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ABSTRACT: Gene expression changes during cell differentiation are thought to be coordinated by histone modifications, but still little is known about the role of specific histone deacetylases (HDACs) in cell fate decisions in vivo. Here we demonstrate that the catalytic function of HDAC2 is required in adult, but not embryonic neurogenesis. While brain development and adult stem cell fate were normal upon conditional deletion of HDAC2 or in mice lacking the catalytic activity of HDAC2, neurons derived from both zones of adult neurogenesis die at a specific maturation stage. This phenotype is correlated with an increase in proliferation and the aberrant maintenance of proteins normally expressed only in progenitors, such as Sox2, also into some differentiating neurons, suggesting that HDAC2 is critically required to silence progenitor transcripts during neuronal differentiation of adult generated neurons. This cell-autonomous function of HDAC2 exclusively in adult neurogenesis reveals clear differences in the molecular mechanisms regulating neurogenesis during development and in adulthood.
Neuron Glia Biology 04/2010; 6(2):93-107. · 1.34 Impact Factor
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Hans Zischka,
Nathanael Larochette,
Florian Hoffmann,
Daniela Hamöller,
Nora Jägemann,
Josef Lichtmannegger,
Luise Jennen,
Josef Müller-Höcker,
Frigga Roggel, Martin Göttlicher,
Angelika M Vollmar,
Guido Kroemer
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ABSTRACT: A pathological increase of the permeability of the mitochondrial membranes may culminate in the irreversible rupture of the mitochondrial outer membrane. Such a permeability transition is lethal because it results in the release of death-inducing molecules from mitochondria and/or metabolic failure. Current methods to assess this outer membrane damage are mostly indirect or scarcely representative of the overall mitochondrial population. Here we present an analytical and preparative approach using free flow electrophoresis to directly distinguish rat liver mitochondria that have undergone the permeability transition from unaffected organelles or from organelles that are damaged to a minor degree. Mitochondrial populations, which considerably differ in outer membrane integrity or cytochrome c content, were separated by this means. We further show that the relative abundance of each population depends on the dose of the permeability transition inducer and the duration of the treatment time. Finally, we have employed this approach to investigate the impairment of mitochondria that were isolated from livers subjected to ischemia/reperfusion damage.
Analytical Chemistry 08/2008; 80(13):5051-8. · 5.86 Impact Factor
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ABSTRACT: This protocol describes the purification of mitochondria from rat liver with the aid of zone electrophoresis in a free flow device (ZE-FFE). Starting from liver homogenate, cell debris and nuclei are removed by low speed centrifugation. A crude mitochondrial fraction is obtained by medium speed centrifugation and is further purified by washing followed by a Nycodenz gradient centrifugation. Lysosomes and microsomes are located at the upper parts of the gradient, whereas mitochondria are found in the medium part of the gradient. A subsequent purification step with ZE-FFE efficiently removes remaining lysosomes and microsomes and, importantly, damaged mitochondrial structures. The resulting purified mitochondria can be concentrated by centrifugation and used for further experiments. Finally, possible modifications of this protocol with respect to the isolation of pure lysosomes are discussed.
Methods in molecular biology (Clifton, N.J.) 02/2008; 424:333-48.
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ABSTRACT: Histone deacetylases (HDAC) reverse the acetylation of histone and nonhistone proteins and thereby modulate chromatin structure and function of nonhistone proteins. Many tumor cell lines and experimental tumors respond to HDAC inhibition. To assess the role of an individual HDAC isoenzyme in physiology and tumor development, HDAC2-mutant mice were generated from a gene trap embryonic stem cell clone. These mice express a catalytically inactive fusion protein of the NH(2)-terminal part of HDAC2 and beta-galactosidase, which fails to integrate into corepressor complexes with mSin3B. They are the first class 1 HDAC mutant mice that are viable although they are approximately 25% smaller than their littermates. Cell number and thickness of intestinal mucosa are reduced. Mutant embryonic fibroblasts fail to respond to insulin-like growth factor I (IGF) by the IGF-I-induced increase in cell number observed in wild-type cells. These data suggest a novel link between HDACs and IGF-I-dependent responses. Crossing of HDAC2-mutant with tumor-prone APC(min) mice revealed tumor rates that are lower in HDAC2-deficient mice by 10% to 100% depending on segment of the gut and sex of the mice. These mice provide evidence that the key functions of HDAC2, although not essential for survival of the organism, play a rate-limiting role for tumor development in vivo.
Cancer Research 11/2007; 67(19):9047-54. · 7.86 Impact Factor
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ABSTRACT: The aryl hydrocarbon receptor (AhR) has a fundamental role during postnatal liver development and is essential for mediating dioxin toxicity. However, the genetic programs mediating, both, the toxic and physiological effects downstream of the transcription factor AhR are in major parts unknown. We have identified the proto-oncogene c-jun as a novel target gene of AhR. Induction of c-jun depends on activation of p38-mitogen-activated protein kinase (MAPK) by an AhR-dependent mechanism. None of the kinases that are known to phosphorylate p38-MAPK is activated by AhR. Neither the dephosphorylation rate of p38-MAPK is reduced. Furthermore, increased p38-MAPK phosphorylation in response to dioxins does not require ongoing transcription. These findings establish activating 'cross-talk' with MAPK signaling as a novel principle of AhR action, which is apparently independent of the AhR's function as a DNA-binding transcriptional activator.
