- Infectious Disease
Assistant Professor (UTL), Department of Medicine, Department of Microbiology and Immunology (2011 - Present)
Instructor of Medicine, Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine (2009 - 2011)
Infectious Diseases Fellowship, Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine (2004 - 2008)
Postdoctoral Fellowship. Supervisor: Dr. Jeffrey S. Glenn, Division of Gastroenterology and Hepatology, Stanford University School of Medicine (2003 - 2004)
Medical Internship and Residency, Internal Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA (1999 - 2002)
Research Studentship, Supervisor: Dr. Michael C. Carroll., Brigham and Womens Hospital and the Center for Blood Research, Harvard Medical School, Boston, MA (1999 - 1999)
Rotating internship (part of the M.D. requirements in Israel), Suraski Medical Center, Tel-Aviv, Israel (1997 - 1998)
Honors & Awards
Research Scholar Grant, American Cancer Society (2014)
Clinical Scientist Development Award, Doris Duke Charitable Foundation (2013)
Stanford Bio-X Interdisciplinary Initiative Program Award, Stanford, Bio-X (2012)
IDSA 2012 IDWeek Investigator Award, Infectious Diseases Society of America (IDSA) (2012)
IDSA 2009 Program Committee Choice Award, Infectious Diseases Society of America (IDSA) (July 2009)
DDC Pilot/Feasibility Award, Stanford Digestive Disease Center (DDC) (March 2009)
ITI Young Investigator Innovation Award, Stanford Institute for Immunity, Transplantation, and Infection (ITI) (Dec 2008)
Mentored Clinical Scientist Development Award (KO8), NIH/NIAID (Sept 2008 - July 2013)
American Liver Foundation Postdoctoral Fellowship Award, American Liver Foundation (ALF) (July 2006)
Deans Fellowship Award, Stanford University School of Medicine, Stanford, CA (2004)
Fellow Travel Award, International Symposium on Hepatitis C Virus & Related Viruses (2004)
Excellence in Teaching Housestaff Award, Harvard Medical School, Boston, MA (2002)
Outstanding Thesis Award, Sackler School of Medicine, Tel-Aviv University (1999)
Deans Honor List (in four consecutive years), Sackler School of Medicine, Tel-Aviv University (1994-1997)
M.D. graduation magna cum laude, Sackler School of Medicine, Tel-Aviv University (1997)
B.A. graduation magna cum laude, Sackler School of Medicine, Tel-Aviv University (1994)
Residency:Beth Israel Deaconess Med Center/Harvard (2002) MA
Fellowship:Stanford University - Infectious Diseases (2009) CA
Board Certification: Infectious Disease, American Board of Internal Medicine (2006)
Internship:Beth Israel Deaconess Med Center/Harvard (2000) MA
Medical Education:Sackler School of Medicine (1999) Israel
BA, Sackler School of Medicine, Israel, Medical sciences (1994)
MD, Sackler School of Medicine, Israel, Medicine (1999)
Current Research and Scholarly Interests
The goals of my lab are to better understand virus-host protein interactions, identify host partners conservatively required by multiple viruses, and develop broad-spectrum host-centered antiviral approaches with a high genetic barrier for resistance. We combine novel proteomic approaches, including microfluidics platforms, with molecular virology, biochemical, and genomic approaches to achieve these goals. We focus on viruses from the Flaviviridae family (hepatitis C and dengue), as well as HIV.
1. Mechanisms by which Flaviviridae and HIV hijack intracellular membrane trafficking pathways for mediating viral assembly, release, and direct cell-to-cell spread. We have identified several sorting signals within Flaviviridae proteins that are involved in mediating key steps in the viral cycle. We are currently mapping the interaction networks of these signals with human proteins, and investigating the functional relevance, regulatory mechanisms, and inhibition of these interactions. Additional projects involve interactions with cytoskeleton dynamics proteins, ESCRT machinery and more.
2. Mechanisms of HCV-related cancer. Chronic HCV infection is a major cause of hepatocellular carcinoma and is also associated with non-Hodgkin lymphoma. We study virus-host interactions involved in facilitating viral persistence (a precursor to HCV-related oncogenesis).
