Heat Shock Factor 4a (HSF4a) Represses HSF2 Expression and HSF2-Mediated Transcriptional Activity

Heat shock factors (HSFs) are the main transcriptional regulators of the stress-induced expression of heat shock protein genes. HSF2, which is one of the HSFs, is activated during differentiation and development but it is unclear how they regulate during cellular processes. Here, we examined the role of HSF4a on the regulation of HSF2 in HEK 293 cells. Wefound that HSF2 levels are negatively correlated with HSF4a expression and that overexpression of HSF4a reduces hemin-induced HSF2 mRNA and protein levels. Moreover, hemin-induced activation of HSF2 was also markedly inhibited in HSF4a expressed cells. Immunoprecipitation assay showed that HSF2 binds to the oligomerization domain of HSF4a. Hemin treatment inhibited their interaction and induced localization of HSF2 and HSF4a in nuclear. In addition, we found that HSF4a or HSF4a DNA binding domain (117 aa) inhibited the activity of hemin-induced HSP70 promoter. Consequently, HSF4a inhibits HSF2 expression or transcriptional activity through negative regulation of HSF2 binding to the HSP70 promoter. In summary, our findings suggest novel mechanisms of HSF2 regulation controlled by HSF4a.