Influence de la connexine 43 sur le phénotype des cellules cancéreuses prostatiques et sur le développement de métastases osseuses

Prostate cancer (PCa) has the highest incidence in men with bone metastasis occurring in 80% of cases and mainly characterized by osteoblastic lesions. The mechanisms by which prostate cancer cells are induced to metastasize to bone are variable and complex, implicating oncogenes, pro-angiogenic factors and adhesion molecules. Among the different interacting molecules, Connexins (Cxs) could participate in this process. Connexins are transmembrane protein involved in Direct Gap Junction Intercellular Communication (GJIC) in order to maintain tissue homeostasis and the coordination of cellular activities. Studies have shown that PCa cells are deficient in some Cx isoforms (Cx32, Cx43) in primary tumors. However, recent studies suggest that Cx43 could be implicated in the last stages of the tumorigenic process as a promoter of cancer cell dissemination with a putative role of heterocellular coupling with environmental cells in the migration, diapedesis and metastatic processes. Furthemore, cumulated data support the involvement of Cx43 and GJIC in the differentiation process of bone-forming osteoblastic cells and bone turnover. Indeed, in vivo, Cx43-null mice presented mineralization defects in craniofacial bones and ribs and in vitro a decreased differentiation potential of OB cells was clearly demonstrated. Therefore, we have investigated the role of Cx43 on the metastatic potential of PCa cells and on their bone impact in vivo. To examine the effects of increased expression of Cx43 gene in PCa cells, we have performed retroviral infection in two well characterized cell lines representing different stages of cancer progression: PC3 (aggressive) and LNCaP (less metastatic). After overexpression, in PC3 cells, Cx43 was restricted to the cytoplasmic part and no cell-to-cell communication was measured. Conversely, in LNCaP cells, Cx43 was mainly observed in appositional membranes and a functional GJIC was demonstrated by gap-FRAP and preloading assays. Moreover after overexpression, phenotypic characterization of both cell types demonstrated significant differences in adhesion, invasion, proliferation and secretome profile. Cx43 appears to alter the behavior of LNCaP making them more aggressive. To study the impact of prostate cancer cells overexpressing Cx43 on bone, intratibial injections in nude mice were performed. Mice were imaged by means of tomographic and scintigraphic analyses vs. Time. Both cell types developed osteolytic tumors. Cx43 overexpression in LNCaP cells induced a 4 fold increase of tumour incidence compared to mock cells. After Cx43 overexpression, tibial bone volume was clearly decreased compared to control confirming the higher osteolytic ability of LNCaP. For PC-3 cells, no difference was observed after Cx43 overexpression but a preliminary study of the spread after intracardiac injection has shown a slowdown in the development of bone metastases. Finally, co-cultures with murine osteoblasts have shown that cancer cells promote the expression of RANKL by osteoblasts, an activator of osteoclasts, with a decrease of the osteoblastic differentiation. These effects are independent of the level of Cx43 expression. Only the proliferation of osteoblasts was significantly modified by Cx43 overexpression in prostatic cancer cells. Our in vitro study demonstrates that Cx43 could influence the metastatic status of PCa cells with increased aggressiveness of LNCaP. In vivo, our data validate the potential implication of this connexin in the bone impact during metastasis.