Disruption of the interaction between mutationally activated Gα(q) and Gβγ attenuates aberrant signaling

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 Gα(q/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 Gα(q/11), retain binding to Gβγ, and this interaction is necessary for signaling. Here, we demonstrate that disrupting the interaction between Gβγ and Gα(q) is sufficient to inhibit aberrant signaling driven by CA Gα(q). Introduction of the I25A point mutation in the N-terminal α helical domain of CA Gα(q) to inhibit Gβγ binding, overexpression of the G protein Gα(o) to sequester Gβγ, and siRNA depletion of Gβ subunits inhibited or abolished CA Gα(q) signaling to the MAPK and YAP pathways. Moreover, in HEK 293 cells and in UM cell lines, we show that Gα(q)-Q209P and Gα(q)-R183C are more sensitive to the loss of Gβγ interaction than Gα(q)-Q209L. Our study challenges the idea that CA Gα(q/11) signals independently of Gβγ and demonstrates differential sensitivity between the Gα(q)-Q209L, Gα(q)-Q209P, and Gα(q)-R183C mutants.