title: The nucleosome assembly activity of NAP1 is enhanced by Alien.
abstract: The assembly of nucleosomes into chromatin is essential for the compaction of DNA and inactivation of the DNA template to modulate and repress gene expression. The nucleosome assembly protein 1, NAP1, assembles nucleosomes independent of DNA synthesis and was shown to enhance coactivator-mediated gene expression, suggesting a role for NAP1 in transcriptional regulation. Here, we show that Alien, known to harbor characteristics of a corepressor of nuclear hormone receptors such as of the vitamin D receptor (VDR), binds in vivo and in vitro to NAP1 and modulates its activity by enhancing NAP1-mediated nucleosome assembly on DNA. Furthermore, Alien reduces the accessibility of the histones H3 and H4 for NAP1-promoted assembly reaction. This indicates that Alien sustains and reinforces the formation of nucleosomes. Employing deletion mutants of Alien suggests that different regions of Alien are involved in enhancement of NAP1-mediated nucleosome assembly and in inhibiting the accessibility of the histones H3 and H4. In addition, we provide evidence that Alien is associated with chromatin and with micrococcus nuclease-prepared nucleosome fractions and interacts with the histones H3 and H4. Furthermore, chromatin immunoprecipitation and reimmunoprecipitation experiments suggest that NAP1 and Alien localize to the endogenous CYP24 promoter in vivo, a VDR target gene. Based on these findings, we present here a novel pathway linking corepressor function with nucleosome assembly activity.
authors.affiliation: Institute of Human Genetics and Anthropology, Friedrich Schiller University, 07740 Jena, Germany.
authors.forename: Maren
authors.initials: M
authors.lastname: Eckey
authors.forename: Wei
authors.initials: W
authors.lastname: Hong
authors.forename: Maria
authors.initials: M
authors.lastname: Papaioannou
authors.forename: Aria
authors.initials: A
authors.lastname: Baniahmad
mesh_terms: D000075686:COP9 Signalosome Complex; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002843:Chromatin / Q000378:metabolism; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006657:Histones / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D056490:Nucleosome Assembly Protein 1; D009707:Nucleosomes / Q000378:metabolism*; D018167:Receptors, Calcitriol / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D015398:Signal Transduction / Q000502:physiology*; D014158:Transcription, Genetic; D020798:Two-Hybrid System Techniques
chemical_list: C402762:COPS2 protein, human; D018797:Cell Cycle Proteins; D002843:Chromatin; D006657:Histones; C533556:NAP1 protein, S cerevisiae; C533557:NAP1L1 protein, human; D009687:Nuclear Proteins; D056490:Nucleosome Assembly Protein 1; D009707:Nucleosomes; D018167:Receptors, Calcitriol; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D000075686:COP9 Signalosome Complex