Bone metastases are frequent and severe complications of prostate cancer (PCa). Recently, the TMPRSS2:ERG gene fusion, which results in the aberrant androgen-dependent expression of the ERG transcription factor, has been shown to be the most common gene rearrangement in PCa. This study investigates a potential role of the gene fusion in the development and phenotype of PCa bone metastases. We previously established cell clones from a PCa cell line (PC3c), over-expressing different levels of TMPRSS2:ERG. In vivo analysis of bone lesions induced by intra-tibial injections of PC3c-TMPRSS2:ERG clones in mice (ethical approval DR2014-32) showed an increase of osteoblastic phenotype compared with control cells. Furthermore, a transcriptomic study of these clones showed a change of expression in many genes, including endothelin-1 (ET-1). Since ET-1 is known to be involved in osteoblast proliferation and in osteoblastic metastasis formation in PCa, we therefore investigated the transcriptional regulation of ET-1 by fusion proteins. In vitro, we have shown that this gene was overexpressed in PC3c-TMPRSS2:ERG clones, depending on ERG expression levels, and was inhibited by ERG silencing. In silico analysis of the promoter of ET-1 revealed the presence of several potential binding sites of ERG. Chromatin immunoprecipitation experiments demonstrated a direct binding to one of them. Moreover, using a cohort of human carcinoma prostate samples (ethical approval CSTMT-042), we were able to establish a correlation between the expression of ET-1 and the expression of the fusion gene TMPRSS2:ERG, reinforcing the link between ET-1 and the fusion. Taken together, these results strongly suggest that the TMPRSS2:ERG gene fusion contributes to the osteoblastic phenotype of PCa bone metastases and that ET-1 is a crucial target gene regulated by the transcription factor ERG.
Disclosure: The authors declared no competing interests. This work was supported by grants from the Centre national de la recherche scientifique (CNRS), La Ligue contre le Cancer (Comité du Pas-de-Calais) and the Institut national du cancer (INCa_4419). Carine Delliaux is a recipient of PhD fellowships from the Institut Pasteur of Lille/ Nord-Pas-de-Calais Regional Council (Région Nord-Pas-de-Calais).