Nmi interacts with Hsp105[beta] and enhances the Hsp105[beta]-mediated Hsp70 expression

The mammalian stress protein Hsp105α is expressed constitutively and is further induced under stress conditions, whereas the alternative spliced form, Hsp105[beta] is only expressed during mild heat shock. We previously reported that Hsp105α is localized mainly in the cytoplasm, whereas Hsp105[beta] is localized in the nucleus. Consistent with the different localization of these proteins, Hsp105[beta] but not Hsp105α induces the expression of the major stress protein Hsp70. We here identified N-myc and Stat interactor (Nmi), as an Hsp105[beta]-binding protein by yeast two-hybrid screening. Immunoprecipitation and pull-down assay showed that Nmi interacts with Hsp105[beta] in vivo and in vitro . Luciferase reporter gene assay and Western blotting showed that Nmi enhanced both the Hsp105[beta]-induced phosphorylation of Stat3 and the Hsp105[beta]-induced activation of the hsp70 promoter in a manner that is dependent on the Stat3-binding site, which results in an increase in Hsp70 protein levels. Most importantly, mild heat shock-induced Hsp70 expression, which is dependent on Hsp105[beta], is suppressed by knockdown of endogenous Nmi. These results suggest that Nmi has a role as a positive regulator of Hsp105[beta]-mediated hsp70 gene expression along the Stat3 signaling pathway. * Nmi is identified as an Hsp105[beta]-binding protein by yeast two-hybrid screening. * Nmi interacts with Hsp105[beta] in vitro and in vivo, and activates the hsp70 promoter. * Nmi acts as an Hsp70 inducer with Hsp105[beta] and may have a role in stress signaling.