Consistently, knockdown of endogenous RNF144A in human breast cancer MDA-MB-231 cells by specific short hairpin RNAs (shRNAs) targeting human RNF144A (shRNF144A) decreased the ubiquitination levels of endogenous PARP1 (Figure 3C, left panel, compare lane 3 with 2). Here, RNF144A is linked to breast cancer.