DEFICIENT INDUCTION OF HUMAN HSP70 HEAT-SHOCK GENE-TRANSCRIPTION IN Y79 RETINOBLASTOMA CELLS DESPITE ACTIVATION OF HEAT-SHOCK FACTOR-1

One of the basic features of the inducible heat shock response is the activation of heat shock factor which results in the rapid transcriptional induction of the heat shock genes. Although it is widely considered that the heat shock response is ubiquitous, several reports have indicated that the transcriptional response can vary in both intensity and kinetics and often in a tissue-specific manner. Of interest have been studies on the expression of heat shock genes in the brain, particularly observations that certain cultured neuronal cells exhibit a diminished heat shock response. We demonstrate that transcription of the gene encoding a 70-kDa heat shock protein (hsp70) is diminished upon heat shock in Y79 human retinoblastoma cells (which are of neuronal origin) despite both the activation of heat shock factor 1 and induced transcription of another heat shock gene, hsp90 alpha. This uncoupling of stress-induced transcription of the hsp70 and hsp90 alpha genes, which are typically coordinately regulated in response to stress, appears to be due to the selective inability of trans-acting factors, including heat shock factor 1, to bind in vivo to the hsp70 promoter as the result of a chromatin-mediated effect.