A Phosphorylation Dependent Regulatory Switch at the Gα12 N‐terminus Modulates Cell Growth Signaling

Abstract

The G12/13 subfamily of heterotrimeric guanine nucleotide binding proteins (G proteins) is composed of Gα12 and Gα13, which play important intracellular signaling roles including activation of serum response factor (SRF). SRF activates transcription of serum response element (SRE) regulated genes involved in cell growth and tumorigenic events. Although crystal structures for Gα12 and Gα13 have been reported, very little is understood about the structure and function of these proteins at the N‐terminus. Previous reports have suggested serine phosphorylation occurs near the N‐terminus of Gα12. To identify the target serine in Gα12 and its possible role in SRF signaling, a series of point mutations were engineered to either abolish or mimic serine phosphorylation. Replacing a Gα12‐specific N‐terminal serine with the phosphomimic aspartic acid disrupted Gα12 signaling to SRF, as measured by firefly luciferase assays. Signaling by Gα13 was unaffected by phosphomimics of potentially homologous serines, suggesting a Gα12‐specific mechanism. Insertion of the Gα12 N‐terminus harboring the phosphomimic into Gα13 bestowed negative regulation of SRF signaling upon this chimeric protein. These results point to a kinase‐dependent switching mechanism at the N‐terminus of Gα12 that governs its growth signaling. Currently, we are investigating protein interactions affected by the phosphomimic and screening potential kinases for phosphorylation of Gα12.Support or Funding InformationNC GlaxoSmithKline Foundation; UNC Lineberger Comprehensive Cancer Center; NC Biotechnology Center