Effect of hyperthermia on selective expression of HL-60 heat shock proteins

Hyperthermia is used experimentally to treat human malignancy. The effect of heat delivery rate and thermotolerance on the expression of heat shock proteins (hsp) by the human HL-60 cell line before and after differentiation was studied. This leukemia cell synthesized multiple hsp in response to elevated temperatures. The most obvious and consistent proteins were within the highly conserved stress-inducible family of polypeptides hsp70 which resolved as a hsp69/72 doublet. Cells which were made thermotolerant by gradual heating selectively failed to express the hsp70 doublet even though other hsp were synthesized. Mature HL-60 cells induced to differentiate by incubation in retinoic acid expressed a full complement of hsp when exposed to immediate heat, but there was selective deletion of hsp70 with gradual hyperthermia. This model for selective induction of hsp confirms that synthesis of hsp and thermotolerance can be dissociated in the HL-60. It suggests that the hsp70 does not play an obligatory role in thermotolerance of this human leukemia cell.