Dual regulation of heat-shock transcription factor (HSF) activation and DNA-binding activity by H2O2: role of thioredoxin

摘要

pThe heat-shock (HS) response is a ubiquitous cellular response to stress, involving the transcriptional activation of HS genes. Reactive oxygen species (ROS) have been shown to regulate the activity of a number of transcription factors. We investigated the redox regulation of the stress response and report here that in the human pre-monocytic line U937 cells, Hsub2/subOsub2/sub induced a concentration-dependent transactivation and DNA-binding activity of heat-shock factor-1 (HSF-1). DNA-binding activity was, however, lower with Hsub2/subOsub2/sub than with HS. We thus hypothesized a dual regulation of HSF by oxidants. We found that oxidizing agents, such as Hsub2/subOsub2/sub and diamide, as well as alkylating agents, such as iodoacetic acid, abolished, iin vitro/i, the HSF-DNA-binding activity induced by HS iin vivo/i. The effects of Hsub2/subOsub2/subiin vitro/i were reversed by the sulphydryl reducing agent dithiothreitol and the endogenous reductor thioredoxin (TRX), while the effects of iodoacetic acid were irreversible. In addition, TRX also restored the DNA-binding activity of HSF oxidized iin vivo/i, while it was found to be itself induced iin vivo/i by both HS and Hsub2/subOsub2/sub. Thus, Hsub2/subOsub2/sub exerts dual effects on the activation and the DNA-binding activity of HSF: on the one hand, Hsub2/subOsub2/sub favours the nuclear translocation of HSF, while on the other, it alters HSF-DNA-binding activity, most likely by oxidizing critical cysteine residues within the DNA-binding domain. HSF thus belongs to the group of ROS-modulated transcription factors. We propose that the time required for TRX induction, which may restore the DNA-binding activity of oxidized HSF, provides an explanation for the delay in heat-shock protein synthesis upon exposure of cells to ROS./p