ACTIVATION OF HEAT-SHOCK-FACTOR-1 DNA-BINDING PRECEDES STRESS-INDUCEDSERINE PHOSPHORYLATION - EVIDENCE FOR A MULTISTEP PATHWAY OF REGULATION

Exposure of mammalian cells in culture to the antiinflammatory drugs s odium salicylate or indomethacin results in activation of heat shock f actor 1 (HSF1) DNA binding activity. We have previously shown that the drug-induced HSF1 becomes associated with the heat shock elements of the hsp70 promoter, yet transcription of the hsp70 gene is not induced (Jurivich, D. A., Sistonen, L., Kroes, R. A., and Morimoto, R. I. (19 92) Science 255, 1243-1245). In this study, we have examined the basis for uncoupling the heat shock transcriptional response. Comparison of heat shock and drug-induced forms of HSF1 has revealed that the trans criptionally inert drug-induced HSF1 is constitutively but not inducib ly serine-phosphorylated, whereas heat shock-induced HSF1 is both cons titutively and inducibly serine-phosphorylated. The transcriptionally inert intermediate represented by drug-induced HSF1 can be converted t o the transcriptionally active state by a subsequent exposure to heat shock. The only detectable change in HSF1 is the acquisition of induci ble serine phosphorylation. These data reveal that acquisition of the trimeric DNA binding state of HSF1 is independent of and precedes indu cible phosphorylation and furthermore that inducible phosphorylation c orrelates with transcriptional activation.