Identification of Heat Shock Protein 90-Associated 84-kDa Phosphoprotein.

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In eukaryotic cells, HSP 90 is associated with several protein kinases and regulates their activities. HSP 90 was also reported to possess an autophosphorylase activity. In this study, we examined in vitro autophosphorylation of HSP 90, which was purified from chick muscle. We show that HSP 90 was not phosphorylated in vitro, but an 84-kDa protein (p 84) was highly phosphorylated. P 84 was neither HSP 90 nor its degradative product, as it was not detected by an antibody (BF 4) specific to HSP 90 in denaturing immunoprecipitation and Western blot analysis. Phosphorylation of a protein similar to p 84 was also detected with purified human brain and HeLa HSP 90, indicating that p 84 is present in many different types of cells. P 84 appeared to exist as large complexes, as determined by HPLC and native gel electrophoresis. Native immunoprecipitation using anti-HSP90 (BF 4)-conjugated Affigel revealed that this phosphoprotein is specifically associated with HSP 90. The interaction of p 84 and HSP 90 was not affected by p 84 phosphorylation. In addition, p 84 phosphorylation was prevented by the presence of divalent cations such as Mg2+ and Mn2+. In contrast, p 84 phosphorylation was significantly activated by addition of exogenous Ca2+- between 100 and 500 μM, although it was blocked by higher concentrations (>1mM) of Ca2+. HSP 90, but not p 84, could be phosphorylated by casein kinase II. Finally, p 84 phosphorylation was specifically prevented by heroin, but not by other kinase inhibitors, indicating that p 84 phosphorylation may be regulated by heme-regulated protein kinase.
社団法人日本生化学会の論文

Identification of Heat Shock Protein 90-Associated 84-kDa Phosphoprotein.

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