Shear Stress Induces Hepatocyte PAI-1 Gene Expression Through Cooperative Sp1/Ets-1 Activation of Transcription

Partial hepatectomy causes hemodynamic changes which increases portal blood flow in the remaining lobe, where the expression of immediate-early genes, including plasminogen activator inhibitor-1 (PAI-1), is induced. We hypothesized that a hyperdynamic circulatory state occurring in the remaining lobe induces immediate-early gene expression. In this study, we investigated whether the mechanical force generated by flowing blood, shear stress, induces PAI-1 expression in hepatocytes. When cultured rat hepatocytes were exposed to flow, PAI-1 mRNA levels began to increase within 3 hours, peaked at levels significantly higher than the static control levels, and then gradually decreased. The flow-induced PAI-1 expression was shear-stress- rather than shear-rate-dependent, and accompanied by increased hepatocyte production of PAI-1 protein. Shear stress increased PAI-1 transcription, but did not affect PAI-1 mRNA stability. Functional analysis of the 2.1-kb PAI-1 5'-promoter indicated that a 278-bp segment containing transcription factors Sp1 and Ets-1 consensus sequences was critical to the shear-stress-dependent increase of PAI-1 transcription. Mutations of both the Sp1 and Ets-1 consensus sequences, but not of either one alone, markedly prevented basal PAI-1 transcription and abolished the response of the PAI-1 promoter to shear stress. Electrophoretic mobility shift assays and chromatin immunoprecipitaion showed binding of Sp1 and Ets-1 to each consensus sequence under static conditions, which increased in response to shear stress. In conclusion, hepatocyte PAI-1 expression is flow-sensitive and transcriptionally regulated by shear stress via cooperative interactions between Sp1 and Ets-1.