Robert H. Silverman, Ph.D.
Staff and Professor
Mal and Lea Bank Chair
Innate defense against viruses and cancer.
There are two principal areas of research in my laboratory. The first concerns antiviral innate immunity mediated by interferons (IFN). RNase L is a principal effector of the IFN-inducible antiviral response and is thus critically important for human health. Viral replication in higher vertebrates is restrained by IFNs. IFNs cause cells to transcribe genes for antiviral proteins, including the 2',5'-oligoadenylate synthetases (OAS). The viral pathogen associated molecular pattern (PAMP), double-stranded RNA, activates OAS. OAS produces 2’,5’-oligo(rA) whose function is to stimulate RNase L. The OAS-RNase L system constitutes a classical innate immune pathway that rapidly responds to PAMPs to produce a broadly active antiviral response. In our prior studies, we purified and cloned RNase L, knocked it out in mice, established its antiviral and apoptotic activities in vivo, and determined that it initiates transcriptional signaling pathways. We have found that RNase L cleaves viral RNA as well as self-RNA to generate small RNA products that stimulate IFN-beta synthesis through the RNA recognition receptors, RIG-I and MDA5, and their adapter IPS-1/MAVS. We further showed with Dr. Susan Weiss (University of Pennsylvania) that the ns2 gene of mouse hepatitis virus is a 2'-5'-phosphodiesterase that blocks antiviral innate immunity by preventing activation of RNase L, thus allowing hepatitis. These studies highlight a novel mode of regulation of the IFN antiviral response with broad implications for the control of viral infections and cancer that extend beyond hepatitis to virus-mediated pathologies in other organ systems.The second area of research concerns the role of innate immunity and genetics in prostate cancer. Prostate cancer is the leading cause of non-cutaneous malignancies and the second leading cause of cancer-related deaths among American men. Hereditary prostate cancer (HPC), which accounts for 43% of early onset cases and about 9% of all cases, is due to germline mutations in HPC genes. HPC1 encodes RNase L, thus implicating an antiviral pathway in tumor suppression. We are investigating the potential role of RNase L in prostate cancer by focusing on viral infections, inflammation and apoptosis. Our future goals are to probe fundamental events and biologic endpoints surrounding RNase L that impact on viral replication cycles and tumor biology.
Silverman, R.H., Skehel, J.J., James, T.C., Wreschner, D.H., and Kerr, I.M. Ribosomal RNA cleavage as an index of ppp(A2'p)nA activity in interferon-treated encephalomyocarditis virus-infected cells. J. Virol., 46, 1051-1055, 1983.
Silverman, R.H., Jung, D.D., Nolan-Sorden, N.L., Dieffenbach, C.W., Kedar, V.P., and SenGupta, D. Purification and analysis of murine 2-5A-dependent RNase. J. Biol. Chem., 263, 7336-7341, 1988.
Berkhout, B., Silverman, R.H., and Jeang, K.-T. Tat trans-activates the human immunodeficiency virus through a nascent RNA target. Cell, 59, 273-282, 1989.
Zhou, A., Hassel, B.A., and Silverman, R.H. Expression cloning of 2-5A-dependent RNase-a uniquely regulated mediator of interferon action. Cell, 72, 753-765, 1993.
Hassel, B.A., Zhou, A., Sotomayor, C., Maran, A., and Silverman, R.H. A dominant negative mutant of 2-5A-dependent RNase suppresses antiproliferative and antiviral effects of interferon. EMBO J., 12, 3297-3304, 1993.
Dong, B., Xu,L., Zhou,A., Hassel, B.A., Lee,X., Torrence, P.F., and Silverman,R.H. Intrinsic molecular activities of the interferon-induced 2-5A-dependent RNase. J. Biol. Chem., 269, 14153-14158, 1994.
Maran, A., Maitra, R.K., Kumar, A., Dong, B., Xiao, W., Li, G., Williams, B.R.G., Torrence, P.F., and Silverman, R.H. Blockage of NF-B signaling by selective ablation of an mRNA target by 2-5A-antisense. Science, 265, 789-792, 1994.
