RelA-Induced Interferon Response Negatively Regulates Proliferation
Fig 6
RelA and IFN-γ converge on IRF1 to suppress CDK4 and inhibit proliferation.
A. Stable HMEC expressing sh-GFP or sh-RelA were generated. The cells were treated with IFN-λ1 of IFN-γ for 48 hours following which whole cell extracts were prepared and analyzed by immunoblot using indicated antibodies. B. HRA-kd-IRF1 and HRA-IRF2 cells were cultured according to the scheme in S5C Fig and whole cell lysates were analyzed by immunoblot using indicated antibodies. C. Proliferation assay was performed using HRA, HRA-kd-IRF1 and HRA-IRF2 cells in the presence and absence of Dox as indicated. The bar plots indicate growth of cells in the span of 72 hours normalized to growth in the absence of Dox. Error bars indicate triplicate samples. Rescue of RelA-induced proliferation arrest by knocking down IRF1 or co-expressing IRF2 was statistically significant (p-value: 3.4 E -12 and 1.1 E -15 respectively). D. Schematic representation of the findings in this study. Increased basal activity of RelA when expressed at high levels in epithelial cells and tumors induces IRF1. Increase in IRF1 causes up-regulation of Interferon Response Factors like STAT1 and orchestrates an interferon response. The interferon response down-regulates CDK4 and up-regulates of p27 leading to Rb hypo-phosphorylation which suppresses proliferation. Stimulation with IFN-γ elicits a similar response except that IRF1 induction is directed through STAT1. The IRF1-STAT1 positive feedback circuit may be essential for the interferon response and suppression of proliferation.