Sp1-mediated downregulation of P2X(4) receptor gene transcription in endothelial cells exposed to shear stress

Endothelial purinoceptors play an important role in vascular responses to e xtracellular adenine nucleotides and hemodynamic forces. Here we report tha t P2X(4) purinoceptor expression in human umbilical vein endothelial cells is transcriptionally downregulated by fluid shear stress. When human umbili cal vein endothelial cells were subjected to a laminar shear stress of 15 d yn/cm(2), P2X(4) mRNA levels began to decrease within 1 h and further decre ased with time, reaching 60% at 24 h. Functional analysis of the 1.9- kb P2 X(4) 5'-promoter indicated that a 131-bp segment (-112 to +19 bp relative t o the transcription start site) containing a consensus binding site for the Sp1 transcription factor was critical for the shear stress responsiveness. Mutations of the Sp1 site decreased the basal level of transcription and a bolished the response of the P2X(4) promoter to shear stress. Electrophoret ic mobility shift assays showed a marked decrease in binding of Sp1 to the Sp1 consensus element in shear-stressed cells, suggesting that Sp1 mediates the shear stress-induced downregulation of P2X(4) gene transcription.