Abstract
Abstract p73 is a member of the p53 tumor suppressor family, which can trigger cell cycle arrest and apoptosis through its ability to bind p53 DNA target sites, thereby it acts as a negative regulator of tumorigenesis. Similar to p53, at normal state p73 is maintained at very low level but it rapidly gets induced upon genotoxic stress. Accumulating evidences demonstrated that p73 is mainly regulated at the protein level but its significance is still not clearly understood. It is believed that it is a consequence of post-translational modifications (PTMs) of p73 upon DNA damage. Emerging reports suggested that other than PTMs, various co-factors are responsible for regulating its level and activity. But all these reports remained inadequate to explain the molecular mechanisms behind regulation and activity of p73 under non-stressed and stressed conditions. The aim of our study is to find out novel interactors of p73 which distinctively affect its stability and activity in normal state and upon DNA damage. We employed a proteomic approach to identify differential interactors of p73 under unstressed and genotoxic stress conditions. We prepared adenovirus system to ectopically overexpress dual-tagged p73 into cells. Our tandem affinity purification screening lead us to identification of many p73-associated proteins. Among the novel interactors, TRIM28, a RING-type E3 ligase, was of particular interest because it interacts with p73 under unstressed condition but no visible interaction was detected after DNA damage. We show here that TRIM28 ubiquitylates and targets p73 for proteasome-mediated degradation in unstressed conditions. Upon genotoxic stress, p73 gets phosphorylated at tyrosine 99 position in c-Abl-dependent manner leading to abrogation of its interaction with TRIM28 which subsequently leads to p73 stabilization. Another protein, MED15 was of particular interest because it interacts with p73 in phosphorylation-dependent manner and it serves as a coactivator of p73. Interestingly, we found that phosphorylation of p73 is a prerequisite for its interaction with MED15. Furthermore, loss of MED15 leads to decline in p73-mediated transactivation of its downstream target genes under DNA damaging conditions. Therefore, we propose a model in which DNA damage-induced phosphorylation of p73 affects its interaction with its negative regulator and leads to its preferential association with its coactivator. Citation Format: Yatendra K. Satija, Sanjeev Das. The Pursuit of p73 Regulation: interaction partners tell many different stories. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1392. doi:10.1158/1538-7445.AM2014-1392
Published Version
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