Erythropoiesis, EPO, macrophages, and bone.
Systematic discovery of mutation-specific synthetic lethals by mining pan-cancer human primary tumor data.
2017; 8: 15580-?
The regulation of erythropoiesis in the bone marrow microenvironment is a carefully orchestrated process that is dependent upon both systemic and local cues. Systemic erythropoietin (EPO) production by renal interstitial cells plays a critical role in maintaining erythropoietic homeostasis. In addition, there is increasing clinical and preclinical data linking changes in EPO and erythropoiesis to altered skeletal homeostasis, suggesting a functional relationship between the regulation of erythropoiesis and bone homeostasis. As key local components of the bone marrow microenvironment and erythropoietic niche, macrophage subsets play important roles in both processes. In this review, we summarize our current understanding of the cellular and molecular mechanisms that may facilitate the coordinated regulation of erythropoiesis and bone homeostasis.
View details for DOI 10.1016/j.bone.2018.03.014
View details for PubMedID 29551752
Inhibition of the GAS6/AXL pathway augments the efficacy of chemotherapies
JOURNAL OF CLINICAL INVESTIGATION
2017; 127 (1): 183-198
Two genes are synthetically lethal (SL) when defects in both are lethal to a cell but a single defect is non-lethal. SL partners of cancer mutations are of great interest as pharmacological targets; however, identifying them by cell line-based methods is challenging. Here we develop MiSL (Mining Synthetic Lethals), an algorithm that mines pan-cancer human primary tumour data to identify mutation-specific SL partners for specific cancers. We apply MiSL to 12 different cancers and predict 145,891 SL partners for 3,120 mutations, including known mutation-specific SL partners. Comparisons with functional screens show that MiSL predictions are enriched for SLs in multiple cancers. We extensively validate a SL interaction identified by MiSL between the IDH1 mutation and ACACA in leukaemia using gene targeting and patient-derived xenografts. Furthermore, we apply MiSL to pinpoint genetic biomarkers for drug sensitivity. These results demonstrate that MiSL can accelerate precision oncology by identifying mutation-specific targets and biomarkers.
View details for DOI 10.1038/ncomms15580
View details for PubMedID 28561042
Targeting integrins with RGD-conjugated gold nanoparticles in radiotherapy decreases the invasive activity of breast cancer cells.
International journal of nanomedicine
2017; 12: 5069–85
The AXL receptor and its activating ligand, growth arrest-specific 6 (GAS6), are important drivers of metastasis and therapeutic resistance in human cancers. Given the critical roles that GAS6 and AXL play in refractory disease, this signaling axis represents an attractive target for therapeutic intervention. However, the strong picomolar binding affinity between GAS6 and AXL and the promiscuity of small molecule inhibitors represent important challenges faced by current anti-AXL therapeutics. Here, we have addressed these obstacles by engineering a second-generation, high-affinity AXL decoy receptor with an apparent affinity of 93 femtomolar to GAS6. Our decoy receptor, MYD1-72, profoundly inhibited disease progression in aggressive preclinical models of human cancers and induced cell killing in leukemia cells. When directly compared with the most advanced anti-AXL small molecules in the clinic, MYD1-72 achieved superior antitumor efficacy while displaying no toxicity. Moreover, we uncovered a relationship between AXL and the cellular response to DNA damage whereby abrogation of AXL signaling leads to accumulation of the DNA-damage markers γH2AX, 53BP1, and RAD51. MYD1-72 exploited this relationship, leading to improvements upon the therapeutic index of current standard-of-care chemotherapies in preclinical models of advanced pancreatic and ovarian cancer.
View details for DOI 10.1172/JCI85610
View details for Web of Science ID 000392271300021
View details for PubMedID 27893463
View details for PubMedCentralID PMC5199716
Cabozantinib inhibits tumor growth and metastasis of a patient-derived xenograft model of papillary renal cell carcinoma with MET mutation
CANCER BIOLOGY & THERAPY
2017; 18 (11): 863–71
Reprogramming the immunological microenvironment through radiation and targeting Axl
Gold nanoparticles (AuNPs) have recently attracted attention as clinical agents for enhancing the effect of radiotherapy in various cancers. Although radiotherapy is a standard treatment for cancers, invasive recurrence and metastasis are significant clinical problems. Several studies have suggested that radiation promotes the invasion of cancer cells by activating molecular mechanisms involving integrin and fibronectin (FN). In this study, polyethylene-glycolylated AuNPs (P-AuNPs) were conjugated with Arg-Gly-Asp (RGD) peptides (RGD/P-AuNPs) to target cancer cells expressing RGD-binding integrins such as α5- and αv-integrins. RGD/P-AuNPs were internalized more efficiently and colocalized with integrins in the late endosomes and lysosomes of MDA-MB-231 cells. A combination of RGD/P-AuNPs and radiation reduced cancer cell viability and increased DNA damage compared to radiation alone in MDA-MB-231 cells. Moreover, the invasive activity of breast cancer cell lines after radiation treatment was significantly inhibited in the presence of RGD/P-AuNPs. Microarray analyses revealed that the expression of FN in irradiated cells was suppressed by combined use of RGD/P-AuNPs. Reduction of FN and downstream signaling may be involved in suppressing radiation-induced invasive activity by RGD/P-AuNPs. Our study suggests that RGD/P-AuNPs can target integrin-overexpressing cancer cells to improve radiation therapy by suppressing invasive activity in addition to sensitization. Thus, these findings provide a possible clinical strategy for using AuNPs to treat invasive breast cancer following radiotherapy.
View details for DOI 10.2147/IJN.S137833
View details for PubMedID 28860745
View details for PubMedCentralID PMC5560413
The Receptor Tyrosine Kinase AXL in Cancer Progression.
2016; 8 (11)
Increasing evidence suggests that ionizing radiation therapy (RT) in combination with checkpoint immunotherapy is highly effective in treating a subset of cancers. To better understand the limited responses to this combination we analysed the genetic, microenvironmental, and immune factors in tumours derived from a transgenic breast cancer model. We identified two tumours with similar growth characteristics but different RT responses primarily due to an antitumour immune response. The combination of RT and checkpoint immunotherapy resulted in cures in the responsive but not the unresponsive tumours. Profiling the tumours revealed that the Axl receptor tyrosine kinase is overexpressed in the unresponsive tumours, and Axl knockout resulted in slower growth and increased radiosensitivity. These changes were associated with a CD8(+) T-cell response, which was improved in combination with checkpoint immunotherapy. These results suggest a novel role for Axl in suppressing antigen presentation through MHCI, and enhancing cytokine release, which promotes a suppressive myeloid microenvironment.
View details for DOI 10.1038/ncomms13898
View details for Web of Science ID 000390399500001
View details for PubMedID 28008921
View details for PubMedCentralID PMC5196438
AXL modulates extracellular matrix protein expression and is essential for invasion and metastasis in endometrial cancer.
The AXL receptor tyrosine kinase (AXL) has emerged as a promising therapeutic target for cancer therapy. Recent studies have revealed a central role of AXL signaling in tumor proliferation, survival, stem cell phenotype, metastasis, and resistance to cancer therapy. Moreover, AXL is expressed within cellular components of the tumor microenvironment where AXL signaling contributes to the immunosuppressive and protumorigenic phenotypes. A variety of AXL inhibitors have been developed and are efficacious in preclinical studies. These agents offer new opportunities for therapeutic intervention in the prevention and treatment of advanced disease. Here we review the literature that has illuminated the cellular and molecular mechanisms by which AXL signaling promotes tumor progression and we will discuss the therapeutic potential of AXL inhibition for cancer therapy.
View details for PubMedID 27834845
View details for PubMedCentralID PMC5126763
Cabozantinib inhibits tumor growth and metastasis of a patient-derived xenograft model of papillary renal cell carcinoma with MET mutation.
Cancer biology & therapy
The receptor tyrosine kinase AXL promotes migration, invasion, and metastasis. Here, we evaluated the role of AXL in endometrial cancer. High immunohistochemical expression of AXL was found in 76% (63/83) of advanced-stage, and 77% (82/107) of high-grade specimens and correlated with worse survival in uterine serous cancer patients. In vitro, genetic silencing of AXL inhibited migration and invasion but had no effect on proliferation of ARK1 endometrial cancer cells. AXL-deficient cells showed significantly decreased expression of phospho-AKT as well as uPA, MMP-1, MMP-2, MMP-3, and MMP-9. In a xenograft model of human uterine serous carcinoma with AXL-deficient ARK1 cells, there was significantly less tumor burden than xenografts with control ARK1 cells. Together, these findings underscore the therapeutic potentials of AXL as a candidate target for treatment of metastatic endometrial cancer.
View details for DOI 10.18632/oncotarget.12637
View details for PubMedID 27764792
Polycomb repressive complex 2 regulates skeletal growth by suppressing Wnt and TGF-beta signalling
MET plays an important role in the development and progression of papillary renal cell carcinoma (pRCC). Evaluation of efficacy of MET inhibitors against pRCC has been hampered by limited preclinical models depicting MET abnormalities. We established a new patient-derived xenograft (PDX) model of pRCC carrying an activating mutation of MET and tested the ability of cabozantinib, an inhibitor of receptor tyrosine kinases including MET, to inhibit tumor growth and metastasis. Precision-cut, thin tissue slices from a pRCC specimen obtained by nephrectomy were implanted under the renal capsule of RAG2(-/-)γC(-/-) mice to establish first generation TSG-RCC-030. Histologic and genetic fidelity and metastatic potential of this model were characterized by immunohistochemistry, direct DNA sequencing and quantitative polymerase chain reaction (qPCR). The effect of cabozantinib on tumor growth and metastasis was evaluated. Whether measurements of circulating tumor DNA (ctDNA) by allele-specific qPCR could be used as a biomarker of tumor growth and response to therapy was determined. Subrenal and subcutaneous tumor grafts showed high take rates and metastasized to the lung. Both primary tumors and metastases expressed typical markers of pRCC and carried the same activating MET mutation as the parental tumor. Cabozantinib treatment caused striking tumor regression and inhibited lung metastasis in TSG-RCC-030. Plasma ctDNA levels correlated with tumor volume in control mice and changed in response to cabozantinib treatment. TSG-RCC-030 provides a realistic preclinical model to better understand the development and progression of pRCC with MET mutation and accelerate the development of new therapies for pRCC.
View details for PubMedID 27715452
Targeting MET and AXL overcomes resistance to sunitinib therapy in renal cell carcinoma
2016; 35 (21): 2687-2697
Polycomb repressive complex 2 (PRC2) controls maintenance and lineage determination of stem cells by suppressing genes that regulate cellular differentiation and tissue development. However, the role of PRC2 in lineage-committed somatic cells is mostly unknown. Here we show that Eed deficiency in chondrocytes causes severe kyphosis and a growth defect with decreased chondrocyte proliferation, accelerated hypertrophic differentiation and cell death with reduced Hif1a expression. Eed deficiency also causes induction of multiple signalling pathways in chondrocytes. Wnt signalling overactivation is responsible for the accelerated hypertrophic differentiation and kyphosis, whereas the overactivation of TGF-β signalling is responsible for the reduced proliferation and growth defect. Thus, our study demonstrates that PRC2 has an important regulatory role in lineage-committed tissue cells by suppressing overactivation of multiple signalling pathways.