3. Molecular mechanisms underlying HCV-HIV co-infection.
4. Furthering novel high-throughput proteomic technologies for screening and mapping virus-host interactomes and for screening small molecule libraries for inhibitors of protein-protein interactions.
Independent Studies (6)
- Directed Reading in Medicine
MED 299 (Aut, Win, Spr, Sum)
- Early Clinical Experience in Medicine
MED 280 (Aut, Win, Spr, Sum)
- Graduate Research
MED 399 (Aut, Win, Spr, Sum)
- Medical Scholars Research
MED 370 (Aut, Win, Spr, Sum)
- Out-of-Department Advanced Research Laboratory in Experimental Biology
BIO 199X (Aut, Win, Spr)
- Undergraduate Research
MED 199 (Aut, Win, Spr, Sum)
- Directed Reading in Medicine
Graduate and Fellowship Programs
Selective Inhibitors of Cyclin G Associated Kinase (GAK) as Anti-Hepatitis C Agents
JOURNAL OF MEDICINAL CHEMISTRY
2015; 58 (8): 3393-3410
Cyclin-G associated kinase (GAK) emerged as a promising drug target for the treatment of viral infections. However, no potent and selective GAK inhibitors have been reported in the literature to date. This paper describes the discovery of isothiazolo[5,4-b]pyridines as selective GAK inhibitors, with the most potent congeners displaying low nanomolar binding affinity for GAK. Co-crystallization experiments revealed that these compounds behaved as classic type I ATP-competitive kinase inhibitors. In addition, we have demonstrated that these compounds exhibit a potent activity against hepatitis C virus (HCV) by inhibiting two temporally distinct steps in the HCV lifecycle (i.e. viral entry and assembly). Hence, these GAK inhibitors represent chemical probes to study GAK function in different disease areas where GAK has been implicated (including viral infection, cancer and Parkinson's disease).
View details for DOI 10.1021/jm501759m
View details for Web of Science ID 000353602200009
View details for PubMedID 25822739
- Infectious disease. Combating emerging viral threats. Science 2015; 348 (6232): 282-283
AP-2-Associated Protein Kinase 1 and Cyclin G-Associated Kinase Regulate Hepatitis C Virus Entry and Are Potential Drug Targets
JOURNAL OF VIROLOGY
2015; 89 (8): 4387-4404
Hepatitis C virus (HCV) enters its target cell via clathrin-mediated endocytosis. AP-2-associated protein kinase 1 (AAK1) and cyclin G-associated kinase (GAK) are host kinases that regulate clathrin adaptor protein (AP)-mediated trafficking in the endocytic and secretory pathways. We previously reported that AAK1 and GAK regulate HCV assembly by stimulating binding of the μ subunit of AP-2, AP2M1, to HCV core protein. We also discovered that AAK1 and GAK inhibitors, including the approved anticancer drugs sunitinib and erlotinib, could block HCV assembly. Here, we hypothesized that AAK1 and GAK regulate HCV entry independently of their effect on HCV assembly. Indeed, silencing AAK1 and GAK expression inhibited entry of pseudoparticles and cell culture grown-HCV and internalization of Dil-labeled HCV particles with no effect on HCV attachment or RNA replication. AAK1 or GAK depletion impaired epidermal growth factor (EGF)-mediated enhanced HCV entry and endocytosis of EGF receptor (EGFR), an HCV entry cofactor and erlotinib's cancer target. Moreover, either RNA interference-mediated depletion of AP2M1 or NUMB, each a substrate of AAK1 and/or GAK, or overexpression of either an AP2M1 or NUMB phosphorylation site mutant inhibited HCV entry. Last, in addition to affecting assembly, sunitinib and erlotinib inhibited HCV entry at a postbinding step, their combination was synergistic, and their antiviral effect was reversed by either AAK1 or GAK overexpression. Together, these results validate AAK1 and GAK as critical regulators of HCV entry that function in part by activating EGFR, AP2M1, and NUMB and as the molecular targets underlying the antiviral effect of sunitinib and erlotinib (in addition to EGFR), respectively.Understanding the host pathways hijacked by HCV is critical for developing host-centered anti-HCV approaches. Entry represents a potential target for antiviral strategies; however, no FDA-approved HCV entry inhibitors are currently available. We reported that two host kinases, AAK1 and GAK, regulate HCV assembly. Here, we provide evidence that AAK1 and GAK regulate HCV entry independently of their role in HCV assembly and define the mechanisms underlying AAK1- and GAK-mediated HCV entry. By regulating temporally distinct steps in the HCV life cycle, AAK1 and GAK represent "master regulators" of HCV infection and potential targets for antiviral strategies. Indeed, approved anticancer drugs that potently inhibit AAK1 or GAK inhibit HCV entry in addition to assembly. These results contribute to an understanding of the mechanisms of HCV entry and reveal attractive host targets for antiviral strategies as well as approved candidate inhibitors of these targets, with potential implications for other viruses that hijack clathrin-mediated pathways.
