ARF6 controls WNT5A receptor internalization to promote uveal melanoma invasion and metastasis

Introduction: Uveal melanoma is the most common primary ocular malignancy and there is currently no effective treatment for metastatic uveal melanoma largely because of the lack of understanding of the molecular mechanisms underlying this cancer. Although activating oncogenic mutations in GNAQ and GNA11 are present in 95% of uveal melanoma tumors, virtually nothing is known about the molecular mechanisms that drive oncogenesis in the remaining 5% of uveal melanomas that possess only wild type Gαq alleles and the molecular and cellular mechanisms that promote metastasis have not yet been discovered. This latter deficit in knowledge is extremely vexing, given that metastatic disease causes death in most uveal melanoma patients. We have recently shown that ADP-ribosylation factor 6 (ARF6), a small GTPase, is an immediate downstream effector of oncogenic Gαq and controls the entire major signaling pathways known to drive Gαq-mediated tumor formation and growth in uveal melanoma cells that have an activating mutation in Gαq. Moreover, in cutaneous melanoma, stimulation of the receptor by WNT5A activates ARF6 and controls metastasis via the release of β-catenin from N-cadherin and β-catenin9s subsequent nuclear transport. Previous studies have also demonstrated that ARF6 plays a role in the internalization of various classes of membrane receptors including receptor tyrosine kinase (RTK) and G protein coupled receptor (GPCR) to control signal transduction, and WNT5A and its receptor promote tumor invasion and metastasis via receptor internalization in human cancers. Based on these intriguing findings, we postulate that ARF6 might be functioning to control tumor invasion and metastasis in uveal melanomas. Experimental Procedures: To test our hypothesis, we conducted cell invasion assays on uveal melanoma cell lines while targeting ARF6 expression by siRNA or ARF6 activity by pharmacological inhibition. We then proceeded with cell fractionation to look for any differences in the properties of subcellular components in treated cells compared to untreated cells. Unpublished findings: Here we show that WNT5A is expressed at high levels in Gαq wild type uveal melanoma cells and that WNT5A activates ARF6 through ROR2 receptor. When we block ARF6 expression by knockdown or ARF6 activity with a small molecule inhibitor, uveal melanoma invasion is significantly reduced. Notably, ARF6 is necessary for WNT5A-mediated ROR2 internalization. Conclusions: This work indicates that ARF6 functions in the internalization of WNT5A receptor to activate the signaling pathways that drive invasion and metastasis in uveal melanoma. These results would suggest that targeting ARF6 activation might be an effective therapy for the treatment of all uveal melanomas, regardless of their mutational status for Gαq. Citation Format: Donghan Shin, Coulson P. Rich, Lehi Acosta, Jackson R. Richards, Jae Hyuk Yoo, Allie H. Grossmann, Zongzhong Tong, Alan L. Mueller, Weiquan Zhu, Dean Y. Li, Shannon J. Odelberg. ARF6 controls WNT5A receptor internalization to promote uveal melanoma invasion and metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5157.