Activation of G proteins by GIV-GEF is a pivot point for insulin resistance and sensitivity |
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Authors: | Gary S Ma Inmaculada Lopez-Sanchez Nicolas Aznar Nicholas Kalogriopoulos Shabnam Pedram Krishna Midde Theodore P Ciaraldi Robert R Henry Pradipta Ghosh |
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Institution: | Emory University;aDepartment of Medicine, University of California, San Diego, School of Medicine, La Jolla, CA 92093;cDepartment of Cell and Molecular Medicine, University of California, San Diego, School of Medicine, La Jolla, CA 92093;bDepartment of Veterans Affairs, VA San Diego Healthcare System, San Diego, CA 92161 |
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Abstract: | Insulin resistance (IR) is a metabolic disorder characterized by impaired insulin signaling and cellular glucose uptake. The current paradigm for insulin signaling centers upon the insulin receptor (InsR) and its substrate IRS1; the latter is believed to be the sole conduit for postreceptor signaling. Here we challenge that paradigm and show that GIV/Girdin, a guanidine exchange factor (GEF) for the trimeric G protein Gαi, is another major hierarchical conduit for the metabolic insulin response. By virtue of its ability to directly bind InsR, IRS1, and phosphoinositide 3-kinase, GIV serves as a key hub in the immediate postreceptor level, which coordinately enhances the metabolic insulin response and glucose uptake in myotubes via its GEF function. Site-directed mutagenesis or phosphoinhibition of GIV-GEF by the fatty acid/protein kinase C-theta pathway triggers IR. Insulin sensitizers reverse phosphoinhibition of GIV and reinstate insulin sensitivity. We also provide evidence for such reversible regulation of GIV-GEF in skeletal muscles from patients with IR. Thus GIV is an essential upstream component that couples InsR to G-protein signaling to enhance the metabolic insulin response, and impairment of such coupling triggers IR. We also provide evidence that GIV-GEF serves as therapeutic target for exogenous manipulation of physiological insulin response and reversal of IR in skeletal muscles. |
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