GLUCOCORTICOID-MEDIATED GENE SUPPRESSION OF RAT CYTOKINE-INDUCED NEUTROPHIL CHEMOATTRACTANT CINC GRO, A MEMBER OF THE INTERLEUKIN-8 FAMILY,THROUGH IMPAIRMENT OF NF-KAPPA-B ACTIVATION

The glucocorticoid dexamethasone inhibited the production of the rat c ytokine-induced neutrophil chemoattractant CINC/gro, a counterpart of human melanoma growth-stimulating activity that belongs to the interle ukin-8 (IL-8) family, in the normal rat kidney epithelial cell line NR K-52E stimulated with interleukin-1 beta (IL-1 beta), lipopolysacchari de, or tumor necrosis factor alpha. The accumulation of CINC/gro mRNA induced by these activators was also decreased comparably by dexametha sone, A nuclear run-on assay revealed that dexamethasone decreased the IL-1 beta-induced transcription of the CINC/gro gene, The half-life o f CINC/gro mRNA transcripts did not change significantly after exposur e to dexamethasone, suggesting that this glucocorticoid acts mainly at the transcriptional level, Transfection with luciferase expression ve ctors containing 5'-deleted and mutated CINC/gro gene sequences demons trated that the 5'-flanking region containing the NF-kappa B binding s ite is involved in the IL-1 beta- and dexamethasone-induced activation and repression of the CINC/gro gene expression, respectively, Further more, a tandem repeat of the NF-kappa B sequence in the CINC/gro gene conferred the inducibility by IL-1 beta and suppression of luciferase activity by dexamethasone. In an electrophoretic mobility shift assay, dexamethasone diminished the IL-1 beta-induced formation of NF-kappa B complexes, which consisted of p65 and p50. Western blotting revealed that dexamethasone inhibited the IL-1 beta-induced translocation of p 65 hom the cytoplasm into the nucleus, while the nuclear level of NF-k appa B p50 remained almost unchanged. In addition, the degradation of I kappa B-alpha induced by IL-1 beta was not inhibited by dexamethason e. These results indicated that the suppression of the CINC/gro gene t ranscription by glucocorticoid occurs through the impairment of NF-kap pa B activation, possibly by interference with the translocation of NF -kappa B p65 from the cytoplasm into the nucleus, thereby suppressing transactivation of the CINC/gro gene.