View details for DOI 10.1038/ncomms12047
View details for Web of Science ID 000379092100001
View details for PubMedID 27329220
Hypoxic control of metastasis
2016; 352 (6282): 175-180
Antiangiogenic therapy resistance occurs frequently in patients with metastatic renal cell carcinoma (RCC). The purpose of this study was to understand the mechanism of resistance to sunitinib, an antiangiogenic small molecule, and to exploit this mechanism therapeutically. We hypothesized that sunitinib-induced upregulation of the prometastatic MET and AXL receptors is associated with resistance to sunitinib and with more aggressive tumor behavior. In the present study, tissue microarrays containing sunitinib-treated and untreated RCC tissues were stained with MET and AXL antibodies. The low malignant RCC cell line 786-O was chronically treated with sunitinib and assayed for AXL, MET, epithelial-mesenchymal transition (EMT) protein expression and activation. Co-culture experiments were used to examine the effect of sunitinib pretreatment on endothelial cell growth. The effects of AXL and MET were evaluated in various cell-based models by short hairpin RNA or inhibition by cabozantinib, the multi-tyrosine kinases inhibitor that targets vascular endothelial growth factor receptor, MET and AXL. Xenograft mouse models tested the ability of cabozantinib to rescue sunitinib resistance. We demonstrated that increased AXL and MET expression was associated with inferior clinical outcome in patients. Chronic sunitinib treatment of RCC cell lines activated both AXL and MET, induced EMT-associated gene expression changes, including upregulation of Snail and β-catenin, and increased cell migration and invasion. Pretreatment with sunitinib enhanced angiogenesis in 786-0/human umbilical vein endothelial cell co-culture models. The suppression of AXL or MET expression and the inhibition of AXL and MET activation using cabozantinib both impaired chronic sunitinib treatment-induced prometastatic behavior in cell culture and rescued acquired resistance to sunitinib in xenograft models. In summary, chronic sunitinib treatment induces the activation of AXL and MET signaling and promotes prometastatic behavior and angiogenesis. The inhibition of AXL and MET activity may overcome resistance induced by prolonged sunitinib therapy in metastatic RCC.
View details for DOI 10.1038/onc.2015.343
View details for Web of Science ID 000377472700003
View details for PubMedID 26364599
Biology of the bone marrow microenvironment and myelodysplastic syndromes.
Molecular genetics and metabolism
2015; 116 (1-2): 24-28
Metastatic disease is the leading cause of cancer-related deaths and involves critical interactions between tumor cells and the microenvironment. Hypoxia is a potent microenvironmental factor promoting metastatic progression. Clinically, hypoxia and the expression of the hypoxia-inducible transcription factors HIF-1 and HIF-2 are associated with increased distant metastasis and poor survival in a variety of tumor types. Moreover, HIF signaling in malignant cells influences multiple steps within the metastatic cascade. Here we review research focused on elucidating the mechanisms by which the hypoxic tumor microenvironment promotes metastatic progression. These studies have identified potential biomarkers and therapeutic targets regulated by hypoxia that could be incorporated into strategies aimed at preventing and treating metastatic disease.
View details for DOI 10.1126/science.aaf4405
View details for Web of Science ID 000373681600036
View details for PubMedID 27124451
Oxygen-sensing PHDs regulate bone homeostasis through the modulation of osteoprotegerin
GENES & DEVELOPMENT
2015; 29 (8): 817-831
Myelodysplastic syndromes (MDS) are characterized by cytopenias resulting from ineffective hematopoiesis with a predisposition to transform to acute myeloid leukemia (AML). Recent evidence suggests that the hematopoietic stem cell microenvironment contributes to the pathogenesis of MDS. Inflammation and hypoxia within the bone marrow are key regulators of hematopoietic stem and progenitor cells that can lead to several bone marrow failure syndromes, including MDS. In this brief review, we provide an overview of the clinical and molecular features of MDS, the bone marrow microenvironment, and specific pathways that lead to abnormal blood cell development in MDS. Characterization of key steps in the pathogenesis of MDS will lead to new approaches to treat patients with this disease.
View details for DOI 10.1016/j.ymgme.2015.07.004
View details for PubMedID 26210353
View details for PubMedCentralID PMC4618471
Hypoxic induction of AKAP12 variant 2 shifts PKA-mediated protein phosphorylation to enhance migration and metastasis of melanoma cells
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2015; 112 (14): 4441-4446
The bone microenvironment is composed of niches that house cells across variable oxygen tensions. However, the contribution of oxygen gradients in regulating bone and blood homeostasis remains unknown. Here, we generated mice with either single or combined genetic inactivation of the critical oxygen-sensing prolyl hydroxylase (PHD) enzymes (PHD1-3) in osteoprogenitors. Hypoxia-inducible factor (HIF) activation associated with Phd2 and Phd3 inactivation drove bone accumulation by modulating osteoblastic/osteoclastic cross-talk through the direct regulation of osteoprotegerin (OPG). In contrast, combined inactivation of Phd1, Phd2, and Phd3 resulted in extreme HIF signaling, leading to polycythemia and excessive bone accumulation by overstimulating angiogenic-osteogenic coupling. We also demonstrate that genetic ablation of Phd2 and Phd3 was sufficient to protect ovariectomized mice against bone loss without disrupting hematopoietic homeostasis. Importantly, we identify OPG as a HIF target gene capable of directing osteoblast-mediated osteoclastogenesis to regulate bone homeostasis. Here, we show that coordinated activation of specific PHD isoforms fine-tunes the osteoblastic response to hypoxia, thereby directing two important aspects of bone physiology: cross-talk between osteoblasts and osteoclasts and angiogenic-osteogenic coupling.
View details for DOI 10.1101/gad.255000.114
View details for Web of Science ID 000353027600004
View details for PubMedID 25846796
Osteoblasts: a novel source of erythropoietin.
