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Impairing RGS protein function
Mutations in the genes encoding the α subunits of heterotrimeric G proteins are associated with cancer. In particular, mutations that prevent the Gα subunits from hydrolyzing GTP, thus rendering them constitutively active, are pro-oncogenic. DiGiacomo et al. surveyed cancer-associated mutations in regulator of G protein signaling (RGS) proteins, which are physiological inhibitors of G proteins. Through bioinformatics analysis, genetic interaction studies in yeast, and functional assays in mammalian cells, the authors showed that many cancer-associated RGS mutants fail to inhibit G protein signaling because of reduced protein stability or impaired interactions with their targets. With these tools, further cancer-associated mutations in RGS proteins can be characterized.
Abstract
The advent of deep-sequencing techniques has revealed that mutations in G protein–coupled receptor (GPCR) signaling pathways in cancer are more prominent than was previously appreciated. An emergent theme is that cancer-associated mutations tend to cause enhanced GPCR pathway activation to favor oncogenicity. Regulators of G protein signaling (RGS) proteins are critical modulators of GPCR signaling that dampen the activity of heterotrimeric G proteins through their GTPase-accelerating protein (GAP) activity, which is conferred by a conserved domain dubbed the “RGS-box.” Here, we developed an experimental pipeline to systematically assess the mutational landscape of RGS GAPs in cancer. A pan-cancer bioinformatics analysis of the 20 RGS domains with GAP activity revealed hundreds of low-frequency mutations spread throughout the conserved RGS domain structure with a slight enrichment at positions that interface with G proteins. We empirically tested multiple mutations representing all RGS GAP subfamilies and sampling both G protein interface and noninterface positions with a scalable, yeast-based assay. Last, a subset of mutants was validated using G protein activity biosensors in mammalian cells. Our findings reveal that a sizable fraction of RGS protein mutations leads to a loss of function through various mechanisms, including disruption of the G protein–binding interface, loss of protein stability, or allosteric effects on G protein coupling. Moreover, our results also validate a scalable pipeline for the rapid characterization of cancer-associated mutations in RGS proteins.
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