Kochupurakkal, BoseWang, Zhigang C.Hua, TonyCulhane, AedinRodig, ScottRajkovic-Molek, KoraljkaLazaro, Jean-BernardRichardson, AndreaBiswas, DebajitIglehart, James2016-10-132015Kochupurakkal, Bose S., Zhigang C. Wang, Tony Hua, Aedin C. Culhane, Scott J. Rodig, Koraljka Rajkovic-Molek, Jean-Bernard Lazaro, Andrea L. Richardson, Debajit K. Biswas, and J. Dirk Iglehart. 2015. “RelA-Induced Interferon Response Negatively Regulates Proliferation.” Edited by Irina U Agoulnik. PLoS ONE 10 (10) (October 13): e0140243. doi:10.1371/journal.pone.0140243.1932-6203http://nrs.harvard.edu/urn-3:HUL.InstRepos:29003678Both oncogenic and tumor-suppressor activities are attributed to the Nuclear Factor kappa B (NF-kB) pathway. Moreover, NF-kB may positively or negatively regulate proliferation. The molecular determinants of these opposing roles of NF-kB are unclear. Using primary human mammary epithelial cells (HMEC) as a model, we show that increased RelA levels and consequent increase in basal transcriptional activity of RelA induces IRF1, a target gene. Induced IRF1 upregulates STAT1 and IRF7, and in consort, these factors induce the expression of interferon response genes. Activation of the interferon pathway down-regulates CDK4 and up-regulates p27 resulting in Rb hypo-phosphorylation and cell cycle arrest. Stimulation of HMEC with IFN-γ elicits similar phenotypic and molecular changes suggesting that basal activity of RelA and IFN-γ converge on IRF1 to regulate proliferation. The anti-proliferative RelA-IRF1-CDK4 signaling axis is retained in ER+/HER2- breast tumors analyzed by The Cancer Genome Atlas (TCGA). Using immuno-histochemical analysis of breast tumors, we confirm the negative correlation between RelA levels and proliferation rate in ER+/HER2- breast tumors. These findings attribute an anti-proliferative tumorsuppressor role to basal RelA activity. Inactivation of Rb, down-regulation of RelA or IRF1, or upregulation of CDK4 or IRF2 rescues the RelA-IRF1-CDK4 induced proliferation arrest in HMEC and are points of disruption in aggressive tumors. Activity of the RelA-IRF1-CDK4 axis may explain favorable response to CDK4/6 inhibition observed in patients with ER+ Rb competent tumors.en-USJournal Article2016-10-1310.1371/journal.pone.0140243