32PBMP-4 production by bladder cancer cells favors tumor progression and promotes the development of a pro-tumoral immune environment

Aim/Background: Bladder cancer (BC) is a current clinical and social problem. At diagnosis, most patients present non-muscle invasive tumor, characterized by high recurrence rate which may progress to muscle invasive disease and metastatic spreading. BMP-dependent signaling arising from stromal bladder tissue mediates urothelial homeostasis by promoting urothelial cell differentiation. However, the possible role of BMP ligands in BC is still unclear. Methods: We have measure BMP4 expression by bladder cancer cell lines and further characterize the impact of that BMP4 expression upon monocyte/macrophage polarization by in vitro experiments. Results: Using a series of human BC cell lines and patient samples, we observed increased expression of BMP4 in advanced stages and undifferentiated tumors in close correlation with epithelial-mesenchymal transition (EMT). In agreement, the p-Smad 1,5,8 staining in tumors showing EMT signs was reduced in parallel with increased miR-21 and reduced BMPR2 expression. Remarkably, BMP4 expression also correlates with markers of type-2 macrophage differentiation. In vitro experiments shows that both recombinant BMP4 and BMP4-containing conditioned media from BC cell lines favors monocytes differentiation towards macrophages with a M2 phenotype as shown by the expression and secretion of IL-10, together with immunomodulatory effector functions that contributes to create a tumor promoting environment. Conclusions: All these findings suggest that BMP-4 secretion by BC cells provide the M2 signal necessary for pro-tumoral immune environment. In addition, the repression of BMPR2 by miR-21 makes the tumor cells refractory to the pro-differentiating actions mediated by BMP ligands favoring tumor growth. Collectively our data highlight the importance of BMP signaling in bladder tumorigenesis and suggest new potential therapeutic approaches for managing BC. Legal entity responsible for the study: Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT) Funding: MINECO grants SAF2012-34378 and SAF2015-66015-R, Comunidad Autónoma de Madrid grant S2010/BMD-2470 (Oncocycle Program), MSyC grant ISCIII-RETIC RD12/0036/0009 and PIE 15/00076 to JMP Disclosure: All authors have declared no conflicts of interest.