Convergence of p53 and transforming growth factor β (TGFβ) signaling on activating expression of the tumor suppressor gene maspin in mammary epithelial cells

Using two-dimensional difference gel electrophoresis, we identified the tumor suppressor gene maspin as a transforming growth factor beta (TGF beta) target gene in human mammary epithelial cells. TGF beta up-regulatesMaspin expression both at the RNA and protein levels. This up-regulation required Smad2/3 function and intact p53-binding elements in the Maspin promoter. DNA affinity immunoblot and chromatin immunoprecipitation revealed the presence of both Smads and p53 at the Maspin promoter in TGF beta-treated cells, suggesting that both transcription factors cooperate to induce Maspin transcription. TGF beta did not activate Maspin-luciferase reporter in p53-mutant MDA-MB-231 breast cancer cells, which exhibit methylation of the endogenous Maspin promoter. Expression of ectopic p53, however, restored ligand-induced association of Smad2/3 with a transfected Maspin promoter. Stable transfection of Maspin inhibited basal and TGF beta-stimulated MDA-MB-231 cell motility. Finally, knockdown of endogenous Maspin in p53 wild-type MCF10A/HER2 cells enhanced basal and TGF beta-stimulated motility. Taken together, these data support cooperation between the p53 and TGF beta tumor suppressor pathways in the induction of Maspin expression, thus leading to inhibition of cell migration.