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

When we depleted endogenous CRTC1 in HepG2.2.15 cells, expression of HBx protein was diminished ( Figure 7D, lanes 2 and 3 compared to 1) , suggesting a physiological role of CRTC1 in maintaining HBx protein stability. Such destabilization effect on HBx was unlikely due to an effect of CRTC1 on X promoter, which was shown to be unresponsive to CRTC1 ( Figure 2B ). The stabilization of CRTC1 was also seen in pHBV1.3D-transfected HepG2 cells ( Figure 7E , lane 2 compared to 1). In sharp contrast, the steady-state level of CRTC1 remained unchanged (Figure 7E , lane 3 compared to 1 and 2) when HepG2 cells were transfected with pHBV1.3D-X − , an X-deficient molecular clone of HBV (25) . Although an X transcript was expressed from this clone at lower level ( Figure 7E , lane 3 compared to 2), no functional HBx protein would be produced as shown in the literature (25) . Thus, the stabilization of CRTC1 in HBV-replicating cells is HBx dependent.