Functional relevance of the candidate genes MSMB, NCOA4, TIMM23 and PARG in the prostate cancer risk region 10q11 for the emergence of oncogenic TMPRSS2:ERG fusions

Abstract

Genome-wide association studies (GWAS) have identified the inherited variant rs10993994 in 10q11 as being associated with prostate cancer risk. Beyond this trait association, the variant was functionally correlated with an altered DNA repair capacity and with the TMPRSS2:ERG fusion positive prostate cancer. Since an error-prone DNA repair predisposes for the generation of chromosomal rearrangements, this relationship seems not to be arbitrary. The present work was based on the hypothesis that the variant rs10993994 exerts its risk increasing effects by an error-prone double strand break repair, thus promoting oncogenic rearrangements. To find the causal perpetrator of the presumed pathomechanism, the candidate genes MSMB, NCOA4, TIMM23 and PARG in 10q11 were tested on their functional implication in the generation of TMPRSS2:ERG fusions. PARP1, the negative regulator of PARG, was also tested on its effect on the formation of fusions. According to the TMPRSS2:ERG induction assay, fusions were generated in prostate cancer cells by stimulation with dihydrotestosterone and γ-radiation. TMPRSS2:ERG fusion transcripts were quantified by quantitative Real Time-Polymerase Chain Reaction (qRT-PCR). Down-regulation of PARG using siRNA led to a significant 3.0-fold increase in the number of fusions, whereas down-regulation of the other candidate genes did not result in a significant effect on the formation of fusions. Since previous studies showed that silenced PARG expression increases the cellular poly(ADP-ribose) level, not only PARG but also alterations in the poly(ADP-ribose) equilibrium may cause the observed increase. However, down-regulation of PARP1, the opposite regulator of the poly(ADP ribose) level, did not have a significant effect on the generation of fusions. The results of this work provide the first experimental evidence for a causal implication of PARG in the generation of TMPRSS2:ERG fusions in prostate cancer. Supporting the hypothesis of error-prone DNA repair as causal mechanism for the observed risk increase, PARG may be transcriptionally influenced by the variant rs10993994, impairing a proficient DNA repair and predisposing for the generation of oncogenic rearrangements. The results of the present work contribute to the identification of functional mechanisms that may cause individually inherited susceptibility to prostate cancer.