Dong, B. and Silverman, R.H. 2-5A-dependent RNase molecules dimerize during activation by 2-5A. J. Biol. Chem., 270, 4133-4137, 1995.
Wang, L., Zhou, A., Vasavada, S., Dong, B., Nie, H., Church, J.M., Williams, B.R.G., Banerjee, S., and Silverman, R.H. Elevated levels of 2-5A dependent RNase L occur as an early event in colorectal tumorigenesis. Clinical Cancer Research, 1, 1421-1428,1995.
Dong, B. and Silverman, R.H. A bipartite model of 2-5A-dependent RNase L. J. Biol. Chem. 272, 22236-22242, 1997.
Zhou, A., Paranjape, J., Brown, T.L., Nie, H., Naik, S., Dong, B., Chang, A., Trapp, B. Fairchild, R., Colmenares, C., and Silverman, R.H. Interferon action and apoptosis are defective in mice devoid of 2',5'-oligoadenylate dependent RNase L. EMBO J. 16, 6355-6363,1997.
Maitra, R.K. and Silverman, R. H. Regulation of HIV replication by 2',5'-oligoadenylate dependent RNase L. J. Virology 72, 1146-1152, 1998.
Der, S., Zhou, A., Williams, B.R.G., and Silverman, R.H. Identification of Genes Differentially Regulated by IFN- or Using Oligonucleotide Arrays. Proc. Natl. Acad. Sci. 95,15623-15628, 1998.
Zhou, A., Paranjape, J.M., Der, S.D., and Williams, B.R.G. and Silverman, R.H. Novel Innate Mechanisms of Interferon Action are Revealed in Triply Deficient Mice. Virology, 258, 435-440, 1999.
Dong, B., Niwa, M., Walter, P. and Silverman, R.H. Basis for Regulated RNA Cleavage by Functional Analysis of RNase L and Ire1p, RNA, 7, 361-373, 2001.
Silverman, R.H., Halloum, A., Zhou, A., Dong, B., Al-Zoghaibi, F., Kushner, D., Zhou, Q., Zhao, J., Wiedmer, T., and Sims, P.J. Suppression of Ovarian Carcinoma Cell Growth In Vivo by the Interferon-Inducible Plasma Membrane Protein, Phospholipid Scramblase 1. Cancer Research, 62, 397-402, 2002.
Carpten, J., N. Nupponen, S. Isaacs, R. Sood, C. Robbins, J. Xu, M. Faruque, T. Moses, C. Ewing, E. Gillanders, P. Hu, P. Bujnovszky, I. Makalowska, A. Baffoe-Bonnie, D. Faith, J. Smith, D. Stephan, K. Wiley, M. Brownstein, D. Gildea, B. Kelly, R. Jenkins, G. Hostetter, M. Matikainen, J. Schleutker, K. Klinger, T. Connors, Y. Xiang, Z. Wang, A. Demarzo, N. Papadopoulos, O-P. Kallioniemi, R. Burk, D. Meyer, H. Grönberg, P. Meltzer, R. Silverman, J. Bailey-Wilson, P. Walsh, W. Isaacs, J. Trent. Germline Mutations in the Ribonuclease L (RNase L) Gene in Hereditary Prostate Cancer 1 (HPC1) -Linked Families. Nature Genetics, 30, 181-184, 2002.
Xiang, Y., Condit, R.C., Vijaysri, S., Jacobs, B., Williams, B.R.G. and Silverman, R.H. Blockade of Interferon Induction and Action by the E3L Double-Stranded RNA Binding Proteins of Vaccinia Virus. J. Virol. 76, 5251-5259, 2002.
Xiang, Y., Wang, Z., Murakami, J., Plummer, S., Klein, E.A., Carpten, J., Trent, J., Isaacs W., Casey, G., and Silverman, R. H. Effects Of RNase L Mutations Associated With Prostate Cancer On Apoptosis Induced By 2’,5’-Oligoadenylates. Cancer Res. 63, 6795-6801, 2003.
