Biomedical subjects

Axel Behrens

Publications and source records attributed to Axel Behrens.

15 recordsLinked to original sources

PubMed2006

Role of the AP-1 transcription factor c-Jun in developing, adult and injured brain.

The transcription factor activator protein-1 (AP-1) consists of a variety of dimers composed of members of the Jun and Fos families of proteins. However, it is the up-regulation of c-jun that is a particularly common event in the developing, adult as well as in injured nervous system that serves as a model of transcriptional control of brain function. In view of the long list of excellent in depth overviews on the different members of the Jun family and associated molecules, the primary focus of the current paper is to focus on c-Jun specifically and discuss the evidence on the involvement of this transcription factor in ischaemia and stroke, in seizures, during learning and memory, or following axonal injury and during successful regeneration. Functional studies employing in vivo strategies using gene deletion, targeted expression of dominant negative isoforms and pharmacological inhibitors all suggest a bipotential role of c-Jun, in mediating neurodegeneration and cell death, as well as in plasticity and repair. Phosphorylation of c-Jun, and the activation of its upstream kinases (Jun N-terminal Kinase (JNK) 1-3, JNK kinases (JNKK)) is required in many but not in all forms of these events, with only a partial overlap of the Jun-, JNK- or JNKK(n)-dependent functions. Moreover, a better understanding of the non-overlapping roles could considerably increase the potential of pharmacological agents to improve neurological outcome following trauma, neonatal encephalopathy and stroke, or neurodegenerative disease.

Animals↗

PubMed2005

Synthesis and characterization of molybdenum oxo complexes of two tripodal ligands: reactivity studies of a functional model for molybdenum oxotransferases.

Reaction of the tetradentate ligand N-(2-hydroxybenzyl)-N,N-bis(2-pyridylmethyl)amine (L-OH) with MoO2Cl2 in methanol in the presence of NaOMe and PF6- results in the formation of [MoO2(L-O)]PF6. Similarly, the reaction of N-(2-mercaptobenzyl)-N,N-bis(2-pyridylmethyl)amine (L-SH) with MoO2(acac)2 leads to the formation of [MoO2(L-S)]+. The dioxo-molybdenum complex [MoO2(L-O)]+ reacts with phosphines in methanol to afford phosphine oxides and an air-sensitive molybdenum complex, tentatively identified as [Mo(IV)O(L-O)(OCH3)]. The latter complex is capable of reducing biological oxygen donors such as DMSO or nitrate, thereby mimicking the activity of DMSO reductase and nitrate reductase. Reaction of [MoO2(L-O)]PF6 with PPh3 in other solvents than methanol leads to the formation of the Mo(V) dimer [(L-O)OMo(micro-O)MoO(L-O)](PF6)2. The crystal structures of [MoO2(L-O)]PF6 and the micro-oxo bridged dimer are presented.

Crystallography, X-Ray↗

PubMed2005

Interaction of phosphorylated c-Jun with TCF4 regulates intestinal cancer development.

The proto-oncoprotein c-Jun is a component of the AP-1 transcription factor, the activity of which is augmented in many tumour types. An important mechanism in the stimulation of AP-1 function is amino-terminal phosphorylation of c-Jun by the c-Jun N-terminal kinases (JNKs). Phosphorylated c-Jun is biologically more active, partially because it acquires the ability to interact with binding partners. Here we show that phosphorylated c-Jun interacts with the HMG-box transcription factor TCF4 to form a ternary complex containing c-Jun, TCF4 and beta-catenin. Chromatin immunoprecipitation assays revealed JNK-dependent c-Jun-TCF4 interaction on the c-jun promoter, and c-Jun and TCF4 cooperatively activated the c-jun promoter in reporter assays in a beta-catenin-dependent manner. In the Apc(Min) mouse model of intestinal cancer, genetic abrogation of c-Jun N-terminal phosphorylation or gut-specific conditional c-jun inactivation reduced tumour number and size and prolonged lifespan. Therefore, the phosphorylation-dependent interaction between c-Jun and TCF4 regulates intestinal tumorigenesis by integrating JNK and APC/beta-catenin, two distinct pathways activated by WNT signalling.

Adenomatous Polyposis Coli Protein↗

PubMed2005

Specific pathophysiological functions of JNK isoforms in the brain.