Oncogene 08/2005; 24(31):4975-83. · 6.37 Impact Factor
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ABSTRACT: Glucocorticoid receptor (GR)-mediated transrepression of the transcription factors AP-1 and NF-kappaB, responsible for most of the anti-inflammatory effects of glucocorticoids, is initiated by the tethering of GR to the promoters of target genes. We report that this tethering is mediated by a nuclear isoform of the focal adhesion LIM domain protein Trip6. Trip6 functions as a coactivator for both AP-1 and NF-kappaB. As shown by chromatin immunoprecipitation, Trip6 is recruited to the promoters of target genes together with AP-1 or NF-kappaB. In the presence of glucocorticoids, GR joins the Trip6 complex. Reducing the level of Trip6 by RNA interference or abolishing its interaction with GR by dominant-negative mutation eliminates transrepression. We propose that GR tethering to the target promoter through Trip6 forms the basis of transrepression, and that Trip6 exerts its nuclear functions by acting as a molecular platform, enabling target promoters to integrate activating or repressing signals.
Genes & Development 11/2004; 18(20):2518-28. · 11.66 Impact Factor
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ABSTRACT: Inappropriate control of expression of genetic information is the cause of many forms of cancer. Aberrant transcriptional repression by recruitment of histone deacetylases (HDACs) is a key step in pathogenesis of myeloid leukemia. We recently reported that development of colonic cancer involves alterations in the transcriptional repression machinery by increased expression of HDAC2 upon loss of the APC tumor suppressor. Increased expression of HDAC2 is essential for prevention of apoptosis of HT-29 colonic cancer cells. We now discuss whether HDAC2 also plays a role for aberrant cell cycle regulation and expression of the p21(Cip/Waf) cell cycle inhibitor. Whereas inhibition of HDACs by valproic acid or trichostatin A increases p21 expression, selective interference with HDAC2 by siRNA transfection or reconstitution of wildtype APC does not affect p21 expression. Likewise, treatment of HT-29 cells with the HDAC inhibitor valproic acid leads to a moderate inhibition of cell cycle progression in the G1 phase whereas interference with HDAC2 expression does not. Thus, HDAC2 appears to serve a preferential role in the prevention of apoptosis and not in cell cycle control similar to the specific importance of HDAC1 for cell cycle regulation or HDAC 9 for the stress response of the heart.
Cell cycle (Georgetown, Tex.) 11/2004; 3(10):1240-2. · 5.36 Impact Factor
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ABSTRACT: Inappropriate transcriptional repression involving histone deacetylases (HDACs) is a prominent cause for the development of leukemia. We now identify faulty expression of a specific mediator of transcriptional repression in a solid tumor. Loss of the adenomatosis polyposis coli (APC) tumor suppressor induces HDAC2 expression depending on the Wnt pathway and c-Myc. Increased HDAC2 expression is found in the majority of human colon cancer explants, as well as in intestinal mucosa and polyps of APC-deficient mice. HDAC2 is required for, and sufficient on its own to prevent, apoptosis of colonic cancer cells. Interference with HDAC2 by valproic acid largely diminishes adenoma formation in APC(min) mice. These findings point toward HDAC2 as a particularly relevant potential target in cancer therapy.
Cancer Cell 06/2004; 5(5):455-63. · 26.57 Impact Factor
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Oliver H Krämer,
Ping Zhu,
Heather P Ostendorff,
Martin Golebiewski,
Jens Tiefenbach,
Marvin A Peters,
Boris Brill,
Bernd Groner,
Ingolf Bach,
Thorsten Heinzel, Martin Göttlicher
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ABSTRACT: Histone-modifying enzymes play essential roles in physiological and aberrant gene regulation. Since histone deacetylases (HDACs) are promising targets of cancer therapy, it is important to understand the mechanisms of HDAC regulation. Selective modulators of HDAC isoenzymes could serve as efficient and well-tolerated drugs. We show that HDAC2 undergoes basal turnover by the ubiquitin-proteasome pathway. Valproic acid (VPA), in addition to selectively inhibiting the catalytic activity of class I HDACs, induces proteasomal degradation of HDAC2, in contrast to other inhibitors such as trichostatin A (TSA). Basal and VPA-induced HDAC2 turnover critically depend on the E2 ubiquitin conjugase Ubc8 and the E3 ubiquitin ligase RLIM. Ubc8 gene expression is induced by both VPA and TSA, whereas only TSA simultaneously reduces RLIM protein levels and therefore fails to induce HDAC2 degradation. Thus, poly-ubiquitination and proteasomal degradation provide an isoenzyme-selective mechanism for downregulation of HDAC2.
The EMBO Journal 08/2003; 22(13):3411-20. · 9.20 Impact Factor
