THU502 CYR61, A Member Of The CCN Protein Family, Regulates IGF1 In Metastatic Prostate Cancer

Disclosure: G.L. Ortiz Hernandez: None. M. Walker: None. L. Woods-Burnham: None. R.A. Kittles: None. C.A. Casiano: None. S.L. Neuhausen: None. The cysteine-rich angiogenic inducer 61 (CYR61) is a member of the cellular communication network (CCN) protein family that can be induced by growth factors. CYR61-specific functions are dependent on cellular context. In prostate cancer (PCa), CYR61 contributes to cell growth and survival through its interactions with extracellular ligands, such as integrins avb3 and a6b4, in the extracellular matrix space. Interestingly, CYR61 contains an insulin-like growth factor-binding protein domain suggesting that it may interact with insulin-like growth factor-1 (IGF1). High serum levels of IGF1 are directly linked to PCa development and recently have been studied as a predictor of metastatic disease. Given the important roles that IGF1 and CYR61 play in PCa and their potential interaction, it is critical to investigate their molecular interplay. We hypothesize that the interaction of CYR61 and IGF1 contributes to aggressive tumor properties (e.g., proliferation, tumorsphere formation) in PCa. Using immunoblotting, we demonstrated that CYR61 is upregulated in the androgen receptor-negative and glucocorticoid receptor-positive (AR-/GR+) metastatic cell line, PC3, and downregulated in the docetaxel-resistant cell line PC3-DR. Furthermore, optimized knockdown of CYR61 using siRNA significantly reduced PC3 cell proliferation, viability, and prostasphere formation. To examine the underlying mechanisms associated with IGF1 signaling, we assessed the activation of the PI3/Akt and MAPK pathways in PC3 cells with CYR61 silenced. CYR61 siRNA-mediated knockdown decreased activation of the PI3/Akt pathway but did not alter the MAPK pathway. We also initiated studies to determine the co-localization of CYR61 and IGF1 using immunofluorescence microscopy (IF). Based on the initial IF observations, we will proceed to examine if their interaction is primarily intra- or extra-cellular and whether interactions differ based on AR signaling. Using both PC3 and MDA-PCa-2b, which is AR+/GR+, we will co-immunoprecipitate CYR61 with IGF1 to assess intracellular interactions and use the AVidity-based EXtracellular Interaction Screen (AVEXIS) system for extracellular interactions. The correlation between PCa aggressiveness and circulating levels of CYR61 and IGF1 is poorly studied. Therefore, our goal is to establish the contribution of CYR61-IGF1 protein-protein interaction to PCa cell proliferation and tumor aggressiveness. Presentation: Thursday, June 15, 2023