Shear stress-dependent regulation of the human beta-tubulin folding cofactor D gene

The flowing blood generates shear stress at the endothelial cell surface. T he endothelial cells modify their phenotype by alterations in gene expressi on in response to different levels of fluid shear stress. To identify genes involved in this process, human umbilical vein endothelial cells were expo sed to laminar shear stress (venous or arterial levels) in a cone-and-plate apparatus for 24 hours. Using the method of RNA arbitrarily primed polymer ase chain reaction, we cloned a polymerase chain reaction fragment represen ting an mRNA species downregulated by arterial compared with venous shear s tress (shear stress downregulated gene-1, SSD-1). According to Northern blo t analysis, corresponding SSD-1 cDNA clones revealed a similar, time-depend ent downregulation after 24 hours of arterial shear stress compared with ve nous shear stress or static controls. Three SSD-1 mRNA species of 2.8, 4.1, and 4.6 kb were expressed in a tissue-specific manner. The encoded amino a cid sequence of the human endothelial SSD-1 isoform (4.1-kb mRNA species) r evealed 80.4% identity and 90.9% homology to the bovine beta -tubulin foldi ng cofactor D (tfcD) gene. Downregulation of tfcD mRNA expression by shear stress was defined at the level of transcription by nuclear run-on assays. The tfcD protein was downregulated by arterial shear stress. The shear stre ss-dependent downregulation of tfcD mRNA and protein was attenuated by the NO synthase inhibitor N omega -nitro-L-arginine methyl ester, Furthermore, the NO donor DETA-NO downregulated tfcD mRNA. Because tfcD was shown to be a microtubule-destabilizing protein, our data suggest a shear stress-depend ent regulation of the microtubular dynamics in human endothelial cells.