Caveolin-1 down-regulates inducible nitric oxide synthase via the proteasome pathway in human colon carcinoma cells.
To investigate whether caveolin-1 (cav-1) may modulate inducible nitric oxide synthase (iNOS) function in intact cells, the human intestinal carcinoma cell lines HT29 and DLD1 that have low endogenous cav-1 levels were transfected with cav-1 cDNA. In nontransfected cells, iNOS mRNA and protein levels were increased by the addition of a mix of cytokines. Ectopic expression of cav-1 in both cell lines correlated with significantly decreased iNOS activity and protein levels. This effect was linked to a posttranscriptional mechanism involving enhanced iNOS protein degradation by the proteasome pathway, because (i) induction of iNOS mRNA by cytokines was not affected and (ii) iNOS protein levels increased in the presence of the proteasome inhibitors N-acetyl-Leu-Leu-Norleucinal and lactacystin. In addition, a small amount of iNOS was found to cofractionate with cav-1 in Triton X-100-insoluble membrane fractions where also iNOS degradation was apparent. As has been described for endothelial and neuronal NOS isoenzymes, direct binding between cav-1 and human iNOS was detected in vitro. Taken together, these results suggest that cav-1 promotes iNOS presence in detergent-insoluble membrane fractions and degradation there via the proteasome pathway.
Felley-Bosco
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Institute of Pharmacology and Toxicology, University of Lausanne, Bugnon 27, 1005 Lausanne, Switzerland. emanuela.felley-bosco@ipharm.unil.ch
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D051242:Caveolin 1; D022461:Caveolins / Q000096:biosynthesis* / Q000235:genetics; D002458:Cell Fractionation; D003110:Colonic Neoplasms; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D016207:Cytokines / Q000378:metabolism / Q000494:pharmacology; D003902:Detergents; D015536:Down-Regulation; D015870:Gene Expression; D019073:HT29 Cells; D006801:Humans; D009097:Multienzyme Complexes / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000096:biosynthesis* / Q000235:genetics; D052247:Nitric Oxide Synthase Type II; D017830:Octoxynol; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D015398:Signal Transduction; D012995:Solubility; D014407:Tumor Cells, Cultured
C495540:CAV1 protein, human; D051242:Caveolin 1; D022461:Caveolins; D016207:Cytokines; D003902:Detergents; D009097:Multienzyme Complexes; D011480:Protease Inhibitors; D017830:Octoxynol; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex