Bio

Professional Education


  • Bachelor of Science, University of Guelph (2011)
  • Doctor of Philosophy, University of British Columbia (2018)

Stanford Advisors


Research & Scholarship

Lab Affiliations


Publications

All Publications


  • IRES-dependent ribosome repositioning directs translation of a+1 overlapping ORF that enhances viral infection NUCLEIC ACIDS RESEARCH Kerr, C. H., Wang, Q. S., Moon, K., Keatings, K., Allan, D. W., Foster, L. J., Jan, E. 2018; 46 (22): 11952–67

    Abstract

    RNA structures can interact with the ribosome to alter translational reading frame maintenance and promote recoding that result in alternative protein products. Here, we show that the internal ribosome entry site (IRES) from the dicistrovirus Cricket paralysis virus drives translation of the 0-frame viral polyprotein and an overlapping +1 open reading frame, called ORFx, via a novel mechanism whereby a subset of ribosomes recruited to the IRES bypasses 37 nucleotides downstream to resume translation at the +1-frame 13th non-AUG codon. A mutant of CrPV containing a stop codon in the +1 frame ORFx sequence, yet synonymous in the 0-frame, is attenuated compared to wild-type virus in a Drosophila infection model, indicating the importance of +1 ORFx expression in promoting viral pathogenesis. This work demonstrates a novel programmed IRES-mediated recoding strategy to increase viral coding capacity and impact virus infection, highlighting the diversity of RNA-driven translation initiation mechanisms in eukaryotes.

    View details for DOI 10.1093/nar/gky1121

    View details for Web of Science ID 000456714000028

    View details for PubMedID 30418631

    View details for PubMedCentralID PMC6294563

  • Transmission of Cricket paralysis virus via exosome-like vesicles during infection of Drosophila cells SCIENTIFIC REPORTS Kerr, C. H., Dalwadi, U., Scott, N. E., Yip, C. K., Foster, L. J., Jan, E. 2018; 8: 17353

    Abstract

    Viruses are classically characterized as being either enveloped or nonenveloped depending on the presence or absence of a lipid bi-layer surrounding their proteinaceous capsid. In recent years, many studies have challenged this view by demonstrating that some nonenveloped viruses (e.g. hepatitis A virus) can acquire an envelope during infection by hijacking host cellular pathways. In this study, we examined the role of exosome-like vesicles (ELVs) during infection of Drosophilia melanogaster S2 cells by Cricket paralysis virus (CrPV). Utilizing quantitative proteomics, we demonstrated that ELVs can be isolated from both mock- and CrPV-infected S2 cells that contain distinct set of proteins compared to the cellular proteome. Moreover, 40 proteins increased in abundance in ELVs derived from CrPV-infected cells compared to mock, suggesting specific factors associate with ELVs during infection. Interestingly, peptides from CrPV capsid proteins (ORF2) and viral RNA were detected in ELVs from infected cells. Finally, ELVs from CrPV-infected cells are infectious suggesting that CrPV may hijack ELVs to acquire an envelope during infection of S2 cells. This study further demonstrates the diverse strategies of nonenveloped viruses from invertebrates to vertebrates to acquire an envelope in order to evade the host response or facilitate transmission.

    View details for DOI 10.1038/s41598-018-35717-5

    View details for Web of Science ID 000451182100025

    View details for PubMedID 30478341

    View details for PubMedCentralID PMC6255767

  • A Viral Protein Restricts Drosophila RNAi Immunity by Regulating Argonaute Activity and Stability CELL HOST & MICROBE Nayak, A., Kim, D., Trnka, M. J., Kerr, C. H., Lidsky, P. V., Stanley, D. J., Rivera, B., Li, K. H., Burlingame, A. L., Jan, E., Frydman, J., Gross, J. D., Andino, R. 2018; 24 (4): 542-+

