Inducible Nitric Oxide Synthase Binds, S-Nitrosylates, and Activates Cyclooxygenase-2.
Kim, S.F., Huri, D.A. and Snyder, S.H. Science, 310, 1966-1970 (December 23, 2005).
Solomon Snyder’s laboratory has built upon earlier work showing that prostaglandin production is altered by stimulants and inhibitors to inducible nitric oxide synthase (iNOS). The new data reveal that nitrosylation activates cyclooxygenase-2 (COX-2) by increasing the apparent Vmax without altering the enzyme’s affinity for its substrate, arachidonic acid. The enzyme may be nitrosylated at many of its 13 cysteine residues, but its activation is associated specifically with nitrosylation at cysteine-526. Moreover, the nitrosylation process involves a binding of iNOS with COX-2, as the two enzymes coprecipitate with an antibody to COX-2. The binding is not dependent upon their respective enzymatic activities, as inhibitors had no effect on their coimmunoprecipitation. Moreover, expression of a COX-2 fragment (484-604), which binds to iNOS, blocks prostaglandin E2 (PGE2) formation in macrophages exposed to an inflammatory stimulus, lipopolysaccharide plus gamma-interferon. Macrophages from iNOS knockout mice provided confirmatory evidence, showing a 70% lower response, as measured by PGE2 formation, to the stimulus.
The results suggest that synergism between the nitric oxide- and prostaglandin-mediated inflammatory pathways hinges on the binding of iNOS to COX-2. Hence, creation of inhibitors to iNOS that block both this enzyme’s activity and its binding to COX-2 may prove highly effective in treating inflammatory diseases.
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