Abstract 3483: Activation of thromboxane A2 receptor-alpha promotes tumor growth and angiogenesis through expression of VEGF in prostate cancer
Authors: Ekambaram Prasanna , Ashton Anthony , Dilly Ashok-Kumar , Cai Yinlong , Tucker Stephanie , Honn Kenneth V. 
Published: June 2012

The primary objective of this study is to investigate the role of TXA2R signaling in prostate cancer progression and metastasis. Thromboxane A2 (TXA2) is a major arachidonic acid metabolite that signals through TXA2 receptors to induce platelet aggregation and smooth muscle contraction. TXA2 receptors (TP) are expressed as two different isoforms in humans- TP-alpha (TPα) and TP-beta (TPβ), which share both common and distinct signaling pathways. Previous studies have established the important role played by TXA2R isoforms in several cancers such as bladder, lung and breast cancer. But the role played by TXA2R signaling in prostate cancer (PCa) progression is not well understood. Our data indicates that human prostate cancer cell lines such as PC3, DU145, PC3M and LNCaP only express the TPα isoform but not the TPβ isoform. Also expression of TPα was higher in PCa cells compared to normal prostate epithelial cells. Results from the angiogenesis array indicated that activation of TXA2 receptors using TXA2 mimetic-IBOP resulted in an increase in angiogenesis related proteins such as VEGF, MMP9 and uPA in DU145 cells. To further confirm the role of TPα activation on VEGF, which is one of the most potent and predominant angiogenic factor, Real-time PCR and ELISA for human VEGF was performed that showed an increased expression of VEGF in response to IBOP in DU145 cells. To further understand the mechanisms behind TPα mediated VEGF expression, immunoblotting was performed on DU145 cells lysates treated with IBOP in order to analyze the phosphorylation status of downstream targets with phospho-specific antibodies. Activation of TXA2 signaling by IBOP did result in phosphorylation of downstream targets such as Src kinase, EGFR kinase and ERK. To verify whether EGFR kinase is involved in TPα induced VEGF expression, we pre-treated these cells with an EGFR kinase inhibitor AG1478 before treatment with IBOP. Results from Real-time PCR and ELISA suggest that inhibition of EGFR kinase did result in reduced VEGF mRNA and protein expression that confirmed its role in TPα mediated angiogenesis. Over expression of TPα in another PCa cell line, PC3 (PC3-TPα) that has lower endogenous expression of TPα also resulted in an increase in VEGF expression. Increased angiogenesis was further verified by a preliminary in vivo study that showed mice injected with PC3-TPα cells exhibited greater tumor growth and increased neovascularization compared to mice with PC3-Neo cells. Taken together, these data suggests that, activation of TPα receptor in PCa cells induced the expression of pro angiogenic factors such as VEGF and hence might play an important role in prostate cancer progression and metastasis.

Acknowledgements: This research was supported by NIH Grant 1R01 CA114051-01A1.

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 3483. doi:10.1158/1538-7445.AM2011-3483