title: Epigenetic silencing of miR-26A1 in chronic lymphocytic leukemia and mantle cell lymphoma: Impact on EZH2 expression.
abstract: Downregulation of miR26A1 has been reported in various B-cell malignancies; however, the mechanism behind its deregulation remains largely unknown. We investigated miR26A1 methylation and expression levels in a well-characterized series of chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). From 450K methylation arrays, we first observed miR26A1 (cg26054057) as uniformly hypermethylated in MCL (n = 24) (all >75%), while CLL (n = 18) showed differential methylation between prognostic subgroups. Extended analysis using pyrosequencing confirmed our findings and real-time quantitative PCR verified low miR26A1 expression in both CLL (n = 70) and MCL (n = 38) compared to normal B-cells. Notably, the level of miR26A1 methylation predicted outcome in CLL, with higher levels seen in poor-prognostic, IGHV-unmutated CLL. Since EZH2 was recently reported as a target for miR26A1, we analyzed the expression levels of both miR26A1 and EZH2 in primary CLL samples and observed an inverse correlation. By overexpression of miR26A1 in CLL and MCL cell lines, reduced EZH2 protein levels were observed using both Western blot and flow cytometry. In contrast, methyl-inhibitor treatment led to upregulated miR26A1 expression with a parallel decrease of EZH2 expression. Finally, increased levels of apoptosis were observed in miR26A1-overexpressing cell lines, further underscoring the functional relevance of miR26A1. In summary, we propose that epigenetic silencing of miR26A1 is required for the maintenance of increased levels of EZH2, which in turn translate into a worse outcome, as shown in CLL, highlighting miR26A1 as a tumor suppressor miRNA.
authors.affiliation: a Department of Clinical Chemistry and Transfusion Medicine , Institute of Biomedicine, Sahlgrenska Academy, Gothenburg University , Sweden.
authors.forename: Pradeep Kumar
authors.initials: PK
authors.lastname: Kopparapu
authors.affiliation: b Department of Immunology , Genetics and Pathology, Science for Life Laboratory, Uppsala University , Uppsala , Sweden.
authors.forename: Sujata
authors.initials: S
authors.lastname: Bhoi
authors.affiliation: b Department of Immunology , Genetics and Pathology, Science for Life Laboratory, Uppsala University , Uppsala , Sweden.
authors.forename: Larry
authors.initials: L
authors.lastname: Mansouri
authors.affiliation: a Department of Clinical Chemistry and Transfusion Medicine , Institute of Biomedicine, Sahlgrenska Academy, Gothenburg University , Sweden.
authors.forename: Laleh S
authors.initials: LS
authors.lastname: Arabanian
authors.affiliation: c Central European Institute of Technology, Masaryk University and University Hospital Brno , Czech Republic.
authors.forename: Karla
authors.initials: K
authors.lastname: Plevova
authors.affiliation: c Central European Institute of Technology, Masaryk University and University Hospital Brno , Czech Republic.
authors.forename: Sarka
authors.initials: S
authors.lastname: Pospisilova
authors.affiliation: d Department of Laboratory Medicine , Division of Pathology, Karolinska University Hospital , Sweden.
authors.forename: Agata M
authors.initials: AM
authors.lastname: Wasik
authors.affiliation: e Department of Molecular Medicine , University of Pavia , Italy.
authors.forename: Giorgio Alberto
authors.initials: GA
authors.lastname: Croci
authors.affiliation: d Department of Laboratory Medicine , Division of Pathology, Karolinska University Hospital , Sweden.
authors.forename: Birgitta
authors.initials: B
authors.lastname: Sander
authors.affiliation: e Department of Molecular Medicine , University of Pavia , Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Paulli
authors.affiliation: b Department of Immunology , Genetics and Pathology, Science for Life Laboratory, Uppsala University , Uppsala , Sweden.
authors.forename: Richard
authors.initials: R
authors.lastname: Rosenquist
authors.affiliation: a Department of Clinical Chemistry and Transfusion Medicine , Institute of Biomedicine, Sahlgrenska Academy, Gothenburg University , Sweden.
authors.forename: Meena
authors.initials: M
authors.lastname: Kanduri
mesh_terms: D017209:Apoptosis / Q000235:genetics; D045744:Cell Line, Tumor; D019175:DNA Methylation / Q000235:genetics*; D000071221:Enhancer of Zeste Homolog 2 Protein / Q000096:biosynthesis* / Q000235:genetics; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000235:genetics* / Q000473:pathology; D020522:Lymphoma, Mantle-Cell / Q000235:genetics* / Q000473:pathology; D035683:MicroRNAs / Q000096:biosynthesis* / Q000235:genetics; D011401:Promoter Regions, Genetic
chemical_list: D000071221:Enhancer of Zeste Homolog 2 Protein; D035683:MicroRNAs; C528163:MIRN26 microRNA, human; C498409:EZH2 protein, human
keywords: Chronic lymphocytic leukemia; DNA methylation; mantle cell lymphoma; microRNA; tumor suppressor