SPECIFIC ACTIVATION OF BETA-CASEIN KINASE BY THE INFLAMMATORY CYTOKINES INTERLEUKIN-1 AND TUMOR-NECROSIS-FACTOR

Increases (5-fold) in the rate of phosphorylation of beta-casein were observed in extracts of human gingival fibroblasts that had been stimu lated by interleukin 1 (IL-1) or tumour necrosis factor (TNF). The ind uced kinase was cytosolic and had little activity on alpha-casein. Its chromatographic behaviour on anion-exchange and gel-filtration column s was similar to that of beta-casein kinase, an enzyme detected origin ally in MRC-5 cells stimulated by IL-1 and TNF. Phosphopeptide maps of beta-casein confirmed that the kinase activated in gingival fibroblas ts had the same substrate specificity as beta-casein kinase. In gingiv al fibroblasts, beta-casein kinase activity was maximum after 15 min o f stimulation by IL-1 or TNF, and remained activated for several hours . Activations of small heat-shock protein (hsp27) kinase and mitogen-a ctivated protein (MAP) kinase were also maximum 15 min after stimulati on, but decreased to background levels within the next 30 min. Study o f the effects of 21 agents other than IL-1 or TNF showed that none act ivated beta-casein kinase, whereas several activated MAP kinase or hsp 27 kinase. beta-casein kinase was also detected in extracts of bovine articular chondrocytes and human endothelial cells stimulated by IL-1 or TNF. Semi-purified preparations of fibroblast beta-casein kinase we re not inactivated by phosphatases in vitro. Our results suggest that it may be involved in responses specific to IL-1 and TNF in a wide ran ge of cell types and that its activation probably involves mechanisms other than its phosphorylation.