The interleukin‐1‐stimulated protein kinase that phosphorylates heat shock protein hsp27 is activated by MAP kinase

Abstract

In KB cells, interleukin‐1 (IL‐1), epidermal growth factor and phorbol ester transiently activated both MAP kinase and a serine kinase which phosphorylated the heat shock protein hsp27. Extracts made from IL‐1‐stimulated KB cells phosphorylated recombinant hsp27, in vitro, on serine residues 78 and 82 which are contained within Arg‐X‐X‐Ser motifs similar to those phosphorylated by the ribosomal protein S6 kinases. Upon size exclusion chromatography, however, hsp27 kinase eluted as a single peak of activity at 50–60 kDa, clearly separated from ribosomal protein S6 kinases. Treatment of partially purified hsp27 kinase with protein phosphatase‐2a reduced its activity by 80%. De‐phosphorylated hsp27 kinase could be approximately 50% reactivated by a factor present in IL‐1‐treated cell extracts in the presence of ATP. This factor co‐eluted with MAP kinase after partial purification by DEAE‐cellulose, phenyl Sepharose, and size exclusion chromatography. Purified sea star p44^mpk and recombinant ERK2 MAP kinases were also capable of re‐activating hsp27 kinase to a similar extent. These data suggest that hsp27 kinase is downstream from, and probably a direct target of MAP kinase.