Differential effects of heat shock and UVB light upon stress protein expression in epidermal keratinocytes

Heat stress and ultraviolet light in the UVB range ("sunburn spectrum," 290-320 nm) were found to alter the synthesis of specific proteins in cultured keratinocytes derived from mouse skin. Using giant two-dimensional gels, approximately 2,000 cellular polypeptides labeled with [35S]methionine at 4-5 h after exposure to heat or to UVB were analyzed. Cells conditioned at sublethal temperatures (42 degrees C for 1 h, or 47 degrees C for 15 min) developed thermotolerance, while cells conditioned with UVB did not develop thermotolerance. Under these heat or UVB conditions, 19 stress proteins were observed. Proteins fell into three classes based upon their inducibility by heat or UVB, dose-response, and induction mechanism (transcriptional versus post-transcriptional) as defined by metabolic blockade with cordycepin (3'-deoxyadenosine). Class 1 proteins were inducible only by heat shock. They included three major heat-shock proteins (hsp 72, hsp 78, hsp 90) and a 42.5-kDa, pI 5.43 protein, and all were induced at the transcriptional level. Class 2 proteins were inducible by heat and by UVB. These included hsp 110 and eight additional polypeptides. All but one were affected by heat at the post-transcriptional level and were induced by UVB at both low (20 mJ/cm2) and high (80 mJ/cm2) doses. Class 3 proteins were inducible only at high UVB doses (survival < 10%). Class 1 and Class 2 proteins could be functionally involved in thermotolerance, while Class 3 proteins are more likely related to damage or cell death.