Abstract

The rapid transcriptional activation of heat shock genes in response to stress is crucial for the cellular survival and the development of thermotolerance. Although heat shock response is a widespread phenomenon, certain cells exhibit a diminished induction of heat shock gene expression upon stress stimuli. Here we have analyzed the development of thermotolerance and induction of distinct Hsp70 encoding genes in three cell lines representing different hematopoietic cell types. We show that in response to heat shock, cell survival and induction of thermotolerance are impaired in Raji and HL60 cells, as compared with K562 cells. Accordingly, transcriptional induction of the hsp70 gene is diminished in Raji and HL60 cells. This appears to be due to inability of transcription factors, including HSF1 to bind to the hsp70.1 promoter in vivo. Consistent with the genomic footprint, analysis of hsp70.1 mRNA expression using a specific 3'-untranslated region probe reveals that induction of the hsp70.1 gene upon heat shock is completely abolished in Raji and HL60 cells. The suppression of the hsp70.1 promoter is not caused by impaired function of HSF1, since HSF1 is equally activated in all cell types and occupies another heat-inducible promoter, hsp90 alpha. Furthermore, among distinct inducible hsp70 genes, suppression seems to be specific for the hsp70.1 gene, since heat shock results in induction of hsp70.2 and hsp70B' mRNA expression in all cell lines. Taken together, our results demonstrate that distinct Hsp70-encoding genes contribute to the heat shock response in a cell type-dependent manner.

Highlights

  • The rapid transcriptional activation of heat shock genes in response to stress is crucial for the cellular survival and the development of thermotolerance

  • Cell Survival, Development of Thermotolerance, and Induction of Heat Shock Gene Expression Vary between K562, Raji, and HL60 Cell Lines—To determine whether distinct hematopoietic cell types respond to heat stress differently, we compared the cellular survival of K562, HL60, and Raji cells after heat shock

  • It is worth of noting that Raji cells had a higher spontaneous rate of apoptosis, since the number of cells containing hypodiploid DNA was greater in untreated Raji cells in comparison with K562 and HL60 cells

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Summary

Introduction

The rapid transcriptional activation of heat shock genes in response to stress is crucial for the cellular survival and the development of thermotolerance. Consistent with the genomic footprint, analysis of hsp70.1 mRNA expression using a specific 3؅-untranslated region probe reveals that induction of the hsp70.1 gene upon heat shock is completely abolished in Raji and HL60 cells. Among distinct inducible hsp70 genes, suppression seems to be specific for the hsp70.1 gene, since heat shock results in induction of hsp70.2 and hsp70B؅ mRNA expression in all cell lines.

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