INTERLEUKIN-1 ACTIVATES A NOVEL PROTEIN-KINASE CASCADE THAT RESULTS IN THE PHOSPHORYLATION OF HSP27

An IL-1-stimulated protein kinase cascade resulting in phosphorylation of the small heat shock protein hsp27 has been identified in KB cells . It is distinct from the p42 MAP kinase cascade. An upstream activato r kinase phosphorylated a 40 kDa kinase (p40) upon threonine and tyros ine residues, which in turn phosphorylated a 50 kDa kinase (p50) upon threonine (and some serine) residues. p50 phosphorylated hsp27 upon se rine. p40 and p50 were purified to near homogeneity. All three compone nts were inactivated by protein phosphatase 2A, and p40 was inactivate d by protein tyrosine phosphatase 1B. The substrate specificity of p40 differed from that of p42 and p54 MAP kinases. The upstream activator was not a MAP kinase kinase. p50 resembled MAPKAPK-2 and may be ident ical.