Translocation of the non‐receptor protein GIV/Girdin to the plasma membrane activates heterotrimeric G proteins

Abstract

Receptor tyrosine kinases (RTKs) and integrins have been traditionally considered to trigger signaling cascades different from those activated by G protein‐coupled receptors (GPCRs). However, GIV (aka Girdin) is a Guanine nucleotide Exchange Factor (GEF) that activates heterotrimeric G protein signaling downstream of RTKs and integrins. GIV is recruited to the cytoplasmic tail of RTKs and integrins upon stimulation, but the mechanism of activation of its GEF function is not well understood. We combined assays in yeast and BRET‐based biosensors in mammalian cells to investigate if association of GIV with the plasma membrane was sufficient to drive G protein activation. We found that GIV does not co‐fractionate with its substrate G protein Gαi3 on cell membranes of unstimulated cells. Anchoring of GIV to the plasma membrane of yeast cells in a constitutive manner or its rapid translocation to the plasma membrane of mammalian cells via chemically‐induced dimerization (CID) leads to robust G protein activation. GIV's Gα‐Binding and Activating (GBA) motif is necessary and sufficient for G protein activation upon membrane translocation. Furthermore, we engineered a synthetic protein to show that recruitment of GIV's GBA motif to membranes via association with active RTKs upon stimulation with a natural ligand, instead of via CID, is also sufficient for G protein activation. These results reveal that recruitment of GIV to membranes in close proximity to its substrate G protein is a mayor mechanism responsible for the activation of its G protein regulatory function.Support or Funding InformationThis work was supported by NIH grants (R01GM108733, R01GM112631) and American Cancer Society (RSG‐13‐362‐01‐TBE)