    Abstract

    The dicistrovirus, Cricket paralysis virus (CrPV) encodes an RNA interference (RNAi) suppressor, 1A, which modulates viral virulence. Using the Drosophila model, we combined structural, biochemical, and virological approaches to elucidate the strategies by which CrPV-1A restricts RNAi immunity. The atomic resolution structure of CrPV-1A uncovered a flexible loop that interacts with Argonaute 2 (Ago-2), thereby inhibiting Ago-2 endonuclease-dependent immunity. Mutations disrupting Ago-2 binding attenuates viral pathogenesis in wild-type but not Ago-2-deficient flies. CrPV-1A also contains a BC-box motif that enables the virus to hijack a host Cul2-Rbx1-EloBC ubiquitin ligase complex, which promotes Ago-2 degradation and virus replication. Our study uncovers a viral-based dual regulatory program that restricts antiviral immunity by direct interaction with and modulation of host proteins. While the direct inhibition of Ago-2 activity provides an efficient mechanism to establish infection, the recruitment of a ubiquitin ligase complex enables CrPV-1A to amplify Ago-2 inactivation to restrict further antiviral RNAi immunity.

    View details for PubMedID 30308158

  • Cardiolipin synthase A colocalizes with cardiolipin and osmosensing transporter ProP at the poles of Escherichia coli cells MOLECULAR MICROBIOLOGY Romantsov, T., Gonzalez, K., Sahtout, N., Culham, D. E., Coumoundouros, C., Garner, J., Kerr, C. H., Chang, L., Turner, R. J., Wood, J. M. 2018; 107 (5): 623–38

    Abstract

    Osmosensing by transporter ProP is modulated by its cardiolipin (CL)-dependent concentration at the poles of Escherichia coli cells. Other contributors to this phenomenon were sought with the BACterial Two-Hybrid System (BACTH). The BACTH-tagged variants T18-ProP and T25-ProP retained ProP function and localization. Their interaction confirmed the ProP homo-dimerization previously established by protein crosslinking. YdhP, YjbJ and ClsA were prominent among the putative ProP interactors identified by the BACTH system. The functions of YdhP and YjbJ are unknown, although YjbJ is an abundant, osmotically induced, soluble protein. ClsA (CL Synthase A) had been shown to determine ProP localization by mediating CL synthesis. Unlike a deletion of clsA, deletion of ydhP or yjbJ had no effect on ProP localization or function. All three proteins were concentrated at the cell poles, but only ClsA localization was CL-dependent. ClsA was shown to be N-terminally processed and membrane-anchored, with dual, cytoplasmic, catalytic domains. Active site amino acid replacements (H224A plus H404A) inactivated ClsA and compromised ProP localization. YdhP and YjbJ may be ClsA effectors, and interactions of YdhP, YjbJ and ClsA with ProP may reflect their colocalization at the cell poles. Targeted CL synthesis may contribute to the polar localization of CL, ClsA and ProP.

    View details for DOI 10.1111/mmi.13904

    View details for Web of Science ID 000425521900003

    View details for PubMedID 29280215

  • Disruption of Stress Granule Formation by the Multifunctional Cricket Paralysis Virus 1A Protein JOURNAL OF VIROLOGY Khong, A., Kerr, C. H., Yeung, C. L., Keatings, K., Nayak, A., Allan, D. W., Jan, E. 2017; 91 (5)

    Abstract

    Stress granules (SGs) are cytosolic ribonucleoprotein aggregates that are induced during cellular stress. Several viruses modulate SG formation, suggesting that SGs have an impact on virus infection. However, the mechanisms and impact of modulating SG assembly in infected cells are not completely understood. In this study, we identify the dicistrovirus cricket paralysis virus 1A (CrPV-1A) protein that functions to inhibit SG assembly during infection. Moreover, besides inhibiting RNA interference, CrPV-1A also inhibits host transcription, which indirectly modulates SG assembly. Thus, CrPV-1A is a multifunctional protein. We identify a key R146A residue that is responsible for these effects, and mutant CrPV(R146A) virus infection is attenuated in Drosophila melanogaster S2 cells and adult fruit flies and results in increased SG formation. Treatment of CrPV(R146A)-infected cells with actinomycin D, which represses transcription, restores SG assembly suppression and viral yield. In summary, CrPV-1A modulates several cellular processes to generate a cellular environment that promotes viral translation and replication.IMPORTANCE RNA viruses encode a limited set of viral proteins to modulate an array of cellular processes in order to facilitate viral replication and inhibit antiviral defenses. In this study, we identified a viral protein, called CrPV-1A, within the dicistrovirus cricket paralysis virus that can inhibit host transcription, modulate viral translation, and block a cellular process called stress granule assembly. We also identified a specific amino acid within CrPV-1A that is important for these cellular processes and that mutant viruses containing mutations of CrPV-1A attenuate virus infection. We also demonstrate that the CrPV-1A protein can also modulate cellular processes in human cells, suggesting that the mode of action of CrPV-1A is conserved. We propose that CrPV-1A is a multifunctional, versatile protein that creates a cellular environment in virus-infected cells that permits productive virus infection.

