Interferon-α Acts on the S/G2/M Phases to Induce Apoptosis in the G1 Phase of an IFNAR2-expressing Hepatocellular Carcinoma Cell Line

Background: The mode of action of interferon- has been unknown. Results: Its point of action in the cell cycle was analyzed by single cell tracking using time lapse confocal imaging. Conclusion: Interferon- activates p63 in S/G(2)/M and induces apoptosis and cell cycle arrest in the subsequent G(1). Significance: Tracking cell cycle progression is crucial for understanding the mechanisms of interferon-. Interferon- (IFN-) is used clinically to treat hepatocellular carcinoma (HCC), although the detailed therapeutic mechanisms remain elusive. In particular, IFN- has long been implicated in control of the cell cycle, but its actual point of action has not been clarified. Here, using time lapse imaging analyses of the human HCC cell line HuH7 carrying a fluorescence ubiquitination-based cell cycle indicator (Fucci), we found that IFN- induced cell cycle arrest in the G(0)/G(1) phases, leading to apoptosis through an IFN- type-2 receptor (IFNAR2)-dependent signaling pathway. Detailed analyses by time lapse imaging and biochemical assays demonstrated that the IFN-/IFNAR2 axis sensitizes cells to apoptosis in the S/G(2)/M phases in preparation for cell death in the G(0)/G(1) phases. In summary, this study is the first to demonstrate the detailed mechanism of IFN- as an anticancer drug, using Fucci-based time lapse imaging, which will be informative for treating HCC with IFN- in clinical practice.