title: Big mitogen-activated protein kinase (BMK1)/ERK5 protects endothelial cells from apoptosis.
abstract: Blood flow that is steady and laminar is known to be atheroprotective. One likely mechanism is enhanced endothelial cell (EC) survival. Because the mitogen-activated protein kinases (MAPKs) are known regulators of cell survival, we investigated the role of Big MAPK-1 (BMK1 or ERK5), which is potently stimulated by fluid shear stress. To activate BMK1, we overexpressed constitutively active (CA)-MEK5 in bovine lung microvascular ECs (BLMECs). Cell apoptosis was induced by growth factor deprivation (0% serum for 24 hours). Analysis of cell viability with MTT assay showed that activation of BMK1 by CA-MEK5 significantly improved cell viability from 48% to 87% and decreased apoptotic cells from 49% to 10%. Growth factor deprivation induced caspase-3 activity 5.2-fold, which was inhibited (approximately 60%) by CA-MEK5 overexpression. In contrast, inhibiting BMK1 activity by overexpressing dominant-negative BMK1 (DN-BMK1) stimulated apoptosis in BLMECs. Steady laminar fluid shear stress inhibited BLMEC apoptosis, and this protective effect was also reduced significantly by overexpressing DN-BMK1. Analysis of antiapoptotic mechanisms showed that both shear stress and CA-MEK5 stimulated phosphorylation of Bad on Ser112 and Ser136, whereas DN-BMK1 inhibited phosphorylation. Phosphorylation of Bad induced by BMK1 activation was independent of Akt, PKA, or p90RSK kinase activity. These results suggest that BMK1 activation by steady laminar flow is atheroprotective by inhibiting EC apoptosis via phosphorylation of Bad.
authors.affiliation: Center for Cardiovascular Research and Department of Medicine, University of Rochester, Rochester, NY, USA.
authors.forename: Xinchun
authors.initials: X
authors.lastname: Pi
authors.forename: Chen
authors.initials: C
authors.lastname: Yan
authors.forename: Bradford C
authors.initials: BC
authors.lastname: Berk
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002417:Cattle; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D042783:Endothelial Cells / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D004789:Enzyme Activation; D020287:In Situ Nick-End Labeling; D048671:MAP Kinase Kinase 5; D048054:Mitogen-Activated Protein Kinase 7; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D013314:Stress, Mechanical; D013997:Time Factors; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D051025:bcl-Associated Death Protein
chemical_list: D002352:Carrier Proteins; D016895:Culture Media, Serum-Free; D011518:Proto-Oncogene Proteins; D014409:Tumor Necrosis Factor-alpha; D051025:bcl-Associated Death Protein; D003513:Cycloheximide; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D017868:Cyclic AMP-Dependent Protein Kinases; D048054:Mitogen-Activated Protein Kinase 7; D020928:Mitogen-Activated Protein Kinases; D048671:MAP Kinase Kinase 5; D020929:Mitogen-Activated Protein Kinase Kinases; D053148:Caspase 3; D020169:Caspases