TP53 and breast cancer: ARF may also be regulated by CTCF, as it lies within the same locus as P16. Conversely, CTCF may also function as an oncogene, as CTCF knockdown resulted in an increased expression of P53 or the pro-apoptotic protein BAX in WT and mutant P53 breast cancer cell lines, respectively, which both increased apoptosis [369,370].