PML and breast cancer: To investigate whether ERβ relies on such synergism to exert its repressive actions in breast cancer, we analyzed breast cancer cells that carry wild-type p53 for expression of p53-regulated genes that are involved in cell-cycle arrest, apoptosis, and senescence including p21, GADD45A, PUMA, PAI-1, BAX, and promyelocytic leukemia protein (PML).