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Articles by K Yoshikawa
Total Records ( 3 ) for K Yoshikawa
  R. J Ward , L Lee , K Graham , T Satkunendran , K Yoshikawa , E Ling , L Harper , R Austin , E Nieuwenhuis , I. D Clarke , C. c Hui and P. B. Dirks
 

Subpopulations of tumorigenic cells have been identified in many human tumors, although these cells may not be very rare in some types of cancer. Here, we report that medulloblastomas arising from Patched-1–deficient mice contain a subpopulation of cells that show a neural precursor phenotype, clonogenic and multilineage differentiation capacity, activated Hedgehog signaling, wild-type Patched-1 expression, and the ability to initiate tumors following allogeneic orthotopic transplantation. The normal neural stem cell surface antigen CD15 enriches for the in vitro proliferative and in vivo tumorigenic potential from uncultured medulloblastomas, supporting the existence of a cancer stem cell hierarchy in this clinically relevant mouse model of cancer. [Cancer Res 2009;69(11):4682–90]

  H Suzuki , E Yamamoto , M Nojima , M Kai , H. o Yamano , K Yoshikawa , T Kimura , T Kudo , E Harada , T Sugai , H Takamaru , T Niinuma , R Maruyama , H Yamamoto , T Tokino , K Imai , M Toyota and Y. Shinomura
 

Altered expression of microRNA (miRNA) is strongly implicated in cancer, and recent studies have shown that the silencing of some miRNAs is associated with CpG island hypermethylation. To identify epigenetically silenced miRNAs in gastric cancer (GC), we screened for miRNAs induced by treatment with 5-aza-2’-deoxycytidine and 4-phenylbutyrate. We found that miR-34b and miR-34c are epigenetically silenced in GC and that their downregulation is associated with hypermethylation of the neighboring CpG island. Methylation of the miR-34b/c CpG island was frequently observed in GC cell lines (13/13, 100%) but not in normal gastric mucosa from Helicobacter pylori-negative healthy individuals. Transfection of a precursor of miR-34b and miR-34c into GC cells induced growth suppression and dramatically changed the gene expression profile. Methylation of miR-34b/c was found in a majority of primary GC specimens (83/118, 70%). Notably, analysis of non-cancerous gastric mucosae from GC patients (n = 109) and healthy individuals (n = 85) revealed that methylation levels are higher in gastric mucosae from patients with multiple GC than in mucosae from patients with single GC (27.3 versus 20.8%; P < 0.001) or mucosae from H. pylori-positive healthy individuals (27.3 versus 20.7%; P < 0.001). These results suggest that miR-34b and miR-34c are novel tumor suppressors frequently silenced by DNA methylation in GC, that methylation of miR-34b/c is involved in an epigenetic field defect and that the methylation might be a predictive marker of GC risk.

  Y Mezaki , N Yamaguchi , K Yoshikawa , M Miura , K Imai , H Itoh and H. Senoo
 

Hepatic stellate cells (HSCs) are the major site of retinoid storage, and their activation is a key process in liver fibrogenesis. We have previously shown that expression of the retinoic acid receptor alpha (RAR) is upregulated in activated rat HSCs at a posttranscriptional level and that these RAR proteins showed a speckled distribution in the cytosol, despite their possession of a nuclear localization signal (NLS). In this report, we further characterize these cytosolic RAR proteins by using exogenously expressed RAR protein fragments or mutants tagged with a green fluorescent protein. Substitution of four amino acids, 161–164 from lysine to alanine, abolished the NLS. Exogenously expressed RAR protein fragments containing an NLS were localized exclusively in the nuclei of activated rat HSCs and never colocalized with the endogenous RAR proteins in the cytosol, suggesting that the NLS of endogenous RAR proteins is masked. Biochemical analysis showed that 65% of RAR proteins in activated HSCs were insoluble in a mixture of detergents. The insolubility of RAR proteins makes it difficult to identify RAR proteins in activated HSCs. Therefore, we propose that insoluble, speckled cytosolic distribution of RAR proteins represents a new marker of HSC activation. (J Histochem Cytochem 57:687–699, 2009)

 
 
 
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