FLUID SHEAR-STRESS ACTIVATION OF EGR-1 TRANSCRIPTION IN CULTURED HUMAN ENDOTHELIAL AND EPITHELIAL-CELLS IS MEDIATED VIA THE EXTRACELLULAR SIGNAL-RELATED KINASE-1 2 MITOGEN-ACTIVATED PROTEIN-KINASE PATHWAY/

The primary response transcription factor, early growth response-1 (Eg r-1), is rapidly activated by a variety of extracellular stimuli. Egr- 1 binds to a sequence found in the promoters of genes involved in vasc ular injury, such as PDGF-A and tissue factor, and tr ans-activates th eir expression in en dothelial cells in response to fluid shear stress . Here we show that egr-1 mRNA is increased after 30 min of flow in hu man aortic endothelial cell and HeLa cell cultures. Transient transfec tion of HeLa cells with reporter gene constructs driven by the murine or human egr-1 5' flanking sequence revealed a five-and ninefold induc tion, respectively, in transcriptional activity after exposure to a sh ear stress of 5 dynes/cm(2) for 3 h. Deletion of sequences in the muri ne promoter containing two AP1 sites and an inhibitory Egr-1 binding s equence, did not reduce shear stress inducibility, However, progressiv e deletion of five serum response elements, reduced both the basal pro moter activity and its capacity to be activated by shear stress. Furth er examination indicated that the three upstream serum response elemen ts are predominantly responsible for shear stress activation of the eg r-1 promoter. Treatment of cells with PD98059, a specific inhibitor of mitogen-activated protein kinase-l inhibited shear stress activation of egr-1. We suggest that egr-1 activation by shear stress involves ac tivation of Elk-l but not c-jun activity. These data, which are consis tent with previous findings for shear mediated signaling via the mitog en-activated protein kinase cascade, now implicate shear modulation of the Egr-1 transcription factor in this pathway.