| Research Abstract |
Background and aim : Translation of hepatitis C virus(HCV) is an essential step of the viral replication and is mediated by an internal ribosome entry site(IRES). We previously reported that HCV-IRES is most active during the synthetic(S) or mitotic(M) phases and lowest during the quiescent(G0) phases. Here we investigated responsible host factors that regulate HCV-IRES. Methods : We synchronized the cell cycle progression of RCF-26,that constitutively express dicistronic RNA transcripts containing two reporter genes separated by a functional HCV-IRES. Then we evaluated dynamism of genes expression of host factors and kinetics of HCV-IRES activity in cells at various points during the cell cycle using a CDNA microarray. We also validated a significance of identified host factors on HCV replication in vivo. Results : HCV-IRES activity correlated with a gene cluster induced in S and G2/M phases. Interestingly, most of initiation factors that bind or interact with HCV-IRES(PCBP2,PTB,eIF3,eIF2gamma,eIF2 beta, La protein and RNLPL) were induced during the S and G2/M phases. Especially, expressions of La protein, PTB and eBR3(p116,170) were predominantly repressed in quiescent(G0) and induced in S and G2/M phases. The suppression or overexpression of La protein, PTB and eIF3(p170) in RCF-26 significantly changed HCV-IRES activity. In the livers of patients with chronic hepatitis C, the expression of La protein was significantly increased and correlated with the amount of HCV-RNA. Conclusions : The translation of HCV is regulated by cellular proteins that vary in abundance during the cell cycle. Of these, La protein is a potent regulator and would enhance HCV replication in regenerating hepatocytes in patients with chronic hepatitis C.
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