title: The counteradhesive protein SPARC regulates an endothelial paracellular pathway through protein tyrosine phosphorylation.
abstract: SPARC (Secreted Protein Acidic and Rich in Cysteine) regulates the transendothelial flux of macromolecules through a paracellular pathway. We now have demonstrated that SPARC-induced increments in albumin flux across postconfluent endothelial cell (EC) monolayers are mediated, in part, through protein tyrosine phosphorylation. SPARC increased tyrosine phosphorylation of EC proteins up to 12-fold within 1 h. The phosphotyrosine-containing proteins were immunolocalized to the intercellular boundaries. Two substrates for SPARC-induced tyrosine phosphorylation were identified as beta-catenin and paxillin. Inhibition of tyrosine kinases with herbimycin A or genistein reversed the barrier dysfunction induced by SPARC by 71% and 49%, respectively. Herbimycin A also protected against SPARC-induced intercellular gap formation. In contrast, inhibition of tyrosine phosphatases with sodium orthovanadate or phenylarsine oxide enhanced the loss of barrier function associated with SPARC treatment by 120% and 88%, respectively. These data indicate that SPARC influences EC-EC interactions through a tyrosine phosphorylation-dependent signaling pathway.
authors.affiliation: Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, 21201, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Young
authors.forename: P
authors.initials: P
authors.lastname: Wang
authors.forename: S E
authors.initials: SE
authors.lastname: Goldblum
mesh_terms: D000418:Albumins / Q000378:metabolism; D016227:Benzoquinones; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000302:isolation & purification; D004727:Endothelium / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019833:Genistein / Q000494:pharmacology; D015151:Immunoblotting; D007365:Intercellular Junctions / Q000187:drug effects; D047029:Lactams, Macrocyclic; D015676:Osteonectin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D051419:Paxillin; D010750:Phosphoproteins / Q000737:chemistry / Q000302:isolation & purification; D010766:Phosphorylation / Q000187:drug effects; D019000:Phosphotyrosine / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011809:Quinones / Q000494:pharmacology; D017828:Rifabutin / Q000031:analogs & derivatives; D015534:Trans-Activators; D051176:beta Catenin
chemical_list: D000418:Albumins; D016227:Benzoquinones; D003598:Cytoskeletal Proteins; D004791:Enzyme Inhibitors; D047029:Lactams, Macrocyclic; D015676:Osteonectin; D051419:Paxillin; D010750:Phosphoproteins; D011809:Quinones; D015534:Trans-Activators; D051176:beta Catenin; D017828:Rifabutin; D019000:Phosphotyrosine; C020754:herbimycin; D019833:Genistein; D011505:Protein-Tyrosine Kinases