Ha-ras(val12) induces HSP70b transcription via the HSE/HSF1 system, but HSP70b expression is suppressed in Ha-ras(val12)-transformed cells.
Heat shock proteins (Hsps) are overexpressed in many tumors, but are downregulated in some tumors. To check for a direct effect of Ha-Ras(val12) on HSP70 transcription, we transiently expressed the oncoprotein in Rat1 fibroblasts and monitored its effect on HSP70b promoter-driven reporter gene. We show that expression of Ha-Ras(val12) induced this promoter. Promoter analysis via systematic deletions and point mutations revealed that Ha-Ras(val12) induces HSP70b transcription via heat shock elements (HSEs). Also, Ha-Ras(val12) induction of HSE-mediated transcription was dramatically reduced in HSF1-/- cells. Yet, residual effect of Ha-Ras(val12) that was still measured in HSF1-/- cells suggests that some of the Ha-Ras(val12) effect is Hsf1-independent. When HSF1-/- cells, stably expressing Ha-Ras(val12), were grown on soft agar only small colonies were formed suggesting a role for heat shock factor 1 (Hsf1) in Ha-Ras(val12)-mediated transformation. Although Ha-ras(Val12) seems to be an inducer of HSP70's expression, we found that in Ha-ras(Val12-)transformed fibroblasts expression of this gene is suppressed. This suppression is correlated with higher sensitivity of Ha-ras(val12)-transformed cells to heat shock. We suggest that Ha-ras(Val12) is involved in Hsf1 activation, thereby inducing the cellular protective response. Cells that repress this response are perhaps those that acquire the capability to further proliferate and become transformed clones.
Stanhill
A
A
Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.
Levin
V
V
Hendel
A
A
Shachar
I
I
Kazanov
D
D
Arber
N
N
Kaminski
N
N
Engelberg
D
D
D021581:Active Transport, Cell Nucleus; D000818:Animals; D002461:Cell Line, Transformed; D004268:DNA-Binding Proteins / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology*; D017930:Genes, Reporter; D018840:HSP70 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics*; D006367:HeLa Cells; D000076249:Heat Shock Transcription Factors; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D041681:NIH 3T3 Cells; D015689:Oncogene Protein p21(ras) / Q000502:physiology*; D010084:Oxidation-Reduction; D010766:Phosphorylation; D051381:Rats; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; C000619706:HSF1 protein, human; D018840:HSP70 Heat-Shock Proteins; D000076249:Heat Shock Transcription Factors; C000619709:Hsf1 protein, rat; D014157:Transcription Factors; D015689:Oncogene Protein p21(ras)