Translocation of Glycosylphosphatidylinositol-Anchored Proteins from Plasma Membrane Microdomains to Lipid Droplets in Rat Adipocytes Is Induced by Palmitate, H2O2, and the Sulfonylurea Drug Glimepiride

• Published in: Molecular pharmacology 2008-05, Vol.73 (5), p.1513-1529
• Main Authors: Müller, Günter, Wied, Susanne, Walz, Nicole, Jung, Christian
• Format: Article
• Language: English
• Subjects: 5'-Nucleotidase - metabolism; Adenosine - metabolism; Adipocytes - drug effects; Adipocytes - enzymology; Adipocytes - metabolism; Animals; Cattle; Cholesterol - deficiency; Cyclic AMP - metabolism; Glucose Oxidase - pharmacology; Glycosylphosphatidylinositols - metabolism; Hydrogen Peroxide - pharmacology; Intracellular Space - drug effects; Intracellular Space - metabolism; Lipid Metabolism - drug effects; Lipolysis - drug effects; Membrane Microdomains - drug effects; Membrane Microdomains - metabolism; Palmitates - pharmacology; Phosphoric Diester Hydrolases - metabolism; Protein Transport - drug effects; Rats; Sulfonylurea Compounds - pharmacology; Triglycerides - biosynthesis; Type C Phospholipases - metabolism
• ISSN: 0026-895X; 1521-0111
• DOI: 10.1124/mol.107.043935

Inhibition of lipolysis by palmitate, H 2 O 2 , and the antidiabetic sulfonylurea drug, glimepiride, in rat adipocytes has been shown previously to rely on the concerted degradation of cAMP by the glycosylphosphatidylinositol (GPI)-anchored phosphodiesterase Gce1 and 5′-nucleotidase CD73, which both gain access to the lipid droplets (LDs). The present report demonstrates the translocation of Gce1 and CD73, harboring the intact GPI anchor, from detergent-insoluble glycolipid-enriched plasma membrane domains (DIGs) to the LDs in response to palmitate, H 2 O 2 , and glimepiride by analysis of their steady-state distribution using photoaffinity labeling and activity determination as well as of their redistribution after pulse or equilibrium metabolic labeling. We were surprised to find that palmitate, H 2 O 2 , and glimepiride induced the activation of the GPI-specific phospholipase C (GPI-PLC) at DIGs of rat adipocytes, leading to anchorless Gce1 and CD73. Inhibition of the GPI-PLC or the presence of nonhydrolyzable substrate analogs of Gce1 and CD73 interfered with the palmitate-, H 2 O 2 -, and glimepiride-induced 1) lipolytic cleavage of Gce1 and CD73, 2) translocation of their GPI-anchored versions from DIGs to LDs, 3) up-regulation of cAMP degradation, and 4) inhibition of lipolysis. These data suggest a novel insulin-independent antilipolytic mechanism in rat adipocytes, which relies on the palmitate-, H 2 O 2 -, and glimepiride-induced and GPI-PLC-dependent translocation of (c)AMP-degrading GPI-anchored proteins from the adipocyte plasma membrane to LDs. The findings may shed new light on the biogenesis and degradation of LDs in response to physiological and pharmacological stimuli.