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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 activator kinase phosphorylated a 40 kDa kinase (p40) upon threonine and tyrosine residues, which in turn phosphorylated a 50 kDa kinase (p50) upon threonine (and some serine) residues. p50 phosphorylated hsp27 upon serine. p40 and p50 were purified to near homogeneity. All three components were inactivated by protein phosphatase 2A, and p40 was inactivated 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 identical.

Original publication




Journal article



Publication Date





1039 - 1049


Amino Acid Sequence, Cell-Free System, Cells, Cultured, Enzyme Activation, Heat-Shock Proteins, Humans, Interleukin-1, Intracellular Signaling Peptides and Proteins, Mitogen-Activated Protein Kinase 1, Mitogen-Activated Protein Kinase Kinases, Molecular Sequence Data, Phosphoprotein Phosphatases, Phosphorylation, Protein Kinases, Protein Phosphatase 2, Protein Tyrosine Phosphatases, Protein-Serine-Threonine Kinases, Protein-Tyrosine Kinases, Signal Transduction