80% of gastric and 95% of duodenal ulcers.(1)H pylori is also the first bacterium to be classified as a definite carcinogen by the World Health Organization's International Agency for Research on Cancer because of its epidemiologic relationship to gastric adenocarcinoma and gastric mucosa-associated lymphoid tissue lymphoma.(2) In the last 25 years, since H pylori was first described and cultured, a complete paradigm shift has occurred in our clinical approach to these gastric diseases, and more than 20,000 scientific publications have appeared on the subject. From the medical point of view, H pylori is a formidable pathogen responsible for much morbidity and mortality worldwide. However, H pylori infection occurs in approximately half of the world population, with disease being an exception rather than the rule. Understanding how this organism interacts with its host is essential for formulating an intelligent strategy for dealing with its most important clinical consequences. This review offers an insight into H pylori host-bacterial interactions.

    View details for DOI 10.1053/j.gastro.2007.11.009

    View details for Web of Science ID 000252066400036

    View details for PubMedID 18166359

  • Listeria monocytogenes invades the epithelial junctions at sites of cell extrusion PLOS PATHOGENS Pentecost, M., Otto, G., Theriot, J. A., Amieva, M. R. 2006; 2 (1): 29-40

    Abstract

    Listeria monocytogenes causes invasive disease by crossing the intestinal epithelial barrier. This process depends on the interaction between the bacterial surface protein Internalin A and the host protein E-cadherin, located below the epithelial tight junctions at the lateral cell-to-cell contacts. We used polarized MDCK cells as a model epithelium to determine how L. monocytogenes breaches the tight junctions to gain access to this basolateral receptor protein. We determined that L. monocytogenes does not actively disrupt the tight junctions, but finds E-cadherin at a morphologically distinct subset of intercellular junctions. We identified these sites as naturally occurring regions where single senescent cells are expelled and detached from the epithelium by extrusion. The surrounding cells reorganize to form a multicellular junction that maintains epithelial continuity. We found that E-cadherin is transiently exposed to the lumenal surface at multicellular junctions during and after cell extrusion, and that L. monocytogenes takes advantage of junctional remodeling to adhere to and subsequently invade the epithelium. In intact epithelial monolayers, an anti-E-cadherin antibody specifically decorates multicellular junctions and blocks L. monocytogenes adhesion. Furthermore, an L. monocytogenes mutant in the Internalin A gene is completely deficient in attachment to the epithelial apical surface and is unable to invade. We hypothesized that L. monocytogenes utilizes analogous extrusion sites for epithelial invasion in vivo. By infecting rabbit ileal loops, we found that the junctions at the cell extrusion zone of villus tips are the specific target for L. monocytogenes adhesion and invasion. Thus, L. monocytogenes exploits the dynamic nature of epithelial renewal and junctional remodeling to breach the intestinal barrier.

    View details for DOI 10.1371/journal.ppat.0020003

    View details for Web of Science ID 000202894100004

    View details for PubMedID 16446782

  • Helicobacter pylori CagA induces a transition from polarized to invasive phenotypes in MDCK cells PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Bagnoli, F., Buti, L., Tompkins, L., Covacci, A., Amieva, M. R. 2005; 102 (45): 16339-16344

    Abstract

    CagA is a bacterial effector protein of Helicobacter pylori that is translocated via a type IV secretion system into gastric epithelial cells. We previously described that H. pylori require CagA to disrupt the organization and assembly of apical junctions in polarized epithelial cells. In this study, we provide evidence that CagA expression is not only sufficient to disrupt the apical junctions but also perturbs epithelial differentiation. CagA-expressing cells lose apicobasal polarity and cell-cell adhesion, extend migratory pseudopodia, and degrade basement membranes, acquiring an invasive phenotype. Expression of the CagA C-terminal domain, which contains the tyrosine phosphorylated EPIYA motifs, induces pseudopodial activity but is not sufficient to induce cell migration. Conversely, the N terminus targets CagA to the cell-cell junctions. Neither domain is sufficient to disrupt cell adhesion or cell polarity, but coexpressed in trans, the N terminus determines the localization of both polypeptides. We show that CagA induces a morphogenetic program in polarized Madin-Darby canine kidney cells resembling an epithelial-to-mesenchymal transition. We propose that altered cell-cell and cell matrix interactions may serve as an early event in H. pylori-induced carcinogenesis.

    View details for Web of Science ID 000233283700039

    View details for PubMedID 16258069

  • Important bacterial gastrointestinal pathogens in children: A pathogenesis perspective PEDIATRIC CLINICS OF NORTH AMERICA Amieva, M. R. 2005; 52 (3): 749-?

