Emerging insights into the coactivator role of NCoA62/SKIP in Vitamin D-mediated transcription

NCoA62/SKIP was discovered as a nuclear protein that interacts with the Vitamin D receptor (VDR) and the SKI oncoprotein. NCoA62/SKIP expresses properties consistent with other nuclear receptor transcriptional coactivator proteins. For example, NCoA62/SKIP interacts selectively with the VDR–RXR heterodimer, it forms a ternary complex with liganded VDR and steroid receptor coactivator (SRC) proteins, and it synergizes with SRCs to augment 1,25-dihydroxyvitamin D 3 [1,25-(OH) 2 D 3 ]- and VDR-activated transcription. Chromatin immunoprecipitation studies show that NCoA62/SKIP is recruited in a 1,25-(OH) 2 D 3 -dependent manner to native Vitamin D responsive gene promoters and it enters these promoter complexes after VDR and SRC entry. This suggests that NCoA62/SKIP functions at a distal step in the transactivation process. Recent studies indicate that NCoA62/SKIP is a component of the spliceosome machinery and interacts with important splicing factors such as prp8 and the U5 200 kDa helicase. Functional studies also support an involvement of NCoA62/SKIP in mRNA splicing. Collectively, these data suggest a pivotal role for NCoA62/SKIP in coupling transcriptional regulation by VDR to RNA splicing. They further solidify an important role for VDR/NR-interactors downstream of the transcription process in determining the overall response of Vitamin D and steroid hormone regulated genes.