title: Promoter hypomethylation regulates CD133 expression in human gliomas.
abstract: Brain tumor-initiating cells (BTICs) have been enriched using antibodies against the cell surface protein CD133; however, the biological relevance and the regulatory mechanism of CD133 expression in human gliomas are not yet understood. In this study, we initially demonstrated that CD133 was overexpressed in high-grade human glioblastomas where CD133-positive cells were focally observed as a micro-cluster. In addition, CD133 transcripts with exon 1A, 1B, or 1C were predominantly expressed in glioblastomas. To elucidate the mechanism regulating this aberrant expression of CD133, three proximal promoters (P1, P2, and P3) containing a CpG island were isolated. In U251MG and T98G glioblastoma cells, the P1 region flanking exon 1A exhibited the highest activity among the three promoters, and this activity was significantly inactivated by in vitro methylation. After treatment with the demethylating agent 5-azacytidine and/or the histone deacetylase inhibitor valproic acid, the expression level of CD133 mRNA was significantly restored in glioma cells. Importantly, hypomethylation of CpG sites within the P1, P2, and P3 regions was observed by bisulfite sequencing in human glioblastoma tissues with abundant CD133 mRNA. Taken together, our results indicate that DNA hypomethylation is an important determinant of CD133 expression in glioblastomas, and this epigenetic event may be associated with the development of BTICs expressing CD133.
authors.affiliation: Laboratory of Molecular and Cellular Pathology, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo 060-8638, Japan.
authors.forename: Kouichi
authors.initials: K
authors.lastname: Tabu
authors.forename: Ken
authors.initials: K
authors.lastname: Sasai
authors.forename: Taichi
authors.initials: T
authors.lastname: Kimura
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.forename: Eiko
authors.initials: E
authors.lastname: Aoyanagi
authors.forename: Shinji
authors.initials: S
authors.lastname: Kohsaka
authors.forename: Mishie
authors.initials: M
authors.lastname: Tanino
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishihara
authors.forename: Shinya
authors.initials: S
authors.lastname: Tanaka
mesh_terms: D020121:5' Untranslated Regions; D000071916:AC133 Antigen; D015703:Antigens, CD / Q000235:genetics* / Q000378:metabolism; D000964:Antimetabolites, Antineoplastic / Q000378:metabolism; D001374:Azacitidine / Q000378:metabolism; D001932:Brain Neoplasms / Q000235:genetics* / Q000378:metabolism; D018899:CpG Islands / Q000187:drug effects; D019175:DNA Methylation; D015972:Gene Expression Regulation, Neoplastic; D005909:Glioblastoma / Q000235:genetics* / Q000378:metabolism; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D010455:Peptides / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D020121:5' Untranslated Regions; D000071916:AC133 Antigen; D015703:Antigens, CD; D000964:Antimetabolites, Antineoplastic; D006023:Glycoproteins; C000606023:PROM1 protein, human; D010455:Peptides; D001374:Azacitidine