    Abstract

    This article focuses on the five most common bacterial enteropathogens of the developed world--Helicobacter pylori, Escherichia coli, Shigella, Salmonella, and Campylobacter--from the perspective of how they cause disease and how they relate to each other. Basic and recurring themes of bacterial pathogenesis, including mechanisms of entry, methods of adherence, sites of cellular injury, role of toxins, and how pathogens acquire particular virulence traits (and antimicrobial resistance), are discussed.

    View details for DOI 10.1016/j.pcl.2005.03.002

    View details for Web of Science ID 000230166000006

    View details for PubMedID 15925661

  • Breaking into the epithelial apical-junctional complex - news from pathogen hackers CURRENT OPINION IN CELL BIOLOGY Vogelmann, R., Amieva, M. R., FALKOW, S., Nelson, W. J. 2004; 16 (1): 86-93

    Abstract

    The epithelial apical-junctional complex is a key regulator of cellular functions. In addition, it is an important target for microbial pathogens that manipulate the cell to survive, proliferate and sometimes persist within a host. Out of a myriad of potential molecular targets, some bacterial and viral pathogens have selected a subset of protein targets at the apical-junctional complex of epithelial cells. Studying how microbes use these targets also teaches us about the inherent physiological properties of host molecules in the context of normal junctional structure and function. Thus, we have learned that three recently uncovered components of the apical-junctional complex of the Ig superfamily--junctional adhesion molecule, Nectin and the coxsackievirus and adenovirus receptor--are important regulators of junction structure and function and represent critical targets of microbial virulence gene products.

    View details for DOI 10.1016/j.ceb.2003.12.002

    View details for Web of Science ID 000188769900013

    View details for PubMedID 15037310

  • Disruption of the epithelial apical-junctional complex by Helicobacter pylori CagA SCIENCE Amieva, M. R., Vogelmann, R., Covacci, A., Tompkins, L. S., NELSON, W. J., FALKOW, S. 2003; 300 (5624): 1430-1434

    Abstract

    Helicobacter pylori translocates the protein CagA into gastric epithelial cells and has been linked to peptic ulcer disease and gastric carcinoma. We show that injected CagA associates with the epithelial tight-junction scaffolding protein ZO-1 and the transmembrane protein junctional adhesion molecule, causing an ectopic assembly of tight-junction components at sites of bacterial attachment, and altering the composition and function of the apical-junctional complex. Long-term CagA delivery to polarized epithelia caused a disruption of the epithelial barrier function and dysplastic alterations in epithelial cell morphology. CagA appears to target H. pylori to host cell intercellular junctions and to disrupt junction-mediated functions.

    View details for Web of Science ID 000183181800045

    View details for PubMedID 12775840

  • Helicobacter pylori enter and survive within multivesicular vacuoles of epithelial cells CELLULAR MICROBIOLOGY Amieva, M. R., Salama, N. R., Tompkins, L. S., FALKOW, S. 2002; 4 (10): 677-690

    Abstract

    Although intracellular Helicobacter pylori have been described in biopsy specimens and in cultured epithelial cells, the fate of these bacteria is unknown. Using differential interference contrast (DIC) video and immunofluorescence microscopy, we document that a proportion of cell-associated H. pylori enter large cytoplasmic vacuoles, where they remain viable and motile and can survive lethal concentrations of extracellular gentamicin. Entry into vacuoles occurs in multiple epithelial cell lines including AGS gastric adenocarcinoma, Caco-2 colon adenocarcinoma and MDCK kidney cell line, and depends on the actin cytoskeleton. Time-lapse microscopy over several hours was used to follow the movement of live H. pylori within vacuoles of a single cell. Pulsed, extracellular gentamicin treatments show that the half-life of intravacuolar bacteria is on the order of 24 h. Viable H. pylori repopulate the extracellular environment in parallel with the disappearance of intravacuolar bacteria, suggesting release from the intravacuolar niche. Using electron microscopy and live fluorescent staining with endosomal dyes, we observe that H. pylori-containing vacuoles are similar in morphology to late endosomal multivesicular bodies. VacA is not required for these events, as isogenic vacA- mutants still enter and survive within the intravacuolar niche. The exploitation of an intravacuolar niche is a new aspect of the biological life cycle of H. pylori that could explain the difficulties in eradicating this infection.

