SMAD2 and neoplasm: MmuPV1 E6 shares key cellular targets and biological activities with the beta-HPV 5 and 8 E6 proteins that affect key tumor suppressor gene functions, including the ability to bind the NOTCH transcriptional coactivator MAML1 and the SMAD2 and SMAD3 mediators of transforming growth factor beta (TGF-β) signaling (15).