Molecular mechanisms involved in the regulation of the endothelial nitric oxide synthase

Abstract

The endothelial nitric oxide synthase (eNOS), the expression of which is regulated by a range of transcriptional and posttranscriptional mechanisms, generates nitric oxide (NO) in response to a number of stimuli. The physiologically most important determinants for the continuous generation of NO and thus the regulation of local blood flow are fluid shear stress and pulsatile stretch. Although eNOS activity is coupled to changes in endothelial cell Ca(2+) levels, an increase in Ca(2+) alone is not sufficient to affect enzyme activity because the binding of calmodulin (CaM) and the flow of electrons from the reductase to the oxygenase domain of the enzyme is dependent on protein phosphorylation and dephosphorylation. Two amino acids seem to be particularly important in regulating eNOS activity and these are a serine residue in the reductase domain (Ser(1177)) and a threonine residue (Thr(495)) located within the CaM-binding domain. Simultaneous alterations in the phosphorylation of Ser(1177) and Thr(495) in response to a variety of stimuli are regulated by a number of kinases and phosphatases that continuously associate with and dissociate from the eNOS signaling complex. eNOS associated proteins, such as caveolin, heat shock protein 90, eNOS interacting protein, and possibly also motor proteins provide the scaffold for the formation of the protein complex as well as its intracellular localization.

Arginase II Contributes to the Ca 2+ /CaMKII/eNOS Axis by Regulating Ca 2+ Concentration Between the Cytosol and Mitochondria in a p32‐Dependent Manner

“…CaM binds to a CaM‐binding motif that inhibits Thr495 phosphorylation and then facilitates NADPH‐dependent electron flow from the reductase domain to the oxygenase domain by displacing an adjacent autoinhibitory loop of eNOS. CaMKII mediates Ser1177 phosphorylation in the reductase domain, and then NO production is increased by enhancing the electron flux through the reductase domain 39. Therefore, arginase activity adjusts the phosphorylation of 2 important amino acids, Ser1177 and Thr495, when eNOS is activated through a Ca 2+ ‐dependent mechanism.…”

Mechanisms of β3‐adrenoceptor‐induced eNOS activation in right atrial and left ventricular human myocardium

“…Activation of eNOS by translocation, dissociation from caveolin-1 and subsequent binding of calcium-calmodulin is the main mechanism leading to increased eNOS activity (Wu, 2002). In addition, phosphorylation at eNOS Ser1177 , eNOS Thr495 and eNOS Ser114 could be identified as additional mechanisms modulating eNOS activity (Bauer et al, 2003; for reviews, see Goligorsky et al, 2002;Flemming & Busse, 2003). Whereas eNOS Ser1177 phosphorylation has been implicated with an activation of the enzyme, phosphorylation of eNOS Ser114 and eNOS Thr495 has been demonstrated to decrease enzyme activity (Dimmeler et al, 1999;Bauer et al, 2003;Flemming & Busse, 2003).…”

“…Very recently, the phosphorylation/dephosphorylation of eNOS Thr495 (Lin et al, 2003), as well as of eNOS Ser114 (Flemming & Busse, 2003), has been speculated to be an intrinsic switch mechanism that determines whether eNOS generates NO versus superoxide anions. Furthermore, evidence is provided that a kind of cross-talk or interrelationship may exist between eNOS Ser1177 , eNOS Ser114 and eNOS Thr495 phosphorylation, at least in endothelial cells (Dimmeler et al, 1999;Bauer et al, 2003;Flemming & Busse, 2003).…”

“…Furthermore, evidence is provided that a kind of cross-talk or interrelationship may exist between eNOS Ser1177 , eNOS Ser114 and eNOS Thr495 phosphorylation, at least in endothelial cells (Dimmeler et al, 1999;Bauer et al, 2003;Flemming & Busse, 2003).…”

Shear stress‐induced angiogenesis in mouse muscle is independent of the vasodilator mechanism and quickly reversible

“…Nitric oxide (NO), generated by nNOS in muscle fibres (Balon & Nadler 1994) or eNOS in blood vessel endothelium in response to an increased shear stress (Fleming & Busse 2003), contributes to the hyperaemia observed during acute muscle contractions in animals (Hirai et al . 1994) and humans (Boushel 2003, Schrage et al .…”