The role of heat shock factor 1 in transcriptional regulation of high mobility group box

Background: Previous study suggests that high mobility group box 1 (HMGB1) can be a potential late inflammatory mediator. However, whether heat shock factor 1 (HSF1) regulate HMGB1 expression via binding to heat shock element (HSE) is not known.

Objective:We investigated the role of HSF1 in the transcriptional regulation of HMGB1 protein.

Methods: A probe that included HMGB1 promoter region containing HSE was synthesized for electrophoretic mobility shift assay (EMSA) to determine the binding of HSF1 and HSE in the promoter region of HMGB1 gene. Mutant mouse HMGB1 promoter was prepared by PCR amplification on a template of wild-type plasmid DNA with site-directed mutant primers. The mutant DNA fragments were also inserted into a corresponding plasmid. In addition, luciferase reporter plasmids of HMGB1 promoter were constructed to transfect RAW264.7 cells. After that, luciferase activity was measured to assay the effects of the HSF1 transfection on the promoter activity.

Results: EMSA result showed a retardation strap after the coculture of biotin labeled HSF1 binding fragment and nuclear protein extracts. The retardation phenomenon could be competed by unlabeled probe and not by unlabeled mutant probe. A super retardation strap was present after adding HSF1 monoclonal antibody. After the HSE core sites was mutated, the relative luciferase activity of the mutant plasmid decreased by 4.26 folds compared with that in the wild-type (23.54±1.68 vs.100.25±3.26, p <0.01). EMSA assay also confirmed that there were HSF1 binding sites HSE (-668bp~-651bp) in the promoter region of HMGB1. The mutation of the core base of HSF1 binding sites decreased the transcriptional activity of HMGB1.

Conclusion: HSF1 can bind to the promoter region HSE (-668bp~-651bp) of HMGB1, which down-regulates the expression of HMGB1.