Fluid flow regulates E-selectin protein levels in human endothelial cells by inhibiting translation

Objective: The purpose of this study was to determine the mechanism with which fluid flow inhibits endothelial E-selectin expression. Methods: Cultured human umbilical vein endothelial cells were stimulated with inflammatory agonists (tumor necrosis factor-α [TNF-α], interleukin-1β, oncostatin M, or phorbol ester) in the presence or absence of fluid flow (peak shear stress, ∼12 dynes/cm²) imposed with an orbital shaker. E-selectin expression was assessed with ribonuclease protection assay, immunoblotting, enzyme-linked immunosorbent assay, or metabolic labeling as appropriate. Results: All agonists caused human umbilical vein endothelial cells to express E-selectin protein. Fluid flow inhibited E-selectin protein levels by about 50% in response to TNF-α but had no effect on total E-selectin messenger RNA (mRNA) expression. Flow inhibited E-selectin protein production even after initiation of E-selectin transcription. Flow did not cause E-selectin to be shed from the cell surface nor was E-selectin degradation accelerated. Although fluid flow did not reduce total cellular E-selectin mRNA levels in response to TNF-α, the amount of E-selectin mRNA present in the actively translated polysome fraction was markedly attenuated. Conclusion: These findings indicate that E-selectin expression is subject to translational and transcriptional control. Fluid mechanical forces can regulate endothelial phenotype by targeting translational control points.