Current osteoporosis reports
2014; 12 (4): 428-432
Scaffold proteins are critical hubs within cells that have the ability to modulate upstream signaling molecules and their downstream effectors to fine-tune biological responses. Although they can serve as focal points for association of signaling molecules and downstream pathways that regulate tumorigenesis, little is known about how the tumor microenvironment affects the expression and activity of scaffold proteins. This study demonstrates that hypoxia, a common element of solid tumors harboring low oxygen levels, regulates expression of a specific variant of the scaffold protein AKAP12 (A-kinase anchor protein 12), AKAP12v2, in metastatic melanoma. In turn, through a kinome-wide phosphoproteomic and MS study, we demonstrate that this scaffolding protein regulates a shift in protein kinase A (PKA)-mediated phosphorylation events under hypoxia, causing alterations in tumor cell invasion and migration in vitro, as well as metastasis in an in vivo orthotopic model of melanoma. Mechanistically, the shift in AKAP12-dependent PKA-mediated phosphorylations under hypoxia is due to changes in AKAP12 localization vs. structural differences between its two variants. Importantly, our work defines a mechanism through which a scaffold protein can be regulated by the tumor microenvironment and further explains how a tumor cell can coordinate many critical signaling pathways that are essential for tumor growth through one individual scaffolding protein.
View details for DOI 10.1073/pnas.1418164112
View details for Web of Science ID 000352287800067
View details for PubMedID 25792458
Osteoblasts: a novel source of erythropoietin.
Current osteoporosis reports
2014; 12 (4): 428-432
Direct regulation of GAS6/AXL signaling by HIF promotes renal metastasis through SRC and MET
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2014; 111 (37): 13373-13378
Loss of VHL in mesenchymal progenitors of the limb bud alters multiple steps of endochondral bone development.
2014; 393 (1): 124-136
Osteoblasts are an important cellular component of the bone microenvironment controlling bone formation and hematopoiesis. Understanding the cellular and molecular mechanisms by which osteoblasts regulate these processes is a rapidly growing area of research given the important implications for bone therapy, regenerative medicine, and hematopoietic stem cell transplantation. Here we summarize our current knowledge regarding the cellular and molecular crosstalk driving bone formation and hematopoiesis and will discuss the implications of a recent finding demonstrating that osteoblasts are a cellular source of erythropoietin .
View details for DOI 10.1007/s11914-014-0236-x
View details for PubMedID 25204993
PHD inhibition mitigates and protects against radiation-induced gastrointestinal toxicity via HIF2.
Science translational medicine
2014; 6 (236): 236ra64-?
Adaptation to low oxygen tension (hypoxia) is a critical event during development. The transcription factors Hypoxia Inducible Factor-1α (HIF-1α) and HIF-2α are essential mediators of the homeostatic responses that allow hypoxic cells to survive and differentiate. Von Hippel-Lindau protein (VHL) is the E3 ubiquitin ligase that targets HIFs to the proteasome for degradation in normoxia. We have previously demonstrated that the transcription factor HIF-1α is essential for survival and differentiation of growth plate chondrocytes, whereas HIF-2α is not necessary for fetal growth plate development. We have also shown that VHL is important for endochondral bone development, since loss of VHL in chondrocytes causes severe dwarfism. In this study, in order to expand our understanding of the role of VHL in chondrogenesis, we conditionally deleted VHL in mesenchymal progenitors of the limb bud, i.e. in cells not yet committed to the chondrocyte lineage. Deficiency of VHL in limb bud mesenchyme does not alter the timely differentiation of mesenchymal cells into chondrocytes. However, it causes structural collapse of the cartilaginous growth plate as a result of impaired proliferation, delayed terminal differentiation, and ectopic death of chondrocytes. This phenotype is associated to delayed replacement of cartilage by bone. Notably, loss of HIF-2α fully rescues the late formation of the bone marrow cavity in VHL mutant mice, though it does not affect any other detectable abnormality of the VHL mutant growth plates. Our findings demonstrate that VHL regulates bone morphogenesis as its loss considerably alters size, shape and overall development of the skeletal elements.
View details for DOI 10.1016/j.ydbio.2014.06.013
View details for PubMedID 24972088
PHD Inhibition Mitigates and Protects Against Radiation-Induced Gastrointestinal Toxicity via HIF2.
Science translational medicine
2014; 6 (236): 236ra64-?
CTGF is a therapeutic target for metastatic melanoma.
2014; 33 (9): 1093-1100
Radiation-induced gastrointestinal (GI) toxicity can be a major source of morbidity and mortality after radiation exposure. There is an unmet need for effective preventative or mitigative treatments against the potentially fatal diarrhea and water loss induced by radiation damage to the GI tract. We report that prolyl hydroxylase inhibition by genetic knockout or pharmacologic inhibition of all PHD (prolyl hydroxylase domain) isoforms by the small-molecule dimethyloxallyl glycine (DMOG) increases hypoxia-inducible factor (HIF) expression, improves epithelial integrity, reduces apoptosis, and increases intestinal angiogenesis, all of which are essential for radioprotection. HIF2, but not HIF1, is both necessary and sufficient to prevent radiation-induced GI toxicity and death. Increased vascular endothelial growth factor (VEGF) expression contributes to the protective effects of HIF2, because inhibition of VEGF function reversed the radioprotection and radiomitigation afforded by DMOG. Additionally, mortality from abdominal or total body irradiation was reduced even when DMOG was given 24 hours after exposure. Thus, prolyl hydroxylase inhibition represents a treatment strategy to protect against and mitigate GI toxicity from both therapeutic radiation and potentially lethal radiation exposures.
View details for DOI 10.1126/scitranslmed.3008523
View details for PubMedID 24828078
View details for PubMedCentralID PMC4136475
Regulation of Bone Marrow Angiogenesis by Osteoblasts during Bone Development and Homeostasis.
Frontiers in endocrinology
2013; 4: 85-?