    View details for DOI 10.1128/JVI.01779-16

    View details for Web of Science ID 000394356400008

    View details for PubMedID 28003491

    View details for PubMedCentralID PMC5309961

  • Molecular analysis of the factorless internal ribosome entry site in Cricket Paralysis virus infection SCIENTIFIC REPORTS Kerr, C. H., Ma, Z., Jang, C. J., Thompson, S. R., Jan, E. 2016; 6: 37319

    Abstract

    The dicistrovirus Cricket Paralysis virus contains a unique dicistronic RNA genome arrangement, encoding two main open reading frames that are driven by distinct internal ribosome entry sites (IRES). The intergenic region (IGR) IRES adopts an unusual structure that directly recruits the ribosome and drives translation of viral structural proteins in a factor-independent manner. While structural, biochemical, and biophysical approaches have provided mechanistic details into IGR IRES translation, these studies have been limited to in vitro systems and little is known about the behavior of these IRESs during infection. Here, we examined the role of previously characterized IGR IRES mutations on viral yield and translation in CrPV-infected Drosophila S2 cells. Using a recently generated infectious CrPV clone, introduction of a subset of mutations that are known to disrupt IRES activity failed to produce virus, demonstrating the physiological relevance of specific structural elements within the IRES for virus infection. However, a subset of mutations still led to virus production, thus revealing the key IRES-ribosome interactions for IGR IRES translation in infected cells, which highlights the importance of examining IRES activity in its physiological context. This is the first study to examine IGR IRES translation in its native context during virus infection.

    View details for DOI 10.1038/srep37319

    View details for Web of Science ID 000388176500001

    View details for PubMedID 27853311

    View details for PubMedCentralID PMC5112510

  • Commandeering the Ribosome: Lessons Learned from Dicistroviruses about Translation JOURNAL OF VIROLOGY Kerr, C. H., Jan, E. 2016; 90 (12): 5538–40

    Abstract

    To replicate, all viruses depend entirely on the enslavement of host cell ribosomes for their own advantage. To this end, viruses have evolved a multitude of translational strategies to usurp the ribosome. RNA-based structures known as internal ribosome entry sites (IRESs) are among the most notable mechanisms employed by viruses to seize host ribosomes. In this article, we spotlight the intergenic region IRES from the Dicistroviridae family of viruses and its importance as a model for IRES-dependent translation and in understanding fundamental properties of translation.

    View details for DOI 10.1128/JVI.00737-15

    View details for Web of Science ID 000377227600002

    View details for PubMedID 27053555

    View details for PubMedCentralID PMC4886786

  • Temporal Regulation of Distinct Internal Ribosome Entry Sites of the Dicistroviridae Cricket Paralysis Virus VIRUSES-BASEL Khong, A., Bonderoff, J. M., Spriggs, R. V., Tammpere, E., Kerr, C. H., Jackson, T. J., Willis, A. E., Jan, E. 2016; 8 (1)

