Abstract 552: PEPD is an essential regulator of p53 tumor suppressor

Abstract

Abstract Peptidase D (PEPD), also known as prolidase among other names, is an enzyme that hydrolyzes dipeptides with proline or hydroxyproline at the carboxy terminus and is believed to be important for collagen metabolism, as proline and hydroxyproline are very abundant in collagen. Interestingly, we recently found that eliminating cellular PEPD causes cell death and tumor regression due to p53 activation. Here, we show that PEPD binds to and suppresses over half of nuclear and cytoplasmic p53 under normal conditions, independent of its enzymatic activity. PEPD binds to the proline-rich domain in p53, which inhibits phosphorylation of nuclear p53 and MDM2-mediated mitochondrial translocation of nuclear and cytoplasmic p53. Indeed, PEPD competes with MDM2 for p53 binding. However, the PEPD-p53 complex is critical for p53 response to stress, as stress signals doxorubicin (DOX) and hydrogen peroxide each must free p53 from PEPD in order to achieve robust p53 activation, which is mediated by reactive oxygen species. Thus, PEPD stores p53 for stress response, but this also renders cells dependent on PEPD for survival as it suppresses p53. Our results reveal a major p53 regulatory mechanism and a critical physiological function of PEPD. The p53-PEPD system likely operates in most if not all cells, since both p53 and PEPD are expressed ubiquitously. Disrupting PEPD suppression of p53 may be an important therapeutic strategy in cancer, as our data show that PEPD knockdown by RNA interference in tumors in mice causes p53 activation in the tumor tissues and tumor regression. Our study also reveals a previously unrecognized anticancer mechanism of DOX. We show that the key step in DOX-induced p53 activation is the disruption of p53 association with PEPD via reactive oxygen species. This finding also raises the intriguing question of whether other stress-inducing anticancer agents also disrupt the PEPD-p53 complex for p53 activation and suggests that antioxidants may inhibit the anticancer activity of DOX and other agents by inhibiting p53 separation from PEPD. This work is supported by NCI grants and Roswell Park Alliance Foundation Grants. Citation Format: Lu Yang, Yun Li, Arup Bhattacharya, Yuesheng Zhang. PEPD is an essential regulator of p53 tumor suppressor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 552.