Metastatic melanoma remains a devastating disease with a 5-year survival rate of less than five percent. Despite recent advances in targeted therapies for melanoma, only a small percentage of melanoma patients experience durable remissions. Therefore, it is critical to identify new therapies for the treatment of advanced melanoma. Here, we define connective tissue growth factor (CTGF) as a therapeutic target for metastatic melanoma. Clinically, CTGF expression correlates with tumor progression and is strongly induced by hypoxia through HIF-1 and HIF-2-dependent mechanisms. Genetic inhibition of CTGF in human melanoma cells is sufficient to significantly reduce orthotopic tumor growth, as well as metastatic tumor growth in the lung of severe combined immunodeficient (SCID) mice. Mechanistically, inhibition of CTGF decreased invasion and migration associated with reduced matrix metalloproteinase-9 expression. Most importantly, the anti-CTGF antibody, FG-3019, had a profound inhibitory effect on the progression of established metastatic melanoma. These results offer the first preclinical validation of anti-CTGF therapy for the treatment of advanced melanoma and underscore the importance of tumor hypoxia in melanoma progression.Oncogene advance online publication, 25 February 2013; doi:10.1038/onc.2013.47.
View details for DOI 10.1038/onc.2013.47
View details for PubMedID 23435419
Blood and bones Osteoblastic HIF signaling regulates erythropoiesis
2012; 11 (12): 2221-2222
The HIF Signaling Pathway in Osteoblasts Directly Modulates Erythropoiesis through the Production of EPO
2012; 149 (1): 63-74
Bone marrow is a highly heterogeneous and vascularized tissue. The various cell types populating the bone marrow extensively communicate with each other, and cell-to-cell cross talk is likely to be essential for proper bone development and homeostasis. In particular, the existence of osteogenesis and angiogenesis coupling has been recently proposed. Despite its high degree of vascularization, a gradient of oxygenation is present in the bone marrow, and the endosteal surface of cortical bone appears to be among the most hypoxic areas in the body. Oxygen (O2) is both an essential metabolic substrate and a regulatory signal that is in charge of a specific genetic program. An important component of this program is the family of transcription factors known as hypoxia-inducible factors (HIFs). In this Perspective, we will summarize our current knowledge about the role of the HIF signaling pathway in controlling bone development and homeostasis, and especially in regulating the crosstalk between osteoblasts, progenitor cells, and bone marrow blood vessels.
View details for DOI 10.3389/fendo.2013.00085
View details for PubMedID 23847596
A central role for hypoxic signaling in cartilage, bone, and hematopoiesis.
Current osteoporosis reports
2011; 9 (2): 46-52
Osteoblasts are an important component of the hematopoietic microenvironment in bone. However, the mechanisms by which osteoblasts control hematopoiesis remain unknown. We show that augmented HIF signaling in osteoprogenitors results in HSC niche expansion associated with selective expansion of the erythroid lineage. Increased red blood cell production occurred in an EPO-dependent manner with increased EPO expression in bone and suppressed EPO expression in the kidney. In contrast, inactivation of HIF in osteoprogenitors reduced EPO expression in bone. Importantly, augmented HIF activity in osteoprogenitors protected mice from stress-induced anemia. Pharmacologic or genetic inhibition of prolyl hydroxylases1/2/3 in osteoprogenitors elevated EPO expression in bone and increased hematocrit. These data reveal an unexpected role for osteoblasts in the production of EPO and modulation of erythropoiesis. Furthermore, these studies demonstrate a molecular role for osteoblastic PHD/VHL/HIF signaling that can be targeted to elevate both HSCs and erythroid progenitors in the local hematopoietic microenvironment.
View details for DOI 10.1016/j.cell.2012.01.051
View details for Web of Science ID 000302235400010
View details for PubMedID 22464323
View details for PubMedCentralID PMC3408231
AXL Is an Essential Factor and Therapeutic Target for Metastatic Ovarian Cancer
2010; 70 (19): 7570-7579
Hypoxic signaling plays an essential role in maintaining oxygen homeostasis and cell survival. Hypoxia-inducible transcription factors HIF-1 and HIF-2 are central mediators of the cellular response to hypoxia by regulating the expression of genes controlling metabolic adaptation, oxygen delivery, and survival in response to oxygen deprivation. Recent studies have identified an important role for HIF-1 and HIF-2 in the regulation of skeletal development, bone formation, and regeneration, as well as joint formation and homeostasis. In addition, overexpression of HIF-1 and HIF-2 is clinically associated with osteosarcoma and osteoarthritis. Together, these findings implicate hypoxic signaling as a central regulator of bone biology and disease.
View details for DOI 10.1007/s11914-011-0047-2
View details for PubMedID 21360287
Regulation of the Histone Demethylase JMJD1A by Hypoxia-Inducible Factor 1 alpha Enhances Hypoxic Gene Expression and Tumor Growth
MOLECULAR AND CELLULAR BIOLOGY
2010; 30 (1): 344-353
The receptor tyrosine kinase AXL is thought to play a role in metastasis; however, the therapeutic efficacy of an AXL-targeting agent remains largely untested in metastatic disease. In this study, we defined AXL as a therapeutic target for metastatic ovarian cancer. AXL is primarily expressed in metastases and advanced-stage human ovarian tumors but not in normal ovarian epithelium. Genetic inhibition of AXL in human metastatic ovarian tumor cells is sufficient to prevent the initiation of metastatic disease in vivo. Mechanistically, inhibition of AXL signaling in animals with metastatic disease results in decreased invasion and matrix metalloproteinase activity. Most importantly, soluble human AXL receptors that imposed a specific blockade of the GAS6/AXL pathway had a profound inhibitory effect on progression of established metastatic ovarian cancer without normal tissue toxicity. These results offer the first genetic validation of GAS6/AXL targeting as an effective strategy for inhibition of metastatic tumor progression in vivo. Furthermore, this study defines the soluble AXL receptor as a therapeutic candidate agent for treatment of metastatic ovarian cancer, for which current therapies are ineffective.
