Office 129 / Lab 232
PA Biotechnology Center
3805 Old Easton Road
Doylestown, PA 18902

TEL: 215-489-4903
FAX: 215-489-4920

Pamela.Norton@drexelmed.edu

Ph.D. 1986, Tufts University, Boston, Massachusetts

Keywords:

Hepatitis B virus, antiviral agents, extracellular matrix, liver disease, RNA processing

Research Interests:

Chronic viral hepatitis is one of the major causes of liver disease, and represents a critical risk factor for liver cirrhosis and hepatocellular carcinoma. Infection with hepatitis B virus (HBV) can result in chronic infection, but the events that lead from infection to severe disease many years later are incompletely understood. An important theme of our research is to investigate virus-host cell molecular interactions and understand their role in virus pathology. Studies to identify changes that HBV infection causes within the infected host cell utilize cultured cell based models of HBV infection. These studies have identified a number of host cell genes that are either up- or down-regulated by the presence of HBV. A number of apolipoprotein genes are down-regulated; current investigation centers on determining the molecular mechanism by which the change in gene regulation occurs, and whether metabolic perturbations are a hallmark of viral infection. In contrast, the gene for the extracellular matrix protein fibronectin is up-regulated by the HBV transactivator, HBx. As fibronectin is also up-regulated early in models of fibrotic liver injury, it is possible that the virus contributes directly in the pathogenesis of liver fibrosis, the common prequel to cirrhosis.

Vaccination has proven effective in decreasing the incidence of new HBV infections, but has little therapeutic efficacy. The devastating consequences of chronic HBV infection compel our efforts to develop novel antiviral drugs. The drugs that are currently available target the viral polymerase (lamivudine and adefovir) or the host immune system (interferon). We have been characterizing members of a novel class of antiviral agents based on modifications of the prototype imino sugar deoxynojirimycin or DNJ (right). The imino sugars inhibit host glucosidases interfering with correct glycan processing; secretion of incompletely processed glycoproteins from the endoplasmic reticuluum is impaired. Certain viral glycoproteins such as the HBV MHBs and LHBs proteins have a strong requirement for correct glycoprocessing for secretion. Thus, blocking glycoprotein secretion selectively reduces virus secretion. In addition, blocking secretion results in increased intracellular degradation of viral protein by the protoeasome, leading to enhanced presentation of antigenic peptides by MHC-I. One member of this class of compounds is being tested in vivo against the related woodchuck hepatitis virus in conjunction with therapeutic vaccination to test the hypothesis that increased antigen presentation will enhance vaccination efficacy.

In complementary studies, we have been investigating the ability of the host cell to recognize and defend itself against HBV infection, as these activities might also be exploited as antiviral targets. Interferon is known to reduce HBV replication in cell culture as well as in vivo, suggesting that non-immune factors contribute to anti-viral activity. We have found that the gene for a recently identified anti-viral host factor, APOBEC3G, is induced by interferon. The APOBEC3s belong to a family of cytidine deaminases thought to result in increased mutation of DNA (and possibly RNA). Studies are aimed at identifying the effects of APOBEC3 family members on HBV replication. These molecular analyses draw on our long experience in the area of mRNA processing.

Publications

• Gorski, G.K., Aros, M.C., and P.A. Norton. Characterization of fibronectin alternative splicing during mouse liver development reveals a novel isoform present transiently during late gestation. Gene Expression, 6: 139-149, 1996.
• Mirza, A., Liu, S.-L., Frizell, E., Zhu, J., Maddukuri, S., Martinez, J., Davies, P., Schwarting, R., Norton, P., and M.A. Zern. A role for tissue transglutaminase in hepatic injury and fibrogenesis, and its regulation by nuclear factor-kappaB (NF-kappaB). Am. J. Physiol., 35: G281-G288, 1997.
• Santos, R.M., Norton, P.A., Degli Esposti, S., and M.A. Zern. TGF-beta isoforms in alcoholic liver disease. J. Gastroenterol, 33: 383-389, 1998.
• Kuo, B.A., and P.A. Norton. Role of fibronectin exon B sequences in exon recognition. Nucl. Acids Res, 27: 3945-3952, 1999.
• Zhu, J., Wu, J., Frizell, E., Liu, S.-L., Bashey, R., Rubin, R., Norton, P., and M.A. Zern. Rapamycin inhibits stellate cell proliferation in vitro and limits fibrogenesis in an in vivo model of liver fibrosis. Gastroenterol., 117: 1198-1204, 1999.
• Wu, J., Liu, S.-L. Zhu, J.L., Norton, P.A., Nojiri, S., Hoek, J.B., and M.A. Zern. Roles of tissue transglutaminase in ethanol-induced inhibition of hepatocyte proliferation and beta 1-adrenergic signal transduction. J. Biol. Chem., 275: 22213-22219, 2000.
• Norton, P.A., and L.C. Steel, eds. "Gene Transfer Methods: Introducing DNA into Living Cells and Organisms", BioTechniques Press, Eaton Publishing, Natick, MA, 2000.
• Kuo, B.A., Uporova, T.M., Liang, H., Bennett, V.D., Tuan, R.S., and P.A. Norton. Alternative splicing during chondrogenesis: modulation of fibronectin exon EIIIA splicing by SR proteins. J. Cell. Biochem., 86: 45-55, 2002.
• Norton, P.A., Gong, Q., Mehta, A.S., Lu, X., and T.M. Block. Hepatitis B virus-mediated changes in apolipoprotein mRNA abundance in cultured hepatoma cells. J. Virol., 77: 5503-5506, 2003.
• Norton, P.A., and C.J. Pachuk. Methods for DNA introduction into mammalian cells. In "Gene Transfer and Expression in Mammalian Cells", S.C. Makrides, ed., Elsevier Science B.V. Amsterdam, 263-277, 2003.
• Flanagan, M.A., Liang, H., and P.A. Norton. Alternative splicing of fibronectin mRNAs in chondrosarcoma cells: Role of far upstream intron sequences. J. Cell. Biochem., 90: 709-718, 2003.
• Norton, P.A., H.M.G.P.V. Reis, S. Prince, J. Larkin, J. Pan, J. Liu, Q. Gong, M. Zhu, and M.A. Feitelson. Activation of fibronectin gene expression by Hepatitis B virus X antigen. J. Viral. Hep., 11:332-341, 2004.
• Norton, P.A., B. Conyers, Q. Gong, L.F. Steel, T.M. Block, and A.S. Mehta. Assays for glucosidase inhibitors with potential antiviral activities: secreted alkaline phosphatase as a surrogate marker. J. Virol. Methods 124:167-172, 2005.
• Liang, H., R.S. Tuan and P.A. Norton. (2005) Forced expression of a splicing factor promotes chondrogenesis. Exp. Cell Res., in press (epub available).
• Gu, B., P. Mason, L. Wang, P.Norton, N. Bourne, R. Moriarty, A. Mehta, and T. Block. (2006) Improved antiviral profiles of deoxynojirimycins with conformation-locking and hydroxylated side chains against Bovine Viral Diarrhea virus, West Nile virus, Dengue virus and Hepatitis B virus. Antiviral Chem. Chemother., in press.

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