Hitoshi Okazawa

A novel octamer binding transcription factor is differentially expressed in mouse embryonic cells

We have identified a novel octamer binding factor (Oct-3) in P19 embryonal carcinoma cells. Oct-3, which recognizes the typical octamer motif (ATTTGCAT) as well as the AT-rich sequence TTAAAATTCA, is present in P19 stem cells but disappears when the cells are induced to differentiate by retinoic acid (RA). Cloned cDNA corresponding to Oct-3 encodes a protein of 377 amino acids. Oct-3 has a conserved POU domain, but the remaining part is distinct from other POU domain-containing proteins such as Oct-1 and Oct-2. mRNA of 1.5 kb coding for Oct-3 is abundant in P19 stem cells but is dramatically repressed during RA-induced differentiation. Repression of the 1.5 kb mRNA is rapid and specific to RA. In mouse, oct-3 mRNA is undetectable in all the adult organs examined. The N-terminal proline-rich region of Oct-3, when fused to the DNA binding domain of c-Jun, functions as a transcriptional activating domain. We suggest that Oct-3 is a novel octamer binding transcription factor that is developmentally regulated during mouse embryogenesis.

Interaction between Mutant Ataxin-1 and PQBP-1 Affects Transcription and Cell Death

PQBP-1 was isolated on the basis of its interaction with polyglutamine tracts. In this study, using in vitro and in vivo assays, we show that the association between ataxin-1 and PQBP-1 is positively influenced by expanded polyglutamine sequences. In cell lines, interaction between the two molecules induces apoptotic cell death. As a possible mechanism underlying this phenomenon, we found that mutant ataxin-1 enhances binding of PQBP-1 to the C-terminal domain of RNA polymerase II large subunit (Pol II). This reduces the level of phosphorylated Pol II and transcription. Our results suggest the involvement of PQBP-1 in the pathology of spinocerebellar ataxia type 1 (SCA1) and support the idea that modified transcription underlies polyglutamine-mediated pathology.

The oct3 gene, a gene for an embryonic transcription factor, is controlled by a retinoic acid repressible enhancer.

Oct3 is an embryonic octamer‐binding transcription factor, whose expression is rapidly repressed by retinoic acid (RA). In this report, we have determined the transcriptional control region of the oct3 gene and studied the mechanism of the RA‐mediated repression. The chromosomal oct3 gene consists of five exons. Three subdomains of the POU region and transactivating domain are located in separate exons. Transcription initiates at multiple sites in the GC‐rich region lacking a typical TATA box. The upstream 2 kb region can confer the cell type‐specific expression and RA‐mediated repression. Analysis of the upstream region by deletion mutagenesis locates a cis element (RARE1) which functions as a stem cell‐specific, yet RA‐repressible, enhancer. Footprint and gel‐retardation assays show that RARE1 is composed of two domains, each of which is recognized by distinct factors. Microinjection of oct3‐lacZ constructs into fertilized eggs indicates that RARE1 can function in early embryos. We suggest that RARE1 is a critical cis element for oct3 gene expression in embryonic stem cells and for the RA‐mediated repression.

Cystathionine β-synthase, a key enzyme for homocysteine metabolism, is preferentially expressed in the radial glia/astrocyte lineage of developing mouse CNS

Cystathionine β‐synthase (CBS; EC 4.2.1.22) is a key enzyme in the generation of cysteine from methionine. A deficiency of CBS leads to homocystinuria, an inherited human disease characterized by mental retardation, seizures, psychiatric disturbances, skeletal abnormalities, and vascular disorders; however, the underlying mechanisms remain largely unknown. Here, we show the regional and cellular distribution of CBS in the adult and developing mouse brain. In the adult mouse brain, CBS was expressed ubiquitously, but it is expressed most intensely in the cerebellar molecular layer and hippocampal dentate gyrus. Immunohistochemical analysis revealed that CBS is preferentially expressed in cerebellar Bergmann glia and in astrocytes throughout the brain. At early developmental stages, CBS was expressed in neuroepithelial cells in the ventricular zone, but its expression changed to radial glial cells and then to astrocytes during the late embryonic and neonatal periods. CBS was most highly expressed in juvenile brain, and a striking induction was observed in cultured astrocytes in response to EGF, TGF‐α, cAMP, and dexamethasone. Moreover, CBS was significantly accumulated in reactive astrocytes in the hippocampus after kainic acid‐induced seizures, and cerebellar morphological abnormalities were observed in CBS‐deficient mice. Taken together, these results suggest that CBS plays a crucial role in the development and maintenance of the CNS and that radial glia/astrocyte dysfunction might be involved in the complex neuropathological features associated with abnormal homocysteine metabolism.