Li, G., Xiang, Y., Sabapathy, K., and Silverman, R.H. An apoptotic signaling pathway in the interferon antiviral response mediated by RNase L and c-Jun NH2-terminal kinase. J. Biol. Chem., 279, 1123-1131, 2004.
Dong, B., Zhou, Q., Zhao, J. , Zhou, A., Harty, R.N., Bose, S., Banerjee, A., Guenther, J., Slee, Williams, B.R.G., Wiedmer, T., Sims, P.J. and Silverman, R.H. Phospholipid Scramblase 1 (PLSCR1) Potentiates The Antiviral Activity of Interferon. J. Virol. 78, 8983-93, 2004.
Malathi, K., Paranjape, J.M., Ganapathi, R. and R.H. Silverman. HPC1/RNASEL mediates apoptosis of prostate cancer cells treated with 2',5'-oligoadenylates, topoisomerase I inhibitors and TRAIL. Cancer Research, 4, 9144-9151, 2004.
Malathi, K., Paranjape, J.M., Bulanova, E., Shim, M., Guenther-Johnson, J.M., Faber, P.W., Eling, T.E., Williams, B.R.G., and Silverman, R.H. A novel transcriptional signaling pathway in the interferon system mediated by 2'-5'-oligoadenylate activation of RNase L. Proc. Natl. Acad. Sci. 102, 14533-14538, 2005.
Malathi, K., Dong, B., Gale, M., and Silverman, R.H. Small Self RNA Generated by RNase L Amplifies Antiviral Innate Immunity. Nature, 448, 816-819, 2007.
Dong, B. and Silverman, R.H. Androgen stimulates transcription and replication of XMRV (xenotropic murine leukemia virus-related virus). J. Virol., 84:1648-51, 2010 [On the Cover].
Malathi, K., Saito, T., Crochet, N., Barton, D.J.,Gale, M. and Silverman, R.H. RNase L Releases a Small RNA from HCV RNA that Refolds into a Potent PAMP. RNA, 16, 2108-2019, 2010.
Elbahesh H., Jha B.K., Silverman R.H., Scherbik S.V., Brinton M.A. The Flvr-encoded murine oligoadenylate synthetase 1b (Oas1b) suppresses 2-5A synthesis in intact cells. Virology, 409:262-70, 2011.
Jha, B.K., Polyakova, I., Kessler, P., Dong, B., Dickerman, B., Sen, G.C., and Silverman, R.H. Inhibition of RNase L and RNA-dependent protein kinase (PKR) by sunitinib impairs antiviral innate immunity. Journal of Biol. Chem, 286:26319-26, 2011.
Zhang, A., Bogerd, H., Villinger, F., Das Gupta, J., Dong, B., Klein, E.A., Hackett, J., Schochetman, G., Cullen, B.R., and Silverman, R.H. In vivo hypermutation of xenotropic murine leukemia virus-related virus DNA in peripheral blood mononuclear cells of rhesus macaque by APOBEC3 proteins. Virology, 421:28-33, 2011.
Zhao, L., Jha, B., Wu, A., Elliott, R., Ziebuhr, J., Gorbalenya, A.E., Silverman, R.H., Weiss, S.R. 2012. Antagonism of the interferon-induced OAS-RNase Lpathway bymurine coronavirusns2 proteinisrequired for virus replication and liver pathology. Cell Host and Microbe, 11, 607-616, 2012.
Chakrabarti, A., Ghosh, P.K., Banerjee, S., Gaughan, C., and Silverman, R.H. RNase L triggers autophagy in response to viral infections. J. Virol. 86, 11311-21, 2012
Long, T.M., Chakrabarti, A., Ezelle, H.J., Brennan, S., Raufman, J.P., Polyakova, I, Silverman, R.H., and Hassel, B.A. RNase-L deficiency exacerbates experimental colitis and colitis-associated cancer. Inflammatory Bowel Diseases, in press, 2012.