View details for DOI 10.1128/JVI.02705-14
View details for Web of Science ID 000352218400030
View details for PubMedID 25653444
B-cell receptors expressed by lymphomas of hepatitis C virus (HCV)-infected patients rarely react with the viral proteins
2014; 123 (10): 1512-1515
Chronic HCV infection has been implicated in the induction and maintenance of B-cell lymphomas. The strongest evidence for this comes from clinical observations of tumor regressions upon anti-viral treatments. Here we used multiple methods to test the hypothesis that the expansion of HCV-specific B cells gives rise to lymphomas. We obtained lymphoma tissues from HCV-infected lymphoma patients, including some that later regressed upon anti-viral treatments. We expressed the lymphoma B-cell receptors (BCRs) as soluble IgGs and membrane IgMs, and analyzed their reactivity with HCV proteins and with HCV virions. We confirmed previous reports that HCV-associated lymphomas use a restricted immunoglobulin variable region (V) gene repertoire. However, we found no evidence for their binding to the HCV antigens. We conclude that most lymphomas of HCV-infected patients do not arise from B cells aimed at eliminating the virus.
View details for DOI 10.1182/blood-2013-10-532895
View details for Web of Science ID 000335844600018
Identification and Targeting of an Interaction between a Tyrosine Motif within Hepatitis C Virus Core Protein and AP2M1 Essential for Viral Assembly
2012; 8 (8)
Novel therapies are urgently needed against hepatitis C virus infection (HCV), a major global health problem. The current model of infectious virus production suggests that HCV virions are assembled on or near the surface of lipid droplets, acquire their envelope at the ER, and egress through the secretory pathway. The mechanisms of HCV assembly and particularly the role of viral-host protein-protein interactions in mediating this process are, however, poorly understood. We identified a conserved heretofore unrecognized YXX? motif (? is a bulky hydrophobic residue) within the core protein. This motif is homologous to sorting signals within host cargo proteins known to mediate binding of AP2M1, the ? subunit of clathrin adaptor protein complex 2 (AP-2), and intracellular trafficking. Using microfluidics affinity analysis, protein-fragment complementation assays, and co-immunoprecipitations in infected cells, we show that this motif mediates core binding to AP2M1. YXX? mutations, silencing AP2M1 expression or overexpressing a dominant negative AP2M1 mutant had no effect on HCV RNA replication, however, they dramatically inhibited intra- and extracellular infectivity, consistent with a defect in viral assembly. Quantitative confocal immunofluorescence analysis revealed that core's YXX? motif mediates recruitment of AP2M1 to lipid droplets and that the observed defect in HCV assembly following disruption of core-AP2M1 binding correlates with accumulation of core on lipid droplets, reduced core colocalization with E2 and reduced core localization to trans-Golgi network (TGN), the presumed site of viral particles maturation. Furthermore, AAK1 and GAK, serine/threonine kinases known to stimulate binding of AP2M1 to host cargo proteins, regulate core-AP2M1 binding and are essential for HCV assembly. Last, approved anti-cancer drugs that inhibit AAK1 or GAK not only disrupt core-AP2M1 binding, but also significantly inhibit HCV assembly and infectious virus production. These results validate viral-host interactions essential for HCV assembly and yield compounds for pharmaceutical development.
