The use of dansyl lysine to assess heat damage and thermotolerance of normal tissues

Heat shock proteins and molecular chaperones: implications for adaptive responses in the skin

Recent advances in the biology of heat-shock proteins (hsps) are reviewed. These abundant and evolutionarily highly conserved proteins (also called stress proteins) act as molecular escorts. Hsps bind to other cellular proteins, help them to fold into their correct secondary structures, and prevent misfolding and aggregation during stress. Cytoplasmic hsp70 and hsp60 participate in complicated protein-folding pathways during the synthesis of new polypeptides. Close relatives of hsp70 and hsp60 assist in the transport and assembly of proteins inside intracellular organelles. Hsp90 may have a unique role, binding to the glucocorticoid receptor in a manner essential for proper steroid hormone action. Hsps may also be essential for thermotolerance and for prevention and repair of damage caused by ultraviolet B light. A unique class of T lymphocytes, the gamma delta T cells, exhibits a restricted specificity against hsps. These T cells may constitute a general, nonspecific immune mechanism directed against the hsps within invading organisms or against very similar hsps within invading organisms or against very similar hsps expressed by infected (stressed) keratinocytes. Immunologic cross-reactivity between hsps of foreign organisms and of the host may play a role in some autoimmune diseases. Although hsps are expressed in the skin, many questions remain about their role during injury, infection, and other types of cutaneous pathophysiology.

Ultraviolet B-induced apoptosis of keratinocytes in murine skin is reduced by mild local hyperthermia

Two components of sunlight, ultraviolet (UV) B (290-320 nm) and infrared (greater than 700 nm), each cause damage to the skin. However, we recently identified a protective response in which heat reduces UVB-induced killing of cultured keratinocytes. Here, this investigation is extended to the living epidermis. The effects of hyperthermic preconditioning upon UVB-induced apoptosis were studied morphologically with hematoxylin and eosin staining, and biochemically with TUNEL (terminal deoxynucleotide transferase nick-end labeling) to measure endonucleolytic cleavage of DNA in situ. Anesthetized SKH-1 hairless mice were exposed to UVB light (0 to 120 mJ/cm2), after which their skin was biopsied at 24 h and paraffin sections were stained with hematoxylin and eosin or with TUNEL. Apoptotic keratinocytes were found to increase after UVB in a dose-related manner. In contrast, if one flank of the mouse was pretreated at 40 degrees C for 1 h and both flanks subsequently were UVB-irradiated at 6 h, the resulting formation of apoptotic cells was reduced twofold or more in the heated flank. Protection appeared by 3 h, reached a maximum at 6 h, and disappeared by 12 h. In summary, heat induces a transient protective effect that reduces UVB-mediated death of keratinocytes in skin at physiologically attainable doses of heat and UVB.

HSP 70 synthesis in clinical hyperthermia patients: preliminary results of a new technique

PURPOSE

Although thermotolerance may be an important variable in clinical hyperthermia, few means have been described to measure its effect or duration in the clinical setting. This study was undertaken to determine if heat shock protein 70 could be used as an assay to predict the presence of retained thermotolerance in human tumors.

METHODS AND MATERIALS

Tissue samples were obtained from patients undergoing hyperthermia and assayed for heat shock protein 70 synthesis. Eight patients having advanced, persistent, or recurrent malignant tumors had open-ended thermometry catheters placed into the lesion being heated. Through these catheters, tissue samples were obtained using a fine needle aspiration technique. Attempts were made to obtain samples before and after the first three heat treatments. Some samples were labeled immediately with radioactive methionine (35S) at 37 degrees C for 4-8 hr, others were given a test heat dose in vitro and then labeled. Protein synthesis profiles were analyzed by gel electrophoresis and autoradiography.

RESULTS

Preliminary results show that it is possible to obtain tissue from hyperthermia patients in a safe and practical manner, that the rate of heat shock protein 70 synthesis can be measured in a variety of tumors, and that the persistence of thermotolerance in the clinical setting can be shown by the inability to reinduce heat shock protein 70 synthesis.

CONCLUSION

The measurement of heat shock protein 70 using the described technique may provide an assay for retained thermotolerance in clinical hyperthermia. Technical difficulties which need to be addressed include obtaining sufficient tissue in all patients, confirming the presence of tumor in the obtained tissue, and obtaining tissue at more frequent intervals to best determine the kinetics of thermotolerance.

Thermotolerance and the heat shock response in normal human keratinocytes in culture

Protective responses of normal human epidermal keratinocytes in culture, after exposure to elevated temperatures ("heat shock"), were examined. Cell viability, measured 24-48 h after a 20-min heat challenge at temperatures between 37 degrees C and 54 degrees C, declined sharply within a narrow 2 degrees-3 degrees C range. However, conditioning with a mild thermal pretreatment (40 degrees C or 42 degrees C for 1 h) protected the keratinocytes against a subsequent heat challenge. This induced thermotolerance was apparent when cells were challenged at 1, 3, and 6 h after the thermal pre-treatment, but disappeared by 24 h. Heating conditions that induce thermotolerance also stimulated the synthesis of heat-shock proteins (hsp) in these cells. Inductions of prominent 35S-methionine labeled bands at 70, 78, and 90 kDa were observed. However, the increases in synthesis of these heat-shock proteins did not correlate well with thermotolerance, because large increases were also observed at certain elevated temperatures that did not produce improved survival. Keratins observed in these cells (50 and 58 kDa classes) were not induced by heat shock. The development of thermotolerance, and the induction of hsp, were both completely blocked by 3'-deoxyadenosine (cordycepin), an inhibitor of newly synthesized messenger RNA, but not by adenosine, the normal analog. While heat-inducible mRNA apparently mediate some function important for the development of thermotolerance, the nature of that role remains speculative. Overall, our findings establish the existence of a functional thermal protective mechanism in human keratinocytes that appears to require the synthesis of new mRNA.