Chronic viral hepatitis is one of the major causes of liver disease, and represents a critical risk factor for liver cirrhosis and hepatocellular carcinoma (HCC). An important theme of our research is to identify molecular changes that occur with HCC development, and thus might serve as biomarkers for the early detection of disease. One candidate biomarker for HCC is the normal golgi resident protein GP73 (green in figure). We have found that pro-inflammatory cytokines IL-6 and oncostatin M can increase GP73 expression in cells of human liver cancer origin; levels of both cytokines are positively correlated with GP73 levels in people with liver disease. We also have been investigating the causes and consequences of hyperfucosylation of many liver-derived glycoproteins that appear in the circulation of individuals with HCC. A second HCC-related change in glycosylation is an increase in the production of highly branched structures in tumor but not nearby non-tumor tissue. The roles of these altered glycoforms are as yet poorly understood, but they represent potentially important biomarkers for early detection of disease. We are investigating the effects of the cytokines that regulate GP73 on protein glycosylation.
The devastating consequences of chronic HBV infection compel efforts to develop novel antiviral drugs. The drugs that are currently available target the viral polymerase 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. The imino sugars inhibit host glucosidases in the endoplasmic reticulum by interfering with correct N-glycan processing. Certain viral glycoproteins such as the HBV MHBs and LHBs proteins have a strong requirement for correct N-glycosylation for secretion, and imino sugars can selectively reduce 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 in a cell culture based assay. One imino sugar was 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. An exciting outcome of this study was the finding that drug treatment enhanced the cellular immune response to viral antigens. This drug-induced response was associated with reactivity to novel epitopes generated by de-N-glycosylation prior to proteasomal processing and presentation. The ability of certain imino sugars to augment epitope presentation by MHC class I in cultured cells suggests a possible role for these compounds in stimulating the production of virus-specific cytolytic CD8+ T cells.
Selected Research Publications:
"Interleukin-6 and Oncostatin M are elevated in liver disease in conjunction with candidate hepatocellular carcinoma biomarker GP73"
Liang H, Block TM, Wang M, Nefsky B, Long R, Hafner J, Mehta AS, Marrero J, Gish R, and PA Norton
Cancer Biomarkers, in press, 2012.
"Increased levels of tetra-antennary N-linked glycan but not core fucosylation are associated with hepatocellular carcinoma tissue"
Mehta A, Norton P, Liang H, Comunale MA, Wang M, Rodemich-Betesh L, Koszycki A, Noda K, Miyoshi E, and T Block
Cancer Epidemiol. Biomarkers Prev., 21: 925-933, 2012.
"Linkage specific fucosylation of alpha-1-antitrypsin in patients liver cirrhosis and cancer patients: Implications for a biomarker of hepatocellular carcinoma"
Comunale MA, Rodemich-Betesh L, Hafner J, Wang M, Norton P, Di Bisceglie AM, Block T and A Mehta
PLoS One 5, e12419, 2010.
"Glucosidase inhibition results in enhanced presentation by MHC class I of de-N-glycosylated hepatitis B envelope protein epitopes in vitro and in vivo"
Norton PA, Menne S, Sinnathamby G, Betesh L, Cote PJ, Philip R, Mehta AS, Tennant BC and TM Block
Hepatology, 52: 1242-1250, 2010.
"Inhibition of cellular glucosidases results in increased presentation of hepatitis B virus glycoprotein-derived peptides by MHC class I"
Simsek E, Sinnathamby G, Block TM, Liu Y, Philip R, Mehta AS, and PA Norton.
Virology, 384:12-15, 2009.
"The role of the downstream signal sequences in the maturation of the HBV Middle Surface glycoprotein: development of a novel therapeutic vaccine candidate"
Liu Y, Simsek E, Norton P, Sinnathamby G, Philip R, Block TM, Zhou T, and AS Mehta.
Virology, 365: 10-19, 2007.
"N-linked glycosylation of the liver cancer biomarker GP73"
Norton PA, Comunale MA, Krakover J, Rodemich L, Pirog N, D'Amelio A, Philip R, Mehta AS, and TM Block.
J. Cell. Biochem., 104:136-149, 2007.
"A substituted tetrahydro-tetrazolo-pyrimidine is a specific and novel inhibitor of hepatitis B virus surface antigen secretion"
Dougherty AM., Guo H, Westby G, Liu Y, Simsek E, Guo J-T, Mehta A, Norton P, Gu B, Block TM, and A Cuconati.
Antimicrob. Agents Chemother., 51:4427-4437, 2007.
"Imino sugars as antiviral agents"
Norton PA, Gu B, and TM Block.
In Iminosugars: From Synthesis to Therapeutic Applications. P. Compain and O.R. Martin, eds., John Wiley & Sons, Ltd., London, 209-224, 2007.
"Assays for glucosidase inhibitors with potential antiviral activities: secreted alkaline phosphatase as a surrogate marker"
Norton PA, Conyers B, Gong Q, Steel LF, Block TM, and AS Mehta.
J. Virol. Methods, 124: 167-172, 2005.
"Activation of fibronectin gene expression by Hepatitis B virus X antigen"
Norton PA, Reis HMGPV, Prince S, Larkin J, Pan J, Liu J, Gong Q, Zhu M, and MA Feitelson.
J. Viral. Hep., 11: 332-341, 2004.
"Hepatitis B virus-mediated changes in apolipoprotein mRNA abundance in cultured hepatoma cells"
Norton PA, Gong Q, Mehta AS, Lu X, and TM Block.
J. Virol., 77: 5503-5506, 2003.
"Roles of tissue transglutaminase in ethanol-induced inhibition of hepatocyte proliferation and beta 1-adrenergic signal transduction"
Wu J, Liu S-L, Zhu JL, Norton PA, Nojiri S, Hoek JB, and MA Zern.
J. Biol. Chem., 275: 22213-22219, 2000.
"Rapamycin inhibits stellate cell proliferation in vitro and limits fibrogenesis in an in vivo model of liver fibrosis"
Zhu J, Wu J, Frizell E, Liu S-L, Bashey R, Rubin R, Norton P, and MA Zern.
Gastroenterol., 117: 1198-1204, 1999.
"A role for tissue transglutaminase in hepatic injury and fibrogenesis, and its regulation by nuclear factor-kappaB (NF-kappaB)"
Mirza A, Liu S-L, Frizell E, Zhu J, Maddukuri S, Martinez J, Davies P, Schwarting R, Norton P, and MA Zern.
Am. J. Physiol., 35: G281-G288, 1997.