Mechanism of Autophagic Action of Type I Human Interferon

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Type I IFN induces autophagy in Daudi cells starting at 24 h as indicated by an increase of autophagy markers LC3-II, Atg5-Atg12 complexes, and a decrease of p62. Higher levels of LC3-II were also detected 48 h post IFN-alpha2c treatment in HeLa S3, MDA-MB-231, T98G and A549 cell lines. The increase in expression of autophagy markers correlated with inhibition of mTORC1 activity in Daudi cells. Many signaling pathways play a role in regulation of mTORC1 (e.g. PI3K, AKT). Treatment of Daudi and T98G cells with IFN-alpha2c in combination with either rapamycin (mTORC1 inhibitor) or LY294002 (PI3K inhibitor) increased the level of LC3-II, indicating that the PI3K/AKT/mTORC1 signaling pathway may affect IFN-induced autophagy in Daudi and T98G cells. The role of mTOR and factors upstream of mTOR in Type I IFN-induced autophagy was confirmed by siRNA knockdown experiments. The presence of autophagosomes was shown using transmission electron microscopy. In conclusion, our findings demonstrate a novel function of Type I IFN as an inducer of autophagy in a variety of cancer cell lines.