Differential effects of heat shock on synthesis of Hsp70 and binding activities of heat shock transcriptional factors in CHO and L929 cells

1. 1. CHO and L929 cells were used as a model system for investigating the activities of transcriptional factors involved in hsp70 synthesis. We observed that the heat shock response for hsp70 synthesis is different in CHO and L929 cells. Hsp70 and its mRNA synthesis can be induced by less stressful treatments like 41 or 45°C, 5 min heat shock in L929 cells, but not in CHO cells.

2. 2. Two classes of factors specifically binding to heat shock element (HSE) are observed in CHO and L929 cells; the 37°C constitutive HSE-binding factor (CHBF) and the heat-induced HSE-binding factor (HSF).

3. 3. Heat shock treatments induce the strong HSF-HSE binding in both L929 and CHO cells despite their different response for hsp70 synthesis. The heat-induced formation of HSE-HSF complex appears not consistently to correlate with the hsp70 gene transcription.

4. 4. Heat shock dissociates CHBF from HSE in a heat dose-dependent manner and the dissociation correlates with the transcription of the hsp70 gene.

5. 5. The HSE-CHBF complex in L929 cells is much weaker than that of CHO cells, indicating a potential reason why transcription of the hsp70 gene can be induced by less stressful treatments in L929 cells.

Author Keywords: Heat shock; hsp70 synthesis; gene regulation; heat shock factors