RARB and breast cancer: Moreover, in an effort to understand some of epigenetic mechanisms underlying any changes in RARB transcriptional activity upon the tested combinatorial exposures in breast cancer cells, we assessed expression levels of known DNA methylation modifiers, DNMT1, CDKN1A (p21), and TP53, as well as potential regulator of RARB transcription, PTEN. TP53 is a tumor suppressor relevant for regulation of cellular growth, cell cycle and apoptosis.