Barrier-to-Autointegration Factor Phosphorylation on Ser-4 Regulates Emerin Binding to Lamin A In Vitro and Emerin Localization In Vivo

Department of Cell Biology, Johns Hopkins University, Baltimore, Maryland, United States
Molecular Biology of the Cell (Impact Factor: 4.47). 04/2006; 17(3):1154-63. DOI: 10.1091/mbc.E05-04-0356
Source: PubMed


Barrier-to-autointegration factor (BAF) is a conserved 10-kDa chromatin protein essential in proliferating cells. BAF dimers bind double-stranded DNA, histone H3, histone H1.1, lamin A, and transcription regulators, plus emerin and other LEM-domain nuclear proteins. Two-dimensional gel analysis showed that endogenous human and Xenopus BAF are posttranslationally modified by phosphorylation and potentially other modifications and that they are hyperphosphorylated during mitosis. The invariant Ser-4 residue on BAF is a major site of phosphorylation during both interphase and mitosis. In HeLa cells that overexpressed the phosphomimetic BAF missense mutant S4E, but not S4A, emerin mislocalized from the nuclear envelope, suggesting Ser-4-nonphosphorylated BAF normally promotes emerin localization at the nuclear envelope. Supporting this model, wild-type BAF but not mutant S4E enhanced emerin binding to lamin A in vitro. Thus, Ser-4-unphosphorylated BAF has a positive role in localizing emerin; this role may be disease relevant because loss or mislocalization of emerin causes Emery-Dreifuss muscular dystrophy. Our findings further suggest Ser-4 phosphorylation inhibits BAF binding to emerin and lamin A, and thereby weakens emerin-lamin interactions during both mitosis and interphase.

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Available from: Katherine L Wilson
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    • "We have recently found that GSC self-renewal requires the activity of the gene bällchen (ball) (Herzig et al., 2014), which encodes a member of the metazoan specific VRK-1 protein kinase family (Aihara et al., 2004). ball orthologous from vertebrates and invertebrates encode proteins that phosphorylate the Barrier-to-Autointegration Factor protein (BAF), which is proposed to participate in the establishment of higher order chromatin structures (Gorjánácz et al., 2007; Nichols et al., 2006; Bengtsson and Wilson, 2006; Lancaster et al., 2007). However, phenotypic analyses of Drosophila ball mutants showed that severe chromatin defects are restricted to the oocyte nucleus (Ivanovska et al., 2005). "
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    ABSTRACT: Stem cells continuously generate differentiating daughter cells and are essential for tissue homeostasis and development. Their capacity to self-renew as undifferentiated and actively dividing cells is controlled by either external signals from a cellular environment, the stem cell niche, or asymmetric distribution of cell fate determinants during cell division. Here we report that the protein kinase Bällchen (BALL) is required to prevent differentiation as well as to maintain normal proliferation of neuronal stem cells of Drosophila melanogaster, called neuroblasts. Our results show that the brains of ball mutant larvae are severely reduced in size, which is caused by a reduced proliferation rate of the neuroblasts. Moreover, ball mutant neuroblasts gradually lose the expression of the neuroblast determinants Miranda and aPKC, suggesting their premature differentiation. Our results indicate that BALL represents a novel cell intrinsic factor with a dual function regulating the proliferative capacity and the differentiation status of neuronal stem cells during development.
    Full-text · Article · Sep 2014 · Biology Open
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    • "Phosphorylation of BAF by either the viral B1 or cellular protein kinase VRK1 (vaccinia related kinase 1) strongly inhibits the ability of BAF to bind DNA, thus regulating BAF-mediated assembly of nucleoprotein complexes in both the cytoplasm and nucleus [56], [59], . Phosphorylation of BAF by both viral and cellular kinases occurs at its N-terminus on Thr-2, Thr-3, and Ser-4 [60], [61]. While these sites are highly conserved throughout evolution and regulate BAF in multiple organisms [62]–[64], much remains to be learned about how they control the antiviral capabilities of BAF. "
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    ABSTRACT: BAF (Barrier to Autointegration Factor) is a highly conserved DNA binding protein that senses poxviral DNA in the cytoplasm and tightly binds to the viral genome to interfere with DNA replication and transcription. To counteract BAF, a poxviral-encoded protein kinase phosphorylates BAF, which renders BAF unable to bind DNA and allows efficient viral replication to occur. Herein, we examined how BAF phosphorylation is affected by herpes simplex virus type 1 (HSV-1) infection and tested the ability of BAF to interfere with HSV-1 productive infection. Interestingly, we found that BAF phosphorylation decreases markedly following HSV-1 infection. To determine whether dephosphorylated BAF impacts HSV-1 productive infection, we employed cell lines stably expressing a constitutively unphosphorylated form of BAF (BAF-MAAAQ) and cells overexpressing wild type (wt) BAF for comparison. Although HSV-1 production in cells overexpressing wtBAF was similar to that in cells expressing no additional BAF, viral growth was reduced approximately 80% in the presence of BAF-MAAAQ. Experiments were also performed to determine the mechanism of the antiviral activity of BAF with the following results. BAF-MAAAQ was localized to the nucleus, whereas wtBAF was dispersed throughout cells prior to infection. Following infection, wtBAF becomes dephosphorylated and relocalized to the nucleus. Additionally, BAF was associated with the HSV-1 genome during infection, with BAF-MAAAQ associated to a greater extent than wtBAF. Importantly, unphosphorylated BAF inhibited both viral DNA replication and gene expression. For example, expression of two regulatory proteins, ICP0 and VP16, were substantially reduced in cells expressing BAF-MAAAQ. However, other viral genes were not dramatically affected suggesting that expression of certain viral genes can be differentially regulated by unphosphorylated BAF. Collectively, these results suggest that BAF can act in a phosphorylation-regulated manner to impair HSV-1 transcription and/or DNA replication, which is similar to the antiviral activity of BAF during vaccinia infection.
    Full-text · Article · Jun 2014 · PLoS ONE
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    • "VRKs are found in all metazoan species ranging from worms to humans. VRKs of different species were found to phosphorylate the Barrier-to-Autointegration Factor (BAF) (Bengtsson and Wilson, 2006; Gorjánácz et al., 2007; Lancaster et al., 2007; Nichols et al., 2006), which is involved in the assembly of the nuclear lamina in Caenorhabditis elegans (Gorjánácz et al., 2007) and the organisation of chromatin in the nucleus (Margalit et al., 2007). Moreover, hypomorphic mutations in Drosophila ball cause aberrant chromatin organisation in the oocyte nucleus and an altered pattern of histone modifications (Ivanovska et al., 2005). "
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