Identification of genes responsible for RelA-dependent proliferation arrest in human mammary epithelial cells conditionally expressing RelA

AbstractThe molecular mechanisms responsible for opposing oncogenic and tumor-suppressor activities of NF-kB are obscure. Semi-quantitative immunohistochemistry of primary breast tumors using antibodies to RelA, the pleiotropic NF-kB factor, and Ki67 revealed a negative correlation between RelA levels and Ki67-index among ER+/HER2− tumors [1]. Similarly, expression of AURKA, a marker for proliferation, negatively correlates with expression of NFKBIA, a surrogate for RelA expression and activity, in ER+/HER2− tumors analyzed by The Cancer Genome Atlas [2–4]. Furthermore, conditional expression of RelA using a Tetracycline-inducible system in Human Mammary Epithelial Cells (HRA cells) caused proliferation arrest while withdrawal of Doxycycline (Dox) and suppression of RelA expression in arrested cells restored cell cycle progression [1]. To identify genes responsible for the negative relationship between RelA levels and proliferation, we performed genome-wide gene expression analysis of HRA cells under the following conditions: RelA un-induced, No Dox (ND); Dox induced for 24h; Dox induced for 72h; Dox induced for 24h then Dox withdrawn for 48h. The expression data was submitted to Gene Expression Ominibus (GEO) and the accession number is GSE65040. Analysis of the data identified cross-talk between basal RelA activity and the Interferon pathway mediated by IRF1, a target of RelA [5]. Activation of the Interferon pathway lead to down-regulation of CDK4 expression resulting in RB1 hypo-phosphorylation and suppression of cell cycle progression. The tumor-suppressor activity of NF-kB, specifically RelA, may stem from cross-talk with the Interferon pathway