Identification of Xenopus heat shock transcription factor-2: conserved role of sumoylation in regulating deoxyribonucleic acid-binding activity of heat shock transcription factor-2 proteins.

Heat shock transcription factor (Hsf)-1 and Hsf2 are members of the heat shock factor (HSF) protein family involved in heat shock protein (hsp) gene regulation, a regulation that is critical for the ability of cells to survive exposure to stress conditions. Although the role of Hsf1 in binding and activating transcription of hsp gene promoters in response to cell stress is well established, how Hsf2 enhances stress-induced hsp expression is not understood. To gain an insight into the critical conserved features of the regulation and function of Hsf2, we have identified and characterized the Hsf2 protein from Xenopus laevis. We found that, similar to its human counterpart, Xenopus Hsf2 is sumoylated at lysine 82 and that, as it does in human Hsf2, the modification event of the small ubiquitin-related modifier 1 functions to increase the deoxyribonucleic acid-binding activity of this transcription factor in Xenopus. These results indicate that sumoylation is an evolutionarily conserved modification of Hsf2 proteins, supporting the position of this modification as a critical regulator of Hsf2 function.