    View details for Web of Science ID 000178480600005

    View details for PubMedID 12366404

  • The intestinal stem cell markers Bmi1 and Lgr5 identify two functionally distinct populations PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Yan, K. S., Chia, L. A., Li, X., Ootani, A., Su, J., Lee, J. Y., Su, N., Luo, Y., Heilshorn, S. C., Amieva, M. R., Sangiorgi, E., Capecchi, M. R., Kuo, C. J. 2012; 109 (2): 466-471

    Abstract

    The small intestine epithelium undergoes rapid and continuous regeneration supported by crypt intestinal stem cells (ISCs). Bmi1 and Lgr5 have been independently identified to mark long-lived multipotent ISCs by lineage tracing in mice; however, the functional distinctions between these two populations remain undefined. Here, we demonstrate that Bmi1 and Lgr5 mark two functionally distinct ISCs in vivo. Lgr5 marks mitotically active ISCs that exhibit exquisite sensitivity to canonical Wnt modulation, contribute robustly to homeostatic regeneration, and are quantitatively ablated by irradiation. In contrast, Bmi1 marks quiescent ISCs that are insensitive to Wnt perturbations, contribute weakly to homeostatic regeneration, and are resistant to high-dose radiation injury. After irradiation, however, the normally quiescent Bmi1(+) ISCs dramatically proliferate to clonally repopulate multiple contiguous crypts and villi. Clonogenic culture of isolated single Bmi1(+) ISCs yields long-lived self-renewing spheroids of intestinal epithelium that produce Lgr5-expressing cells, thereby establishing a lineage relationship between these two populations in vitro. Taken together, these data provide direct evidence that Bmi1 marks quiescent, injury-inducible reserve ISCs that exhibit striking functional distinctions from Lgr5(+) ISCs and support a model whereby distinct ISC populations facilitate homeostatic vs. injury-induced regeneration.

    View details for DOI 10.1073/pnas.1118857109

    View details for Web of Science ID 000298950200030

    View details for PubMedID 22190486

  • Tolerance Rather Than Immunity Protects From Helicobacter pylori-Induced Gastric Preneoplasia GASTROENTEROLOGY Arnold, I. C., Lee, J. Y., Amieva, M. R., Roers, A., Flavell, R. A., Sparwasser, T., Mueller, A. 2011; 140 (1): 199-?

    Abstract

    Chronic infection with the bacterial pathogen Helicobacter pylori causes gastric disorders, ranging from chronic gastritis to gastric adenocarcinoma. Only a subset of infected persons will develop overt disease; most remains asymptomatic despite lifelong colonization. This study aims to elucidate the differential susceptibility to H pylori that is found both across and within populations.We have established a C57BL/6 mouse model of H pylori infection with a strain that is capable of delivering the virulence factor cytotoxin-associated gene A (CagA) into host cells through the activity of a Cag-pathogenicity island-encoded type IV secretion system.Mice infected at 5-6 weeks of age with CagA(+)H pylori rapidly develop gastritis, gastric atrophy, epithelial hyperplasia, and metaplasia in a type IV secretion system-dependent manner. In contrast, mice infected during the neonatal period with the same strain are protected from preneoplastic lesions. Their protection results from the development of H pylori-specific peripheral immunologic tolerance, which requires transforming growth factor-? signaling and is mediated by long-lived, inducible regulatory T cells, and which controls the local CD4(+) T-cell responses that trigger premalignant transformation. Tolerance to H pylori develops in the neonatal period because of a biased ratio of T-regulatory to T-effector cells and is favored by prolonged low-dose exposure to antigen.Using a novel CagA(+)H pylori infection model, we report here that the development of tolerance to H pylori protects from gastric cancer precursor lesions. The age at initial infection may thus account for the differential susceptibility of infected persons to H pylori-associated disease manifestations.

    View details for DOI 10.1053/j.gastro.2010.06.047

    View details for Web of Science ID 000285503200036

    View details for PubMedID 20600031

  • The Complete Genome Sequence of Helicobacter pylori Strain G27 JOURNAL OF BACTERIOLOGY Baltrus, D. A., Amieva, M. R., Covacci, A., Lowe, T. M., Merrell, D. S., Ottemann, K. M., Stein, M., Salama, N. R., Guillemin, K. 2009; 191 (1): 447-448

    Abstract

    Helicobacter pylori is a gram-negative pathogen that colonizes the stomachs of over half the world's population and causes a spectrum of gastric diseases including gastritis, ulcers, and gastric carcinoma. The H. pylori species exhibits unusually high levels of genetic variation between strains. Here we announce the complete genome sequence of H. pylori strain G27, which has been used extensively in H. pylori research.