View details for DOI 10.1371/journal.ppat.1002845
View details for Web of Science ID 000308558000023
View details for PubMedID 22916011
The Hepatitis C Virus (HCV) NS4B RNA Binding Inhibitor Clemizole Is Highly Synergistic with HCV Protease Inhibitors
JOURNAL OF INFECTIOUS DISEASES
2010; 202 (1): 65-74
We recently identified a compound, clemizole hydrochloride, that inhibits NS4B's RNA binding and hepatitis C virus (HCV) replication. Although significant, clemizole's antiviral effect is moderate (50% effective concentration of 8 microM against an HCV genotype 2a clone). We hypothesized that the combination of clemizole with other anti-HCV agents can increase the antiviral effect over that achieved with each drug alone and could also decrease the emergence of viral resistance.Luciferase reporter-linked HCV replication assays were used to study the antiviral effects of drug combinations that included clemizole. Data were analyzed using Loewe additivity and Bliss independence models for synergy, and resistance studies were performed using HCV colony formation assays.Clemizole's antiviral effect was highly synergistic with the HCV protease inhibitors SCH503034 and VX950, without toxicity. In contrast, combinations of clemizole with either interferon, ribavirin, or the nucleoside (NM283) and nonnucleoside (HCV796) HCV polymerase inhibitors were additive. Furthermore, combination of clemizole with SCH503034 decreased the frequency of drug-resistant mutants, compared with treatment with either drug alone. Finally, no cross-resistance to clemizole of SCH503034-resistant mutants (or vice versa) was observed.Clemizole can yield high-level synergy with the protease inhibitor class. Inclusion of clemizole in future anti-HCV cocktails can represent an attractive paradigm for increasing current virologic response rates.
View details for DOI 10.1086/653080
View details for Web of Science ID 000278322300008
A small molecule inhibits HCV replication and alters NS4B's subcellular distribution
2010; 87 (1): 1-8
Hepatitis C Virus (HCV) is a leading cause of liver disease and represents a significant public health challenge. Treatments for this disease are inadequate and improved antiviral therapies are necessary. Several such antivirals are in development, most of which target the well-characterized NS3 protease or the NS5B polymerase. In contrast, the nonstructural 4B (NS4B) protein, though essential for HCV RNA replication, has been the subject of few pharmacological studies. One of the functions ascribed to this protein is the ability to form intracellular membrane-associated foci (MAF), which are believed to be related to the sites of viral replication. Here, we report the identification of a small molecule that inhibits HCV replication and disrupts the organization of these MAF. Genetic analysis links the compound's mode of action to the NS4B gene product, and transient transfections of NS4B-GFP demonstrate that treatment with this compound can lead to the formation of novel elongated assemblies of NS4B. Furthermore, an in vitro dynamic light scattering assay provides evidence that the second amphipathic helix of NS4B may be the target of the drug. Our results demonstrate that this molecule represents a new potential class of HCV inhibitors and also provides us with a useful tool for studying the HCV life cycle.
View details for DOI 10.1016/j.antiviral.2010.03.013
View details for Web of Science ID 000279452800001
View details for PubMedID 20363257
Six RNA Viruses and Forty-One Hosts: Viral Small RNAs and Modulation of Small RNA Repertoires in Vertebrate and Invertebrate Systems
2010; 6 (2)
We have used multiplexed high-throughput sequencing to characterize changes in small RNA populations that occur during viral infection in animal cells. Small RNA-based mechanisms such as RNA interference (RNAi) have been shown in plant and invertebrate systems to play a key role in host responses to viral infection. Although homologs of the key RNAi effector pathways are present in mammalian cells, and can launch an RNAi-mediated degradation of experimentally targeted mRNAs, any role for such responses in mammalian host-virus interactions remains to be characterized. Six different viruses were examined in 41 experimentally susceptible and resistant host systems. We identified virus-derived small RNAs (vsRNAs) from all six viruses, with total abundance varying from "vanishingly rare" (less than 0.1% of cellular small RNA) to highly abundant (comparable to abundant micro-RNAs "miRNAs"). In addition to the appearance of vsRNAs during infection, we saw a number of specific changes in host miRNA profiles. For several infection models investigated in more detail, the RNAi and Interferon pathways modulated the abundance of vsRNAs. We also found evidence for populations of vsRNAs that exist as duplexed siRNAs with zero to three nucleotide 3' overhangs. Using populations of cells carrying a Hepatitis C replicon, we observed strand-selective loading of siRNAs onto Argonaute complexes. These experiments define vsRNAs as one possible component of the interplay between animal viruses and their hosts.
