Tyrosine Nitration of PA700 Activates the 26S Proteasome to Induce Endothelial Dysfunction in Mice With Angiotensin II–Induced Hypertension

Abstract

Abstract-The ubiquitin-proteasome system has been implicated in oxidative stress-induced endothelial dysfunction in cardiovascular diseases. However, the mechanism by which oxidative stress alters the ubiquitin-proteasome system is poorly defined. The present study was conducted to determine whether oxidative modifications of PA700, a 26S proteasome regulatory subunit, contributes to angiotensin II (Ang II)-induced endothelial dysfunction. Exposure of human umbilical vein endothelial cells to low concentrations of Ang II, but not vehicle, for 6 hours significantly decreased the levels of tetrahydro-L-biopterin (BH4), an essential cofactor of endothelial NO synthase, which was accompanied by a decrease in GTP cyclohydrolase I, the rate-limiting enzyme for de novo BH4 synthesis. In addition, Ang II increased both tyrosine nitration of PA700 and the 26S proteasome activity, which were paralleled by increased coimmunoprecipitation of PA700 and the 20S proteasome. Genetic inhibition of NAD(P)H oxidase or administration of uric acid (a peroxynitrite scavenger) or N G -nitro-L-arginine methyl ester (nonselective NO synthase inhibitor) significantly attenuated Ang II-induced PA700 nitration, 26S proteasome activation, and reduction of GTP cyclohydrolase I and BH4. Finally, Ang II infusion in mice decreased the levels of both BH4 and GTP cyclohydrolase I and impaired endothelial-dependent relaxation in isolated aortas, and all of these effects were prevented by the administration of MG132, a potent inhibitor for 26S proteasome. We conclude that Ang II increases tyrosine nitration of PA700 resulting in accelerated GTP cyclohydrolase I degradation, BH4 deficiency, and consequent endothelial dysfunction in hypertension.

Tyrosine Nitration of PA700 Links Proteasome Activation to Endothelial Dysfunction in Mouse Models with Cardiovascular Risk Factors

“…4B), consistent with our previous studies [12]. Furthermore, siRNA-mediated PA700/S10B knockdown prevented association of 26S proteasome sub-complexes as expected (Fig.…”

Regulation of the Proteasome by AMPK in Endothelial Cells: The Role of O-GlcNAc Transferase (OGT)

“…During CVD, the endothelium losses its homoeostatic potential to inhibit the disease process [38]. We [39], [40], [41] and others [42] have shown that the UPS can contribute to the development of endothelial dysfunction, which is reflected as enhanced 26S proteasome activity, an accelerated degradation of endothelial-protective molecules (such as the guanosine 5-triphosphate cyclohydrolase I or GTPCH I, the rate limiting enzyme essential for the de novo synthesis of an eNOS co-factor [39], [40], [43]), and consequent impaired endothelium-dependent vasorelaxation. Most importantly, we have discovered that such an impairment can be restored by activation of AMPK [43].…”

Redox Regulation of Dihydrofolate Reductase

“…17 The 26S proteasome responsible for this degradation has been shown for getting activated by nitration of specific tyrosine residues in the setting of hyperglycemia 17 and experimental hypertension, 18 only leaving the salvage pathway for restoration of BH 4 levels via reduction of dihydrobiopterin (BH 2 ) by dihydrofolate reductase (DHFR). 19 Taking into account that BH 4 plays an essential role for eNOS function, its oxidative depletion or simultaneous inhibition of its de novo synthesis will ultimately lead to eNOS dysfunction/uncoupling, despite the futile counterregulatory upregulation of DHFR expression and activity.…”