Abstract 3473: Endothelin axis autocrine loop is positively regulated by the interplay between ET-1 and hypoxia-inducible factor-1α in melanoma cells

Abstract

Abstract Phenotypic and genotypic analyses of cutaneous melanoma have identified the endothelin B receptor (ETBR) as tumor progression marker, thus representing a potential therapeutic target. We previously demonstrated that ETBR activation by endothelin (ET)-1, promotes melanoma progression and lymphatic vessel growth through a hypoxia-inducible factor (HIF)-1α-mediated mechanism and cooperates with hypoxia to increase this effect. In this study we show that in melanoma cells ETs increase ET-1 and ETBR mRNA and protein expression and their promoter activity that were completely blocked by the selective ETBR antagonist, BQ788, supporting the presence of a positive ET-1-autocrine loop. Moreover when melanoma cells were exposed to hypoxia the induction of both ETBR and ET-1 was markedly enhanced demonstrating that hypoxia potentiates the ET-1-autocrine loop by reinforcing the expression of ETBR and the secretion of ET-1 that, in turn, increases simultaneously ET-1/ETBR expression. Silencing HIF-1α or HIF-2α significantly reduced the promoter activity and the expression of ET-1 and ETBR in response to hypoxia or ETs. Chromatin immunoprecipitation assay showed increased HIF-1α and HIF-2α binding to ET-1 and ETBR promoter in response to hypoxia or ET-1 stimulation. Interestingly, ETs through ETBR enhance both vascular endothelial growth factor (VEGF)-A and VEGF-C mRNA and protein expression and promoter activity. At functional level silencing of HIF-1α and HIF-2α inhibited the ET-1 and hypoxia-induced VEGF-A and VEGF-C expression, providing that hypoxia and ET-1 axis share the same transcriptional machinery through which may control angiogenic and lymphangiogenic response. Moreover, in melanoma xenografts, ETBR antagonist suppressed tumor growth, neovascularization-related effectors, indicating that targeting ETBR related signalling cascade may represent a novel treatment of melanoma by impairing the positive feedback loop between ET axis and hypoxic melanoma microenvironment. Supported by AIRC. 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 3473. doi:10.1158/1538-7445.AM2011-3473