Effect of MCAM on the aggressive phenotype in human prostate cancer.

Abstract

e23135 Background: Prostate Cancer (PCa) is the most common cancer in males and the second leading cause of death from cancer in men. Understanding the factors that regulate homing and survival of metastatic cancer cells in the bone is important for the identification of new therapeutic targets. High MCAM expression has been detected in the stroma of lytic and blastic lesions in preclinical models of PCa bone metastasis. The objective of this study is to characterize the role of MCAM in the maintenance of the aggressive phenotype in human PCa. Methods: We knocked and down MCAM in the lytic PC-3M-Pro4Luc2_dTomato and in the blastic C4-2B_dTomato PCa cell lines. Validation was done at both protein and RNA level. We performed functional assays such as migration and proliferation. RT-qPCR was used to test MCAM knockdown on EMT markers. The effect of the knockdown on the maintenance of cancer stem/progenitor-like cells was measured by ALDEFLUOR. Results: MCAM knockdown reduced proliferation in PC-3M-Pro4Luc2_dTomato PCa cells and resulted in increased E-Cadherin expression. Metastatic human PCa cells target the hematopoietic stem cell (HSC) niche in the bone marrow at the level of an “endosteal/osteoblast” niche and a “vascular/perivascular” niche. We set-up an in vitro model of “osteoblast niche” to study the prostate cancer cells upon co-culture with osteoblasts and to determine the effects on cancer stem/progenitor-like markers. We found that MCAM is required for the osteoblast-mediated induction of ALDH activity on PCa cells and MCAM knockdown prevented the increase in the size of the ALDHhigh subpopulation in PC-3M-Pro4Luc2_dTomato, mediated by human osteoblasts. Additionally, MCAM knockdown in PCa cells co-culture with osteoblast, prevented the induction of MCAM expression by osteoblasts. Finally, MCAM is significantly increased in the ALDHhigh cells and identifies a new subset of ALDHhigh / MCAMhigh cells which could be depleted upon MCAM knockdown. Conclusions: We detected a new subset of ALDHhigh/MCAMhigh cells and demonstrated the MCAM influences the maintenance of an aggressive-mesenchymal phenotype in human PCa. Therefore, MCAM represent an interesting target molecule to modulate the behavior of aggressive PCa cells.