View details for DOI 10.1371/journal.ppat.1000764
View details for Web of Science ID 000275295900016
View details for PubMedID 20169186
Discovery of a hepatitis C target and its pharmacological inhibitors by microfluidic affinity analysis
2008; 26 (9): 1019-1027
More effective therapies are urgently needed against hepatitis C virus (HCV), a major cause of viral hepatitis. We used in vitro protein expression and microfluidic affinity analysis to study RNA binding by the HCV transmembrane protein NS4B, which plays an essential role in HCV RNA replication. We show that HCV NS4B binds RNA and that this binding is specific for the 3' terminus of the negative strand of the viral genome with a dissociation constant (Kd) of approximately 3.4 nM. A high-throughput microfluidic screen of a compound library identified 18 compounds that substantially inhibited binding of RNA by NS4B. One of these compounds, clemizole hydrochloride, was found to inhibit HCV RNA replication in cell culture that was mediated by its suppression of NS4B's RNA binding, with little toxicity for the host cell. These results yield new insight into the HCV life cycle and provide a candidate compound for pharmaceutical development.
View details for DOI 10.1038/nbt.1490
View details for Web of Science ID 000259074700025
View details for PubMedID 18758449
The nucleotide binding motif of hepatitis C virus NS4B can mediate cellular transformation and tumor formation without ha-ras co-transfection
2008; 47 (3): 827-835
Hepatitis C virus (HCV) is an important cause of chronic liver disease and is complicated by hepatocellular carcinoma (HCC). Mechanisms whereby the virus promotes cellular transformation are poorly understood. We hypothesized that the guanosine triphosphatase activity encoded in the HCV NS4B protein's nucleotide binding motif (NBM) might play a role in the transformation process. Here we report that NS4B can transform NIH-3T3 cells, leading to tumor formation in vivo. This transformation was independent of co-transfection with activated Ha-ras. Detailed analyses of NS4B mutants revealed that this transforming activity could be progressively inhibited and completely abrogated by increasing genetic impairment of the NS4B nucleotide binding motif.NS4B has in vitro and in vivo tumorigenic potential, and the NS4B transforming activity is indeed mediated by its NBM. Moreover, our results suggest that pharmacological inhibition of the latter might inhibit not only HCV replication but also the associated HCC.
View details for DOI 10.1002/hep.22108
View details for Web of Science ID 000253698900009
View details for PubMedID 18081150
TBC1D20 is a Rab1 GTPase-activating protein that mediates hepatitis C virus replication
JOURNAL OF BIOLOGICAL CHEMISTRY
2007; 282 (50): 36354-36361
Like other viruses, productive hepatitis C virus (HCV) infection depends on certain critical host factors. We have recently shown that an interaction between HCV nonstructural protein NS5A and a host protein, TBC1D20, is necessary for efficient HCV replication. TBC1D20 contains a TBC (Tre-2, Bub2, and Cdc16) domain present in most known Rab GTPase-activating proteins (GAPs). The latter are master regulators of vesicular membrane transport, as they control the activity of membrane-associated Rab proteins. To better understand the role of the NS5A-TBC1D20 interaction in the HCV life cycle, we used a biochemical screen to identify the TBC1D20 Rab substrate. TBC1D20 was found to be the first known GAP for Rab1, which is implicated in the regulation of anterograde traffic between the endoplasmic reticulum and the Golgi complex. Mutation of amino acids implicated in Rab GTPase activation by other TBC domain-containing GAPs abrogated the ability of TBC1D20 to activate Rab1 GTPase. Overexpression of TBC1D20 blocked the transport of exogenous vesicular stomatitis virus G protein from the endoplasmic reticulum, validating the involvement of TBC1D20 in this pathway. Rab1 depletion significantly decreased HCV RNA levels, suggesting a role for Rab1 in HCV replication. These results highlight a novel mechanism by which viruses can hijack host cell machinery and suggest an attractive model whereby the NS5A-TBC1D20 interaction may promote viral membrane-associated RNA replication.