    View details for DOI 10.1128/JB.01416-08

    View details for Web of Science ID 000261628100047

    View details for PubMedID 18952803

  • The role of bacterial pathogens in cancer CURRENT OPINION IN MICROBIOLOGY Vogelmann, R., Amieva, M. R. 2007; 10 (1): 76-81

    Abstract

    The association of Helicobacter pylori with gastric cancer is the best-studied relationship between a bacterial infection and cancer. Other bacterial pathogens in humans and rodents are now being recognized as potentially having a direct role in carcinogenesis. Thus, it might be possible to understand the pathogenesis and prevention of certain cancers by studying the bacterial infections associated with them, and their effects on the host. However, the mechanisms by which bacteria contribute to cancer formation are complex, and recent investigations show that they involve the interplay between chronic inflammation, direct microbial effects on host cell physiology and, ultimately, changes in tissue stem cell homeostasis.

    View details for DOI 10.1016/j.mib.2006.12.004

    View details for Web of Science ID 000244809900013

    View details for PubMedID 17208515

  • Helicobacter pylori and gastric cancer: What can be learned by studying the response of gastric epithelial cells to the infection? CANCER EPIDEMIOLOGY BIOMARKERS & PREVENTION Mueller, A., FALKOW, S., Amieva, M. R. 2005; 14 (8): 1859-1864

    Abstract

    The development of gastric adenocarcinoma is closely linked to chronic infection with the bacterial pathogen Helicobacter pylori. One Helicobacter-specific virulence factor in particular, the CagA protein, has emerged as a main effector molecule in the interaction of H. pylori with gastric epithelial cells and has been implicated in gastric carcinogenesis. This review highlights the latest insights that have been gained into the pathogenesis of the disease by transcriptional profiling approaches studying gene expression in normal gastric tissue and gastric cancer tissue from human biopsy material as well as animal models of Helicobacter infection. The potential role of CagA as a bacterial oncoprotein is also discussed.

    View details for DOI 10.1158/1055-9965.EPI-04-0820

    View details for Web of Science ID 000231195600004

    View details for PubMedID 16103426

  • Jarisch-Herxheimer reaction associated with ciprofloxacin administration for tick-borne relapsing fever PEDIATRIC INFECTIOUS DISEASE JOURNAL Webster, G., Schiffman, J. D., Dosanjh, A. S., Amieva, M. R., Gans, H. A., Sectish, T. C. 2002; 21 (6): 571-573

    Abstract

    A 14-year-old girl was seen at a community clinic with a chief complaint of abdominal pain and fevers and was treated with oral ciprofloxacin for presumed pyelonephritis. She became tachycardic and hypotensive after her first dose of antibiotic, and she developed disseminated intravascular coagulation. She was admitted to our hospital for presumed sepsis. Her outpatient peripheral blood smear was reviewed, revealing spirochetes consistent with Borrelia sp. To our knowledge this is the first reported case of the Jarisch-Herxheimer reaction to ciprofloxacin.

    View details for DOI 10.1097/01.inf.0000015641.27909.b6

    View details for Web of Science ID 000176194400018

    View details for PubMedID 12182387

  • Imaging of dynamic changes of the actin cytoskeleton in microextensions of live NIH3T3 cells with a GFP fusion of the F-actin binding domain of moesin. BMC cell biology Litman, P., Amieva, M. R., FURTHMAYR, H. 2000; 1: 1-?

    Abstract

    The cell surface undergoes continuous change during cell movement. This is characterized by transient protrusion and partial or complete retraction of microspikes, filopodia, and lamellipodia. This requires a dynamic actin cytoskeleton, moesin, components of Rho-mediated signal pathways, rearrangement of membrane constituents and the formation of focal adhesion sites. While the immunofluorescence distribution of endogenous moesin is that of a membrane-bound molecule with marked enhancement in some but not all microextensions, the C-terminal fragment of moesin co-distributes with filamentous actin consistent with its actin-binding activity. By taking advantage of this property we studied the spontaneous protrusive activity of live NIH3T3 cells, expressing a fusion of GFP and the C-terminal domain of moesin.C-moesin-GFP localized to stress fibers and was enriched in actively protruding cellular regions such as filopodia or lamellipodia. This localization was reversibly affected by cytochalasin D. Multiple types of cytoskeletal rearrangements were observed that occurred independent of each other in adjacent regions of the cell surface. Assembly and disassembly of actin filaments occurred repeatedly within the same space and was correlated with either membrane protrusion and retraction, or no change in shape when microextensions were adherent.Shape alone provided an inadequate criterion for distinguishing between retraction fibers and advancing, retracting or stable filopodia. Fluorescence imaging of C-moesin-GFP, however, paralleled the rapid and dynamic changes of the actin cytoskeleton in microextensions. Regional regulatory control is implicated because opposite changes occurred in close proximity and presumably independent of each other. This new and sensitive tool should be useful for investigating mechanisms of localized actin dynamics in the cell cortex.