View details for DOI 10.1158/0008-5472.CAN-10-1267
View details for Web of Science ID 000282647700021
View details for PubMedID 20858715
Hypoxia-Inducible Factor 2 Regulates Hepatic Lipid Metabolism
MOLECULAR AND CELLULAR BIOLOGY
2009; 29 (16): 4527-4538
The hypoxia-inducible transcription factors (HIFs) directly and indirectly mediate cellular adaptation to reduced oxygen tensions. Recent studies have shown that the histone demethylase genes JMJD1A, JMJD2B, and JARID1B are HIF targets, suggesting that HIFs indirectly influence gene expression at the level of histone methylation under hypoxia. In this study, we identify a subset of hypoxia-inducible genes that are dependent on JMJD1A in both renal cell and colon carcinoma cell lines. JMJD1A regulates the expression of adrenomedullin (ADM) and growth and differentiation factor 15 (GDF15) under hypoxia by decreasing promoter histone methylation. In addition, we demonstrate that loss of JMJD1A is sufficient to reduce tumor growth in vivo, demonstrating that histone demethylation plays a significant role in modulating growth within the tumor microenvironment. Thus, hypoxic regulation of JMJD1A acts as a signal amplifier to facilitate hypoxic gene expression, ultimately enhancing tumor growth.
View details for DOI 10.1128/MCB.00444-09
View details for Web of Science ID 000272569200028
View details for PubMedID 19858293
Bringing H2AX into the Angiogenesis Family
2009; 15 (6): 459-461
In mammals, the liver integrates nutrient uptake and delivery of carbohydrates and lipids to peripheral tissues to control overall energy balance. Hepatocytes maintain metabolic homeostasis by coordinating gene expression programs in response to dietary and systemic signals. Hepatic tissue oxygenation is an important systemic signal that contributes to normal hepatocyte function as well as disease. Hypoxia-inducible factors 1 and 2 (HIF-1 and HIF-2, respectively) are oxygen-sensitive heterodimeric transcription factors, which act as key mediators of cellular adaptation to low oxygen. Previously, we have shown that HIF-2 plays an important role in both physiologic and pathophysiologic processes in the liver. HIF-2 is essential for normal fetal EPO production and erythropoiesis, while constitutive HIF-2 activity in the adult results in polycythemia and vascular tumorigenesis. Here we report a novel role for HIF-2 in regulating hepatic lipid metabolism. We found that constitutive activation of HIF-2 in the adult results in the development of severe hepatic steatosis associated with impaired fatty acid beta-oxidation, decreased lipogenic gene expression, and increased lipid storage capacity. These findings demonstrate that HIF-2 functions as an important regulator of hepatic lipid metabolism and identify HIF-2 as a potential target for the treatment of fatty liver disease.
View details for DOI 10.1128/MCB.00200-09
View details for Web of Science ID 000268310000016
View details for PubMedID 19528226
Stable expression of HIF-1 alpha in tubular epithelial cells promotes interstitial fibrosis
AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY
2008; 295 (4): F1023-F1029
The cell's ability to sense and respond to DNA damage is critical to maintain homeostasis and prevent the development of cancer. Paradoxically, Economopoulou et al. recently reported that a DNA damage response protein, H2AX, promotes tumor growth and angiogenesis.
View details for DOI 10.1016/j.ccr.2009.05.004
View details for Web of Science ID 000266686500003
View details for PubMedID 19477424
Hypoxia-inducible factor-2 regulates vascular tumorigenesis in mice
2008; 27 (40): 5354-5358
Chronic hypoxia accelerates renal fibrosis. The chief mediator of the hypoxic response is hypoxia-inducible factor 1 (HIF-1) and its oxygen-sensitive component HIF-1alpha. HIF-1 regulates a wide variety of genes, some of which are closely associated with tissue fibrosis. To determine the specific role of HIF-1 in renal fibrosis, we generated a knockout mouse in which tubular epithelial expression of von Hippel-Lindau tumor suppressor (VHL), which acts as a ubiquitin ligase to promote proteolysis of HIF-1alpha, was targeted. We investigated the effect of VHL deletion (i.e., stable expression of HIF-1alpha) histologically and used the anti-HIF-1alpha agent [3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole] (YC-1) to test whether inhibition of HIF-1alpha could represent a novel approach to treating renal fibrosis. The area of renal fibrosis was significantly increased in a 5/6 renal ablation model of VHL-/- mice and in all VHL-/- mice at least 60 wk of age. Injection of YC-1 inhibited the progression of renal fibrosis in unilateral ureteral obstruction model mice. In conclusion, HIF-1alpha appears to be a critical contributor to the progression of renal fibrosis and could be a useful target for its treatment.
View details for DOI 10.1152/ajprenal.90209.2008
View details for Web of Science ID 000259913000019
View details for PubMedID 18667485
The role of hypoxia-inducible factors in tumorigenesis
CELL DEATH AND DIFFERENTIATION
2008; 15 (4): 678-685
The von Hippel-Lindau tumor suppressor pVHL regulates the stability of hypoxia-inducible factors (HIF)-1 and -2, oxygen-sensitive basic helix-loop-helix transcription factors, which mediate the hypoxic induction of angiogenic growth factors such as vascular endothelial growth factor. Loss of pVHL function results in constitutive activation of HIF-1 and HIF-2 and is associated with the development of highly vascularized tumors in multiple organs. We have used a conditional gene-targeting approach to investigate the relative contributions of HIF-1 and HIF-2 to VHL-associated vascular tumorigenesis in a mouse model of liver hemangiomas. Here we demonstrate genetically that conditional inactivation of HIF-2alpha suppressed the development of VHL-associated liver hemangiomas and that angiogenic gene expression in hepatocytes is predominantly regulated by HIF-2 and not by HIF-1. These findings suggest that HIF-2 is the dominant HIF in the pathogenesis of VHL-associated vascular tumors and that pharmacologic targeting of HIF-2 may be an effective strategy for their treatment.
