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Absence of HSP28 Synthesis and Phosphorylation during the Development of Chronic Thermotolerance in Murine L929 Cells¹

Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, Michigan 48073

We investigated the correlation between chronic thermotolerance development and phosphorylation, synthesis, or expression of the HSP28 family in murine L929 cells. Chronic thermotolerance developed during heating at 41.5°C as indicated by a biphasic survival curve. However, heat-induced phosphorylation of HSP28 was not detected. Furthermore, we failed to detect HSP28 synthesis during chronic heating by using two-dimensional polyacrylamide gel electrophoresis. The lack of HSP28 synthesis was also confirmed in acute thermotolerance. Similar results were observed in NIH 3T3 cells. Although Southern blots clearly demonstrated the presence of the HSP28 gene in genomic DNA, Northern blots failed to demonstrate its expression. Unlike HSP28, the expression of constitutive and inducible HSP70 genes, along with the synthesis of their proteins, were stimulated during chronic heating at 41.5°C in L929 cells. These results suggest that HSP28 synthesis and its phosphorylation are not required to develop both chronic and acute thermotolerance in L929 cells.

¹ To whom requests for reprints should be addressed, at Department of Radiation Oncology, Research Laboratories, William Beaumont Hospital, 3601 W. Thirteen Mile Road, Royal Oak, Michigan 48073.

² Supported by National Cancer Institute Grants CA48000, CA44550, and CA49715 and William Beaumont Hospital Research Institute Grants 90-06 and 91-10.

Received 5/14/92. Accepted 8/ 7/92.