    View details for PubMedID 11112983

  • Disruption of dynamic cell surface architecture of NIH3T3 fibroblasts by the N-terminal domains of moesin and ezrin: in vivo imaging with GFP fusion proteins JOURNAL OF CELL SCIENCE Amieva, M. R., Litman, P., Huang, L. Q., Ichimaru, E., Furthmayr, H. 1999; 112 (1): 111-125

    Abstract

    Lamellipodia, filopodia, microspikes and retraction fibers are characteristic features of a dynamic and continuously changing cell surface architecture and moesin, ezrin and radixin are thought to function in these microextensions as reversible links between plasma membrane proteins and actin microfilaments. Full-length and truncated domains of the three proteins were fused to green fluorescent protein (GFP), expressed in NIH3T3 cells, and distribution and behaviour of cells were analysed by using digitally enhanced differential interference contrast (DIC) and fluorescence video microscopy. The amino-terminal (N-)domains of all three proteins localize to the plasma membrane and fluorescence recordings parallel the dynamic changes in cell surface morphology observed by DIC microscopy of cultured cells. Expression of this domain, however, significantly affects cell surface architecture by the formation of abnormally long and fragile filopodia that poorly attach and retract abnormally. Even more striking are abundant irregular, branched and motionless membraneous structures that accumulate during retraction of lamellipodia. These are devoid of actin, endogenous moesin, ezrin and radixin, but contain the GFP-labeled domain. While a large proportion of endogenous proteins can be extracted with non-ionic detergents as in untransfected control cells, >90% of N-moesin and >60% of N-ezrin and N-radixin remain insoluble. The minimal size of the domain of moesin required for membrane localization and change in behavior includes residues 1-320. Deletions of amino acid residues from either end result in diffuse intracellular distribution, but also in normal cell behavior. Expression of GFP-fusions of full-length moesin or its carboxy-terminal domain has no effect on cell behavior during the observation period of 6-8 hours. The data suggest that, in the absence of the carboxy-terminal domain, N-moesin, -ezrin and -radixin interact tightly with the plasma membrane and interfere with normal functions of endogeneous proteins mainly during retraction.

    View details for Web of Science ID 000078294600010

    View details for PubMedID 9841908

  • The plasma membrane-actin linking protein, ezrin, is a glomerular epithelial cell marker in glomerulogenesis, in the adult kidney and in glomerular injury KIDNEY INTERNATIONAL Hugo, C., Nangaku, M., Shankland, S. J., Pichler, R., Gordon, K., Amieva, M. R., Couser, W. G., FURTHMAYR, H., JOHNSON, R. J. 1998; 54 (6): 1934-1944

    Abstract

    Ezrin belongs to a family of plasma membrane-cytoskeleton linking, actin binding proteins (Ezrin-radixin-Moesin family) involved in signal transduction, growth control, cell-cell adhesion, and microvilli formation.The expression of ezrin was examined in glomerular cells in culture, during kidney development, in the mature kidney, and in five different experimental kidney disease models in the rat.Ezrin was specifically expressed in glomerular epithelial cells in developing glomeruli in mature glomeruli and in glomerular epithelial cells in culture. Distinct from its other family members, moesin and radixin, which are predominantly expressed in glomerular endothelial and mesangial areas, ezrin protein (by immunohistochemistry) was specifically and exclusively modulated during podocyte injury and regeneration. Ezrin immunohistochemistry was able to visualize cell body attenuation, pseudocysts, and in particular vacuolation of injured podocytes, a feature that usually has to be identified at the ultrastructural level, and was strikingly increased in binucleated podocytes or podocytes that were partially or completely detached from the underlying GBM (frequently also binucleated). Infiltrating macrophages also express ezrin, but can easily be differentiated from podocytes by their round shape and higher level of expression.Ezrin likely has a role in the cytoskeletal organization, such as reassembling of acting filaments accompanying podocyte injury and regeneration. Since suitable light microscopic markers for the identification of glomerular epithelial cells are rare, ezrin may also be a useful marker for podocytes in normal and injured glomeruli.

