Induction of Huh-7 cell apoptosis by HCV core proteins via CK1α-p53-Bid signaling pathway

Hepatitis C virus (HCV)-infected liver cells sensitize host cells to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced cell apoptosis; however, the precise mechanisms are unknown. In the present study, flow cytometry demonstrated that the Annexin V-positive Huh-7 cell number was higher in groups transfected with core proteins when compared with the pcDNA3.1 group. The mRNA and protein expression levels of B-cell lymphoma 2 (Bcl-2) were negatively associated, while Bcl-2-associated X protein (Bax) were positively correlated, with cell apoptotic rate, which, were verified by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting. There were no significant differences in the expressions of casein kinase 1 (CK1)-ε, CK1γ or CK1δ; however, the mRNA and protein levels of CK1α were markedly higher in groups transfected with the T (those derived from the HCV-J6 strain), NT (those derived from non-tumor tissues) and C191 (those derived from tumor tissues) HCV core proteins than in mock group. When compared with the Mock and Negative Control (control known-down) groups, the mRNA and protein levels of CK1α were lower in the CK1α known-down group, and there were no marked Huh-7 cell morphological changes among the 3 groups. There was more sensitivity to cell apoptosis in CK1α-silenced, however, not in non-CK1α-silenced, Huh-7 cells. BH3 interacting-domain death agonist (Bid) protein levels in CK1α-silenced Huh-7 cells were higher when compared with non-CK1α-silenced Huh-7 cells, and the level of p53 that translocated to the nucleus increased. Chromatin immunoprecipitation-PCR demonstrated that p53 bound to human Bid gene promoter. The level of the Bid promoter in CK1α-silenced Huh-7 cells was significantly higher than in the non-CK1α-silenced Huh-7 cells. Electron microscopy indicated that p53 knockdown decreased HCV core protein and TRAIL-induced cell apoptosis. Bid/caspase-8 protein levels in CK1α-silenced Huh-7 cells that were transfected with p53 siRNA were lower than in the control group. The present study demonstrated that HCV core proteins sensitize host cells to TRAIL-induced cell apoptosis by activating the CK1α-p53-Bid dependent pathway.