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Fluid shear stress maintains vascular homoeostasis by influencing endothelial gene expression. One mechanism by which shear stress achieves this is through induction of transcription factors, including Krüppel-like Factor 2 (KLF2; LKLF). We have previously reported that a 62 base pair (bp) region of the KLF2 promoter is responsible for its shear stress-induced expression in murine microvascular endothelial cell cultures. In this study, we find that the 62 bp shear stress response region is conserved in human HUVEC cultures and contains a 30 bp tripartite palindrome motif. Continuing our work in murine microvascular EOMA cells, electrophoretic mobility supershift and chromatin immunoprecipitation assays demonstrate that the PCAF acetyltransferase and the coactivator hnRNP D bind this region in as components of the shear stress regulatory complex. Immunoprecipitation experiments indicate that PCAF and hnRNP D interact, suggesting that PCAF is targeted to an hnRNP D binding site in the KLF2 promoter. We have also characterized a PI3K-dependent/Akt-independent pathway responsible for shear stress-induced KLF2 promoter nuclear binding, activation, and mRNA expression. Furthermore, the shear stress response region of the KLF2 promoter was specifically immunoprecipitated by antibodies against acetylated histones H3 and H4 in shear stressed, but not static, cells. PI3K inhibition blocked both histone acetylation and PCAF/hnRNP D binding, suggesting that PCAF is the functional acetyltransferase. Finally, we have found that KLF2 increases eNOS expression at both the mRNA and protein levels in murine endothelial cultures, an effect that is also blocked by PI3K inhibition. These results define the DNA regulatory element, signal transduction pathway and molecular mechanism activating the flow-dependent expression of a vital endothelial transcription factor.
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J. Vasc. Biol. 42, Sup:2 (2005) p58