    Abstract

    Internal ribosome entry is a key mechanism for viral protein synthesis in a subset of RNA viruses. Cricket paralysis virus (CrPV), a member of Dicistroviridae, has a positive-sense single strand RNA genome that contains two internal ribosome entry sites (IRES), a 5'untranslated region (5'UTR) and intergenic region (IGR) IRES, that direct translation of open reading frames (ORF) encoding the viral non-structural and structural proteins, respectively. The regulation of and the significance of the CrPV IRESs during infection are not fully understood. In this study, using a series of biochemical assays including radioactive-pulse labelling, reporter RNA assays and ribosome profiling, we demonstrate that while 5'UTR IRES translational activity is constant throughout infection, IGR IRES translation is delayed and then stimulated two to three hours post infection. The delay in IGR IRES translation is not affected by inhibiting global translation prematurely via treatment with Pateamine A. Using a CrPV replicon that uncouples viral translation and replication, we show that the increase in IGR IRES translation is dependent on expression of non-structural proteins and is greatly stimulated when replication is active. Temporal regulation by distinct IRESs within the CrPV genome is an effective viral strategy to ensure optimal timing and expression of viral proteins to facilitate infection.

    View details for DOI 10.3390/v8010025

    View details for Web of Science ID 000373915000013

    View details for PubMedID 26797630

    View details for PubMedCentralID PMC4728584

  • The 5 ' Untranslated Region of a Novel Infectious Molecular Clone of the Dicistrovirus Cricket Paralysis Virus Modulates Infection JOURNAL OF VIROLOGY Kerr, C. H., Wang, Q. S., Keatings, K., Khong, A., Allan, D., Yip, C. K., Foster, L. J., Jan, E. 2015; 89 (11): 5919–34

    Abstract

    Dicistroviridae are a family of RNA viruses that possesses a single-stranded positive-sense RNA genome containing two distinct open reading frames (ORFs), each preceded by an internal ribosome entry site that drives translation of the viral structural and nonstructural proteins, respectively. The type species, Cricket paralysis virus (CrPV), has served as a model for studying host-virus interactions; however, investigations into the molecular mechanisms of CrPV and other dicistroviruses have been limited as an established infectious clone was elusive. Here, we report the construction of an infectious molecular clone of CrPV. Transfection of in vitro-transcribed RNA from the CrPV clone into Drosophila Schneider line 2 (S2) cells resulted in cytopathic effects, viral RNA accumulation, detection of negative-sense viral RNA, and expression of viral proteins. Transmission electron microscopy, viral titers, and immunofluorescence-coupled transwell assays demonstrated that infectious viral particles are released from transfected cells. In contrast, mutant clones containing stop codons in either ORF decreased virus infectivity. Injection of adult Drosophila flies with virus derived from CrPV clones but not UV-inactivated clones resulted in mortality. Molecular analysis of the CrPV clone revealed a 196-nucleotide duplication within its 5' untranslated region (UTR) that stimulated translation of reporter constructs. In cells infected with the CrPV clone, the duplication inhibited viral infectivity yet did not affect viral translation or RNA accumulation, suggesting an effect on viral packaging or entry. The generation of the CrPV infectious clone provides a powerful tool for investigating the viral life cycle and pathogenesis of dicistroviruses and may further understanding of fundamental host-virus interactions in insect cells.Dicistroviridae, which are RNA viruses that infect arthropods, have served as a model to gain insights into fundamental host-virus interactions in insect cells. Further insights into the viral molecular mechanisms are hampered due to a lack of an established infectious clone. We report the construction of the first infectious clone of the dicistrovirus, cricket paralysis virus (CrPV). We show that transfection of the CrPV clone RNA into Drosophila cells led to production of infectious particles that resemble natural CrPV virions and result in cytopathic effects and expression of CrPV proteins and RNA in infected cells. The CrPV clone should provide insights into the dicistrovirus life cycle and host-virus interactions in insect cells. Using this clone, we find that a 196-nucleotide duplication within the 5' untranslated region of the CrPV clone increased viral translation in reporter constructs but decreased virus infectivity, thus revealing a balance that interplays between viral translation and replication.

