RGS7 is recurrently mutated in melanoma and promotes migration and invasion of human cancer cells

Abstract

Analysis of 501 melanoma exomes revealed RGS7, which encodes a GTPase-accelerating protein (GAP), to be a tumor-suppressor gene. RGS7 was mutated in 11% of melanomas and was found to harbor three recurrent mutations (p.R44C, p.E383K and p.R416Q). Structural modeling of the most common recurrent mutation of the three (p.R44C) predicted that it destabilizes the protein due to the loss of an H-bond and salt bridge network between the mutated position and the serine and aspartic acid residues at positions 58 as 61, respectively. We experimentally confirmed this prediction showing that the p.R44C mutant protein is indeed destabilized. We further show RGS7 p.R44C has weaker catalytic activity for its substrate Gαo, thus providing a dual mechanism for its loss of function. Both of these effects are expected to contribute to loss of function of RGS7 resulting in increased anchorage-independent growth, migration and invasion of melanoma cells. By mutating position 56 in the R44C mutant from valine to cysteine, thereby enabling the formation of a disulfide bridge between the two mutated positions, we slightly increased the catalytic activity and reinstated protein stability, leading to the rescue of RGS7′s function as a tumor suppressor. Our findings identify RGS7 as a novel melanoma driver and point to the clinical relevance of using strategies to stabilize the protein and, thereby, restore its function.

Structural organization of a major neuronal G protein regulator, the RGS7-Gβ5-R7BP complex

“…Reminiscent of this, we find that the dynamic β-hairpin of RGS7 is stabilized upon R7BP binding, suggesting it role in binding and likely undergoing conformational rearrangements. Curiously, a pathogenic mutation (R44C) in the β-hairpin of RGS7 that causes melanoma reduces the stability of RGS7 and its catalytic activity, further supporting the importance of conformational transitions in this region in regulating RGS7 function (Qutob et al, 2018).…”

“…More than 30 RGS proteins have been identified and grouped into six subfamilies (Zheng et al, 1999). Among them, the R7 family (RGS6, RGS7, RGS9, and RGS11) stands out for its evolutionary conservation in all animals from worm to man and crucial roles in multiple processes and organ systems including nervous and cardiovascular system function, vision, movement control, and cellular proliferation with ever growing causal connection to many diseases from blindness to cancer (Ahlers et al, 2016; Qutob et al, 2018; Yang et al, 2013; Anderson et al, 2009b). A unique hallmark of R7 RGS proteins is their modular architecture encompassing several domains and subunits.…”

“…A few documented examples include regulation of mGluR in retina bipolar (Cao et al, 2012), GABA(B) in hippocampal CA1 (Fajardo-Serrano et al, 2013; Ostrovskaya et al, 2014), µ-opioid in striatal neurons (Sutton et al, 2016; Anderson et al, 2010; Masuho et al, 2013), and M3 muscarinic receptors in the pancreatic β-cells (Wang et al, 2017). Given these roles, perhaps not surprisingly, the RGS7 complex has been found to play a critical role in vision, learning and memory, drug addiction, insulin production, and cancer progression (Qutob et al, 2018; Sutton et al, 2016; Wang et al, 2017). Furthermore, there is a growing appreciation that the RGS7 complex can be exploited as a target for drug development with the hopes of increasing efficacy, selectivity, and the side effect profile of existing GPCR medications (Muntean et al, 2018).…”

A network approach to prioritizing susceptibility genes for genome‐wide association studies

“…COL22A1 , RGS7 , WWOX , and CELF2 were four genes selected based on all three metrics. RGS7 has been identified as a tumor‐suppressor gene resulting in the invasion of human cancer cells (Aissani, Wiener, & Zhang, ; Qutob et al, ). Żelazowski et al () studied the correlation of WWOX gene expression in CRC patients and proved the tumor‐suppressive role of WWOX gene expression in the colon.…”

Deep phylogeny of cancer drivers and compensatory mutations

“…Furthermore, multiple modes of somatic mosaicism have been documented 20 where reversion or de novo compensatory mutations mitigate the effects of a deleterious germline variant 21 , 22 . Compensatory mutations for drivers have been engineered in vitro yielding both a method for validating driver status and general information about protein structure and function 23 – 27 . However, few studies (for example, the identification of mutually compensatory mutations in TP53) provide examples of such compensatory pairs of mutations in orthologs of cancer driver genes from other species 28 .…”