Abstract 1691: TMPRSS2:ERG fusion enhances osteoblastic phenotype of prostate cancer bone metastases

Abstract

Abstract Background: Bone metastases are the major cause of morbidity and mortality in prostate cancer (PCa) patients. Recently, TMPRSS2:ERG gene fusions produced by rearrangements along chromosome 21 was found in more than 50% of PCa samples, resulting in androgen-dependent aberrant expression of the functional ERG transcription factor. Interestingly, ERG transcription factor has been previously shown to be involved in bone development. This study is therefore focused on investigating whether TMPRSS2:ERG gene fusions are involved in PCa bone metastasis development. Methods: We previously established cell clones overexpressing TMPRSS2:ERG from two PCa cell lines, PC3 and PC3c. We first studied induced bone lesion phenotype using in vivo intra-tibial injection models. Secondly, we analyzed transcriptional changes induced by ERG transcription factors in PC3c clones to identify potential target genes. Then, direct target genes were further validated and investigated in vitro using RT-qPCR, ELISA, siRNA and ChIP techniques. Importantly, using a cohort of prostate carcinoma samples, we validated the expression correlation between ERG and its target target genes expression in human pathology. Results: Bone lesions induced in vivo by intra-tibial injections of PC3 or PC3c cells are known to be osteolytic or mixed (osteoblastic/osteolytic) respectively. Interestingly, intra-tibial injections of PC3c clones expressing the fusion showed a statistically significant increase of osteoblastic phenotype compared to control cells. Furthermore, intra-tibial injections of PC3 clones expressing the fusion showed a strong decrease of osteolytic phenotype, reinforcing our previous result in PC3c clones. Among the genes identified by transcriptomic study and dysregulated in PC3c clones expressing the fusion, we have identified the ERG candidate target Endothelin-1 (ET-1), which is known to be involved in osteoblast proliferation and in osteoblastic metastasis formation in PCa. Indeed, we found that ET-1 expression was up-regulated in PC3c-TMPRSS2:ERG clones, and the up-regulation was dependent on ERG expression levels. Importantly, silencing of ERG resulted in decreased expression of ET-1. In silico analysis of the promoter of ET-1 revealed the presence of several potential binding sites of ERG. ChIP experiments followed by qPCR demonstrated a direct binding to one of them. Moreover, in human PCa samples, there was a significant expression correlation between ET-1 and fusion gene TMPRSS2:ERG, reinforcing the direct functional link between ET-1 and the fusion in PCa. Conclusion: Taken together, these results strongly suggest that the TMPRSS2:ERG gene fusion contributes to the osteoblastic phenotype of PCa bone metastases and ET-1 is one of the involved factors, directly regulated by the transcription factor ERG. Citation Format: Carine Delliaux, Tian V. Tian, Mathilde Bouchet, Anaïs Fradet, Nathalie Vanpouille, Anne Flourens, Rachel Deplus, Xavier Leroy, Yvan de Launoit, Edith Bonnelye, Martine Duterque-Coquillaud. TMPRSS2:ERG fusion enhances osteoblastic phenotype of prostate cancer bone metastases. [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 1691.