    View details for DOI 10.1128/JVI.00463-15

    View details for Web of Science ID 000353907900016

    View details for PubMedID 25810541

    View details for PubMedCentralID PMC4442438

  • Analysis of Strains Lacking Known Osmolyte Accumulation Mechanisms Reveals Contributions of Osmolytes and Transporters to Protection against Abiotic Stress APPLIED AND ENVIRONMENTAL MICROBIOLOGY Murdock, L., Burke, T., Coumoundouros, C., Culham, D. E., Deutch, C. E., Ellinger, J., Kerr, C. H., Plater, S. M., To, E., Wright, G., Wood, J. M. 2014; 80 (17): 5366–78

    Abstract

    Osmolyte accumulation and release can protect cells from abiotic stresses. In Escherichia coli, known mechanisms mediate osmotic stress-induced accumulation of K(+) glutamate, trehalose, or zwitterions like glycine betaine. Previous observations suggested that additional osmolyte accumulation mechanisms (OAMs) exist and their impacts may be abiotic stress specific. Derivatives of the uropathogenic strain CFT073 and the laboratory strain MG1655 lacking known OAMs were created. CFT073 grew without osmoprotectants in minimal medium with up to 0.9 M NaCl. CFT073 and its OAM-deficient derivative grew equally well in high- and low-osmolality urine pools. Urine-grown bacteria did not accumulate large amounts of known or novel osmolytes. Thus, CFT073 showed unusual osmotolerance and did not require osmolyte accumulation to grow in urine. Yeast extract and brain heart infusion stimulated growth of the OAM-deficient MG1655 derivative at high salinity. Neither known nor putative osmoprotectants did so. Glutamate and glutamine accumulated after growth with either organic mixture, and no novel osmolytes were detected. MG1655 derivatives retaining individual OAMs were created. Their abilities to mediate osmoprotection were compared at 15°C, 37°C without or with urea, and 42°C. Stress protection was not OAM specific, and variations in osmoprotectant effectiveness were similar under all conditions. Glycine betaine and dimethylsulfoniopropionate (DMSP) were the most effective. Trimethylamine-N-oxide (TMAO) was a weak osmoprotectant and a particularly effective urea protectant. The effectiveness of glycine betaine, TMAO, and proline as osmoprotectants correlated with their preferential exclusion from protein surfaces, not with their propensity to prevent protein denaturation. Thus, their effectiveness as stress protectants correlated with their ability to rehydrate the cytoplasm.

    View details for DOI 10.1128/AEM.01138-14

    View details for Web of Science ID 000341486500021

    View details for PubMedID 24951793

    View details for PubMedCentralID PMC4136119

  • Salinity-Dependent Impacts of ProQ, Prc, and Spr Deficiencies on Escherichia coli Cell Structure JOURNAL OF BACTERIOLOGY Kerr, C. H., Culham, D. E., Marom, D., Wood, J. M. 2014; 196 (6): 1286–96

    Abstract

    ProQ is a cytoplasmic protein with RNA chaperone activities that reside in FinO- and Hfq-like domains. Lesions at proQ decrease the level of the osmoregulatory glycine betaine transporter ProP. Lesions at proQ eliminated ProQ and Prc, the periplasmic protease encoded by the downstream gene prc. They dramatically slowed the growth of Escherichia coli populations and altered the morphologies of E. coli cells in high-salinity medium. ProQ and Prc deficiencies were associated with different phenotypes. ProQ-deficient bacteria were elongated unless glycine betaine was provided. High-salinity cultures of Prc-deficient bacteria included spherical cells with an enlarged periplasm and an eccentric nucleoid. The nucleoid-containing compartment was bounded by the cytoplasmic membrane and peptidoglycan. This phenotype was not evident in bacteria cultivated at low or moderate salinity, nor was it associated with murein lipoprotein (Lpp) deficiency, and it differed from those elicited by the MreB inhibitor A-22 or the FtsI inhibitor aztreonam at low or high salinity. It was suppressed by deletion of spr, which encodes one of three murein hydrolases that are redundantly essential for enlargement of the murein sacculus. Prc deficiency may alter bacterial morphology by impairing control of Spr activity at high salinity. ProQ and Prc deficiencies lowered the ProP activity of bacteria cultivated at moderate salinity by approximately 70% and 30%, respectively, but did not affect other osmoregulatory functions. The effects of ProQ and Prc deficiencies on ProP activity are indirect, reflecting their roles in the maintenance of cell structure.

    View details for DOI 10.1128/JB.00827-13

    View details for Web of Science ID 000332628700016

    View details for PubMedID 24443528

    View details for PubMedCentralID PMC3957721