Characterization of the heat shock response in M-14 human melanoma cells continuously exposed to supranormal temperatures

The heat shock response elicited in a human melanoma cell line (M-14) by continuous exposures to supranormal temperatures has been characterized. The electrophoretic patterns of polypeptides labeled in vivo at different time-intervals during a continuous heating at 42°C show that the hyperthermic stress induces the synthesis of three HSPs, with molecular weights, respectively, of 86 kDa, 70-72 kDa and 26 kDa. The relative rate of synthesis of the 70-72 kDa HSP-the preeminent HSP-increases during the first hours of treatment, reaching the maximum value after about 9 hr. Later on, the rate of synthesis of this protein progressively decreases, finally attaining a steady state level only slightly exceeding the constitutive one. On the contrary, the smaller molecular weight HSP is synthesized at an apparently constant rate in the course of 21 hr of heating treatment. A continuous exposure at 40°C induces the synthesis of the same three HSPs observed in cells heated at 42°C, but the rate of synthesis of all these HSPs is not so greatly enhanced over the control values as in the 42°C-heated cells. Moreover, the repression of the 70-72 kDa HSP synthesis is faster, taking place within 4-6 hr of treatment. Coomassie blue stained gels show that a polypeptide, coincident with the 70-72 kDa HSP, accumulates in the course of a continuous heating either at 42°C and at 40°C. The final intracellular level attained by this protein species results higher in 42°C-treated cells than in 40°C-treated ones. Hybridization experiments between total RNAs obtained from cells heated at 42°C and a radioactive DNA probe (containing sequences complementary to the mRNA coding for the human 70 kDa HSP) demonstrate that the kinetics of accumulation and decay of the 70 kDa HSP-mRNAs correlate with the kinetics of induction and repression of the corresponding protein.