The transcriptional coactivator Yes-associated protein (YAP) has been shown to interact with and to enhance p73-dependent apoptosis in response to DNA damage. Here, we show that YAP requires the promyelocytic leukemia gene (PML) and nuclear body localization to coactivate p73. YAP imparts selectivity to p73 by promoting the activation of a subset of p53 and/or p73 target promoters. Endogenous p73, YAP, and p300 proteins are concomitantly recruited onto the regulatory regions of the apoptotic target gene p53AIP1 only when cells are exposed to apoptotic conditions. Silencing of YAP by specific siRNA impairs p300 recruitment and reduces histone acetylation on the p53AIP1 target gene, resulting in delayed or reduced apoptosis mediated by p73. We also found that YAP contributes to the DNA damage-induced accumulation of p73 and potentiates the p300-mediated acetylation of p73. Altogether, our findings identify YAP as a key determinant of p73 gene targeting in response to DNA damage.

p73 has been identified as a structural and functional homolog of the tumor suppressor p53. The transcriptional coactivator Yes-associated protein (YAP) has been demonstrated to interact with and to enhance p73-dependent apoptosis in response to DNA damage. Here, we show the existence of a proapoptotic autoregulatory feedback loop between p73, YAP, and the promyelocytic leukemia (PML) tumor suppressor gene. We demonstrate that PML is a direct transcriptional target of p73/YAP, and we show that PML transcriptional activation by p73/YAP is under the negative control of the proto-oncogenic Akt/PKB kinase. Importantly, we find that PML and YAP physically interact through their PVPVY and WW domains, respectively, causing PML-mediated sumoylation and stabilization of YAP. Hence, we determine a mechanistic pathway in response to DNA damage that could have relevant implications for the treatment of human cancer.

Urothelial bladder cancer (UBC) is heterogeneous at the clinical, pathological, and genetic levels. Tumor invasiveness (T) and grade (G) are the main factors associated with outcome and determine patient management (1). A discovery exome sequencing screen (n=17), followed by a prevalence screen (n=60), identified new genes mutated in this tumor coding for proteins involved in chromatin modification (MLL2, ASXL2, BPTF), cell division (STAG2, SMC1A, SMC1B), and DNA repair (ATM, ERCC2, FANCA). STAG2, a subunit of cohesin, was significantly and commonly mutated/lost in UBC, mainly in tumors of low stage/grade, and its loss was associated with improved outcome. Loss of expression was often observed in chromosomally-stable tumors and STAG2 knockdown in bladder cancer cells did not increase aneuploidy. STAG2 reintroduction in non-expressing cells led to reduced colony formation. Our findings indicate that STAG2 is a novel UBC tumor suppressor acting through mechanisms that are different from its role to prevent aneuploidy.

Mutations in the TP53 tumor suppressor gene are the most frequent genetic alteration in human cancers. These alterations are mostly missense point mutations that cluster in the DNA binding domain. There is growing evidence that many of these mutations generate mutant p53 proteins that have acquired new biochemical and biological properties. Through this gain of function activity, mutant p53 is believed to contribute to tumor malignancy. The purpose of our study was to explore mutant p53 as a target for novel anticancer treatments. To this aim, we inhibited mutant p53 expression by RNA interference in three different cancer cell lines endogenously expressing mutant p53 proteins, and evaluated the effects on the biological activities through which mutant p53 exerts gain of function. We found that depletion of mutant p53 reduces cell proliferation, in vitro and in vivo tumorigenicity, and resistance to anticancer drugs. Our results demonstrate that mutant p53 knocking down weakens the aggressiveness of human cancer cells, and provides further insight into the comprehension of mutant p53 gain of function activity in human tumor.