Interleukin-6 inhibits endothelial nitric oxide synthase activation and increases endothelial nitric oxide synthase binding to stabilized caveolin-1 in human vascular endothelial cells.
OBJECTIVE
We hypothesized a possible mechanism for atherosclerosis in which interleukin-6 (IL-6) might affect the endothelial nitric oxide synthase (eNOS)-caveolin-1 interaction and result in decreased nitric oxide bioavailability in the setting of low-grade inflammation.


METHODS
Because eNOS and caveolin-1 are crucial for vascular tone control, we studied the effects of IL-6 on the expression and activation of eNOS and caveolin-1 in human vascular endothelial cells.


RESULTS
IL-6 inhibited the phosphorylation of eNOS at Ser1177 and the bradykinin-stimulated nitric oxide production; however, eNOS protein expression was not changed. In addition, IL-6 inhibited bradykinin-stimulated Akt phosphorylation at Ser473 and Thr 308 without affecting the Akt protein expression. IL-6 did not alter the mRNA level of caveolin-1; however, the caveolin-1 protein level was significantly increased dose-dependently. The binding of eNOS and caveolin-1 in endothelial cells, as demonstrated by coimmunoprecipitation assay, was increased by IL-6 treatment. IL-6 treatment was found to stabilize caveolin-1 protein and its half-life was estimated to prolong from 7.5 h to longer than 12 h. Furthermore, treatment with PD98059 and short interference RNA of extracellular signal-regulated kinase gene reversed the effects of IL-6 on eNOS and caveolin-1.


CONCLUSIONS
In addition to decreasing Akt phosphorylation, the results of this study demonstrate, for the first time, the molecular mechanism underlying the effect of IL-6 to decrease the nitric oxide bioavailability by increasing the half-life and, therefore, the protein levels of caveolin-1. The increased caveolin-1 proteins bind more eNOS and consequently decrease eNOS activation by reducing the Ser1177 phosphorylation.
Hung
Ming-Jui
MJ
Section of Cardiology, Department of Medicine, Chang Gung Memorial Hospital at Keelung, Keelung, Taiwan.
Cherng
Wen-Jin
WJ
Hung
Ming-Yow
MY
Wu
Hsiao-Ting
HT
Pang
Jong-Hwei S
JH
D050197:Atherosclerosis / Q000209:etiology / Q000378:metabolism; D001483:Base Sequence; D051242:Caveolin 1 / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000235:genetics; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism / Q000494:pharmacology*; D008955:Models, Cardiovascular; D052250:Nitric Oxide Synthase Type III / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000737:chemistry / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction
C495540:CAV1 protein, human; D051242:Caveolin 1; D005419:Flavonoids; C508600:IL6 protein, human; D015850:Interleukin-6; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; C496314:NOS3 protein, human; D052250:Nitric Oxide Synthase Type III; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one