Activation of endoplasmic reticulum stress response by hepatitis C virus proteins

Flaviviruses utilize the endoplasmic reticulum (ER) as the main site for replication and protein synthesis and cause some level of ER stress. In the present study, we evaluated the ability of HCV proteins to induce ER stress response by using a tetracycline-regulated cell line expressing a region of HCV genome containing the structural genes. In this system different levels of HCV protein expression could be obtained by varying the concentration of tetracycline in the medium. Real Time PCR and Western blotting assay demonstrated that HCV mRNA and protein levels reach a maximum value at 24-48 h and decrease at 72 h postinduction. Cell proliferation analysis indicated that HCV synthesis causes cell growth inhibition. The effect was also observed in cells expressing lower levels of HCV proteins. The expression profile of specific genes, which are markers of ER stress response, revealed the upregulation of the chaperone GRP78 and the transcription factor GADD153. Induction of GADD153 correlates with the downregulation of the antiapoptotic Bcl-2 gene suggesting that synthesis of HCV proteins may influence cell fate through the activation of ER stress signaling pathway.