    View details for Web of Science ID 000077129000013

    View details for PubMedID 9853258

  • Hypoxia increases human keratinocyte motility on connective tissue JOURNAL OF CLINICAL INVESTIGATION O'Toole, E. A., Marinkovich, M. P., Peavey, C. L., Amieva, M. R., FURTHMAYR, H., Mustoe, T. A., Woodley, D. T. 1997; 100 (11): 2881-2891

    Abstract

    Re-epithelialization of skin wounds depends upon the migration of keratinocytes from the cut margins of the wound and is enhanced when human keratinocytes are covered with occlusive dressings that induce hypoxia. In this study, two independent migration assays were used to compare cellular motility on connective tissue components under normoxic or hypoxic conditions. Human keratinocytes apposed to collagens or fibronectin exhibited increased motility when subjected to hypoxic (0.2 or 2% oxygen) conditions compared with normoxic (9 or 20% oxygen) conditions. When compared with normoxic cells, hypoxic keratinocytes exhibited increased expression and redistribution of the lamellipodia-associated proteins (ezrin, radixin, and moesin). Furthermore, hypoxic keratinocytes demonstrated decreased secretion of laminin-5, a laminin isoform known to inhibit keratinocyte motility. Hypoxia did not alter the number of integrin receptors on the cell surface, but did induce enhanced secretion of the 92-kD type IV collagenase. These data demonstrate that hypoxia promotes human keratinocyte motility on connective tissue. Hypoxia-driven motility is associated with increased expression of lamellipodia proteins, increased expression of collagenase and decreased expression of laminin-5, the locomotion brake for keratinocytes.

    View details for Web of Science ID 000071007300031

    View details for PubMedID 9389755

  • Phosphorylation of T-558 of moesin detected by site-specific antibodies in RAW264.7 macrophages BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS Nakamura, F., Amieva, M. R., Hirota, C., Mizuno, Y., FURTHMAYR, H. 1996; 226 (3): 650-656

    Abstract

    To determine, whether 558Thr in the carboxyl-terminal domain of moesin is phosphorylated in cells other than platelets, rabbit phosphorylation state-specific antibodies were made to the chemically phosphorylated synthetic hexapeptide KYKpTLR of the moesin sequence, as well as to the unphosphorylated form. The affinity-purified antibody populations were specific for either the phosphorylated or the unmodified peptide conjugated to BSA. Site-specific phosphorylation of moesin is detected in RAW macrophages by Western blot analysis, and immunofluorescence studies demonstrate that phosphorylated moesin is localized in filopodial protrusions. After pretreatment with the phosphatase inhibitor calyculin A, a similar effect to that seen in platelets in found, namely a substantial increase in moesin phosphorylation at 558Thr and redistribution of phospho-moesin together with F-actin into one or more ring-like structures in the cytoplasm, presumably due to binding of phosphorylated moesin to F-actin.

    View details for Web of Science ID A1996VL16400011

    View details for PubMedID 8831671

  • The cytoskeletal linking proteins, moesin and radixin, are upregulated by platelet-derived growth factor, but not basic fibroblast growth factor in experimental mesangial proliferative glomerulonephritis JOURNAL OF CLINICAL INVESTIGATION Hugo, C., Hugo, C., Pichler, R., Gordon, K., Schmidt, R., Amieva, M., Couser, W. G., FURTHMAYR, H., JOHNSON, R. J. 1996; 97 (11): 2499-2508

    Abstract

    The expression of the two cytoskeletal linking proteins, moesin and radixin, was examined in experimental mesangial proliferative nephritis in rats (anti-Thy1 model). Moesin and radixin mRNA and protein are constitutively expressed in all cell types of normal rat glomeruli, except podocytes. In the anti-Thy1 model the expression of moesin and radixin was increased in infiltrating macrophages and in activated, alpha-smooth muscle actin-positive mesangial cells and was concentrated in the cellular extensions of mesangial cells in areas of glomerular remodelling. Studies using neutralizing antibodies demonstrated that the increase in moesin and radixin expression by mesangial cells is mediated by PDGF, but not bFGF. The increase in these cytoskeletal proteins appears to be regulated primarily (radixin) or partially (moesin) posttranscriptionally. The data suggest that PDGF mediated upregulation of the cytoskeletal proteins, moesin and radixin, is important for cell migration and other changes that accompany the coordinated restoration of glomerular architecture after injury.

