Expression of miR-196b is not exclusively MLL-driven but is especially linked to activation of HOXA genes in pediatric acute lymphoblastic leukemia.
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.
Schotte
Diana
D
Erasmus MC-Sophia Children's Hospital, Dept. of Pediatric, Oncology and Hematology, Rotterdam, the Netherlands.
Lange-Turenhout
Ellen A M
EA
Stumpel
Dominique J P M
DJ
Stam
Ronald W
RW
Buijs-Gladdines
Jessica G C A M
JG
Meijerink
Jules P P
JP
Pieters
Rob
R
Den Boer
Monique L
ML
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*
D018398:Homeodomain Proteins; C542543:MIRN196 microRNA, human; D035683:MicroRNAs; D051788:Myeloid-Lymphoid Leukemia Protein; C088144:HoxA protein