Heat shock protein 90beta: a novel mediator of vitamin D action

We investigated the role of Heat shock protein 90 {(Hsp90)} in vitamin D action in Caco-2 cells using geldanamycin {(GA)} to block Hsp90 function and {RNA} interference to reduce Hsp90beta expression. When cells were exposed to {GA,} vitamin D-mediated gene expression and transcriptional activity were inhibited by 69% and 54%, respectively. Gel shift analysis indicated that {GA} reduced vitamin D-mediated {DNA} binding activity of the vitamin D receptor {(VDR).} We tested the specific role of Hsp90beta by knocking down its expression with stably expressed short hairpin {RNA.} Vitamin D-induced gene expression and transcriptional activity were reduced by 90% and 80%, respectively, in Hsp90beta-deficient cells. Nuclear protein for {VDR} and {RXRalpha,} its heterodimer partner, were not reduced in Hsp90beta-deficient cells. These findings indicate that Hsp90beta is needed for optimal vitamin D responsiveness in the enterocyte and demonstrate a specific role for Hsp90beta in {VDR} signaling.