Abstract Cancer progression is frequently driven by chronic inflammation resulting in high expression levels of several cytokines, as for instance Interleukin 6 (IL-6). In prostate cancer patients, high IL-6 serum levels are associated with bad prognosis and IL-6 promotes the progression of prostate cancer to castration resistance. The suppressor of cytokine signaling 3 (SOCS-3) protein is an important negative feedback regulator of the IL-6/JAK/STAT3 signaling pathway. In prostate cancer cell lines with an IL-6 autocrine loop, SOCS-3 is essential for survival. Our group has previously shown that IL-6 can lead to ligand independent trans-activation of the androgen receptor (AR) and recent publications by others have demonstrated that the anti-androgen Enzalutamide can influence IL-6 signaling. Based on these previous findings we hypothesize that there is a bi-directional cross-talk between the IL-6 and AR signaling pathways and that SOCS-3 might be the centerpiece of androgen mediated regulation of IL-6 signaling. AR positive prostate cancer cell lines (LNCaP and DuCaP) were treated with combinations of IL-6, the synthetic androgen R1881 and the anti-androgens Bicalutamide and Enzalutamide to evaluate the effect on SOCS-3 expression and JAK/STAT3 signaling activity. Stable up- and down-regulation of SOCS-3 was achieved by lentiviral gene transfer to study the functional role of SOCS-3 on IL-6 signaling activity in context of AR activity. We found that treatment with physiological levels of IL-6 led to a strong induction of SOCS-3 mRNA in four AR positive cell lines that do not express endogenous IL-6. Stable knockdown of SOCS-3 in AR positive LNCaP cells significantly increased STAT3 phosphorylation, nuclear translocation and transcriptional activity, whereas over-expression had the opposite effects. Additionally, we found that androgen treatment down-regulated SOCS-3 mRNA dose-dependently in LNCaP (p = 0.004) and DuCaP (p = 0.002) whereas the anti-androgens Bicalutamide (p = 0.048) and Enzalutamide (p = 0.005) increased SOCS-3 mRNA. Furthermore, treatment with Enzalutamide was able to inhibit the short-term anti-proliferative effects of IL-6 in LNCaP (p<0.001). These findings demonstrate for the first time that SOCS-3 is expressed and functionally active in AR-positive prostate cancer cell lines as well as negatively regulated by androgenic signaling. We speculate that the inhibition of the short-term anti-proliferative effect of IL-6 is mediated via SOCS-3 and that the up-regulation of SOCS-3 by anti-androgens may be an important factor in the development of castration resistance. Based on our results we conclude that SOCS-3 is regulating the cross-talk between IL-6/STAT3 and AR signaling. Citation Format: Florian Handle, Holger H.H. Erb, Birgit Luef, Frédéric R. Santer, Zoran Culig. Androgenic signaling influences SOCS-3 in prostate cancer cells. [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 5059. doi:10.1158/1538-7445.AM2015-5059