    View details for Web of Science ID A1996UQ23800014

    View details for PubMedID 8647942

  • Phosphorylation of threonine 558 in the carboxyl-terminal actin-binding domain of moesin by thrombin activation of human platelets JOURNAL OF BIOLOGICAL CHEMISTRY Nakamura, F., Amieva, M. R., FURTHMAYR, H. 1995; 270 (52): 31377-31385

    Abstract

    The phosphorylation and localization of the membrane-linking protein moesin was analyzed during early activation of platelets with thrombin. Activated platelets elaborate filopodia and spread to assume flat pancake-like shapes, and moesin is localized in filopodia and cell body. In resting platelets, approximately 25% of moesin molecules are phosphorylated as shown by metabolic labeling with 32P(i) and by isoelectric focusing. Within seconds after exposure to thrombin, phosphorylation increases, reaching a maximum of 35% labeled molecules by 1 min, followed by a decrease to a new basal level within 5 min. This modification affects a single residue, Thr558, which is located within or close to a binding site for F-actin. Rapid shifts (0-100%) in the number of phosphorylated molecules are observed in the presence of inhibitors of serine/threonine kinases and phosphatases. Inhibitors affecting tyrosine phosphorylation also modulate phosphorylation at this site suggesting that the enzymes involved in the modification of Thr558 are regulated by tyrosine phosphorylation. Platelets respond to both extremes of modification by forming extremely long filopodia and the absence of spreading on glass. Completely phosphorylated moesin is concentrated together with F-actin in the center of the cell. The rapid modification of moesin at or near its actin-binding domain suggests a model for regulated membrane-cytoskeleton interaction during cell activation.

    View details for Web of Science ID A1995TN44400078

    View details for PubMedID 8537411

  • SUBCELLULAR-LOCALIZATION OF MOESIN IN DYNAMIC FILOPODIA, RETRACTION FIBERS, AND OTHER STRUCTURES INVOLVED IN SUBSTRATE EXPLORATION, ATTACHMENT, AND CELL-CELL CONTACTS EXPERIMENTAL CELL RESEARCH Amieva, M. R., FURTHMAYR, H. 1995; 219 (1): 180-196

    Abstract

    Moesin, a member of the talin-4.1 superfamily, is a linking protein of the submembraneous cytoskeleton. It is expressed in variable amounts in cells of different phenotypes such as macrophages, lymphocytes, fibroblastic, endothelial, epithelial, and neuronal cell lines. In this report we show that moesin is not randomly distributed throughout the cortical cytoskeleton, but rather that it is concentrated in specialized microdomains. It is localized in the intracellular core of microextensions known as filopodia, microvilli, microspikes, and retraction fibers. This subcellular distribution follows closely the dynamic changes in cell shape that take place when cells attach, spread, and move spontaneously or in response to extracellular signals. This suggests a similar function for moesin in diverse cell types related to the dynamic restructuring of domains of the plasma membrane and underlying membrane skeleton. Support for this comes from studies on PC-12 cells, which respond to NGF by extending neurites and moesin is redistributed from a diffuse localization to growth cone filopodia. In fibroblastic (NIH3T3) or macrophage (RAW264.7) cell lines, moesin is found in filopodia appearing at random on the cell surface soon after the cells are placed in culture, begin to attach, and spread. In polarized epithelial cells (LLC-PK1), moesin is associated with peripheral filopodia and apical microvilli. The cellular microextensions containing moesin are devoid of microtubules, focal contact proteins such as vinculin, and cortical cytoskeletal elements such as protein 4.1, but they do contain varying amounts of actin microfilaments. This localization of moesin in microextensions is not influenced by cytochalasin B. Treatment of cells with phorbolester (PMA) causes rapid cell spreading, disappearance of filopodia and retraction fibers, and moesin does not accumulate in the actin-rich lamellae that form at the cellular edges. After removal of PMA, cells retract and moesin again becomes concentrated in filopodia and retraction fibers. These studies support the hypothesis that filopodia, retraction fibers, and other microextensions of the plasma membrane are unique cellular microdomains with characteristic submembraneous components. Moesin could be involved in the dynamic restructuring of such microdomains by regulating binding interactions between the plasma membrane and the actin cytoskeleton.

