FLUID SHEAR-STRESS INDUCES THE PHOSPHORYLATION OF SMALL HEAT-SHOCK PROTEINS IN VASCULAR ENDOTHELIAL-CELLS

The small molecular mass heat shock protein of 27 kDa (HSP27) has been shown to influence actin filament dynamics and endothelial cell behav ior in ways similar to those observed during laminar flow We have empl oyed human umbilical vein endothelial cells to determine whether fluid shear stress affects HSP27 expression or phosphorylation. After a she ar stress of 16 dyn/cm(2), HSP27 became more highly phosphorylated, wi th maximum increase in phosphorylation levels (3-fold) attained by 30 min and sustained for at least 20 h. HSP27 antigen levels did not chan ge; however, HSP27 mRNA levels decreased by 20% after 16 h. In bovine aortic endothelial cells stably transfected with the wild-type human H SP27 gene, shear stress induced the phosphorylation of both the exogen ous human HSP27 and the endogenous bovine HSP25. The product of a tran sfected mutant HSP27 gene in which the putative phosphorylation sites Ser-15, Ser-78, and Ser-82 had been replaced with Gly was not phosphor ylated. Thus the modulation of HSP27 and its activity by shear stress is mediated through a posttranslational mechanism and differs from the shear stress induction of immediate early genes at the level of trans cription.