Naturally occurring hotspot cancer mutations in Gα13 promote oncogenic signaling

Heterotrimeric G-proteins are signaling switches broadly divided into four families based on the sequence and functional similarity of their G alpha subunits: G(s), G(i/o), G(q/11), and G(12/13). Artificial mutations that activate G alpha subunits of each of these families have long been known to induce oncogenic transformation in experimental systems. With the advent of next-generation sequencing, activating hotspot mutations in G(s), G(i/o), or G(q/11) proteins have also been identified in patient tumor samples. In contrast, patient tumor-associated G(12/13) mutations characterized to date lead to inactivation rather than activation. By using bioinformatic pathway analysis and signaling assays, here we identified cancer-associated hotspot mutations in Arg-200 of G alpha(13) (encoded by GNA13) as potent activators of oncogenic signaling. First, we found that components of a G(12/13)-dependent signaling cascade that culminates in activation of the Hippo pathway effectors YAP and TAZ is frequently altered in bladder cancer. Up-regulation of this signaling cascade correlates with increased YAP/TAZ activation transcriptional signatures in this cancer type. Among the G(12/13) pathway alterations were mutations in Arg-200 of G alpha(13), which we validated to promote YAP/TAZ-dependent (TEAD) and MRTF-A/B-dependent (SRE.L) transcriptional activity. We further showed that this mechanism relies on the same RhoGEF-RhoGTPase cascade components that are up-regulated in bladder cancers. Moreover, G alpha(13) Arg-200 mutants induced oncogenic transformation in vitro as determined by focus formation assays. In summary, our findings on G alpha(13) mutants establish that naturally occurring hotspot mutations in G alpha subunits of any of the four families of heterotrimeric G-proteins are putative cancer drivers.