Hepatitis B Virus X protein and polyploidy in the development of hepatocellular carcinoma
Abstract
Hepatitis B Virus (HBV) X protein (pX) is implicated by an unknown mechanism in hepatocellular carcinoma (HCC) development, characterized by increased rate of chromosomal aberrations. Although most patients clear the infection and develop immunity, chronic infection in 5 to 10% infected patients lead to HCC development in the 4th to 5th decade of life. I demonstrate that tetracycline-regulated pX expression induces multipolar spindles and polyploidy (>4N DNA). To understand the mechanism of pX-mediated polyploidy, I investigated whether pX promotes DNA re-replication. Dual-parameter flow cytometry demonstrates pX-dependent BrdU incorporation in cells with >4N DNA. pX also induces expression of replication initiation factors Cdc6 and Cdtl, while suppressing geminin expression, a negative regulator of re-replication. G2-phase synchronized cells exhibit pX-dependent: (i) nuclear Cdc6 and Mcm5 co-localization; (ii) absence of nuclear geminin; (iii) increased BrdU incorporation; (iv) ATR activation; (v) RAD17 and H2AX phosphorylation; and (vi) co-localization of γ-H2AX with the DNA elongation factor PCNA. I monitor the evolution and the growth of pX-induced polyploidy. I observe that polyploid cells acquire p53-insensitive growth that leads to cell transformation. Thus I was able to formulate a model for liver cancer progression that is initiated by pX induced DNA re-replication.
Degree
Ph.D.
Advisors
Andrisani, Purdue University.
Subject Area
Molecular biology|Cellular biology
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