Elsevier

Nitric Oxide

Volume 7, Issue 2, September 2002, Pages 132-147
Nitric Oxide

Review
Physiological mechanisms regulating the expression of endothelial-type NO synthase

https://doi.org/10.1016/S1089-8603(02)00127-1Get rights and content

Abstract

Although endothelial nitric oxide synthase (eNOS) is a constitutively expressed enzyme, its expression is regulated by a number of biophysical, biochemical, and hormonal stimuli, both under physiological conditions and in pathology. This review summarizes the recent findings in this field. Shear stress, growth factors (such as transforming growth factor-β, fibroblast growth factor, vascular endothelial growth factor, and platelet-derived growth factor), hormones (such as estrogens, insulin, angiotensin II, and endothelin 1), and other compounds (such as lysophosphatidylcholine) upregulate eNOS expression. On the other hand, the cytokine tumor necrosis factor-α and bacterial lipopolysaccharide downregulate the expression of this enzyme. The growth status of cells, the actin cytoskeleton, and NO itself are also important regulators of eNOS expression. Both transcriptional and posttranscriptional mechanisms are involved in the expressional regulation of eNOS. Different signaling pathways are involved in the regulation of eNOS promoter activity and eNOS mRNA stability. Changes in eNOS expression and activity under pathophysiological conditions and the pharmacological modulation of eNOS expression are subject of a subsequent brief review (part 2) to be published in the next issue of this journal.

Section snippets

Expression pattern of eNOS

eNOS was first identified and isolated from bovine aortic endothelial cells [3], [4]. Immunohistochemical studies with a specific antibody to eNOS located the enzyme to various types of endothelial cells (arterial and venous) in many tissues, including human tissues [5]. In addition, eNOS expression has been demonstrated in several nonendothelial cell types and tissues (see Table 1).

Chromosomal localization, genomic structure, and cDNA of eNOS

The human eNOS mRNA is encoded by 26 exons spanning 21–22 kb of genomic DNA [6], [7], [8], [9]. The gene is present as a single copy in the haploid human genome. The human eNOS gene has been assigned to the 7q35→q36 region of chromosome 7 [6], [9]. The bovine eNOS gene spans approximately 20 kb of DNA and also contains 26 exons. Two transcription start sites have been determined which are located 170 and 240 base pairs upstream of the methionine translation initiation codon [10].

Full-length NOS

The cardiovascular phenotype of the eNOS knockout mice

To study the role of eNOS in cardiovascular function, eNOS knockout mice have been generated in several laboratories [18], [19], [20]. All eNOS knockout mice are hypertensive and lack NO-mediated, endothelium-dependent vasodilation [18], [20]. This is strong evidence that endothelial NO is an important systemic vasodilator. In global and focal cerebral ischemia models, eNOS knockout mice demonstrated increased susceptibility to stroke, indicating vascular protective effects of eNOS-derived NO

Characterization of the eNOS promoter

Analyses of the 5-flanking genomic region of human eNOS demonstrated that the promoter contains no TATA box. The promoter exhibits proximal elements such as Sp1 and GATA motifs consistent with a constitutively expressed gene [30], [31] (Fig. 1). Furthermore, the human eNOS promoter exhibits homologies to numerous binding sites for transcription factors such as AP-1, AP-2, ETS, MAZ, NF-1, NF-IL6, NF-κB, p53, PEA3, and YY1, as well as CACCC-, CCAAT-, heavy metal-, acute-phase response-, shear

Regulation of eNOS mRNA stability

eNOS expression is regulated not only at the transcriptional level, but also posttranscriptionally. The stability of the eNOS mRNA can be altered by different compounds and stimuli. These include TNFα [15], [42], LPS [43], statins [44], thrombin [45], Rho GTPases [46], actin cytoskeleton [47], VEGF [48], oxLDL [49], amphotericin B [50], albumin-derived advanced glycosylation end products [51], glucocorticoids [35], hypoxia [52], and the proliferation status of the cells [53].

TNFα downregulates

Specific regulation of eNOS expression

In recent years, multiple compounds and conditions have been described that regulate the expression of the eNOS gene.

Conclusions

The expression of eNOS, although constitutive in endothelial cells and other cell types, is regulated in numerous ways to meet local demand. The array of mechanisms and compounds that control eNOS expression includes biophysical stimuli (such as shear stress, that upregulates eNOS expression and activity), growth factors (such as TGF-β1, FGF, VEGF, or PDGF that usually stimulate eNOS expression), hormones (such as estrogens, insulin, angiotensin II, or endothelin 1, that also increase eNOS

Acknowledgements

Research in the authors' laboratory pertaining to this topic was supported by the Collaborative Research Center SFB 553, Project A1 (to H.L. and U.F.), from the Deutsche Forschungsgemeinschaft.

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