Abstract 2901: Nuclear β-arrestin1 is a critical cofactor of hypoxia-inducible factor-1α signaling in endothelin-1-induced ovarian tumor progression
Authors: Tocci Piera , Cianfrocca Roberta , Rosanò Laura , Caprara Valentina , Sestito Rosanna , Di Castro Valeriana , Bagnato Anna 
Published: July 2016

Abstract
In epithelial ovarian cancer (EOC), endothelin-1 (ET-1)/endothelin A receptor (ETAR) axis has been reported to be involved in invasiveness, epithelial-to-mesenchymal transition, chemoresistance and metastatic dissemination and is thereby associated with poor prognosis. In these cells, ET-1 is able to induce the nuclear translocation and stability of hypoxia-inducible factor-1α (HIF-1α) the principal transcriptional factor that allows cellular adaptation to hypoxia. The importance of co-factors that trigger an epigenetic regulation of HIF-1α within tumor is not well understood. Here we elucidate that ET-1/ETAR-induced pathway physically and functionally couples the scaffold protein β-arrestin1 (β-arr1) to HIF-1α signaling. In EOC cells, ET-1 induced vascular-endothelial growth factor (VEGF), the pro-agiogenic target downstream of HIF-1α through HIF-1α nuclear accumulation. Activation of ET-1/ETAR axis, by mimicking hypoxia, promotes the nuclear association between β-arr1 and HIF-1α on the hypoxia responsive elements (HRE) binding sites. By ChIP assay, nuclear β-arr1 was able to interact with HIF-1α, by promoting the recruitment of p300 acetyltransferase. The formation of this functional complex resulted in enhanced histone acetylation, and gene transcription of HIF-1α downstream targets, such as ET-1 and VEGF, required for cell invasion. The induced release of ET-1 and VEGF by EOC cells, promoted angiogenic effects in endothelial cells, as evaluated by cell migration and tube-like structure formation assays. Interestingly ETAR/β-arr1 promoted the self-amplifying HIF-1α-mediated transcription of ET-1 that sustained a regulatory circuit required for invasiveness and angiogenic responses. These effects were abrogated by the silencing of β-arr1 or HIF-1α or by pharmacological treatment with the dual ET-1 receptor antagonist macitentan. In a murine orthotropic model of metastatic human EOC, treatment with macitentan, or silencing of β-arr1, inhibits intravasation and metastasis formation, suggesting that ET-1, together with VEGF, represents one of such factors that mediates tumor-endothelial cell communications, favoring a permissive environment for metastatic spread. Collectively these findings reveal the interplay of β-arr1 with HIF-1α in the complexity of ET-1/ETAR pathway, mediating epigenetic modifications, to an extent comparable with hypoxia, directly involved in metastatic progression. Targeting ET-1 axis by macitentan may represent a new opportunity to target the orchestration mediated by nuclear β-arr1/HIF-1α complex in EOC, demonstrating that this approved small molecule interfering with stromal compartment, expressing ETBR, and tumor cells, expressing mainly ETAR, can be used in clinical setting for improved therapeutics in EOC.
Citation Format: Piera Tocci, Roberta Cianfrocca, Laura Rosanò, Valentina Caprara, Rosanna Sestito, Valeriana Di Castro, Anna Bagnato. Nuclear β-arrestin1 is a critical cofactor of hypoxia-inducible factor-1α signaling in endothelin-1-induced ovarian tumor progression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2901.