Requirement of CRTC1 coactivator for hepatitis B virus transcription

Tang, Hei-Man Vincent; Gao, Wei-Wei; Chan, Chi-Ping; Cheng, Yun; Chaudhary, Vidyanath; Deng, Jian-Jun; Yuen, Kit-San; Wong, Chun-Ming; Ng, Irene Oi-Lin; Kok, Kin-Hang; Zhou, Jie; Jin, Dong-Yan

To model HBV genome replication, we used HepG2 cells transfected with pHBV1.3D, an HBV molecular clone (9, 23) . In addition, HepG2.2.15 cells, which constitutively produce HBV (31), were also employed. Expression of endogenous CRTC1 protein was more pronounced in pHBV1.3D-transfected HepG2 and in HepG2.2.15 cells ( Figure 1A and B, lanes 2 and 3 or 2-4 compared to 1), whereas the steady-state levels of CREB, CRTC2 and CRTC3 remained largely unchanged. In contrast, the mRNA levels of all three CRTCs were comparable in the presence and absence of HBV ( Figure 1C) , indicating that the effect on CRTC1 occurs at protein but not mRNA level. To verify CRTC1 expression in natural infection of HBV, we examined a small number of HBV-positive or HBV-negative human liver tissues. CRTC1 protein expression was 6-to 18-fold more abundant in HBV-positive samples than in HBV-negative ones ( Figure 1D ). One plausible interpretation to these data is that CRTC1 protein is stabilized in HBV-infected cells.