Dept. of Microbiology and Immunobiology
Harvard Medical School
NRB, Room 930E
77 Avenue Louis Pasteur
Boston, MA 02115
Understanding host-viral interaction is an essential step in developing safe and effective antimicrobials against biodefense agents and emerging pathogens. The early detection of invading viruses by the host depends on a limited number of specific receptors that detect viral patterns and activate signaling cascades, thereby triggering interferon (IFN)-mediated antiviral defense mechanisms. Retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) have emerged as key cytosolic receptors for sensing RNA viruses including paramyxoviruses, influenza virus, Flaviviruses and picornaviruses. In addition, members of the tripartite motif (TRIM) protein family play a major role in the inhibition of virus lifecycles.
Research in my laboratory seeks a better understanding of the molecular mechanisms underlying the IFN-mediated innate immune response against viral infection. Using molecular, biochemical and cell biological approaches, we are identifying and characterizing the regulatory mechanisms that govern the detection of RNA viruses through the cytosolic receptors RIG-I and MDA5 and the subsequent induction of signaling cascades leading to IFN-α/β gene expression. Another area of our research focuses on the detailed mechanisms by which viral proteins antagonize the RIG-I/MDA5-mediated innate immune response and on the understanding of their roles in viral lifecycle.
Regulation of RIG-I-/MDA5-mediated antiviral innate immunity by host factors. Despite the recent rapid progress in deciphering molecular components in the RIG-I/MDA5 signaling pathway, the regulation of their antiviral activities has not been well studied. Our previous work demonstrated that the interconnection between the cytosolic viral RNA receptor RIG-I and a member of the TRIM protein family represents a novel class of regulatory pathway, which is essential for the induction of IFN-mediated host innate immunity against a wide variety of RNA viruses. Specifically, we showed that RIG-I undergoes Lys 63-linked ubiquitination induced by TRIM25 ubiquitin E3 ligase, enabling RIG-I to induce antiviral signal transduction. Ongoing studies are focused on identifying and characterizing novel host factors that play key roles in the regulation of the RIG-I/TRIM25 or MDA5 signaling pathway.
Viral evasion of the RIG-I-/MDA5-mediated innate immune response. Among the virus-host interactions that modulate pathogenesis, the virus-mediated induction and inhibition of the type I IFN system play a critical role. Our studies revealed that the non-structural protein 1 (NS1) of human, swine and avian influenza A virus strains directly interacts with and inhibits the enzymatic activity of TRIM25, resulting in the abolished RIG-I ubiquitination and host antiviral IFN response. These findings unveiled a novel immune evasion mechanism of influenza A virus and also emphasized the vital role of TRIM25 in modulating viral infections. We are now determining the precise mechanism by which influenza NS1 inhibits TRIM25 and how sequence variations in TRIM25 of different species influence the NS1-TRIM25 interaction. Furthermore, our current studies are focused on the identification of novel viral factors that modulate the host antiviral interferon response.
Gack, M.U., Shin, Y.C., Joo, C.H., Urano, T., Liang, C., Sun, L., Takeuchi, O., Akira, S., Chen, Z., Inoue, S., & Jung, J.U. (2007). TRIM25 RING-finger E3 ubiquitin ligase is essential for RIG-I-mediated antiviral activity. Nature 446, 916-920. PMID:17392790
Gack, M.U., Kirchhofer, A., Shin, Y.C., Inn, K., Liang, C., Cui, S., Myong, S., Ha, T.K., Hopfner, K.P., & Jung, J.U. (2008). Roles of RIG-I N-terminal tandem CARD and splice variant in TRIM25-mediated anti-viral signal transduction. Proc. Natl. Acad. Sci. U.S.A. 105(43):16743-8 PMID: 18948594
Myong, S., Cui, S., Cornish, P.V., Kirchhofer, A., Gack, M.U., Jung, J.U., Hopfner, P. & Ha, T. (2009). Cytosolic viral sensor RIG-I is a 5’-triphosphate-dependent translocase on double-stranded RNA. Science. Feb 20;323(5917):1070-4. PMID: 19119185
Gack, M.U., Albrecht, R.A., Urano, T., Inn, K., Huang, I.C., Carnero, E., Farzan, M., Inoue, S., Jung, J.U. & Garcia-Sastre, A. (2009). Influenza A virus NS1 targets the ubiquitin ligase TRIM25 to evade recognition by RIG-I. Cell Host Microbe. May 8;5(5):439-449. PMID: 19454348
Gack, M.U., Nistal-Villán, E., Inn, K., Garcia-Sastre, A. & Jung, J.U. (2010). Phosphorylation-mediated negative regulation of RIG-I anti-viral activity. J Virol 84(7):3220-9. PMID: 20071582
Inn, K.S., Gack, M.U., Tokunaga, F., Shi, M., Wong, L.Y., Iwai, K., and Jung J.U. (2011). Linear ubiquitin assembly complex negatively regulates RIG-I- and TRIM25-mediated type I interferon induction. Molecular Cell 41(3):354-65. PMID: 21292167
Maharaj, N.P., Wies, E., Stoll, A., and Gack, M.U. (2012). Conventional protein kinase C-α (PKC-α) and PKC-β negatively regulate RIG-I antiviral signal transduction.J Virol, 86(3):1358-71. PMID:22114345
Rajsbaum, R., Albrecht, R.A., Maharaj, N.P., Wang, M.K., Versteeg, G.A., Nistal-Villán, E., García-Sastre, A., and Gack, M.U. (2012). Species-specific inhibition of RIG-I ubiquitination and IFN induction by the influenza A virus NS1 protein. PLoS Pathogens 2012 Nov;8(11):e1003059 PMID: 23209422
Wies, E., Wang, M.K., Maharaj, N.P., Chen, K., Zhou, S., Finberg, R. W., and Gack, M.U. (2013). Dephosphorylation of the RNA Sensors RIG-I and MDA5 by the Phosphatase PP1 Is Essential for Innate Immune Signaling. Immunity 2013 Mar 12. doi:10.1016/j.immuni.2012.11.018. PMID: 23499489