Abstract 3208: Semaphorin 3F suppresses telomerase activity

Abstract

Abstract Objectives: Telomerase is a ribonucleoprotein that is active in more than 90% of human tumors, including ovarian cancers. We have previously demonstrated that vascular endothelial growth factor (VEGF) stimulates telomerase activity in ovarian cancer cell lines through cellular VEGF receptors and the ERK1/2 pathway targeting Sp1 sites within the hTERT promoter. Since semaphorin 3F (S3F), a proposed tumor suppressor, has been shown to antagonize VEGF, the purpose of this study was to determine whether S3F inhibits telomerase Methods: Telomerase-positive ovarian cancer cell lines (OV2008, C-13, SW626) and telomerase-negative non-tumorigenic, SV-40 large-T antigen-transfected human ovarian surface epithelium (HOSE) cell lines were evaluated for endogenous RNA and protein expression of S3F, VEGF, and their shared receptors. Cultured cells were either treated with recombinant S3F protein or transiently transfected with cDNA to over-express S3F. Conversely, these cells were transiently transfected with siRNA targeting S3F ± specific receptor inhibitors. RT-PCR and western blot confirmed S3F over-expression, knock-down of S3F, or inhibition of receptors. Telomerase activity was measured by telomerase PCR-ELISA, while RT-PCR and western immunoblotting were utilized to detect S3F as well as to explore the signaling pathway involved in S3F-mediated telomerase regulation. Results: Telomerase activity was suppressed in ovarian cancer cell lines following treatment with S3F recombinant protein or S3F over-expression by transient transfection. Furthermore, siRNAs targeting S3F and NP-2 or treatment with the VEGF receptor inhibitor, CBO-P11, abrogated S3F mediated telomerase inhibition. Over-expression of S3F resulted in up-regulation of phosphorylation of Erk1/2. Conclusions: These data suggest that telomerase is a novel molecular target of S3F. Since, angiogenic and angiostatic factors play an important role in ovarian cancer tumorigenesis, S3F-mediated inhibition of telomerase represents a potential novel target for therapeutic intervention. 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 3208.