KLF2 Is a Novel Transcriptional Regulator of Endothelial Proinflammatory Activation

The vascular endothelium is a critical regulator of vascular function. Diverse stimuli such as proinflammatory cytokines and hemodynamic forces modulate endothelial phenotype and thereby impact on the development of vascular disease states. Therefore, identification of the regulatory factors that mediate the effects of these stimuli on endothelial function is of considerable interest. Transcriptional profiling studies identified the Kruppel-like factor (KLF)2 as being inhibited by the inflammatory cytokine interleukin-1β and induced by laminar shear stress in cultured human umbilical vein endothelial cells. Overexpression of KLF2 in umbilical vein endothelial cells robustly induced endothelial nitric oxide synthase expression and total enzymatic activity. In addition, KLF2 overexpression potently inhibited the induction of vascular cell adhesion molecule-1 and endothelial adhesion molecule E-selectin in response to various proinflammatory cytokines. Consistent with these observations, in vitro flow assays demonstrate that T cell attachment and rolling are markedly attenuated in endothelial monolayers transduced with KLF2. Finally, our studies implicate recruitment by KLF2 of the transcriptional coactivator cyclic AMP response element–binding protein (CBP/p300) as a unifying mechanism for these various effects. These data implicate KLF2 as a novel regulator of endothelial activation in response to proinflammatory stimuli

Tumor Necrosis Factor Alpha-Mediated Reduction of KLF2 Is Due to Inhibition of MEF2 by NF-κB and Histone Deacetylases

Activation of the endothelium by inflammatory cytokines is a key event in the pathogenesis of vascular disease states. Proinflammatory cytokines repress the expression of KLF2, a recently identified transcriptional inhibitor of the cytokine-mediated activation of endothelial cells. In this study the molecular basis for the cytokine-mediated inhibition of KLF2 is elucidated. Tumor necrosis factor alpha (TNF-α) potently inhibited KLF2 expression. This effect was completely abrogated by a constitutively active form of IκBα, as well as treatment with trichostatin A, implicating a role for the NF-κB pathway and histone deacetylases. Overexpression studies coupled with observations with p50/p65 null cells support an essential role for p65. A combination of promoter deletion and mutational analyses, chromatin immunoprecipitation assays, and coimmunoprecipitation studies indicates that p65 and histone deacetylases 4 cooperate to inhibit the ability of MEF2 factors to induce the KLF2 promoter. These studies identify a novel mechanism by which TNF-α can inhibit endothelial gene expression. Furthermore, the inhibition of MEF2 function by p65 and HDAC4 has implications for other cellular systems where these factors are operative