title: Release of glycosylphosphatidylinositol-anchored carboxypeptidase M by phosphatidylinositol-specific phospholipase C upregulates enzyme synthesis.
abstract: Carboxypeptidase M (CPM), a glycosylphosphatidylinositol (GPI)-anchored membrane protein, remained at a constant level in confluent Madin Darby canine kidney (MDCK) cells but was continually released into the medium in soluble form. The released CPM contained ethanolamine, indicating liberation by a phospholipase. Treatment of MDCK cells with 0.01 U/ml phosphatidylinositol-specific phospholipase C for 6 h led to a 5.5-fold increase in soluble CPM, yet the activity in cells remained constant, resulting in a 30% increase in total activity. The increase was due to new protein synthesis as evidenced by inhibition with 0.2 microM cycloheximide and a 63% increase in [35S]methionine incorporation into newly synthesized CPM. MDCK cells treated with 1-alkyl-2-acyl-glycerol, the diglyceride component of mammalian glycosylphosphatidylinositol anchors, exhibited a 36% increase in CPM activity, but diacylglycerols or phorbol esters were ineffective. Thus, release of GPI-anchored CPM can generate a diglyceride signal to replenish and maintain constant levels on the cell surface.
authors.affiliation: Department of Pharmacology, Laboratory of Peptide Research, University of Illinois College of Medicine, Chicago, Illinois, 60612, USA.
authors.forename: X Y
authors.initials: XY
authors.lastname: Li
authors.forename: R A
authors.initials: RA
authors.lastname: Skidgel
mesh_terms: D000818:Animals; D002460:Cell Line; D004075:Diglycerides / Q000494:pharmacology; D004285:Dogs; D058851:GPI-Linked Proteins; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D008666:Metalloendopeptidases / Q000096:biosynthesis / Q000378:metabolism*; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D004075:Diglycerides; D058851:GPI-Linked Proteins; D017261:Glycosylphosphatidylinositols; D010738:Type C Phospholipases; D054801:Phosphoinositide Phospholipase C; C058479:carboxypeptidase M; D008666:Metalloendopeptidases; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D013755:Tetradecanoylphorbol Acetate