Prostate Epithelial RON Signaling Promotes M2 Macrophage Activation to Drive Prostate Tumor Growth and Progression.

Effective treatment of advanced prostate cancer persists as a significant clinical need as only 30% of patients with distant disease survive to 5 years after diagnosis. Targeting signaling and tumor cell-immune cell interactions in the tumor microenvironment has led to the development of powerful immunotherapeutic agents, however, the prostate tumor milieu remains impermeable to these strategies highlighting the need for novel therapeutic targets. In this study, we provide compelling evidence to support the role of the RON receptor tyrosine kinase as a major regulator of macrophages in the prostate tumor microenvironment. We show that loss of RON selectively in prostate epithelial cells leads to significantly reduced prostate tumor growth and metastasis and is associated with increased intratumor infiltration of macrophages. We further demonstrate that prostate epithelial RON loss induces transcriptional reprogramming of macrophages to support expression of classical M1 markers and suppress expression of alternative M2 markers. Interestingly, our results show epithelial RON activation drives upregulation of RON expression in macrophages as a positive feed-forward mechanism to support prostate tumor growth. Using 3D coculture assays, we provide additional evidence that epithelial RON expression coordinates interactions between prostate tumor cells and macrophages to promote macrophage-mediated tumor cell growth. Taken together, our results suggest that RON receptor signaling in prostate tumor cells directs the functions of macrophages in the prostate tumor microenvironment to promote prostate cancer. IMPLICATIONS: Epithelial RON is a novel immunotherapeutic target that is responsible for directing the macrophage antitumor immune response to support prostate tumor growth and progression. ©2020 American Association for Cancer Research.