We have investigated the effect of JNK1 ko, JNK2 ko, JNK3 ko, JNK2+3 ko and c-JunAA mutation on neuronal survival in adult transgenic mice following ischemia, 6-hydroxydopamine induced neurotoxicity, axon transection and kainic acid induced excitotoxicity. Deletion of JNK isoforms indicated the compartment-specific expression of JNK isoforms with 46-kDa JNK1 as the main phosphorylated JNK isoform. Permanent occlusion of the MCA significantly enlarged the infarct area in JNK1 ko, which showed an increased expression of JNK3 in the penumbra. Survival of dopaminergic neurons in the substantia nigra compacta (SNC) following intrastriatal injection of 6-hydroxydopamine was transiently improved in JNK3 ko and c-JunAA mice after 7 days, but not 60 days. Following transection of the medial forebrain bundle, however, JNK3 ko conferred persisting neuroprotection of axotomised SNC neurons. None of the JNK ko and c-JunAA mutation affected the survival of facial motoneurons following peripheral axotomy when investigated after 90 days. Finally, we determined the impact of JNK ko on the survival of animals and the degeneration of hippocampal neurons following kainic acid. JNK3 ko mice were substantially resistant against and survived kainic acid-induced seizures. JNK3 ko and JNK1 ko showed a nonsignificant tendency for decreased or increased death of hippocampal neurons, respectively. Surprisingly, the deletion of a single JNK isoform did not attenuate the immunocytochemical signal of phosphorylated c-Jun irrespective on the experimental set-up. This comprehensive study provides novel insights into the context-dependent physiological and pathological functions of JNK isoforms.

Animals↗

PubMed2004

The AP-1 transcription factor c-Jun is required for efficient axonal regeneration.

Nerve injury triggers numerous changes in the injured neurons and surrounding nonneuronal cells that ultimately result in successful target reinnervation or cell death. c-Jun is a component of the heterodimeric AP-1 transcription factor, and c-Jun is highly expressed in response to neuronal trauma. Here we have investigated the role of c-jun during axonal regeneration using mice lacking c-jun in the central nervous system. After transection of the facial nerve, the absence of c-Jun caused severe defects in several aspects of the axonal response, including perineuronal sprouting, lymphocyte recruitment, and microglial activation. c-Jun-deficient motorneurons were atrophic, resistant to axotomy-induced cell death, and showed reduced target muscle reinnervation. Expression of CD44, galanin, and alpha7beta1 integrin, molecules known to be involved in regeneration, was greatly impaired, suggesting a mechanism for c-Jun-mediated axonal growth. Taken together, our results identify c-Jun as an important regulator of axonal regeneration in the injured central nervous system.

Animals↗

PubMed2004

Tri- and pentanuclear tungsten-(mu-S)-M clusters (M = W, Cu, Ag).

The thiotungstate [Et4N]2[OW(WS4)2], [Et4N]2.1, containing the linear [[S2W(VI)(mu-S)2]2W(IV)=O] core, was prepared from [Et4N]2[WS4] in the presence of the sulfide scavenger Cd2+. Addition of 1,2-bis(o-diphenylphosphinophenyl)ethane (diphosphine) and Cu+ or Ag+ to solutions of 1 in MeCN/DMF led to coordination of the (diphosphine)Cu/Ag fragments to the terminal sulfido ligands of 1, yielding novel linear pentanuclear, heterometallic clusters [mu-[OW(IV)(DMF)(W(VI)S4)2][M(diphosphine)]2], 2 (M = Cu) and 3 (M = Ag). Along with 2, the trinuclear cluster [[mu-(W(VI)S4)[Cu(diphosphine)(2)]], 4, was also obtained. The molecular and crystal structures of [Et4N]2.1, 2.MeCN, 3.MeCN, and 4.2MeCN.CH2Cl2 have been determined.

Journal Article↗

PubMed2004

Disruption of Doppel prevents neurodegeneration in mice with extensive Prnp deletions.

The Prnp gene encodes the cellular prion protein PrP(C). Removal of its ORF does not result in pathological phenotypes, but deletions extending into the upstream intron result in cerebellar degeneration, possibly because of ectopic cis-activation of the Prnd locus that encodes the PrP(C) homologue Doppel (Dpl). To test this hypothesis, we removed Prnd from Prnp(o/o) mice by transallelic meiotic recombination. Balanced loxP-mediated ablation yielded mice lacking both PrP(C) and Dpl (Prn(o/o)), which developed normally and showed unimpaired immune functions but suffered from male infertility. However, removal of the Prnd locus abolished cerebellar degeneration, proving that this phenotype is caused by Dpl upregulation. The absence of compound pathological phenotypes in Prn(o/o) mice suggests the existence of alternative compensatory mechanisms. Alternatively, Dpl and PrP(C) may exert distinct functions despite having partly overlapping expression profiles.

