Induction of inducible nitric-oxide synthase by the heterotrimeric G protein Galpha13.
While the functions of several G protein alpha subunits such as alpha(s( and alpha(q) are relatively well understood, the action of others such as alpha13 remain largely undefined. Because of recent interest in regulation of nitric-oxide synthase (NOS) by G protein-coupled signaling systems and findings that receptors for two proinflammatory substances, thrombin and thromboxane couple to alpha13, we studied the effect of alpha13 on NOS activity in a renal epithelial cell line. We found that stable overexpression of alpha13 or its GTPase-deficient mutant, alpha13Q226L, in a continuous renal epithelial cell line (MCT) increased NOS activity. The increased NOS activity was due to increased expression of the macrophage-inducible form of NOS (iNOS). iNOS protein and activity were not increased in similar cells expressing an activated alpha(s) (alpha(s)Q227L) or were minimally increased in cells expressing activated alpha(i1) (alpha-i1Q204L) and alpha(q) (alpha(q)Q209L), members of the three other G protein alpha chain families. Transient co-expression of alpha13 or alpha13Q226L increased the activity of an iNOS promoter-CAT construct demonstrating that alpha13 increases iNOS expression through transcription. Consequently, alpha13 induces iNOS through a novel mechanism that is distinct from that of other G protein alpha chains and that may mediate the actions of G protein-dependent proinflammatory agents.
Kitamura
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Department of Medicine, University of Florida, Gainesville, 32610, USA.
Singer
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Muallem
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Miller
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D000818:Animals; D002460:Cell Line; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis; D018076:DNA, Complementary; D004790:Enzyme Induction; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D015151:Immunoblotting; D007527:Isoenzymes / Q000096:biosynthesis; D007687:Kidney Tubules, Proximal; D007700:Kinetics; D046911:Macromolecular Substances; D051379:Mice; D019001:Nitric Oxide Synthase / Q000096:biosynthesis* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection
D018076:DNA, Complementary; D007527:Isoenzymes; D046911:Macromolecular Substances; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D019001:Nitric Oxide Synthase; D015500:Chloramphenicol O-Acetyltransferase; D019204:GTP-Binding Proteins