View details for DOI 10.1074/jbc.M705221200
View details for Web of Science ID 000251458300026
View details for PubMedID 17901050
- Mechanisms of resistance to antiviral agents. In Manual of clinical microbiology, 9th edition, Murray PR ed, Baron EJ ed, Jorgensen JH ed, Pfaller MA ed, Tenover FC ed, and Yolken RH ed. American Society of Microbiology. 2007: 1689-04
A nucleotide binding motif in hepatitis C virus (HCV) NS4B mediates HCV RNA replication
JOURNAL OF VIROLOGY
2004; 78 (20): 11288-11295
Hepatitis C virus (HCV) is a major cause of viral hepatitis. There is no effective therapy for most patients. We have identified a nucleotide binding motif (NBM) in one of the virus's nonstructural proteins, NS4B. This structural motif binds and hydrolyzes GTP and is conserved across HCV isolates. Genetically disrupting the NBM impairs GTP binding and hydrolysis and dramatically inhibits HCV RNA replication. These results have exciting implications for the HCV life cycle and novel antiviral strategies.
View details for Web of Science ID 000224229000045
View details for PubMedID 15452248
Prenylation inhibitors: a novel class of antiviral agents
JOURNAL OF ANTIMICROBIAL CHEMOTHERAPY
2003; 52 (6): 883-886
Prenylation is a site-specific lipid modification of proteins. Although first described for a variety of cellular proteins, it has become apparent that viruses can also make use of this post-translational modification provided by their host cells. Depriving a virus access to prenylation can have dramatic effects on the targeted virus's life cycle. Selective pharmacological inhibitors of prenylating enzymes have been developed and shown to have potent antiviral effects in both in vitro and in vivo systems. Because prenylation inhibitors target a host cell function, are available in oral form and are surprisingly well tolerated in human trials, these compounds represent an attractive new class of antiviral agents with potential for broad-spectrum activity. After a brief outline of host cell prenylation pathways, we review below the development of prenylation inhibition as an antiviral strategy applied to a prototype target, hepatitis delta virus (HDV), and discuss the potential application of prenylation inhibitors to a broad range of other viruses.
View details for DOI 10.1093/jac/dkg490
View details for Web of Science ID 000187227000001
View details for PubMedID 14613953
Immunopathogenesis of hepatitis C virus in the immunosuppressed host.
Transplant infectious disease
2002; 4 (2): 85-92
The prevalence of chronic hepatitis C virus (HCV) infection among various groups of immunosuppressed patients is high. These groups include patients co-infected with human immunodeficiency virus (HIV), recipients of organ transplants, and those with hypogammaglobulinemia. The liver disease in the immunosuppressed host is typically severe with an unusually rapid progression to cirrhosis. This is somewhat paradoxical, as the classical model for HCV-induced liver disease assumes that cell-mediated immune responses induce liver injury. It is likely that a combination of viral-related factors and host-related factors plays a role in this accelerated natural history of HCV. Data are accumulating in immunocompromised hosts that address the immunopathogenesis of liver injury, although there are still fundamental gaps in our understanding of this process. In this review, we will focus on our current understanding of the mechanisms of liver injury and how it relates to the accelerated liver disease progression in immunocompromised hosts.
View details for PubMedID 12220245
Complement C4 is protective for lupus disease independent of C3
JOURNAL OF IMMUNOLOGY
2002; 168 (3): 1036-1041
The role of complement C3 in mediating systemic lupus erythematosus (SLE) was examined using a double-knockout C3(null)C4(null) Fas (CD95)-deficient mouse model. Results from this study reveal significant lymphadenopathy, splenomegaly, elevated titers of anti-nuclear Abs and anti-dsDNA Abs, an increased number of anti-dsDNA-producing cells in ELISPOT assay, as well as severe glomerulonephritis in the double-deficient mice. Based on these clinical, serological, and histological parameters, we find that autoimmune disease in the double-knockout group is similar in severity to that in C4(null) lpr mice, but not to that in C3(null) lpr mice. The development of severe SLE in the absence of both classical and alternative complement pathways suggests that it is the absence of C4, and not the presence of C3, that is critical in SLE pathogenesis. Thus, complement C4 provides an important protective role against the development of SLE.
View details for Web of Science ID 000173429300010
View details for PubMedID 11801636