    View details for Web of Science ID A1995RL83100022

    View details for PubMedID 7628534

  • MOESIN, EZRIN, AND P205 ARE ACTIN-BINDING PROTEINS ASSOCIATED WITH NEUTROPHIL PLASMA-MEMBRANES MOLECULAR BIOLOGY OF THE CELL Pestonjamasp, K., Amieva, M. R., Strassel, C. P., Nauseef, W. M., FURTHMAYR, H., LUNA, E. J. 1995; 6 (3): 247-259

    Abstract

    Actin-binding proteins in bovine neutrophil plasma membranes were identified using blot overlays with 125I-labeled F-actin. Along with surface-biotinylated proteins, membranes were enriched in major actin-binding polypeptides of 78, 81, and 205 kDa. Binding was specific for F-actin because G-actin did not bind. Further, unlabeled F-actin blocked the binding of 125I-labeled F-actin whereas other acidic biopolymers were relatively ineffective. Binding also was specifically inhibited by myosin subfragment 1, but not by CapZ or plasma gelsolin, suggesting that the membrane proteins, like myosin, bind along the sides of the actin filaments. The 78- and 81-kDa polypeptides were identified as moesin and ezrin, respectively, by co-migration on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoprecipitation with antibodies specific for moesin and ezrin. Although not present in detectable amounts in bovine neutrophils, radixin (a third and closely related member of this gene family) also bound 125I-labeled F-actin on blot overlays. Experiments with full-length and truncated bacterial fusion proteins localized the actin-binding site in moesin to the extreme carboxy terminus, a highly conserved sequence. Immunofluorescence micrographs of permeabilized cells and cell "footprints" showed moesin co-localization with actin at the cytoplasmic surface of the plasma membrane, consistent with a role as a membrane-actin-linking protein.

    View details for Web of Science ID A1995QR87900002

    View details for PubMedID 7612961

  • RADIXIN IS A COMPONENT OF HEPATOCYTE MICROVILLI IN-SITU EXPERIMENTAL CELL RESEARCH Amieva, M. R., Wilgenbus, K. K., FURTHMAYR, H. 1994; 210 (1): 140-144

    View details for Web of Science ID A1994MP59700021

    View details for PubMedID 8269991

  • EARLY NEUROGENESIS OF THE MOUSE OLFACTORY NERVE - GOLGI AND ELECTRON-MICROSCOPIC STUDIES JOURNAL OF COMPARATIVE NEUROLOGY MARINPADILLA, M., Amieva, M. R. 1989; 288 (2): 339-352

    Abstract

    The early neurogenesis of the mouse olfactory nerve, from its exist at the nasal epithelium to its entrance into the embryonic telencephalon, has been investigated by using the rapid Golgi method and electron microscopy. Previously unrecognized anatomical and possible functional interrelationships between developing olfactory nerve axons and their sheath cells have been observed: 1) at their exit from sensory epithelium (nasal compartment), 2) at their contact with the CNS surface (intracranial compartment), and 3) at their entrance into the embryonic telencephalon (central nervous tissue compartment). Based on these observations the anatomy of the mouse olfactory nerve is herein redefined. Exiting olfactory nerve axons and sheath cells from the same regions of the nasal epithelium establish an early association which is maintained up to their terminal glomerular neuropile. No disruptions have been found in either the olfactory nerve axons or in the continuity of their sheath cells from exit at the nasal epithelium to entrance into the developing olfactory bulb. Corresponding olfactory nerve axons with their sheath cells enter together and become incorporated into the developing olfactory bulb as units. Consequently, the cellular envelope of the olfactory glomerulus must be composed of olfactory sheath cells rather than of glial (astroglial) cells from the CNS. With this simple anatomical arrangement, a topographic map of the sensory epithelium could be established progressively in the developing olfactory bulb. Eventually, "regenerating" olfactory nerve axons from different nasal regions could be guided by their specific sheath cell conduits toward their target glomeruli; hence, the olfactory message may be maintained undisturbed throughout the life span of the animal. In addition, olfactory nerve axons establish synaptic-like contacts with their corresponding sheath cells prior to or during the perforation of the CNS surface. Reciprocal recognition between corresponding axons and their sheath cells at this crucial stage in their neurogenesis may play a significant role in the establishment of their terminal glomerulus. This new concept of the anatomy of the mammalian olfactory nerve should provide insights helpful in clarifying some of the still-unresolved questions regarding the structural and functional organizations of this primitive system.

    View details for Web of Science ID A1989AT46300010

    View details for PubMedID 2794142

Conference Proceedings


  • CDNA SEQUENCE AND INTRACELLULAR LOCALIZATION OF HUMAN RADIXIN Wilgenbus, K. K., Amieva, M., FURTHMAYR, H. GUSTAV FISCHER VERLAG. 1994: 245-245
  • MOESIN, A NEW CYTOSKELETAL PROTEIN AND CONSTITUENT OF FILOPODIA - ITS ROLE IN CELLULAR FUNCTIONS FURTHMAYR, H., Lankes, W., Amieva, M. BLACKWELL SCIENCE INC. 1992: 665-670

    View details for Web of Science ID A1992HG07000030

    View details for PubMedID 1573844

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