Leukemic cells appear to develop less thermotolerance and then to lose their thermotolerance more rapidly than do other tumor cell lines. The reason for this phenomenon is not known. After heat shock (or other environmental stresses), mammalian cells preferentially synthesize a set of proteins known as heat shock proteins (HSPs). HSP-28 and the various isoforms of HSP-70 have been suggested as being responsible for the development of thermotolerance. In these studies, we have attempted to determine by their expression which HSPs positively correlate with the development and decay of thermotolerance and whether the expression of these genes could explain the differing thermotolerance response observed between leukemic and nonleukemic tumor cells. Polymerase chain reaction was used to detect the expression of HSP-28 and several HSP-70 genes. Our data indicate that the expression of all three heat-inducible HSP-70 genes, 70A (Hunt and Morimoto, Proc. Natl. Acad. Sci. USA, 82: 6455–6459, 1985), 70B (Voellmy et al., Proc. Natl. Acad. Sci. USA, 82: 4949–4953, 1985), and 70B′ (Leung et al., Biochem J., 267: 125–132, 1990) correlate with the development and decay of thermotolerance in nonleukemic tumor cell lines after heat or arsenite treatment. HSP-28 (Hickey et al., Nucleic Acids Res., 4: 4127–4145, 1986) failed to correlate with thermotolerance development; it was not induced after 45°C primary heat shock. In leukemic cells, however, none of the HSPs were induced for extended periods of time. The lack of coordinate expression of HSP genes in cells of myeloid origin may explain the poor induction and maintenance of thermotolerance that is observed in these cells.

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This work was supported by NIH Grants CA54093 (N. F. M.) and P01CA44665 (G. M. H.).

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