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See detailTranscription impairment and cell migration defects in elongator-depleted cells: Implication for familial dysautonomia
Close, Pierre ULg; Hawkes, Nicola; Cornez, Isabelle ULg et al

in Molecular Cell (2006), 22(4), 521-531

Mutations in IKBKAP, encoding a subunit of Elongator, cause familial dysautonomia (FD), a severe neuro-developmental disease with complex clinical characteristics. Elongator was previously linked not only ... [more ▼]

Mutations in IKBKAP, encoding a subunit of Elongator, cause familial dysautonomia (FD), a severe neuro-developmental disease with complex clinical characteristics. Elongator was previously linked not only with transcriptional elongation and histone acetylation but also with other cellular processes. Here, we used RNA interference (RNAi) and fibroblasts from FD patients to identify Elongator target genes and study the role of Elongator in transcription. Strikingly, whereas Elongator is recruited to both target and nontarget genes, only target genes display histone H3 hypoacetylation and progressively lower RNAPII density through the coding region in FD cells. Interestingly, several target genes encode proteins implicated in cell motility. Indeed, characterization of IKAP/hELP1 RNAi cells, FD fibroblasts, and neuronal cell-derived cells uncovered defects in this cellular function upon Elongator depletion. These results indicate that defects in Elongator function affect transcriptional elongation of several genes and that the ensuing cell motility deficiencies may underlie the neuropathology of FD patients. [less ▲]

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See detailGlycogen synthase kinase-3 regulates mitochondrial outer membrane permeabilization and apoptosis by destabilization of MCL-1
Maurer, Ulrich; Charvet, Céline; Wagman, Allan et al

in Molecular Cell (2006), 21(6), 749-760

We investigated the role of glycogen synthase kinase-3 (GSK-3), which is inactivated by AKT, for its role in the regulation of apoptosis. Upon IL-3 withdrawal, protein levels of MCL-1 decreased but were ... [more ▼]

We investigated the role of glycogen synthase kinase-3 (GSK-3), which is inactivated by AKT, for its role in the regulation of apoptosis. Upon IL-3 withdrawal, protein levels of MCL-1 decreased but were sustained by pharmacological inhibition of GSK-3, which prevented cytochrome c release and apoptosis. MCL-1 was phosphorylated by GSK-3 at a conserved GSK-3 phosphorylation site (S159). S159 phosphorylation of MCL-1 was induced by IL-3 withdrawal or PI3K inhibition and prevented by AKT or inhibition of GSK-3, and it led to increased ubiquitinylation and degradation of MCLA. A phosphorylation-site mutant (MCL-1(S159A)), expressed in IL-3-dependent cells, showed enhanced stability upon IL-3 withdrawal and conferred increased protection from apoptosis compared to wild-type MCL-1. The results demonstrate that the control of MCLA stability by GSK-3 is an important mechanism for the regulation of apoptosis by growth factors, PI3K, and AKT. [less ▲]

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See detailGSK3-Mediated BCL-3 phosphorylation modulates its degradation and its oncogenicity
Viatour, Patrick ULg; Dejardin, Emmanuel ULg; Warnier, Michael et al

in Molecular Cell (2004), 16(1), 35-45

The oncoprotein BCL-3 is a nuclear transcription factor that activates NF-kappaB target genes through formation of heterocomplexes with p50 or p52. BCL-3 is phosphorylated in vivo, but specific BCL-3 ... [more ▼]

The oncoprotein BCL-3 is a nuclear transcription factor that activates NF-kappaB target genes through formation of heterocomplexes with p50 or p52. BCL-3 is phosphorylated in vivo, but specific BCL-3 kinases have not been identified so far. In this report, we show that BCL-3 is a substrate for the protein kinase GSK3 and that GSK3-mediated BCL-3 phosphorylation, which is inhibited by Akt activation, targets its degradation through the proteasome pathway. This phosphorylation modulates its association with HDAC1, -3, and -6 and attenuates its oncogenicity by selectively controlling the expression of a subset of newly identified target genes such as SLPI and CxcI1. Our results therefore suggest that constitutive BCL-3 phosphorylation by GSK3 regulates BCL-3 turnover and transcriptional activity. [less ▲]

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See detailEnzymatic activity associated with class II HDACs is dependent on a multiprotein complex containing HDAC3 and SMRT/N-CoR.
Fischle, Wolfgang; Dequiedt, Franck ULg; Hendzel, Michael J et al

in Molecular Cell (2002), 9(1), 45-57

Histone deacetylases (HDACs) play a key role in regulating eukaryotic gene expression. The HDAC domain, homologous to the yeast repressors RPD3 and HDA1, is considered necessary and sufficient for ... [more ▼]

Histone deacetylases (HDACs) play a key role in regulating eukaryotic gene expression. The HDAC domain, homologous to the yeast repressors RPD3 and HDA1, is considered necessary and sufficient for enzymatic activity. Here, we show that the catalytic domain of HDAC4 interacts with HDAC3 via the transcriptional corepressor N-CoR/SMRT. All experimental conditions leading to the suppression of HDAC4 binding to SMRT/N-CoR and to HDAC3 result in the loss of enzymatic activity associated with HDAC4. In vitro reconstitution experiments indicate that HDAC4 and other class II HDACs are inactive in the context of the SMRT/N-CoR-HDAC3 complex and do not contribute to its enzymatic activity. These observations indicate that class II HDACs regulate transcription by bridging the enzymatically active SMRT/N-CoR-HDAC3 complex and select transcription factors independently of any intrinsic HDAC activity. [less ▲]

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