THE INTERLEUKIN-1-STIMULATED PROTEIN-KINASE THAT PHOSPHORYLATES HEAT-SHOCK PROTEIN HSP27 IS ACTIVATED BY MAP KINASE

In KB cells, interleukin-l (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-l- stimulated KB cells phosphorylated recombinant hsp27, in vitro, on ser ine residues 78 and 82 which are contained within Arg-X-X-Ser motifs s imilar to those phosphorylated by the ribosomal protein S6 kinases. Up on size exclusion chromatography, however, hsp27 kinase eluted as a si ngle peak of activity at 50-60 kDa, clearly separated from ribosomal p rotein S6 kinases. Treatment of partially purified hsp27 kinase with p rotein phosphatase-2a reduced its activity by 80%. De-phosphorylated h sp27 kinase could be approximately 50% reactivated by a factor present in IL-l-treated cell extracts in the presence of ATP. This factor co- eluted with MAP kinase after partial purification by DEAL-cellulose, p henyl Sepharose, and size exclusion chromatography. Purified sea star p44(mpk) and recombinant ERK2 MAP kinases were also capable of re-acti vating hsp27 kinase to a similar extent. These data suggest that hsp27 kinase is downstream from, and probably a direct target of MAP kinase .