MicroRNA-155 Targets the Transcription Repressor ZNF652 in Chronic Lymphocytic Leukemia (CLL)
T Zhang, K Nie, R Furman, A Chadburn, DM Knowles, W Tam. Weill Cornell Medical College, New York, NY; Northwestern University Feinberg School of Medicine, Chicago, IL
Background: The pathogenesis and prognosis of CLL has been linked to deregulation of microRNAs (miRNA). MicroRNA-155 (miR-155) has been identified as one of the miRNAs in a miRNA gene signature associated with worse prognostic factors and more aggressive clinical course in CLL. Our current study aims at elucidating the mechanisms of how miR-155 contributes to its pathogenesis and disease progression.
Design: B cells purified from 22 IgVh unmutated and 25 IgVh mutated CLL samples were analyzed for miR-155 expression by a modified Invader assay and compared to 6 memory B cell samples isolated by flow sorting from independent reactive tonsils. The 6 samples with the highest or lowest miR-155 expressions from each of the two IgVh groups were selected for cDNA microarray analysis. Differentially expressed genes between these two groups (12 samples each) were analyzed to search for miR-155 target genes and miR-155-associated gene signatures.
Results: 10 of 22 IgVh unmutated CLLs and 10 of 25 IgVh mutated CLLs express miR-155 at levels 2-fold or higher compared to normal memory B cells. Unmutated CLLs tend to have higher miR-155 expressions compared to mutated CLLs (p=0.09). Global expression profiling identified a set of genes differentially expressed between CLLs with high and low miR-155 levels. Among the 8 genes detected above the significance threshold after multiple comparison corrections, 2 were down-regulated and 6 were up-regulated, including BIC, the miR-155 precursor. One of the two down-regulated genes, ZNF652, encodes a potential tumor suppressor with transcription repressor activity and harbors two miR-155 binding sites. Both its mRNA and protein levels negatively correlate with miR-155 levels. In addition, reporter assays demonstrated specific interaction of miR-155 with its 3' untranslated region. High miR-155 in CLL is also associated with a higher level (8 fold) of CB1 cannibinoid receptor (CNR1) mRNA and a lower (6 to 30 fold) Kruppel-like factor (KLF3) mRNA expression.
Conclusions: 40% of CLL over-express miR-155. Our study identified a putative miR-155 target gene that is likely to mediate the pathogenic function of miR-155 in CLL. Studies of other differentially expressed genes may uncover novel mechanisms of miR-155 over-expression in CLL.
Monday, March 9, 2009 8:00 AM
Platform Session: Section D, Monday Morning