Disrupting the interaction between constitutively active Gαqand Gβγ inhibits oncogenic signaling

Abstract ID 94080 Poster Board 351 Uveal melanoma (UM) is the most common primary intraocular tumor in adults. Unfortunately, approximately 50% of patients develop metastases to the liver; upon diagnosis of metastatic burden, the average survival is only 2-8 months. Studying and targeting oncogenic drivers that promote UM progression is essential for developing new therapies for metastatic UM patients. Most UM patients develop mutually exclusive mutations within GNAQ and GNA11 genes, which encode for the heterotrimeric Gα proteins Gαq and Gα11, respectively. More than 90% of UM patients have somatic mutations in Gαq/11 at residues Q209 or R183, which prevents GTP hydrolysis and "locks" the Gα protein in a constitutively active (CA), GTP-bound state, ultimately promoting oncogenic signaling. The MAPK and YAP/TAZ pathways are commonly stimulated via CA Gαq/11. Targeting downstream effectors of CA Gαq/11 has been shown to be generally unsuccessful at inhibiting UM cell proliferation and tumor formation; therefore, finding methods to target CA Gαq/11 directly may be a more successful approach to inhibiting oncogenesis. Although it is generally thought that active, GTP-bound G α subunits are dissociated from and signal independently of Gβγ, accumulating evidence indicates that some CA Gα mutants, such as Gαq/11, retain binding to Gβγ, and this interaction is necessary for signaling. The main objective of this project is to understand the role of Gβγ in regulating CA Gαq/11. We hypothesized that disrupting the interaction between CA Gαq/11 and Gβγ can inhibit oncogenic signaling in UM. Introduction of the I25A point mutation in the N-terminal α helical domain of CA Gαq to inhibit Gβγ binding, overexpression of the G protein Gαo to sequester Gβγ, and siRNA depletion of Gβ subunits inhibited or abolished CA Gαq signaling to the MAPK and YAP pathways. Moreover, in HEK293 cells and UM cell lines, we show that Gαq-Q209P and Gαq-R183C are more sensitive to loss of Gβγ interaction compared to G αq-Q209L. Our study challenges the idea that CA Gαq/11 signals independently of Gβγ and demonstrates differential sensitivity between the G αq-Q209L, G αq-Q209P, and Gαq-R183C mutants. We propose that disrupting the interaction between CA Gαq/11 and Gβγ can inhibit aberrant cell signaling in UM. NIH T32 Training Grant GM144302 – Cellular, Biochemical, and Molecular Sciences Department of Defense, Melanoma Research Program Idea Award ME200047 – "Targeting the interaction of G beta-gamma and Mutant G Alpha q/11 in Uveal Melanoma" NIH R01 GM138943 – "Regulation of Mutationally Activated Gq/11"