Disruption of the interaction between mutationally activated Gαq and Gβγ attenuates aberrant signaling

Abstract

Heterotrimeric G protein stimulation via G protein-coupled receptors promotes downstream proliferative signaling. Mutations can occur in Gα proteins which prevent GTP hydrolysis; this allows the G proteins to signal independently of G protein-coupled receptors and can result in various cancers, such as uveal melanoma (UM). Most UM cases harbor Q209L, Q209P, or R183C mutations in Gαq/11 proteins, rendering the proteins constitutively active (CA). Although it is generally thought that active, GTP-bound Gα 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. Here, we demonstrate that disrupting the interaction between Gβγ and Gαq is sufficient to inhibit aberrant signaling driven by CA Gαq. 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 HEK 293cells and in UM cell lines, we show that Gαq-Q209P and Gαq-R183C are more sensitive to the loss of Gβγ interaction than Gαq-Q209L. Our study challenges the idea that CA Gαq/11 signals independently of Gβγ and demonstrates differential sensitivity between the Gαq-Q209L, Gαq-Q209P, and Gαq-R183C mutants.