The primary response transcription factor, early growth response-1 (Egr-1), is rapidly activated by a variety of extracellular stimuli. Egr-1 binds to a sequence found in the promoters of genes involved in vascular injury, such as PDGF-A and tissue factor, and trans -activates their expression in en

Abstract-Hemodynamic forces such as fluid shear stress have been shown to modulate the activity of an expanding family of genes involved in vessel wall homeostasis and the pathogenesis of vascular disease. We have investigated the effect of shear stress on tissue factor (TF) gene expression in human endothelial cells (ECs) and in a rat arterial model of occlusion. As measured by reverse transcriptase polymerase chain reaction, exposure of ECs to 1.5 N/m 2 shear stress resulted in a time-dependent induction of endogenous TF transcripts of over 5-fold. Transient transfection of TF promoter mutants into cultured ECs suggests the involvement of the transcription factor Egr-1 in mediating the response of the TF promoter to shear stress. To address the importance of flow induction of Egr-1 in vivo, we have established a flow-restricted rat arterial model and determined the level of expressed Egr-1 and TF at the site of restricted flow using immunohistochemistry. We report an increase in the level of Egr-1 and TF protein in ECs expressed at the site of restricted flow. Elevated expression of Egr-1 and TF is restricted to a highly localized area, as evidenced by the fact that no significant increase in level can be detected at arterial sites distal to the site of occlusion. These findings suggest a direct role for Egr-1 in flow-mediated induction of TF and further substantiate the importance of shear stress as a modulator of vascular endothelial gene function in vivo. Key Words: fluid shear stress Ⅲ tissue factor promoter Ⅲ Egr-1 transcription factor Ⅲ vascular endothelial cells E ndothelial cells (ECs) lining the inner surface of blood vessels are constantly exposed to blood flow. Locally disturbed flow at arterial curvatures or bifurcations is characterized by both low and high oscillatory wall shear stresses that are conveyed to the cell as both a change in pressure and a change in the stretch capacity of the EC lining. 1-3 As a consequence of the local perturbation in laminar shear stress, a number of genes have been identified whose promoter activity is positively or negatively regulated by shear stress (reviewed in References 4 to 8). Several cis-acting elements have been implicated in mediating shear modulation of gene expression, and the term shear stress responsive element (SSRE) was first proposed after the identification of the sequence GAGACC. 9 This SSRE was demonstrated to confer shear stress responsiveness on the platelet-derived growth factor (PDGF) B promoter, 9 a heterologous SV40 promoter, 10 and has since been located in a number of other promoters that have been shown to be shear stress responsive in ECs. 11 The GAGACC sequence binds nuclear factor B (NF-B) p50 -p65 heterodimers, and consistent with this observation, the wild-type HIV-1 LTR, but not an LTR lacking the NF-B binding site, was also shown to be responsive to shear stress. 5 Other transcription factors that have been shown to mediate shear stress activation of a promoter are AP1, 12,13 Sp1, 14 and Egr-1. 15 Recently, the transcription fa...

The vascular endothelium, lining the blood vessel wall, is constantly exposed to wall shear stresses generated by flowing blood. Gene regulation, critical for endothelial cell function, depends on complex interactions at the promoter level and utilizes overlapping signal transduction cascades to activate the expression of genes involved in many biological processes.

Destruction of bone tissue due to disease and inefficient bone healing after traumatic injury may be addressed by tissue engineering techniques. Growth factor, cytokine protein, and gene therapies will be developed, which, in conjunction with suitable carriers, will regenerate missing bone or help in cases of defective healing.

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