Activation of p53 by protein inhibitor of activated Stat1 (PIAS1).

The tumor suppressor protein p53 functions as a transcriptional factor that activates genes controlling cell cycle arrest and apoptosis. Here, we report that protein inhibitor of activated Stat1 (PIAS1) interacts with the tetramerization and C-terminal regulatory domains of p53 in yeast two-hybrid analyses. Endogenous PIAS1 is also associated with endogenous p53 in mammalian cells. Ectopic expression of PIAS1 activates p53-mediated expression in mouse embryonic fibroblast cells (p53(-/-)) as well as a variety of other cell lines. Furthermore, ectopic expression of PIAS1 induces p53-mediated expression of cyclin-dependent kinase inhibitor p21 and G(1) arrest of the cell cycle in H1299 cells. In addition, a PIAS1 mutant without the RING-finger domain required for sumoylation could still activate p53-mediated gene expression, indicating that activation of p53 by PIAS1 does not require the RING-finger domain. Taken together, our results suggest that PIAS1 is a novel activator of p53.