Fluid shear stress stimulates big mitogen-activated protein kinase 1 (BMK1) activity in endothelial cells - Dependence on tyrosine kinases and intracellular calcium

Mitogen-activated protein (MAP) kinases including ERK1/2 and JNK play an im portant role in shear stress-mediated gene expression in endothelial cells (EC). A new MAP kinase termed big MAP kinase 1 (BMK1/ERK5) has been shown t o phosphorylate and activate the transcription factor MEF2C, which is highl y expressed in EC, To determine the effects of shear stress on BMK1, bovine aortic EC were exposed to steady laminar flow (shear stress = 12 dynes/cm( 2)). Flow activated BMK1 within 10 min with peak activation at 60 min (7.1 +/- 0.6-fold) in a force-dependent manner. Flow was the most powerful activ ator of BMK1, significantly greater than H2O2 or sorbitol. An important rol e for non-Src tyrosine kinases in flow-mediated BMK1 activation was demonst rated by inhibition with herbimycin A, but not with the Src inhibitor PP1 o r overexpression of kinase-inactive c-Src. BMK1 activation was calcium-depe ndent as shown by inhibition with 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'- tetraacetic acid/acetoxymethyl ester or thapsigargin, As shown by specific inhibitors or activators, flow-mediated BMK1 activation was not regulated b y the following: intracellular redox state; intracellular NO; protein kinas e A, C, or G; calcium/calmodulin-dependent kinase; phosphatidylinositol 3-k inase; or arachidonic acid metabolism. In summary, flow potently stimulates BMK1 in EC by a mechanism dependent on a tyrosine kinase(s) and calcium mo bilization, but not on c-Src, redox state, or NO production.