Roles of G beta gamma in membrane recruitment and activation of p110 gamma/p101 phosphoinositide 3-kinase gamma.
Receptor-regulated class I phosphoinositide 3-kinases (PI3K) phosphorylate the membrane lipid phosphatidylinositol (PtdIns)-4,5-P2 to PtdIns-3,4,5-P3. This, in turn, recruits and activates cytosolic effectors with PtdIns-3,4,5-P3-binding pleckstrin homology (PH) domains, thereby controlling important cellular functions such as proliferation, survival, or chemotaxis. The class IB p110 gamma/p101 PI3K gamma is activated by G ... beta gamma on stimulation of G protein-coupled receptors. It is currently unknown whether in living cells G beta gamma acts as a membrane anchor or an allosteric activator of PI3K gamma, and which role its noncatalytic p101 subunit plays in its activation by G beta gamma. Using GFP-tagged PI3K gamma subunits expressed in HEK cells, we show that G beta gamma recruits the enzyme from the cytosol to the membrane by interaction with its p101 subunit. Accordingly, p101 was found to be required for G protein-mediated activation of PI3K gamma in living cells, as assessed by use of GFP-tagged PtdIns-3,4,5-P3-binding PH domains. Furthermore, membrane-targeted p110 gamma displayed basal enzymatic activity, but was further stimulated by G beta gamma, even in the absence of p101. Therefore, we conclude that in vivo, G beta gamma activates PI3K gamma by a mechanism assigning specific roles for both PI3K gamma subunits, i.e., membrane recruitment is mediated via the noncatalytic p101 subunit, and direct stimulation of G beta gamma with p110 gamma contributes to activation of PI3K gamma.
Mesh Terms:
1-Phosphatidylinositol 3-Kinase, Allosteric Site, Bacterial Proteins, Catalytic Domain, Cell Line, Cell Membrane, Chromatography, Gel, Dimerization, Dose-Response Relationship, Drug, Energy Transfer, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, Green Fluorescent Proteins, Heterotrimeric GTP-Binding Proteins, Humans, Immunoblotting, Luminescent Proteins, Membrane Proteins, Microscopy, Confocal, Models, Biological, Phosphorylation, Plasmids, Protein Binding, Protein Structure, Tertiary, Recombinant Fusion Proteins, Spectrometry, Fluorescence, Transfection
1-Phosphatidylinositol 3-Kinase, Allosteric Site, Bacterial Proteins, Catalytic Domain, Cell Line, Cell Membrane, Chromatography, Gel, Dimerization, Dose-Response Relationship, Drug, Energy Transfer, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, Green Fluorescent Proteins, Heterotrimeric GTP-Binding Proteins, Humans, Immunoblotting, Luminescent Proteins, Membrane Proteins, Microscopy, Confocal, Models, Biological, Phosphorylation, Plasmids, Protein Binding, Protein Structure, Tertiary, Recombinant Fusion Proteins, Spectrometry, Fluorescence, Transfection
J. Cell Biol.
Date: Jan. 06, 2003
PubMed ID: 12507995
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