Abstract 1221: Pontin, a new mutant p53 binding protein, promotes gain-of-function of mutant p53
Authors: Zhao Yuhan , Zhang Cen , Yue Xuetian , Li Xiaoyan , Liu Juan , Yu Haiyang , Yang Qifeng , Feng Zhaohui , Hu Wenwei 
Published: August 2015

Abstract
Tumor suppressor p53 is frequently mutated in human cancers. Many tumor-associated mutant p53 (mutp53) proteins gain new functions in promoting tumorigenesis, defined as gain of function (GOF). The mechanisms for mutp53 GOF are not well-understood. Mutp53 has been reported to interact with some proteins and it has been suggested that some interactions of mutp53 with its binding partners are important for mutp53 GOF through regulating the levels or functions of mutp53 and/or its binding proteins. To understand the molecular mechanisms for mutp53 GOF, we searched for mutp53 binding proteins in thymic lymphomas of R172H mutp53 knock-in (p53R172H/R172H) mice with significant mutp53 protein accumulation by employing an unbiased immunoprecipitation (IP) combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) screening approach. Normal tissues of p53R172H/R172H mice with low mutp53 levels and tumors of p53-/- mice were used as controls.
Using this approach, we identified Pontin, a highly conserved AAA+ ATPase important for various cellular functions, as a new mutp53 binding protein. This Pontin-mutp53 is conserved in both humans and mice. Importantly, this Pontin-mutp53 interaction promotes mutp53 GOF in invasion, migration, and anchorage-independent growth of tumor cells. Furthermore, we found that the C-terminus of Pontin is required for Pontin-mutp53 interaction and mutp53 GOF. The ATPase domain in the C-terminus of Pontin is crucial for its promoting effect on mutp53 GOF; blocking the ATPase activity of Pontin by a Pontin specific ATPase inhibitor or an ATPase deficient dominant-negative Pontin expression vector greatly diminished mutp53 GOF. We found that Pontin was largely co-localized with mutp53 in the nucleus and promotes mutp53 GOF through regulation of mutp53 transcriptional activity; knock-down of Pontin abolished the transcriptional regulation of mutp53 towards a group of genes involved in many important signaling pathways, including gap junction signaling, IGF-1 signaling, EGF signaling etc. Furthermore, overexpression of Pontin is associated with poor survival in cancer patients, especially those containing mutp53 in tumors. This work demonstrates that Pontin promotes mutp53 GOF in tumorigenesis in an ATPase-dependent manner, and raises interesting and intriguing possibilities to block mutp53 GOF in tumors through targeting Pontin or its ATPase activity. In summary, our results highlight an important role and mechanism for Pontin, a new p53 partner, in promoting mutp53 GOF in tumorigenesis.
Citation Format: Yuhan Zhao, Cen Zhang, Xuetian Yue, Xiaoyan Li, Juan Liu, Haiyang Yu, Qifeng Yang, Zhaohui Feng, Wenwei Hu. Pontin, a new mutant p53 binding protein, promotes gain-of-function of mutant p53. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1221. doi:10.1158/1538-7445.AM2015-1221