La protein is a potent regulator of replication of hepatitis C virus in patients with chronic hepatitis C through internal ribosomal entry site-directed translation

Background & Aims: Translation of hepatitis C virus is an essential step of viral replication and is mediated by an internal ribosome entry site. We previously reported that the hepatitis C virus internal ribosome entry site is most active during the synthetic (S) or mitotic (M) phases and lowest during quiescent (G0) phase. Here, we investigated host factors responsible for the regulation of the hepatitis C virus internal ribosome entry site. Methods: We synchronized the cell-cycle progression and evaluated gene-expression dynamics of host factors and kinetics of hepatitis C virus internal ribosome entry site activity in cells at various points during the cell cycle by using a complementary DNA microarray. We also validated the significance of identified host factors on hepatitis C virus replication in vivo. Results: Hepatitis C virus internal ribosome entry site activity correlated with a gene cluster induced in the S and G2/M phases. It is interesting to note that most initiation factors known to bind or interact with the hepatitis C virus internal ribosome entry site [poly(rC)-binding protein 2, polypyrimidine tract binding protein, eukaryotic initiation factor 3, eukaryotic initiation factor 2γ, eukaryotic initiation factor 2β, La protein, and heterogenous nuclear ribonucleoprotein L] were induced during the S and G2/M phases. Expression of La protein, polypyrimidine tract binding protein, and eukaryotic initiation factor 3 (p116, p170) were predominantly repressed in G0 phase and induced in S and G2/M phases. Suppression or overexpression of La protein and polypyrimidine tract binding protein in RCF-26 significantly changed hepatitis C virus internal ribosome entry site activity. In the livers of patients with chronic hepatitis C, expression of La protein was significantly increased and correlated with the amount of hepatitis C virus RNA. Conclusions: Hepatitis C virus uses host factors induced during cell division but not during quiescence for replication. Of these, La protein is a potent regulator and enhances hepatitis C virus replication in regenerating hepatocytes in patients with chronic hepatitis C.