Protein kinase C phosphorylates caldesmon 77 and vimentin and enhances albumin permeability across cultured bovine pulmonary artery endothelial cell monolayers

Cytoskeletal protein (CSP) interactions are critical to the contractile response in muscle and non‐muscle cells. Current concepts suggest that activation of the contractile apparatus occurs through selective phosphorylation by specific cellular kinase systems. Because the Ca 2+ ‐phospholipid‐dependent protein kinase C (PKC) is involved in the regulation of a number of key endothelial cell responses, the hypothesis that PKC modulates endothelial cell contraction and monolayer permeability was tested. Phorbol myristate acetate (PMA), a direct PKC activator, and α‐thrombin, a receptor‐mediated agonist known to increase endothelial cell permeability, both induced rapid, dose‐dependent activation and translocation of PKC in bovine pulmonary artery endothelial cells (BPAEC), as assessed by γ‐[ 32 P]ATP phosphorylation of H1 histone in cellular fractions. This activation was temporally associated with evidence of agonist‐mediated endothelial cell contraction as demonstrated by characteristic changes in cellular morphology. Agonist‐induced activation of the contractile apparatus was associated with increases in BPAEC monolayer permeability to albumin (∼200% increase with 10 −6 M PMA, ∼400% increase with 10 −8 M α‐thrombin). To more closely examine the role of PKC in activation of the contractile apparatus, PKC‐mediated phosphorylation of two specific CSPs, the actin‐ and calmodulin‐binding protein, caldesmon 77 , and the intermediate filament protein, vimentin, was assessed. In vitro phosphorylation of both caldesmon and vimentin was demonstrated by addition of exogenous, purified BPAEC PKC to unstimulated BPAEC homogenates, to purified bovine platelet caldesmon 77 , or to purified smooth muscle caldesmon 150 . Caldesmon 77 and vimentin phosphorylation were observed in intact [ 32 P]‐labeled BPAEC monolayers stimulated with either PMA or α‐thrombin, as detected by immunoprecipitation. In addition, BPAEC pretreatment with the PKC inhibitor, staurosporine, prevented α‐thrombin‐ and PMA‐induced phosphorylation of both cytoskeletal proteins, attenuated morphologic evidence of contraction, and abolished agonist‐induced barrier dysfunction. These results demonstrate that agonist‐stimulated PKC activity results in cytoskeletal protein phosphorylation in BPAEC monolayers, an event which occurs in concert with agonist‐mediated endothelial cell contraction and resultant barrier dysfunction. © 1992 Wiley‐Liss, Inc.