Abstract 434: Prostate cancer cell-derived cathelicidin-related antimicrobial peptide regulates MCP-1 and CXCL1/2 through autocrine signaling

Prostate cancer (PCa) is the most commonly diagnosed cancer and the second leading cause of cancer deaths among males in the United States. Even with conventional therapies PCa metastasizes to advanced stage in many patients, suggesting a need for alternate therapeutic targets to increase patient survival. We have recently shown that elevated levels of the human antimicrobial peptides, leucin leucin-37 (LL-37) and its murine orthologue, cathelicidin-related antimicrobial peptide (CRAMP), were positively associated with PCa progression. In addition, we have observed that PCa-derived CRAMP chemoattracts protumorigenic immune cells, including macrophages, neutrophils, and myeloid-derived suppressor cells (MDSCs) to the tumor microenvironment. To further understand possible protumorigenic immune mechanisms of CRAMP during PCa growth, we studied a relationship between CRAMP and formyl peptide receptor 2 (FPR2) in mouse PCa cell lines. Interestingly, we observed that TRAMP-C1 cells, which express high-level of CRAMP, also express high levels of its receptor, FPR2, whereas its cloned derivative, TRAMP-C1shRNA cells with targeted down-regulation of CRAMP, display decreased level of FPR2 both in mRNA and protein levels. We further characterized downstream target genes of CRAMP-FPR2 signaling pathway. Quantitative real-time PCR results indicated that TRAMP-C1 cells have increased expression of both monocyte chemotactic protein-1 (MCP-1), known to chemoattract monotyes/macrophages, and CXCL1/2, known to chemoattract neutrophils and MDSCs, whereas TRAMP-C1shRNA cells exhibited low levels of MCP-1 and CXCL1/2 mRNA. Moreover, results indicated elevated gene expression of FPR2, MCP-1, and CXCL1/2 in TRAMP-C1shRNA cells following stimulation with exogenous CRAMP peptide in culture. In a separate experiment, we also observed down-regulation of MCP-1 and CXCL1/2 in TRAMP-C1 cells after the blockade of FPR2 by FPR2 inhibitor, suggesting a possible association between CRAMP and FPR2 in TRAMP-C1 cells, influencing the levels of MCP-1 and CXCL1/2 during PCa progression. Chemokines including MCP-1 and CXCL1/2 play a significant role in PCa development by recruiting protumorigenic immune effectors, such as MDSCs, tumor-associated macrophages and neutrophils to the tumor microenvironment. Thus, understanding the role of CRAMP in stimulating PCa cells to produce protumorigenic chemokines will define the immunomodulatory role of CRAMP during PCa progression. Altogether, the data suggest that PCa-derived CRAMP triggers pro-tumorigenic stimuli by influencing levels of protumorigenic chemokines through autocrine and paracrine FPR2 signaling. Ongoing studies to identify transcriptional regulators influenced by CRAMP-FPR2 signaling will further define the precise mechanisms of action of CRAMP, to possibly extend the findings in PCa patients as a potential therapeutic target. Citation Format: Ha-Ram Cha, Jonathan Hensel, Selvarangan Ponnazhagan. Prostate cancer cell-derived cathelicidin-related antimicrobial peptide regulates MCP-1 and CXCL1/2 through autocrine signaling. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 434. doi:10.1158/1538-7445.AM2015-434