Amyloid↗

PubMed2004

The ubiquitin ligase SCFFbw7 antagonizes apoptotic JNK signaling.

Jun N-terminal kinases (JNKs) are essential for neuronal microtubule assembly and apoptosis. Phosphorylation of the activating protein 1 (AP1) transcription factor c-Jun, at multiple sites within its transactivation domain, is required for JNK-induced neurotoxicity. We report that in neurons the stability of c-Jun is regulated by the E3 ligase SCF(Fbw7), which ubiquitinates phosphorylated c-Jun and facilitates c-Jun degradation. Fbw7 depletion resulted in accumulation of phosphorylated c-Jun, stimulation of AP1 activity, and neuronal apoptosis. SCF(Fbw7) therefore antagonizes the apoptotic c-Jun-dependent effector arm of JNK signaling, allowing neurons to tolerate potentially neurotoxic JNK activity.

Amino Acid Sequence↗

PubMed2003

Formation, preservation, and cleavage of the disulfide bond by vanadium.

Reaction of the disulfide [HpicanS](2) (HpicanS is the carboxamide based on picolinate (pic) and o-mercaptoaniline (anS); the [] brackets are used to denote disulfides) with [VOCl(2)(thf)(2)] leads to reductive scission of the disulfide bond and formation of the mixed-valence (V(IV)/V(V)) complex anion [(OVpicanS)(2)mu-O](-) (1), with the dianionic ligand coordinating through the pyridine-N atom, the deprotonated amide-N atom, and thiophenolate-S atom. Reductive cleavage of the SbondS bond is also observed as [VCl(2)(tmeda)(2)] (tmeda=tetramethylethylenediamine) is treated with the disulfides [HsalanS](2) or [HvananS](2) (HsalanS and HvananS are the Schiff bases formed between o-mercaptoaniline and salicylaldehyde (Hsal) or vanillin (Hvan), respectively), yielding the V(III) complexes [VCl(tmeda)(salanS)] (2 a), or [VCl(tmeda)(vananS)] (2 b). The disulfide bond remains intact in the aerial reaction between [HsalanS](2) and [VCl(3)(thf)(3)] to yield the V(V) complex [VOCl[salanS](2)] (3), where (salanS)(2-) coordinates through the two phenolate and one of the imine functions. The S-S bond is also preserved as [VO(van)(2)] or [VO(nap)(2)] (Hnap=2-hydroxynaphthalene-1-carbaldehyde) is treated with bis(2-aminophenyl)disulfide, [anS](2), a reaction which is accompanied by condensation of the aldehyde and the diamine, and complexation of the resulting bis(Schiff bases) [HvananS](2) or [HnapanS](2) to form the complexes [VO[vananS](2)] (4 a) or [VO[napanS](2)] (4 b). In 4 a and 4 b, the phenolate and imine functions, and presumably also one of the disulfide-S atoms, coordinate to V(IV). 2-Mercaptophenyl-2'-pyridinecarboxamide (H(2)picanS) retains its identity in the presence of V(III); reaction between [VCl(3)(thf)(3)] and H(2)picanS yields [V[picanS](2)](-) (5). The dithiophenolate 2,6-bis(mercaptophenylthio)dimethylpyridine (6 a) is oxidized, mediated by VO(2+), to the bis(disulfide) octathiadiaza-cyclo-hexaeicosane 6 b. The relevance of these reactions for the speciation of vanadium under physiological conditions is addressed. [HNEt(3)]-1.0.5 NEt(3,) 3.3 CH(2)Cl(2), [HsalanS](2), [HNEt(3)]-5, and 6 b.4 THF have been characterized by X-ray diffraction analysis.

Crystallography, X-Ray↗

PubMed2003

Physiological and pathological functions of the prion protein homologue Dpl.

A misfolded version of the prion protein PrP(C), known as PrP(Sc), is the major component of scrapie infectivity, the pathological agent in transmissible spongiform encephalopathies. The Prnp gene that encodes the cellular PrP(C) protein was cloned almost 20 years ago, but remained without sequence or structural relatives for over a decade. Only recently a novel protein, named Doppel (Dpl), was identified, which shares significant biochemical and structural homology with PrP(C). When overexpressed, Dpl is neurotoxic and causes a neurological disease. Strikingly, Dpl neurotoxicity is counteracted and prevented by PrP(C). In contrast to its homologue PrP(C), Dpl is dispensable for prion disease progression and for the generation of PrP(Sc), but Dpl appears to have an essential function in male spermatogenesis. Although Dpl research is still in its infancy, the discovery of Dpl has already solved some enigmas of prion biology and an understanding of its physiological function is emerging.

