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Updated: Jul 28, 2026

Biochemical Reconstitution of Steroid Receptor•Hsp90 Protein Complexes and Reactivation of Ligand Binding
Published on: September 21, 2011
Ternary complexes and cooperative interplay between NCoA-62/Ski-interacting protein and steroid receptor coactivators
C Zhang1, T A Baudino, D R Dowd
1Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106, USA.
Abstract:
The vitamin D receptor (VDR) is a ligand-dependent transcriptional factor that binds to vitamin D-responsive elements as a heterodimer with retinoid X receptor (RXR) to regulate target gene transcription. The steroid receptor coactivator (SRC) proteins are coactivators that interact with the AF-2 domain of VDR to augment 1,25-dihydroxyvitamin D3-dependent transcription. In contrast, NCoA-62/Ski-interacting protein (SKIP) is a distinct, activation function-2-independent coactivator for VDR. The current study examined whether these two distinct classes of coactivators impact functionally on VDR-mediated transcription. Using a ternary complex binding assay, we observed a marked preference for the direct interaction of NCoA-62/SKIP with the VDR-RXR heterodimer as compared with the VDR-VDR homodimer or VDR monomer. The liganded VDR also formed a ternary complex with NCoA-62/SKIP and SRC proteins in vitro. Competition experiments using LXXLL peptides showed that NCoA-62/SKIP and SRC coactivators contact different domains of the VDR-RXR heterodimer. Synergistic interplays were observed between NCoA-62/SKIP and SRC coactivators in VDR-mediated transcriptional assays, and protein interference assays indicated a requirement for both NCoA-62/SKIP and SRCs in VDR- mediated transcription. These studies suggest that the ligand-dependent and simultaneous interaction of NCoA-62/SKIP and SRC coactivators with distinct interaction domains within the VDR-RXR heterodimer results in cooperative interplays between coactivators in VDR-mediated transcription.
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