HSP70 and heat shock factor 1 cooperate to repress Ras-induced transcriptional activation of the c-fos gene

Heat shock protein 70 (HSP70) is a molecular chaperone involved in protein folding and resistance to the deleterious effects of stress. Here we show t hat HSP70 suppresses transcription of c-fos, an early response gene that is a key component of the ubiquitous AP-1 transcription factor complex. HSP70 repressed Ras-induced c-fos transcription only in the presence of function al heat shock factor1 (HSF1). This suggests that HSP70 functions as a corep ressor with HSF1 to inhibit c-fos gene transcription. Therefore, besides it s known function in the stress response, HSP70 also has the property of a c orepressor and combines with HSF1 to antagonize Fos expression and may thus impact multiple aspects of cell regulation.