PARP1 and breast cancer: PARP1 inhibitors also efficiently eradicate MCF-7 breast cancer cells,100–102 and PARP1 silencing downregulates the activity of phosphorylated Erk in the nuclei of these cells.37 In HeLa human cervical cancer cells, MAP kinase phosphorylation-mediated the binding of PARP1 to the promoter of cfos.