Egr-1 is Activated in Endothelial Cells Exposed to Fluid Shear Stress and Interacts With a Novel Shear-Stress-Response Element in the PDGF A-Chain Promoter

Abstract

Exposure of vascular endothelial cells to fluid mechanical forces can modulate the expression of many genes involved in vascular physiology and pathophysiology. Here, we report that platelet-derived growth factor (PDGF) A-chain gene expression is induced at the level of transcription in cultured bovine aortic endothelial cells exposed to a physiologic level of steady laminar shear stress (10 dyn/cm2). 5' Deletion analysis of the human PDGF-A promoter revealed that a GC-rich region near the TATA box was required for shear-inducible reporter gene expression. This element conferred shear inducibility onto a heterologous promoter-reporter construct that was otherwise unresponsive to shear stress. The induction of PDGF-A expression by shear was preceded by rapid and transient induction in the expression of the immediate-early gene, egr-1, which binds to GC-rich sequences. Gel shift studies indicated that shear-induced Egr-1 bound to the proximal PDGF-A promoter in a specific and time-dependent manner, displacing Sp1 from their overlapping recognition elements. Overlapping consensus binding sites for Egr-1 and Sp1 also appear in the proximal promoters of several other endothelial genes, including transforming growth factor-beta 1 and tissue factor, whose expression is modulated by shear stress. These findings define the Egr-1 binding site in the proximal PDGF-A promoter as a shear-stress-responsive element and suggest that shear-stimulated Egr-1 gene expression may be a unifying theme in the induction of various other endothelial genes exposed to biomechanical forces.

c-Jun Regulates Shear- and Injury-inducible Egr-1 Expression, Vein Graft Stenosis after Autologous End-to-Side Transplantation in Rabbits, and Intimal Hyperplasia in Human Saphenous Veins

“…Egr-1 is an immediate-early gene, which, like c-Jun, plays a master regulator role by switching on the expression of many pathophysiologically important genes in numerous models of cardiovascular pathology (22). We demonstrated over a decade ago that Egr-1 is induced by shear in vascular endothelial cells (23). However, the transcriptional pathway responsible for its induction by shear is unknown, as is whether Egr-1 is activated in other cell types by shear stress.…”

Fibroblast Growth Factor-2 Induction of Platelet-derived Growth Factor-C Chain Transcription in Vascular Smooth Muscle Cells Is ERK-dependent but Not JNK-dependent and Mediated by Egr-1

“…cause Egr-1 is induced by multiple pro-atherogenic stimuli (14,15,24), PDGF-C transcription may be positively regulated by Egr-1 in SMCs exposed to pathophysiologically relevant stimuli.…”

Temporal Gradient in Shear But Not Steady Shear Stress Induces PDGF-A and MCP-1 Expression in Endothelial Cells

“…Because the egr-1 binding site in the proximal PDGF-A promoter is responsible for its shear stress inducibility, 18 we investigated the effect of NO on egr-1 mRNA expression. EC were exposed to impulse flow in the presence or absence of L-NAA and SPR/NO for 4 hours.…”

“…19,20 Activated egr-1 binds to the proximal PDGF-A promoter by displacing sp-1 from their overlapping recognition element, and the egr-1 binding site has been identified as a cis-element for the induction of PDGF-A by fluid shear. 18 The promoter of MCP-1 gene contains both NFB and AP-1 binding sites, which may coordinately modulate shear inducibility of MCP-1. 20 -22 NO may affect expression of these genes by activation or inactivation of their transcription factors.…”