View details for DOI 10.1038/onc.2008.160
View details for Web of Science ID 000259096100008
View details for PubMedID 18490920
Regulation of iron homeostasis by the hypoxia-inducible transcription factors (HIFs)
JOURNAL OF CLINICAL INVESTIGATION
2007; 117 (7): 1926-1932
Hypoxia-inducible factors (HIFs) are essential mediators of the cellular oxygen-signaling pathway. They are heterodimeric transcription factors consisting of an oxygen-sensitive alpha subunit (HIF-alpha) and a constitutive beta subunit (HIF-beta) that facilitate both oxygen delivery and adaptation to oxygen deprivation by regulating the expression of genes that control glucose uptake, metabolism, angiogenesis, erythropoiesis, cell proliferation, and apoptosis. In most experimental models, the HIF pathway is a positive regulator of tumor growth as its inhibition often results in tumor suppression. In clinical samples, HIF is found elevated and correlates with poor patient prognosis in a variety of cancers. In summary, HIF regulates multiple aspects of tumorigenesis, including angiogenesis, proliferation, metabolism, metastasis, differentiation, and response to radiation therapy, making it a critical regulator of the malignant phenotype.
View details for DOI 10.1038/cdd.2008.21
View details for Web of Science ID 000254041800010
View details for PubMedID 18259193
Hypoxia-inducible factor-2 (HIF-2) regulates hepatic erythropoietin in vivo
JOURNAL OF CLINICAL INVESTIGATION
2007; 117 (4): 1068-1077
Iron is essential for many biological processes, including oxygen delivery, and its supply is tightly regulated. Hepcidin, a small peptide synthesized in the liver, is a key regulator of iron absorption and homeostasis in mammals. Hepcidin production is increased by iron overload and decreased by anemia and hypoxia; but the molecular mechanisms that govern the hepcidin response to these stimuli are not known. Here we establish that the von Hippel-Lindau/hypoxia-inducible transcription factor (VHL/HIF) pathway is an essential link between iron homeostasis and hepcidin regulation in vivo. Through coordinate downregulation of hepcidin and upregulation of erythropoietin and ferroportin, the VHL-HIF pathway mobilizes iron to support erythrocyte production.
View details for DOI 10.1172/JCI31370
View details for Web of Science ID 000247837700024
View details for PubMedID 17557118
Rend cyst development in mice with conditional inactivation of the von Hippel-Lindau tumor suppressor
2006; 66 (5): 2576-2583
Erythropoiesis is critically dependent on erythropoietin (EPO), a glycoprotein hormone that is regulated by hypoxia-inducible factor (HIF). Hepatocytes are the primary source of extrarenal EPO in the adult and express HIF-1 and HIF-2, whose roles in the hypoxic induction of EPO remain controversial. In order to define the role of HIF-1 and HIF-2 in the regulation of hepatic EPO expression, we have generated mice with conditional inactivation of Hif-1alpha and/or Hif-2alpha (Epas1) in hepatocytes. We have previously shown that inactivation of the von Hippel-Lindau tumor suppressor pVHL, which targets both HIFs for proteasomal degradation, results in increased hepatic Epo production and polycythemia independent of Hif-1alpha. Here we show that conditional inactivation of Hif-2alpha in pVHL-deficient mice suppressed hepatic Epo and the development of polycythemia. Furthermore, we found that physiological Epo expression in infant livers required Hif-2alpha but not Hif-1alpha and that the hypoxic induction of liver Epo in anemic adults was Hif-2alpha dependent. Since other Hif target genes such phosphoglycerate kinase 1 (Pgk) were Hif-1alpha dependent, we provide genetic evidence that HIF-1 and HIF-2 have distinct roles in the regulation of hypoxia-inducible genes and that EPO is preferentially regulated by HIF-2 in the liver.
View details for DOI 10.1172/JCI30117
View details for Web of Science ID 000245451700029
View details for PubMedID 17404621
Inactivation of the arylhydrocarbon receptor nuclear translocator (Arnt) suppresses von Hippel-Lindau disease-associated vascular tumors in mice
MOLECULAR AND CELLULAR BIOLOGY
2005; 25 (8): 3163-3172
Inactivation of the von Hippel-Lindau tumor suppressor, pVHL, is associated with both hereditary and sporadic renal cysts and renal cell carcinoma, which are commonly thought to arise from the renal proximal tubule. pVHL regulates the protein stability of hypoxia-inducible factor (HIF)-alpha subunits and loss of pVHL function leads to HIF stabilization. The role of HIF in the development of VHL-associated renal lesions remains to be determined. To investigate the functional consequences of pVHL inactivation and the role of HIF signaling in renal epithelial cells, we used the phosphoenolpyruvate carboxykinase (PEPCK) promoter to generate transgenic mice in which Cre-recombinase is expressed in the renal proximal tubule and in hepatocytes. We found that conditional inactivation of VHL in PEPCK-Cre mutants resulted in renal cyst development that was associated with increased erythropoietin levels and polycythemia. Increased expression of the HIF target gene erythropoietin was limited to the liver, whereas expression of carbonic anhydrase 9 and multidrug resistance gene 1 was up-regulated in the renal cortex of mutant mice. Inactivation of the HIF-alpha binding partner, arylhydrocarbon receptor nuclear translocator (Arnt), but not Hif-1alpha, suppressed the development of renal cysts. Here, we present the first mouse model of VHL-associated renal disease that will provide a basis for further genetic studies to define the molecular events that are required for the progression of VHL-associated renal cysts to clear cell renal cell carcinoma.
