title: Expression of miR-196b is not exclusively MLL-driven but is especially linked to activation of HOXA genes in pediatric acute lymphoblastic leukemia.
abstract: BACKGROUND
  Deregulation of microRNA may contribute to hematopoietic malignancies. MicroRNA-196b (miR-196b) is highly expressed in MLL-rearranged leukemia and has been shown to be activated by MLL and MLL-fusion genes.
  
  
  METHODS
  In order to determine whether high expression of miR-196b is restricted to MLL-rearranged leukemia, we used quantitative stem-loop reverse transcriptase polymerase chain reaction to measure the expression of this microRNA in 72 selected cases of pediatric acute lymphoblastic leukemia i.e. MLL-rearranged and non-MLL-rearranged precursor B-cell and T-cell acute lymphoblastic leukemias. We also determined the expression of HOXA-genes flanking miR-196 by microarray and real-time quantitative polymerase chain reaction. Furthermore, we used CpG island-arrays to explore the DNA methylation status of miR-196b and HOXA.
  
  
  RESULTS
  We demonstrated that high expression of miR-196b is not unique to MLL-rearranged acute lymphoblastic leukemia but also occurs in patients with T-cell acute lymphoblastic leukemia patients carrying CALM-AF10, SET-NUP214 and inversion of chromosome 7. Like MLL-rearrangements, these abnormalities have been functionally linked with up-regulation of HOXA. In correspondence, miR-196b expression in these patients correlated strongly with the levels of HOXA family genes (Spearman's correlation coefficient ≥ 0.7; P≤0.005). Since miR-196b is encoded on the HOXA cluster, these data suggest co-activation of miR-196b and HOXA genes in acute lymphoblastic leukemia. Up-regulation of miR-196b coincides with reduced DNA methylation at CpG islands in the promoter regions of miR-196b and the entire HOXA cluster in MLL-rearranged cases compared to in cases of non-MLL precursor B-cell acute lymphoblastic leukemia and normal bone marrow (P<0.05), suggesting an epigenetic origin for miR-196b over-expression. Although patients with MLL-rearranged acute lymphoblastic leukemia are highly resistant to prednisolone and L-asparaginase, this resistance was not attributed to miR-196b expression.
  
  
  CONCLUSIONS
  High expression of miR-196b is not exclusively MLL-driven but can also be found in other types of leukemia with aberrant activation of HOXA genes. Since miR-196b has been shown by others to exert oncogenic activity in bone marrow progenitor cells, the findings of the present study imply a potential role for miR-196b in the underlying biology of all HOXA-activated leukemias.
authors.affiliation: Erasmus MC-Sophia Children's Hospital, Dept. of Pediatric, Oncology and Hematology, Rotterdam, the Netherlands.
authors.forename: Diana
authors.initials: D
authors.lastname: Schotte
authors.forename: Ellen A M
authors.initials: EA
authors.lastname: Lange-Turenhout
authors.forename: Dominique J P M
authors.initials: DJ
authors.lastname: Stumpel
authors.forename: Ronald W
authors.initials: RW
authors.lastname: Stam
authors.forename: Jessica G C A M
authors.initials: JG
authors.lastname: Buijs-Gladdines
authors.forename: Jules P P
authors.initials: JP
authors.lastname: Meijerink
authors.forename: Rob
authors.initials: R
authors.lastname: Pieters
authors.forename: Monique L
authors.initials: ML
authors.lastname: Den Boer
mesh_terms: D002648:Child; D057890:Epigenomics; D015973:Gene Expression Regulation, Leukemic; D015321:Gene Rearrangement; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D035683:MicroRNAs / Q000096:biosynthesis / Q000235:genetics*; D051788:Myeloid-Lymphoid Leukemia Protein / Q000235:genetics*; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000209:etiology / Q000235:genetics*
chemical_list: D018398:Homeodomain Proteins; C542543:MIRN196 microRNA, human; D035683:MicroRNAs; D051788:Myeloid-Lymphoid Leukemia Protein; C088144:HoxA protein