Abstract 1128: Interleukin-8 increases CXCR7 by non-cononical activation of NF-kb pathway in prostate cancer
Authors: Singh Rajendra K. , Lokeshwar Bal L. 
Published: June 2012

Background & Objectives: IL-8 is a pro-inflammatory chemokine that promotes tumor growth, motility, invasion and angiogenesis in many cancers via activation of two receptors, CXCR1 and CXCR2. CXCR7 is a receptor for CXCL11 and CXCL12 and it interacts with CXCR4 all of which are highly elevated and are implicated in metastatic progression of prostate and other cancers. We showed recently that although CXCR7 does not invoke the classical G-protein coupled receptor activation pathway, it promotes tumor growth, angiogenesis, survival and invasion, in a ligand-independent pathway. Further, we reported that IL-8 up-regulates CXCR7 expression via an unknown mechanism. We hypothesized that IL-8 induces CXCR7 expression by activating NF-kB pathway as the CXCR7 promoter has several NF-KB binding sites. Further, many pro-inflammatory chemokines are the part of NF-kB pathway and known to exert their biological effects through the activation of one or more chemokine receptors.

Methods: All studies were conducted on prostate epithelial (RWPE-1) or tumor cell lines (LNCaP & PC-3). Quantitation of mRNA and protein expressions was performed by Q-PCR, western blotting and flow cytometry. Lipofectamine protocol was used for siRNA & plasmid DNA transfections. Transcription activity was quantitated by Luciferase-reporter activity using Dual-Glo™ Luciferase assay. Matrigel-coated invasion chambers were used to measure basement-membrane invasion activity.

Results & Conclusions: Addition of exogenous IL-8 or constitutive production by IL-8 cDNA transfection in RWPE-1 or LNCaP cultures increased CXCR7 mRNA expression by 4-20-folds respectively. Exogenous IL-8 addition increased CXCR7 mRNA within 15 min, maximizing at 4 h. IL-8 induced CXCR7 expression was significantly abolished by either CXCR1 or CXCR2 non-peptide antagonists, repertaxin & SB 225002, suggesting the requirement for both IL-8 receptors to increase CXCR7 transcription. Furthermore, IL-8 induced CXCR7 expression was inhibited when cells were treated with parthenolide (NF-κB inhibitor) or transfected with NF-kb super-suppressor, prior to IL-8 treatment, indicating effective blocking of NF-kB activation antagonized IL-8 induced CXCR7 mRNA and protein up-regulation. IL-8 induces NF-κB transcription and p65 activation in a time-dependent manner in prostate cells as detected by promoter luciferase activity & western blotting. IL-8 induces IκBα phosphorylation followed by degradation and p65 translocation in non tumorigenic, RWPE-1 cells. Moreover, PC-3 cells transfected with CXCR7 cDNA increased their invasive potential measured by invasion through the matrigel coated invasion chambers. Our data indicate that IL-8 induced CXCR7 expression responsible for prostate cancer invasion and mediates its effect in NF-κB dependent pathway [Grant Support; NIH R01AT003544, VA MERIT Review, VA5312.01 (BLL)].

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 1128. doi:10.1158/1538-7445.AM2011-1128