An RNA-binding protein, hnRNP A1, and a scaffold protein, septin 6, facilitate hepatitis C virus replication.

Hepatitis C virus (HCV) is a positive-sense single-stranded RNA virus. NS5b is an RNA-dependent RNA polymerase that polymerizes the newly synthesized RNA. HCV likely uses host proteins for its replication, similar to other RNA viruses. To identify the cellular factors involved in HCV replication, we searched for cellular proteins that interact with the NS5b protein. HnRNP A1 and septin 6 proteins were identified by coimmunoprecipitation and yeast two-hybrid screening, respectively. Interestingly, septin 6 protein also interacts with hnRNP A1. Moreover, hnRNP A1 interacts with the 5'-nontranslated region (5' NTR) and the 3' NTR of HCV RNA containing the cis-acting elements required for replication. Knockdown of hnRNP A1 and overexpression of C-terminally truncated hnRNP A1 reduced HCV replication. In addition, knockdown of septin 6 and overexpression of N-terminally truncated septin 6 inhibited HCV replication. These results indicate that the host proteins hnRNP A1 and septin 6 play important roles in the replication of HCV through RNA-protein and protein-protein interactions.

E2 of hepatitis C virus inhibits apoptosis.

Hepatitis C virus (HCV) is the major causative agent of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma, and can be involved in very long chronic infections up to 30 years or more. Therefore, it has been speculated that HCV possesses mechanisms capable of modulating host defense systems such as innate and adaptive immunity. To investigate this virus-host interaction, we generated HCV replicons containing various HCV structural proteins and then analyzed the sensitivity of replicon-containing cells to the apoptosis-inducing agent, TRAIL. TRAIL-induced apoptosis was monitored by cleavage of procaspase-3 and procaspase-9 as well as that of their substrate poly(ADP-ribose) polymerase. TRAIL-induced apoptosis was inhibited in cells expressing HCV E2. Moreover, expression of HCV E2 enhanced the colony forming efficiency of replicon-containing cells by 25-fold. Blockage of apoptosis by E2 seems to be related to inhibition of TRAIL-induced cytochrome c release from the mitochondria. Based on these results, we propose that E2 augments persistent HCV infection by blocking host-induced apoptosis of infected cells.

Long-range RNA-RNA interaction between the 5' nontranslated region and the core-coding sequences of hepatitis C virus modulates the IRES-dependent translation.

Hepatitis C virus (HCV) is a positive-sense RNA virus approximately 9600 bases long. An internal ribosomal entry site (IRES) spans the 5' nontranslated region, which is the most conserved and highly structured region of the HCV genome. In this study, we demonstrate that nucleotides 428-442 of the HCV core-coding sequence anneal to nucleotides 24-38 of the 5'NTR, and that this RNA-RNA interaction modulates IRES-dependent translation in rabbit reticulocyte lysate and in HepG2 cells. The inclusion of the core-coding sequence (nucleotides 428-442) significantly suppressed the translational efficiency directed by HCV IRES in dicistronic reporter systems, and this suppression was relieved by site-directed mutations that blocked the long-range interaction between nucleotides 24-38 and 428-442. These findings suggest that the long-range interaction between the HCV 5'NTR and the core-coding nucleotide sequence down-regulate cap-independent translation via HCV IRES. The modulation of protein synthesis by long-range RNA-RNA interaction may play a role in the regulation of viral gene expression.