Hepatitis C virus NS5A protein modulates transcription through a novel cellular transcription factor SRCAP

Hepatitis C virus NS5A protein transcriptionally modulates cellular genes a nd promotes cell growth. NS5A is likely to exert its activity in concert wi th cellular factor(s), Using a yeast two-hybrid screen, we have demonstrate d that NS5A interacts with the C-terminal end of a newly identified cellula r transcription factor, SRCAP, The authenticity of this interaction was ver ified by a mammalian two-hybrid assay, in vitro pull-down experiment, and a n in vivo coimmunoprecipitation assay in human hepatoma (HepG2) cells. An i n vitro transient transfection assay demonstrated that SRCAP can efficientl y activate transcription when recruited by the Gal4 DNA-binding domain to t he promoter. However, down-regulation of p21 promoter activity by NS5A was enhanced following ectopic expression of SRCAP, Together these results sugg est that the interaction of NS5A and SRCAP may be one of the mechanisms by which NS5A exerts its effect on cell growth regulation contributing to hepa titis C virus-mediated pathogenesis.