Biomedical subjects

Shizue Ohsawa

Publications and source records attributed to Shizue Ohsawa.

4 recordsLinked to original sources

PubMed2006

Caspase-mediated changes in Sir2alpha during apoptosis.

Silent information regulator 2 (Sir2) is an NAD(+)-dependent histone deacetylase that establishes repressive chromatin status and extends the life span of both budding yeast and the nematode worm Caenorhabditis elegans. There is growing evidence that its mammalian homologue Sir2alpha protects cells from stress-induced apoptosis. We report here that mammalian Sir2alpha was directly cleaved by both initiator and executioner caspases, and relocated from the nucleus to the cytoplasm in apoptotic cells. These alterations of Sir2alpha were largely inhibited by a caspase-9 dominant-negative mutant or Bcl-xL. Our results indicate that Sir2alpha undergoes dynamic changes in caspase-dependent manner during apoptosis.

Active Transport, Cell Nucleus↗

PubMed2005

Novel function of neuronal PAS domain protein 1 in erythropoietin expression in neuronal cells.

The basic helix loop helix-PAS (bHLH-PAS) transcription factors have diverse roles in physiologic responses to the environment and in early development. One bHLH-PAS protein, neuronal PAS domain protein 1 (NPAS1), is reported to be expressed only in the central nervous system beginning at the late embryonic stage, but its function is unknown. Using an anti-NPAS1 antibody, we have shown that NPAS1 expression in cerebral cortex was observed first around embryonic Day 16.5 (E16.5) and was then dispersed throughout the region as cortical development progressed. From the similarity with hypoxia-inducible factor-1alpha (HIF-1alpha), we investigated whether NPAS1 regulates transcription of erythropoietin (EPO), which is the target of HIF-1alpha and is expressed in the brain during the early developmental stage. In the present study, we have shown that NPAS1 binds to the enhancer region of Epo in vivo. A luciferase reporter assay revealed a repressive effect of NPAS1 on hypoxia-responsive element-regulated gene expression. These results raise the possibility that NPAS1 plays a role in late central nervous system development by modulating EPO expression in response to cellular oxygen level.

Animals↗

PubMed2004

A sulfatase regulating the migratory potency of oligodendrocyte progenitor cells through tyrosine phosphorylation of beta-catenin.

By using cDNA subtraction, we identified an extracellular sulfatase (RsulfFP1) from rat oligodendrocyte progenitor cells (OPCs) whose mRNA expression is down-regulated by tumor necrosis factor-alpha. RsulfFP1 mRNA was expressed specifically in the floor plate and the ventral portion of the rat spinal cord at E15. The expression pattern of RsulfFP1 overlapped with the OPCs, which are also located at the ventral region of the ventricular zone. After this stage, RsulfFP1 expression was attenuated, and the OPCs efficiently migrated throughout the spinal cord. The modification of CG-4 cells, a cell line established from rat O2A cells, by RsulfFP1 activated canonical Wnt signaling. Furthermore, the deletion of RsulfFP1 expression by an antisense oligonucleotide caused impairment of OPC migration in rat spinal cord slice culture. Modification of cells by RsulfFP1 resulted in the increased tyrosine phosphorylation of immunoprecipitated beta-catenin, suggesting that sulfation of the extracellular matrix induced by this sulfatase might be responsible for an increase in Wnt signaling that is involved in the migration of OPCs. Thus, the present study revealed that a sulfatase is responsible for the migration of OPCs and activates intracellular mechanisms that regulate migration.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗

PubMed2003

Heterodimers of bHLH-PAS protein fragments derived from AhR, AhRR, and Arnt prepared by co-expression in Escherichia coli: characterization of their DNA binding activity and preparation of a DNA complex.

AhR (aryl hydrocarbon receptor), AhRR (AhR repressor), and Arnt (AhR nuclear translocator) are members of the bHLH (basic-helix-loop-helix)-PAS (Per-AhR/Arnt-Sim homology sequence) transcription factor superfamily. They associate with each other to form heterodimers, AhR/Arnt or AhRR/Arnt, and bind the XRE (xenobiotic responsive element) sequences in the promoter regions of the target genes to regulate their expression. Their basic regions and HLH motifs mediate DNA binding activity and protein dimerization, respectively. The PAS domain includes two incomplete repeats, PAS-A and PAS-B, and is considered to determine the specificity on protein dimerization. However, the three-dimensional structures of PAS folds reported so far are all monomeric, therefore, little is known about the structural basis of protein interaction through PAS domains. In the present study, we prepared heterodimeric bHLH-PAS domains derived from AhR and Arnt, and AhRR and Arnt by co-expressing each pair in E. coli, and showed that the heterodimers formed exhibited full DNA-binding activity, which was not apparently affected by deletion of the highly basic amino acid cluster most N-terminal as to the HLH region of AhR or AhRR. Methylation of the two CpG sites in the XRE core sequence reduced the binding affinity to heterodimeric proteins, with 5-methylcytosine in the AhR recognition site exhibiting a greater inhibitory effect than that in the Arnt recognition site.

Amino Acid Sequence↗