Abstract 3959: Pigment epithelium-derived factor blocks Interleukin-8 mediated proliferation in prostate cancer cells through PEDF-R/PLA2 receptor and regulation of the nuclear factor-κB and peroxisome proliferator activated receptor γ

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Although extensively studied as part of the immune system, chemokines have lately been investigated as mediators of tumor development. Interleukin-8 (IL8/CXCL8) is a pro-inflammatory and pro-angiogenic transcriptional target of NF-kappaB (NFκB) and has been described as a molecular determinant of androgen independence and progression in prostate cancer (PrCa). We recently demonstrated that IL8 production is inhibited in human PrCa PC3 cells by the Pigment Epithelium Derived Factor (PEDF), a natural secreted angio-inhibitor which blocks PrCa progression. The molecular mechanisms underlying PEDF anti-tumor action are not totally clear. However, it appears that PEDF acts via several receptors with PEDF-R/PLA2 being the first high affinity receptor isolated. In the present work, we characterized the signaling pathway involved in the PEDF inhibitory effect on IL8 expression and assessed the functional effect of IL8 reduction on PrCa cells. In order to validate IL8 repression by PEDF in PrCa cells, we treated Human androgen independent PC3 and DU145 cells with increasing doses of PEDF and quantified after 48 hours IL8 in the conditioned media. ELISA analyses showed that in both PrCa cell lines, PEDF inhibits the production of IL8. We demonstrated that IL8 down-regulation blocked PrCa cell growth in vitro as demonstrated by the use of IL8-specific neutralizing antibody. IL8 reduction was mimicked in cancer cells treated with BAY11-7082 and PDTC, two NFκB-specific inhibitors, and troglitazone, a PPARγ agonist. Accordingly, the expression and transcriptional activity of RelA/p65, the major NFκB subunit, was down-regulated in PrCa cells in response to PEDF whereas PPARγ was found up-regulated. RelA/p65 and IL8 down-regulation induced by PEDF was reversed by the GW9622 PPARγ antagonist suggesting a PPARγ-dependent pathway and locating, therefore, PPARγ upstream of NFκB. To determine if PEDF-R was involved in IL8 repression, we knocked down its expression by small interference RNA (siRNA). In these experiments, we showed that in contrast to cancer cells transfected with the non targeting control siRNA, PEDF-R siRNA transfected cells lost their ability to up-regulate PPARγ and to down-regulate RelA/p65 and IL8 in response to PEDF. In conclusion, in this study we demonstrated that by binding to its receptor, PEDF-R, PEDF could up-regulate PPARγ, leading subsequently to suppressed NFκB-mediated transcriptional activation, reduced production of IL8 and limited proliferation of PrCa cells. These findings reinforce the strong anti-tumor potential of PEDF and suggest a new way by which PEDF curbs prostate tumor growth. These data also emphasize the fact that targeting IL8 may represent a novel therapeutic alternative for PrCa. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3959.