Animals↗

PubMed2003

Impaired intervertebral disc formation in the absence of Jun.

Jun is a major component of the heterodimeric transcription factor AP-1 and is essential for embryonic development, as foetuses that lack Jun die at mid-gestation. Ubiquitous mosaic inactivation of a conditional Jun allele by cre/LoxP-mediated recombination was used to screen for novel functions of Jun and revealed that its absence results in severe malformations of the axial skeleton. More-specific Jun deletion by collagen2a1-cre demonstrated the essential function of Jun in the notochord and sclerotome. Mutant notochordal cells showed increased apoptosis, resulting in hypocellularity of the intervertebral discs. Subsequently, fusion of vertebral bodies caused a scoliosis of the axial skeleton. Thus, Jun is required for axial skeletogenesis by regulating notochord survival and intervertebral disc formation.

Animals↗

PubMed2002

Absence of the prion protein homologue Doppel causes male sterility.

The agent that causes prion diseases is thought to be identical with PrP(Sc), a conformer of the normal prion protein PrP(C). PrP(C)-deficient mice do not exhibit major pathologies, perhaps because they express a protein termed Dpl, which shares significant biochemical and structural homology with PrP(C). To investigate the physiological function of Dpl, we generated mice harbouring a homozygous disruption of the Prnd gene that encodes Dpl. Dpl deficiency did not interfere with embryonic and postnatal development, but resulted in male sterility. Dpl protein was expressed at late stages of spermiogenesis, and spermatids of Dpl mutants were reduced in numbers, immobile, malformed and unable to fertilize oocytes in vitro. Mechanical dissection of the zona pellucida partially restored in vitro fertilization. We conclude that Dpl regulates male fertility by controlling several aspects of male gametogenesis and sperm-egg interaction.

Animals↗

PubMed2002

Impaired postnatal hepatocyte proliferation and liver regeneration in mice lacking c-jun in the liver.

Mice lacking the AP-1 transcription factor c-jun die at mid-gestation showing heart defects and impaired hepatogenesis. To inactivate c-jun in hepatocytes, mice carrying a floxed c-jun allele were generated. Perinatal liver-specific c-jun deletion caused reduced hepatocyte proliferation and decreased body size. After partial hepatectomy, half of the mutants died and liver regeneration was impaired. This phenotype was not present in mice lacking the N-terminal phosphorylation sites of c-Jun. The failure to regenerate was accompanied by increased cell death and lipid accumulation in hepatocytes. Moreover, cyclin-dependent kinases and several cell cycle regulators were affected, resulting in inefficient G(1)-S phase progression. These studies identify c-Jun as a critical regulator of hepatocyte proliferation and survival during liver development and regeneration.

Animals↗

PubMed2002

JunB can substitute for Jun in mouse development and cell proliferation.

The Jun and JunB components of the AP-1 transcription factor are known to have antagonistic functions. Here we show, by a knock-in strategy and a transgenic complementation approach, that Junb can substitute for absence of Jun during mouse development. Junb can rescue both liver and cardiac defects in Jun-null mice in a manner dependent on gene dosage. JunB restores the expression of genes regulated by Jun/Fos, but not those regulated by Jun/ATF, thereby rescuing Jun-dependent defects in vivo as well as in primary fibroblasts and fetal hepatoblasts in vitro. Thus, the transcriptionally less active JunB has the potential to substitute for Jun, indicating that the spatial and temporal regulation of expression of the transcription factor AP-1 may be more important than the coding sequence of its components.

Animals↗

PubMed2002

Small is not beautiful: antagonizing functions for the prion protein PrP(C) and its homologue Dpl.

A conformational variant of the normal prion protein PrP(C) is believed to be identical to PrP(Sc), the agent that causes prion diseases. Recently, a novel protein, named Doppel (Dpl), was identified that shares significant biochemical and structural homology with PrP(C). In specific strains of PrP(C)-deficient mouse lines, Dpl is overexpressed and causes a neurological disease. Dpl neurotoxicity is counteracted and prevented by PrP(C), but the mechanism of antagonistic PrP(C)-Dpl interaction remains elusive. In contrast to its homologue PrP(C), initial studies suggest that Dpl is dispensable for prion disease progression and for the generation of PrP(Sc). Although we are only beginning to understand its function, the discovery of Dpl has already provided some answers to long-standing questions and is transforming our understanding of prion biology.

Animals↗