INTERLEUKIN-1-BETA EXPRESSION AFTER INHIBITION OF PROTEIN PHOSPHATASES IN ENDOTOXIN-TOLERANT CELLS

Endotoxin (lipopolysaccharide [LPS]) is a potent activator of a number of inflammatory genes in blood leukocytes, including interleukin-l (I L-1), Blood leukocytes isolated from patients with septic shock fail t o produce IL-1 in response to LPS, a phenomenon known as endotoxin tol erance. To study the regulation of IL-1 expression in endotoxin-tolera nt cells, the protein phosphatase inhibitor okadaic acid was used to e xamine the effects of protein phosphorylation on IL-1 beta gene expres sion. We found that endotoxin-tolerant cells produced normal levels of IL-1 beta when protein phosphatases were inhibited. In the human pro- monocytic cell line THP-1, okadaic acid increased mRNA accumulation an d synthesis of IL-1 beta protein. Normal and endotoxin-tolerant THP-1 cells accumulated IL-1 beta mRNA and protein with similar delayed kine tics. Okadaic acid stabilization of IL-1 beta mRNA appears to be the p rimary mechanism through which endotoxin-tolerant cells accumulate IL- 1 beta mRNA and protein. Endotoxin-tolerant cells were unable to activ ate transcription in response to okadaic acid. However, the transcript ion factor NF-kappa B, which is known to be involved in IL-1 beta expr ession, was translocated to the nucleus in both normal and endotoxin-t olerant cells after treatment with okadaic acid. These studies reveale d that protein phosphorylation can affect gene expression on at least two distinct levels, transcription factor activation and mRNA stabilit y. Endotoxin-tolerant cells have decreased transcription activation po tential, while IL-1 beta mRNA stability remains responsive to protein phosphorylation.