JNK activation is associated with intracellular β-amyloid accumulation

Abstract c-Jun has been implicated in the pathogenesis of Alzheimer’s disease (AD), but the upstream cascade leading to c-Jun activation in AD is not known. Activation of c-Jun N-terminal kinase (JNK) is obviously a candidate for the upstream event. We tested this possibility focusing on PS1-linked AD. First, we observed that JNK is actually activated in cerebral neurons of PS1-linked AD patients, using immunohistochemistry and Western blot analyses with anti-activated JNK antibodies. We analyzed the relationship between β-amyloid (βA) and JNK activation by using aged transgenic mice overexpressing mutant (M146L) PS1 and human AD brains. The mice showed no neuronal loss but a very few diffuse βA deposits, corresponding to the early stage of PS1-linked AD brain. Some neurons were reactive for anti-βA antibodies in the cerebral cortex. Interestingly, JNK activation was observed in neurons showing intracellular βA immunoreactivity in transgenic mice. Association between intracellular βA and JNK activation was confirmed in cortical neurons of sporadic and PS1-linked AD patients. Furthermore, introduction of βA peptides into the primary culture cortical neurons induced JNK activation and cell death. Collectively, these results suggested that intracellular βA accumulation might trigger JNK activation leading to neuronal death.

Dopaminergic stimulation up-regulates the in vivo expression of brain-derived neurotrophic factor (BDNF) in the striatum

We investigated the effect of dopamine on the in vivo expression of brain‐derived neurotrophic factor (BDNF) in the striatum of mouse. BDNF mRNA expression in the striation, which was Quantified with the reverse transcriptase polymerase chain reaction, was up‐repulated from 2 h after oral administration of levodopa, a precursor of dopamine. The increase was sustained for 16 h. Co‐administrstion of haloperidol partially inhibited dopamine‐induced BDNF enhancement. These data suggest that dopaminergic stimulation directly promotes the expression of BDNF in the striatum in vivo.

Mutant Huntingtin Promotes the Fibrillogenesis of Wild-type Huntingtin A POTENTIAL MECHANISM FOR LOSS OF HUNTINGTIN FUNCTION IN HUNTINGTON'S DISEASE

Aggregation of huntingtin (htt) in neuronal inclusions is associated with the development of Huntingtons disease (HD). Previously, we have shown that mutant htt fragments with polyglutamine (polyQ) tracts in the pathological range (>37 glutamines) form SDS-resistant aggregates with a fibrillar morphology, whereas wild-type htt fragments with normal polyQ domains do not aggregate. In this study we have investigated the co-aggregation of mutant and wild-type htt fragments. We found that mutant htt promotes the aggregation of wild-type htt, causing the formation of SDS-resistant co-aggregates with a fibrillar morphology. Conversely, mutant htt does not promote the fibrillogenesis of the polyQ-containing protein NOCT3 or the polyQ-binding protein PQBP1, although these proteins are recruited into inclusions containing mutant htt aggregates in mammalian cells. The formation of mixed htt fibrils is a highly selective process that not only depends on polyQ tract length but also on the surrounding amino acid sequence. Our data suggest that mutant and wild-type htt fragments may also co-aggregate in neurons of HD patients and that a loss of wild-type htt function may contribute to HD pathogenesis.

Polyglutamine diseases: a transcription disorder?

AbstractVarious molecular processes including unfolded protein response, protein transport, synaptic transmission and transcription are implicated in the pathology of polyglutamine diseases caused by the expanded polyglutamine-containing proteins. More than 20 transcription-related factors have been reported to interact with disease proteins, and the pathological interaction is known to repress gene expression. The whole shape of nuclear events evoked by disease proteins is now emerging with information on these transcription-related factors and with findings on the similarity between nuclear bodies and pathological inclusion bodies. This article reviews ‘transcription theory’, a rapidly growing hypothesis in polyglutamine diseases.

Enhanced SUMOylation in polyglutamine diseases

Small ubiquitin-like modifiers (SUMOs) are proteins homologous to ubiquitin that possibly regulate intranuclear protein localization, nuclear transport, and ubiquitination. We examined patients of DRPLA, SCA1, MJD, and Huntingtons disease and found that neurons in affected regions of the brain react strongly to SUMO-1, a family member of SUMOs. Western blot with a transgenic mouse expressing mutant ataxin-1 showed the increase of SUMOylated proteins in the cerebellar cortex, which we named ESCA1 and ESCA2. These results indicated activation of SUMO-1 system in polyglutamine diseases and predicted its involvement in the pathology.

Proteome analysis of soluble nuclear proteins reveals that HMGB1/2 suppress genotoxic stress in polyglutamine diseases

Nuclear dysfunction is a key feature of the pathology of polyglutamine (polyQ) diseases. It has been suggested that mutant polyQ proteins impair functions of nuclear factors by interacting with them directly in the nucleus. However, a systematic analysis of quantitative changes in soluble nuclear proteins in neurons expressing mutant polyQ proteins has not been performed. Here, we perform a proteome analysis of soluble nuclear proteins prepared from neurons expressing huntingtin (Htt) or ataxin-1 (AT1) protein, and show that mutant AT1 and Htt similarly reduce the concentration of soluble high mobility group B1/2 (HMGB1/2) proteins. Immunoprecipitation and pulldown assays indicate that HMGBs interact with mutant AT1 and Htt. Immunohistochemistry showed that these proteins were reduced in the nuclear region outside of inclusion bodies in affected neurons. Compensatory expression of HMGBs ameliorated polyQ-induced pathology in primary neurons and in Drosophila polyQ models. Furthermore, HMGBs repressed genotoxic stress signals induced by mutant Htt or transcriptional repression. Thus, HMGBs may be critical regulators of polyQ disease pathology and could be targets for therapy development.