View details for DOI 10.1158/0008-5472.CAN-05-3241
View details for Web of Science ID 000235826400014
View details for PubMedID 16510575
Putative intestine-specific enhancers located in 5 ' sequence of the CDX1 gene regulate CDX1 expression in the intestine
AMERICAN JOURNAL OF PHYSIOLOGY-GASTROINTESTINAL AND LIVER PHYSIOLOGY
2004; 286 (5): G872-G880
Patients with germ line mutations in the VHL tumor suppressor gene are predisposed to the development of highly vascularized tumors within multiple tissues. Loss of pVHL results in constitutive activation of the transcription factors HIF-1 and HIF-2, whose relative contributions to the pathogenesis of the VHL phenotype have yet to be defined. In order to examine the role of HIF in von Hippel-Lindau (VHL)-associated vascular tumorigenesis, we utilized Cre-loxP-mediated recombination to inactivate hypoxia-inducible factor-1alpha (Hif-1alpha) and arylhydrocarbon receptor nuclear translocator (Arnt) genes in a VHL mouse model of cavernous liver hemangiomas and polycythemia. Deletion of Hif-1alpha did not affect the development of vascular tumors and polycythemia, nor did it suppress the increased expression of vascular endothelial growth factor (Vegf) and erythropoietin (Epo). In contrast, phosphoglycerokinase (Pgk) expression was substantially decreased, providing evidence for target gene-dependent functional redundancy between different Hif transcription factors. Inactivation of Arnt completely suppressed the development of hemangiomas, polycythemia, and Hif-induced gene expression. Here, we demonstrate genetically that the development of VHL-associated vascular tumors in the liver depends on functional ARNT. Furthermore, we provide evidence that individual HIF transcription factors may play distinct roles in the development of specific VHL disease manifestations.
View details for DOI 10.1128/MCB.25.8.3163-3172.2005
View details for Web of Science ID 000228138500025
View details for PubMedID 15798202
An essential role of Th1 responses and interferon gamma in infection-mediated suppression of neoplastic growth
CANCER BIOLOGY & THERAPY
2003; 2 (6): 687-693
CDX1 is a homeobox transcription factor that plays a critical role in intestinal epithelial cell growth and differentiation. CDX1 gene expression is tightly regulated in a temporal and cell-type specific manner. However, very little is known about the regulatory mechanisms that direct CDX1 gene expression in the intestine. To elucidate these mechanisms, we employed a series of transgenic mouse studies using the 5' flanking sequences of the human CDX1 gene. Transgenic mice containing nucleotides between -5667 and +68 relative to the transcription start site of the CDX1 gene demonstrated ectopic expression of the transgene in the brain and gastric smooth muscle. However, transgenic expression of the nucleotides -15601 to +68 of the CDX1 gene was restricted to the intestinal epithelium, which was identical to endogenous CDX1 gene expression. Taken together, the upstream sequences between -15601 and -5667 contain regulatory elements that direct transgene expression specifically to the intestinal epithelium. Furthermore, DNase I hypersensitivity assays revealed two active chromatin regions in the CDX1 gene (hypertensive sites 1 and 2) located at approximately -5.8 and -6.8 kb upstream of the CDX1 gene, respectively, which may function as potential intestine-specific enhancers.
View details for DOI 10.1152/ajpgi.00326.2003
View details for Web of Science ID 000220693200023
View details for PubMedID 14715525
DNA methylation down-regulates CDX1 gene expression in colorectal cancer cell lines
JOURNAL OF BIOLOGICAL CHEMISTRY
2002; 277 (39): 35795-35800
We had previously demonstrated that in mice acute toxoplasmosis leads to systemic inhibition of angiogenesis and, consequently, strong suppression of neoplastic growth. Here we investigated the role of Th1 cytokines, in particular interferon gamma (IFN-gamma), in this phenomenon. Besides toxoplasma, neoplastic growth was readily blocked during acute infection with other Th1 response-inducing pathogens such as Listeria monocytogenes and lymphocytic choriomeningitis virus (LCMV). In contrast, chronic infection with LCMV (when Th1 responses were strongly suppressed) and acute infection with Schistosoma mansoni (when Th2 responses predominated) afforded no anti-tumor protection. To corroborate the involvement of Th1 cytokines in infection-mediated suppression of neoplastic growth, we utilized mice deficient in interleukin-10 (IL10), a suppressor of Th1 responses. When challenged with B16 cells concomitantly with toxoplasma infection, both IL10-null and wild type mice exhibited resistance to neoplastic growth. However, tumors borne by IL10-null animals were even smaller than those borne by their wild type counterparts. This enhanced resistance correlated with dramatically elevated levels of circulating IFN-gamma, a principal Th1 cytokine. Furthermore, while interleukin-12 and tumor necrosis factor a were dispensable for tumor suppression, in animals deficient in IFN-gamma production or signaling, tumor growth and neovascularization were markedly enhanced. Interestingly, the enhancement was also apparent in uninfected animals suggesting that IFN-gamma and its anti-angiogenic effects underlie both infection-dependent and -independent tumor surveillance.
View details for Web of Science ID 000188846200017
View details for PubMedID 14688478
CDX1 is a homeobox protein that inhibits proliferation of intestinal epithelial cells and regulates intestine-specific genes involved in differentiation. CDX1 expression is developmentally and spatially regulated, and its expression is aberrantly down-regulated in colorectal cancers and colon cancer-derived cell lines. However, very little is known about the molecular mechanism underlying the regulation of CDX1 gene expression. In this study, we characterized the CDX1 gene structure and identified that its gene promoter contained a typical CpG island with a CpG observed/expected ratio of 0.80, suggesting that the CDX1 gene is a target of aberrant methylation. Alterations of DNA methylation in the CDX1 gene promoter were investigated in a series of colorectal cancer cell lines. Combined Bisulfite Restriction Analysis (COBRA) and bisulfite sequencing analysis revealed that the CDX1 promoter is methylated in CDX1 non-expressing colorectal cancer cell lines but not in human normal colon tissue and T84 cells, which express CDX1. Treatment with 5'-aza-2'-deoxycytidine (5-azaC), a DNA methyltransferase inhibitor, induced CDX1 expression in the colorectal cancer cell lines. Furthermore, de novo methylation was determined by establishing stably transfected clones of the CDX1 promoter in SW480 cells and demethylation by 5-azaC-activated reporter gene expression. These results indicate that aberrant methylation of the CpG island in the CDX1 promoter is one of the mechanisms that mediate CDX1 down-regulation in colorectal cancer cell lines.
View details for DOI 10.1074/jbc.M205567200
View details for Web of Science ID 000178275100005
View details for PubMedID 12124393