Phosphoinositides and phosphoinositide-utilizing enzymes in detergent-insoluble lipid domains.
Recent evidence has implicated caveolae/DIGs in various aspects of signal transduction, a process in which polyphosphoinositides play a central role. We therefore undertook a study to determine the distribution of phosphoinositides and the enzymes that utilize them in these detergent-insoluble domains. We report here that the polyphosphoinositide phosphatase, but not several other phosphoinositide-utilizing enzymes, is highly enriched in a low density, Triton-insoluble membrane fraction that contains caveolin. This fraction is also enriched in polyphosphoinositides, containing approximately one-fifth of the total cellular phosphatidylinositol (4,5)P2. Treatment of cells with the tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA), did not alter the distribution of polyphosphoinositides or the polyphosphoinositide phosphatase. However, PMA treatment did lead to a decrease in the mitogen-activated protein kinase and actin present in these domains. PMA also induced the recruitment of protein kinase C alpha to the caveolae/DIGs fraction. These findings suggest that polyphosphoinositides, the polyphosphoinositide phosphatase and protein kinase C play an important role in the structure or function of detergent-insoluble membrane domains.
Hope
H R
HR
Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Pike
L J
LJ
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects; D002478:Cells, Cultured; D003902:Detergents / Q000494:pharmacology*; D004285:Dogs; D005372:Filipin / Q000494:pharmacology; D006028:Glycosphingolipids / Q000737:chemistry*; D008563:Membrane Lipids / Q000737:chemistry*; D010716:Phosphatidylinositols / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012995:Solubility; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D003902:Detergents; D006028:Glycosphingolipids; D008563:Membrane Lipids; D010716:Phosphatidylinositols; D005372:Filipin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D013755:Tetradecanoylphorbol Acetate