Vascular Biology |
From the Department of Biochemistry and Molecular Biology, University of South Florida College of Medicine, Tampa.
Correspondence to Larry P. Solomonson, Department of Biochemistry and Molecular Biology, University of South Florida, College of Medicine, 12901 Bruce B. Downs Blvd, MDC Box 7, Tampa, FL 33612-4799. E-mail lsolomon{at}hsc.usf.edu
AbstractNitric oxide (NO)
production by endothelial cells in response to
bradykinin (Bk) treatment was markedly and synergistically enhanced by
cotreatment with sodium orthovanadate (vanadate), a phosphotyrosine
phosphatase inhibitor. This enhancement was blocked by
tyrosine kinase inhibitors. Calcium ionophore (A23187)
activated production of NO was also enhanced by
cotreatment with vanadate. No significant changes were found in total
endothelial NO synthase (eNOS) protein or in eNOS
distribution between membrane (caveolae) and cytosolic fractions in
response to the various treatments. Vanadate had no direct effect on
eNOS activity, and lysates prepared from cells treated with vanadate
showed little change in specific activity of eNOS. Western blots of
immunoprecipitated eNOS showed the presence of a major
tyrosine-phosphorylated protein band at a mass
corresponding to
125 kDa and 2 minor bands corresponding to
105
and 75 kDa after treatment with vanadate/Bk. No tyrosine
phosphorylation of eNOS after treatment with
vanadate/Bk was observed. Geldanamycin, an inhibitor of
heat shock protein 90, also inhibited the enhancement of NO
production by vanadate/Bk or vanadate/A23187, and there was an
increase in the amount of heat shock protein 90 that
coimmunoprecipitated with eNOS after treatment with vanadate/Bk. These
results show that there is a clear link between tyrosine
phosphorylation and stimulation of eNO
production, which does not appear to involve direct
modification of eNOS, changes in eNOS levels, or compartmentation, but
rather appears to be due to changes in proteins associating with eNOS,
thereby enhancing the state of activation of eNOS.
Key Words: nitric oxide endothelial vanadate bradykinin tyrosine phosphorylation
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