Transient cold shock induces the heat shock response upon recovery at 37 degrees C in human cells

We evaluated the effects of a transient cold shock followed by recovery and incubation at 37 degrees C on the regulation of heat shock gene expression in the IMR-90 human diploid fibroblasts and HeLa cells in tissue culture. We showed that preincubation of cells at 4 degrees C induced the synthesis and accumulation of the heat shock proteins (HSPs) upon recovery at 37 degrees C, and the degree of this induction was directly related to the time that the cells spent at 4 degrees C. Assays on the abundance of the hsp 70 transcript, the hsp 70 gene promoter activity, and the trimerization and activation of heat shock factor (HSF) to bind to its consensus heat shock element (HSE) provided evidence that this induction of the heat shock response in cells recovering from a transient cold shock is attributable to a transcriptional event mediated by the activation of HSF. Further, the induction was a response to the temperature upshift from 4 to 37 degrees C as opposed to the 4 degrees C treatment itself; quantitation of the HSE-binding activity of cells incubated at 4 degrees C without recovery and incubation at 37 degrees C gave no evidence of an activated response. Analysis of the effects of protein synthesis inhibitors demonstrated that neither cycloheximide nor puromycin was effective in blocking the induction of HSE-binding activity in cells recovering from a transient cold shock. Experiments on the time course and temperature dependence of this induction of HSE-binding activity showed that the onset, magnitude, and duration of this induction were directly proportional to the severity of the cold stress (measured by time and temperature). We discuss the possible mechanism(s) involved in this induction of the heat shock genes at 37 degrees C by a transient cold shock and the biological implications of this observation.