LIPOPOLYSACCHARIDE-INDUCED DESENSITIZATION OF JUNB GENE-EXPRESSION INA MOUSE MACROPHAGE-LIKE CELL-LINE, P388D1

Treatment of a mouse macrophage cell line, P388D1, for 1 h with bacter ial LPS caused a transient increase in the level of junB mRNA expressi on. These cells became refractory in terms of the junB gene response t o exposure to a second round of LPS or lipid A, but not to PMA. The LP S-induced desensitized state was not due to the shortening of the half -life of junB mRNA, but was suggested, by nuclear run-on analysis, to be caused by reduction of junB gene transcription. Pretreating cells w ith herbimycin A, a tyrosine kinase inhibitor, substantially inhibited LPS-induced expression of junB mRNA and decreased tyrosine phosphoryl ation of 38- to 42-kDa proteins, which comigrated with p38 and p42 mit ogen-activated protein (MAP) kinases. Parallel to down-regulation of j unB mRNA expression, activation of the p38 MAP kinase was markedly red uced in LPS-tolerant cells, whereas activation of p42 MAP kinase was r elatively constant. The specific p38 MAP kinase inhibitor, SB202190, p otently inhibited LPS-induced junB mRNA expression. These results sugg est that the CPS-induced desensitization of junB gene expression occur s at or upstream of the level of gene transcription and may be involve d ina defective LPS-induced p38 MAP kinase pathway.