Activating mutations in two G??proteins of the q class (G?q), GNAQ and GNA11, are the drivers of oncogenesis in approximately 80% of uveal melanomas. Similar activating mutations of GNAQ are also found in patients with Sturge-Weber syndrome, which can manifest itself as glaucoma and vascular malformations of the conjunctiva, choroid, retina, and episclera. Uveal melanoma is the most common primary ocular tumor, and in approximately 50% of the cases, the tumor will metastasize to other organs, primarily the liver. Once metastasized, the disease is invariably fatal. Activating GNAQ and GNA11 mutations drive uveal melanoma oncogenesis via the control of several recently identified signaling pathways, including phospholipase C- ?/protein kinase C (PLC-?/PKC) and TRIO-RhoA/Rac1 pathways, which activate MAPK/ERK and YAP to induce AP1- and YAP-TEAD-mediated transcription. However, the mechanism(s) by which G?q proteins activate multiple downstream pathways has not been completely elucidated. Preliminary data suggest that the small GTPase ARF6 may act as an immediate downstream effector of activated GNAQ/GNA11 to control all of the currently known oncogenic G?q signaling pathways. Other preliminary data also suggest that G?q may signal through ARF6 to activate ?-catenin signaling by promoting the relocalization of ?-catenin from the cell membrane to the nucleus where it can mediate gene transcription. Preliminary data also support the in vivo role of ARF6 in uveal melanoma. When ARF6 is silenced in uveal melanoma by shRNA or is inhibited with a small molecule inhibitor, tumor establishment and growth is significantly inhibited in an orthotopic xenograft mouse model. Based on these preliminary data, the following aims will be pursued.
In Aim 1, we will investigate whether activated G?q proteins induce ?-catenin signaling via activation of ARF6 in uveal melanoma. We will employ gene silencing via RNA interference and small molecule inhibition of selected targets to assess intracellular localization, transcriptional activity, and function of ?-catenin in uveal melanoma.
In Aim 2, we will elucidate the role of ARF6 in orchestrating known downstream signaling pathways of oncogenic G?q. The same strategies used in Aim 1 will be employed to determine whether ARF6 acts as an immediate downstream effector of activating GNAQ/GNA11 mutations to control (PLC-?/PKC) and TRIORhoA/ Rac1 pathways and AP-1 and YAP-TEAD-mediated transcription.
In Aim 3, we will assess the in vivo function of ARF6 in tumor establishment and growth by using orthotopic xenograft models of human uveal melanoma. The successful completion of these aims will allow us to determine whether ARF6 plays a critical role in G?q signaling, thus providing a promising therapeutic target for the development of drugs that could be used to treat uveal melanoma and possibly other G?q-related disorders such as Sturge-Weber syndrome.
Uveal melanoma is a cancer that begins in the eye but often spreads to other vital organs of the body where it invariably causes death. We have identified a protein that may control several signaling pathways that are thought to play essential roles in uveal melanoma formation. If our study shows that this protein indeed controls uveal melanoma formation, we will have identified a molecular target that could be used to develop effective drugs for the treatment of this often-deadly cancer.
|Zhu, Weiquan; Shi, Dallas S; Winter, Jacob M et al. (2017) Small GTPase ARF6 controls VEGFR2 trafficking and signaling in diabetic retinopathy. J Clin Invest 127:4569-4582|
|Yoo, Jae Hyuk; Shi, Dallas S; Grossmann, Allie H et al. (2016) ARF6 Is an Actionable Node that Orchestrates Oncogenic GNAQ Signaling in Uveal Melanoma. Cancer Cell 29:889-904|
|Grossmann, Allie H; Zhao, Helong; Jenkins, Noah et al. (2016) The small GTPase ARF6 regulates protein trafficking to control cellular function during development and in disease. Small GTPases :1-12|