Increases (5-fold) in the rate of phosphorylation of
beta-casein were observed in extracts of human gingival fibroblasts that had been stimulated by
interleukin 1 (IL-1) or tumour
necrosis factor (TNF). The induced
kinase was cytosolic and had little activity on
alpha-casein. Its chromatographic behaviour on
anion-exchange and gel-filtration columns was similar to that of
beta-casein kinase, an
enzyme detected originally in MRC-5 cells stimulated by
IL-1 and TNF.
Phosphopeptide maps of
beta-casein confirmed that the
kinase activated in gingival fibroblasts had the same substrate specificity as
beta-casein kinase. In gingival fibroblasts,
beta-casein kinase activity was maximum after 15 min of stimulation by
IL-1 or TNF, and remained activated for several hours. Activations of
small heat-shock protein (
hsp27) kinase and
mitogen-activated
protein (MAP)
kinase were also maximum 15 min after stimulation, but decreased to background levels within the next 30 min. Study of the effects of 21 agents other than
IL-1 or TNF showed that none activated
beta-casein kinase, whereas several activated MAP
kinase or
hsp27 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 were 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 range of cell types and that its activation probably involves mechanisms other than its phosphorylation.