STAT1 interacts with RXRα to upregulate ApoCII gene expression in macrophages.

Apolipoprotein CII (apoCII) is a specific activator of lipoprotein lipase and plays an important role in triglyceride metabolism. The aim of our work was to elucidate the regulatory mechanisms involved in apoCII gene modulation in macrophages. Using Chromosome Conformation Capture we demonstrated that multienhancer 2 (ME.2) physically interacts with the apoCII promoter and this interaction facilitates the transcriptional enhancement of the apoCII promoter by the transcription factors bound on ME.2. We revealed that the transcription factor STAT1, previously shown to bind to its specific site on ME.2, is functional for apoCII gene upregulation. We found that siRNA-mediated inhibition of STAT1 gene expression significantly decreased the apoCII levels, while STAT1 overexpression in RAW 264.7 macrophages increased apoCII gene expression. Using transient transfections, DNA pull down and chromatin immunoprecipitation assays, we revealed a novel STAT1 binding site in the -500/-493 region of the apoCII promoter, which mediates apoCII promoter upregulation by STAT1. Interestingly, STAT1 could not exert its upregulatory effect when the RXRα/T3Rß binding site located on the apoCII promoter was mutated, suggesting physical and functional interactions between these factors. Using GST pull-down and co-immunoprecipitation assays, we demonstrated that STAT1 physically interacts with RXRα. Taken together, these data revealed that STAT1 bound on ME.2 cooperates with RXRα located on apoCII promoter and upregulates apoCII expression only in macrophages, due to the specificity of the long-range interactions between the proximal and distal regulatory elements. Moreover, we showed for the first time that STAT1 and RXRα physically interact to exert their regulatory function.

Positive regulation of NADPH oxidase 5 by proinflammatory-related mechanisms in human aortic smooth muscle cells.

NADPH oxidase Nox5 subtype expression is significantly increased in vascular smooth muscle cells (SMCs) underlying fibro-lipid atherosclerotic lesions. The mechanisms that up-regulate Nox5 are not understood. Consequently, we characterized the promoter of the human Nox5 gene and investigated the role of various proinflammatory transcription factors in the regulation of Nox5 in human aortic SMCs. The Nox5 promoter was cloned in the pGL3 basic reporter vector. Functional analysis was done employing 5' deletion mutants to identify the sequences necessary to effect high levels of expression in SMCs. Transcriptional initiation site was detected by rapid amplification of the 5'-cDNA ends. In silico analysis indicated the existence of typical NF-kB, AP-1, and STAT1/STAT3 sites. Transient overexpression of p65/NF-kB, c-Jun/AP-1, or STAT1/STAT3 increased significantly the Nox5 promoter activity. Chromatin immunoprecipitation demonstrated the physical interaction of c-Jun/AP-1 and STAT1/STAT3 proteins with the Nox5 promoter. Lucigenin-enhanced chemiluminescence, real-time PCR, and Western blot assays showed that pharmacological inhibition and the silencing of p65/NF-kB, c-Jun/AP-1, or STAT1/STAT3 reduced significantly the interferon γ-induced Ca(2+)-dependent Nox activity and Nox5 expression. Up-regulated Nox5 correlated with increases in intracellular Ca(2+), an essential condition for Nox5 activity. NF-kB, AP-1, and STAT1/STAT3 are important regulators of Nox5 in SMCs by either direct or indirect mechanisms. Overexpressed Nox5 may generate free radicals in excess, further contributing to SMCs dysfunction in atherosclerosis.

Tyrphostin AG490 reduces NAPDH oxidase activity and expression in the aorta of hypercholesterolemic apolipoprotein E-deficient mice.

Oxidative stress-induced vascular injury represents a major contributor to the pathoetiology of atherosclerosis. Elevated NADPH oxidase (Nox) activity promotes oxidative injury of the cardiovascular cells. Janus-tyrosine-kinase (Jak) family regulate various aspects of the atherosclerotic process e.g., inflammation, cellular growth, proliferation, and migration. Here, we investigated the potential of Jak2 inhibition to counteract Nox-dependent O(2)(•-) formation in atherogenesis in hypercholesterolemic apolipoprotein E-deficient (ApoE(-/-)) mice. Male ApoE(-/-) mice fed a high-fat, cholesterol-rich diet were treated for 5 weeks with either vehicle or tyrphostin AG490 (1 mg/kg), a specific Jak2 inhibitor. Lucigenin-enhanced-chemiluminescence assay, real-time PCR and Western blot analysis revealed that Nox-derived O(2)(•-) generation, Nox1, Nox2, and Nox4 mRNA and protein levels were significantly elevated in the aortas of ApoE(-/-) mice fed a high-fat diet compared to ApoE(-/-) mice fed a normal diet. Treatment with tyrphostin AG490 significantly reduced the up-regulated Nox activity, the expression of each Nox subtype, as well as the protein level of CD68, a macrophage-specific marker. Morphometric analysis showed a marked reduction of atherosclerotic lesions in the aorta of AG490-treated animals. These data provide new insights into the regulation of vascular Nox by tyrphostins in the cardiovascular system. Since Jak2 transduces the signals of various cardiovascular risk factors, pharmacological manipulation of this signaling pathway may represent a novel strategy to reduce oxidative stress in atherosclerosis.