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Down-Regulation of a M_r 90,000 Heat Shock Cognate Protein during Granulocytic Differentiation in HL-60 Human Leukemia Cells¹

Third Department of Internal Medicine, Faculty of Medicine, Kyushu University, Fukuoka, Japan

Modulation of the synthesis of heat shock proteins in HL-60 human promyelocytic leukemia cells during differentiation was studied by metabolic labeling with [³⁵S]methionine and Northern blot analysis. HL-60 cells were found to synthesize constitutively a high levels of a M_r 90,000 protein (heat shock cognate protein, hsc90), which was very closely related to M_r 90,000 heat shock protein, hsp90, as far as molecular weight, isoelectric point, peptide maps, immunoreactivity, and encoded mRNA were concerned. Differentiation induction by dimethyl sulfoxide markedly decreased the level of the hsc90 expression, but preserved the ability to preferentially express hsp90 in response to heat stress. These results suggest distinct regulatory mechanisms of the synthesis between hsc90 and hsp90 although they are indistinguishable by conventional protein or mRNA analysis, and indicate that hsc90 has some role in cell growth and differentiation.

¹ Supported in part by grant from Fukuoka Cancer Society.

² To whom requests for reprints should be addressed, at Third Department of Internal Medicine, Faculty of Medicine, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812, Japan.

Received 7/12/88. Revised 12/22/88. Accepted 1/26/89.