Abstract 1440: Mechanisms of TGF-β1-induced myofibroblast/CAF differentiation in human prostate-derived mesenchymal stem cells.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Reactive stroma in prostate cancer is typified by the co-evolution of myofibroblasts/CAFs. This reactive stroma is associated with most human carcinoma and is predictive of progression. TGF-β1 is a key factor in regulating reactive stroma biology. However, the origin of myofibroblasts and the mechanisms of how TGF-β1 recruits, activates and induces their differentiation are essentially unknown. We have identified mesenchymal stem cells from normal human prostate gland and evaluated their biology in a novel 3D co-culture system. Human prostate-derived mesenchymal stem cells (hpMSCs) were CD44+/CD90+, expressed other mesenchymal stem cell genes, and exhibited multipotent differentiation patterns. When co-cultured with LNCaP cells in Millicell-CM inserts or co-inoculated in nude mice, self-organizing organoids formed with a core of stromal cells and a peripheral mantel of LNCaP cells. To investigate the role of TGF-β1, the hpMSCs were co-cultured with LNCaP cells engineered to overexpress active TGF-β1. Significantly, LNCaP cells engineered to overexpress TGF-β1 induced hpMSC differentiation to prototypical reactive stroma myofibroblasts. Microarray analysis of stroma revealed 1617 gene probes with more than a 2 fold-change in the presence of TGF-β1, showing that expression of TGF-β1 in LNCaP cells drives differential gene expression in hpMSCs. Of those gene expression profiles, RUNX1 and ID1 were identified as key transcription factors in hpMSCs that mediate TGF-β1-induced myofibroblast differentiation. Knockdown of RUNX1 in hpMSCs significantly promoted differentiation to myofibroblasts. Conversely, overexpression of RUNX1 inhibited a myofibroblast gene expression signature. Together, these data implicate RUNX1 as a major regulator of the stem cell state of tissue-derived myofibroblast stem/progenitor cells and therefore a modulator of the co-evolution of reactive stroma. Furthermore, ID1 may function as a negative regulator of reactive stroma formation by promoting proliferation of transiently amplifying cells and inhibiting myofibroblast differentiation. Our data show that reactive stroma in prostate cancer initiates from activation and differentiation of CD44+/CD90+ endogenous hpMSCs through TGF-β1/RUNX1/ID1 pathway. Understanding these mechanisms is important for developing new strategies to target the microenvironment niche. Citation Format: Woosook Kim, David Barron, Rebeca San Martin, Steven Ressler, David Rowley. Mechanisms of TGF-β1-induced myofibroblast/CAF differentiation in human prostate-derived mesenchymal stem cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1440. doi:10.1158/1538-7445.AM2013-1440