p53 phosphorylation at serine 15 is required for transcriptional inductionof the plasminogen activator inhibitor-1 (PAI-1) gene by the alkylating agent N-methyl-N '-nitro-N-nitrosoguanidine

The alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) is a widel y spread environmental carcinogen that causes DNA lesions leading to cell k illing. MNNG can also induce a cell-protective response by inducing the exp ression of DNA repair/transcription-related genes. We recently demonstrated that urokinase-type plasminogen activator, an extracellular protease to wh ich no DNA repair functions have been assigned, was induced by MNNG. Here, we show that the physiological inhibitor of urokinase-type plasminogen acti vator, PAI-1, is also induced by MNNG in a p53-dependent fashion, because M NNG induced PAI-1 in p53-expressing cells but not in p53-/- cells. MNNG ind uced p53 phosphorylation at serine 15, resulting in stabilization of the p5 3 protein, and this phosphorylation event was central for p53-dependent PAI -1 transcription. Finally, we showed that PAI-1 transcriptional induction,b y MNNG required a p53-responsive element located at -136 base pairs in the PAI-1 promoter, because specific mutation of this site abrogated the induct ion. Because PAI-1 is a prognostic factor in many metastatic cancers, being involved in the control of tumor invasiveness, our finding that a genotoxi c agent induces the PAI-1 gene via p53 adds a new feature to the role of th e tumor-suppressor p53 protein. Our results also suggest the possibility th at genotoxic agents contribute to tumor metastasis by inducing PAI-1 withou t involving genetic modification.