title: CD36 ectodomain phosphorylation blocks thrombospondin-1 binding: structure-function relationships and regulation by protein kinase C.
abstract: OBJECTIVE
  CD36 phosphorylation on its extracellular domain inhibits binding of thrombospondin-1. The mechanisms of cellular CD36 ectodomain phosphorylation and whether it can be regulated in cells are not known. We determined structure-function relationships of CD36 phosphorylation related to thrombospondin-1 peptide binding in vitro and explored mechanisms regulating phosphorylation by protein kinase C (PKC) in melanoma cells.
  
  
  RESULTS
  Phosphorylation of CD36 peptide on Thr92 by PKCα suppressed binding of thrombospondin-1 peptides in vitro, and the level of inhibition correlated with the level of phosphorylation. Basal phosphorylation levels of CD36 in vivo in platelets, endothelial cells, and melanoma cells were assessed by immunoprecipitation and immunoblot and were found to be very low. Treatment of CD36-transfected melanoma cells with phorbol 12-myristate 13-acetate (PMA), a PKC activator, induced substantial CD36 phosphorylation and decreased ligand-mediated recruitment of Src-family proteins to CD36. PMA treatment did not induce detectable extracellular or cell surface-associated kinase activity, and both cycloheximide and brefeldin A blocked CD36 phosphorylation.
  
  
  CONCLUSIONS
  New protein synthesis and trafficking through the Golgi are required for PMA-induced CD36 phosphorylation, suggesting that phosphorylation probably occurs intracellularly. These studies suggest a novel in vivo pathway for CD36 phosphorylation that modulates cellular affinity for thrombospondin-related proteins to blunt vascular cell signaling.
authors.affiliation: Department of Cell Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH, USA.
authors.forename: Ling-Yun
authors.initials: LY
authors.lastname: Chu
authors.forename: Roy L
authors.initials: RL
authors.lastname: Silverstein
mesh_terms: D015153:Blotting, Western; D018955:CD36 Antigens / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D042783:Endothelial Cells / Q000201:enzymology; D004789:Enzyme Activation; D020536:Enzyme Activators / Q000494:pharmacology; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D008545:Melanoma / Q000201:enzymology / Q000235:genetics; D010766:Phosphorylation; D011485:Protein Binding; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D025941:Protein Interaction Mapping; D051571:Protein Kinase C-alpha / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D021381:Protein Transport; D013329:Structure-Activity Relationship; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019700:Thrombospondin 1 / Q000737:chemistry / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D018955:CD36 Antigens; D020536:Enzyme Activators; D011500:Protein Synthesis Inhibitors; D019700:Thrombospondin 1; D019061:src-Family Kinases; C496628:PRKCA protein, human; D051571:Protein Kinase C-alpha; D013755:Tetradecanoylphorbol Acetate