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.
Highlights
The vitamin D receptor (VDR)1 is a member of the nuclear hormone receptor (NR) superfamily that regulates target gene transcription in response to 1,25-(OH)2D3 [1]
We directly compared the abilities of NCoA-62 and steroid receptor coactivator (SRC) coactivators (GRIP-1/SRC-2) to interact with the VDR-VDR homodimer or the VDR-retinoid X receptor (RXR) heterodimer complexes using an in vitro ternary complex assay
SRC coactivators such as GRIP-1 and steroid receptor coactivator-1 (SRC-1) interact with NRs in a ligand-dependent manner through the activation function-2 (AF-2) domain, and this interaction is important in modulating the transcriptional response of the liganded receptor [8, 9, 37]
Summary
The vitamin D receptor (VDR) is a member of the nuclear hormone receptor (NR) superfamily that regulates target gene transcription in response to 1,25-(OH)2D3 [1]. SRC-1 interacts with the general transcriptional activator CBP/p300 through a distinct C-terminal domain, most likely as part of a large multi-protein complex assembled at the target gene promoter [19, 20]. Coactivator proteins such as SRC-1 and CBP/p300 possess intrinsic histone acetyltransferase activity, suggesting that ligand-activated receptors may recruit coactivators that function to remodel chromatin structure, permitting greater accessibility of the transcriptional machinery to DNA [21,22,23]. We show cooperative interactions between VDR, NCoA-62/SKIP, and SRC coactivators and a resulting synergistic effect of these two distinct coactivators in VDR-mediated transcription. These cooperative interplays are mediated through interactions of the SRCs and NCoA-62/SKIP coactivators with distinct domains of the VDR that permit ternary complex formation between the liganded VDR/RXR heterodimer and the NCoA-62/SKIP and SRC coactivator proteins
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
