Abstract 3369: Macrophages and their induced cytokines drive the epithelial to mesenchymal transition in prostate cancer cells

Macrophages derived from circulating monocytic myeloid precursors are a major component of leukocyte infiltrate found in tumors and their role in prostate cancer progression is now emerging. Here we investigate the potential of macrophages to induce the epithelial-mesenchymal transition (EMT) in prostate cancer cells. EMT is a critical process for metastasis, and the elucidation of factors that initiate EMT would be beneficial in the development of treatments to halt the dissemination of cancer cells throughout the body. CD14+-peripheral blood monocytes were isolated from healthy donors and stimulated with either interferon gamma (INFγ) or interleukin (IL)-4, factors known to promote the differentiation of monocytes into M1 or M2-type macrophages, respectively. After 48 hours, cells from prostate cancer cell lines PC3 Luc, DU145 Luc, and ARCAP Luc were co-cultured with the macrophages for four days. The cells were passaged three times by trypsination and protein lysates were analyzed by Western Blot for the expression of EMT markers: E-cadherin and vimentin. Our results revealed that cells co-cultured with IL-4-stimulated macrophages expressed lower levels of E-cadherin and higher levels of vimentin compared to control epithelial cells. In addition, three mesenchymal-type subpopulations that were isolated from PC3 cells interacting with IL-4-treated CD14+-cells exhibited a complete loss of E-cadherin. After more than 20 passages, these cells maintained the mesenchymal characteristics in culture and showed a striking up-regulation of the transcription factor ZEB 1, whose expression has been previously correlated with Gleason grade in human prostate tumors. Concurrently, we set out to study the secreted factors by which macrophages may trigger EMT. We treated DU145 Luc and PC3 Luc cells with several cytokines found to be differentially expressed in media containing cancer cells co-cultured with IL-4-stimulated macrophages and evaluated whether any of these factors induced EMT. It was discovered that cells grown in media containing the cytokine, IL-1B, in combination with IL-4 showed a greater display of mesenchymal markers than control cells. In conclusion, these results establish that macrophages can act as potent EMT-inducers in prostate cancer cells, although the exact mediators of this function remain unknown. The data suggests that CD14+ cells stimulated with IL-4 are more effective at triggering EMT than non-stimulated or INFγ-stimulated macrophages, which may pinpoint M2-type macrophages as a mediator of EMT in vivo. Furthermore, the cytokine study revealed that macrophage-induced IL-1B in combination with IL-4 may be an important factor in the mechanism of macrophage-induced EMT. As this transition may represent a major mechanism of prostate cancer metastasis, future research will be focused on elucidating the molecules involved in order to develop novel therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3369. doi:10.1158/1538-7445.AM2011-3369