Abstract 2752: Characterization of the ATM-SPOP pathway in prostate cancer tumorigenesis

Abstract

Abstract The Speckle type Poz Protein (SPOP), an E3 ubiquitin ligase adaptor, has recently been identified as the gene that has the most common somatic point mutations in prostate cancer. SPOP mutations are associated with genomic alterations, indicating a role for SPOP in the maintenance of genome stability. We, and others, have recently demonstrated a critical role of SPOP in the DNA damage response (DDR), suggesting SPOP mutants may represent a subgroup of patients that have hyper sensitivity to DNA damaging therapies. However, how SPOP mutations might impact its function and their roles in the progress of prostate tumorigenesis remain to be extensively studied. Genomic studies have found that SPOP mutations are clustered within its substrate binding pocket. Of a particular interest, Serine119 is found to be frequently mutated to Asparagine (S119N). Using computational modeling, we found that Ser119 resides in the SBC-MATH binding interface and is in close contact with the non-polar residue of the SPOP-binding consensus motif. Therefore we hypothesized that phosphorylation of Serine 119 might directly affect substrate binding. First we characterized prostate cancer cells expressing this mutation and we found that they displayed a suboptimal DNA damage response with prolonged DNA repair. Using an in situ proximity ligation assay, we demonstrate that Serine 119 is essential for SPOP ionizing irradiation induced interaction with the Ataxia Telangiectasia Mutated kinase (ATM), a major hub protein in the DDR. With the evidence of SPOP being a phospho-protein, we further provide in vitro evidence that ATM phosphorylates SPOP on Serine 119 in response to DNA damage. Characterization of the functional significance of ATM-mediated SPOP phosphorylation indicates a wide range of downstream targets regulating cell cycle progression and DNA repair. Taken together, our data reveal a critical pathway linking ATM and SPOP in regulation of prostate cancer initiation and therapeutic responses to DNA damage. This also provides the first evidence of a pathophysiological relevant mutation linked to ATM phosphorylation in the DDR. Citation Format: Joshua Fried, Rebecca Boohaker, Qinghua Zeng, Wei Zhang, Bo Xu. Characterization of the ATM-SPOP pathway in prostate cancer tumorigenesis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2752.