Abstract B78: Osteopontin-c splicing isoform is a key molecule in ovarian cancer progression

Abstract Introduction: Osteopontin (OPN) is a glyphosphoprotein overexpressed in ovarian carcinoma (OC) and is involved in tumorigenesis and metastasis. Alternative splicing of OPN primary transcript generates 3 isoforms, named as OPNa, OPNb, and OPNc. Objective: This study aimed to characterize the expression profile and functional role of each OPN splicing isoform (OPN-SI) in OC. Methodology: The expression patterns of OPN-SI and a series of genes involved in key cancer pathways were analyzed by real-time PCR. In vitro and in vivo functional assays were performed using the ovarian cancer cell line OvCar-3, stably overexpressing the three OPN-SI and conditoned medium secreted by these cells. Results: OPNc, but not OPNa and OPNb, was specifically expressed on OC samples. OPNc splice variant significantly activated OvCar-3 cell proliferation, migration, invasion and anchorage independent cells growth, besides inducing tumor formation in nude mice. We also found that these features are mainly mediated by PI3K/Akt signaling pathway. By using a real time PCR Cancer Gene Array, we found that OvCar-3 OPNc-overexpressing cells are also able to modulate the expression of 34 genes involved in key cancer pathways. Notably, tumors formed by OPNc-overexpressing cells present high expression levels of typical angiogenic markers, such as VEGF-A, VEGFR-2 and CD34. Based on these data, we also investigated the molecular mechanisms by which OPNc stimulates angiogenic processes. Our data showed that OPNc overexpression activates VEGF-A expression and secretion, besides upregulating the expression of c-Fos, c-Jun and phospho-c-Jun. OPNc role on activating the phosphorylation of c-Jun is mediated by the integrin receptor (αvβ3), in an RGD-dependent manner. In addition, OPNc-conditioned medium is able to induce HUVEC endothelial cell proliferation, migration and adhesion. Conclusion: In summary, our data demonstrate that OPNc is able to activate sereral aspects of OC progression, including angiogenesis, mainly by the PI3K/Akt pathway, indicating that this splice variant could be a putative target for further studies aiming to investigate this molecule for new therapeutic approaches for OC. Citation Format: Tatiana M. Tilli, Kivvi D. Mello, Vanessa Franco, Bruno Robbs, João Luiz Wanderley, Fabrício Rass, João P B Viola, Georg Weber, Vincent Castronovo, Akeila Bellahcène, Etel R P Gimba, Etel Gimba. Osteopontin-c splicing isoform is a key molecule in ovarian cancer progression. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr B78.