Abstract 5198: Identification of microRNAs involved in DNA damage response in malignant B cells and their biological and clinical relevance

We and others have shown that expression of miRNAs influences the biology of B cell malignancies (Calin et al., 2005; Mraz et al., 2009, 2012, 2013). The aim of this study was to identify miRNAs involved in the apoptotic response of malignant B cells. Purified primary B cells of chronic lymphocytic leukemia (CLL) patients (pts.) were treated in vitro with fludarabine (F) (LC50 dose of 3.5 μg/ml; 48 h). Five paired (n=10) samples (with and without F) were analyzed using 2 NGS platforms-SOLiD (ABI) and HiSeq (Illumina). The obtained reads were mapped to miRBase using 3 tools (CLC Genomic Workbench, SHRiMP2, miRanalyzer) and data analyzed by a pair-wise comparison with edgeR and baySeq packages (Bioconductor 2.13). The overlap of these 3+2 bioinformatic approaches identified 6 miRNAs significantly changed with DNA damage. RNA-Seq validation on 5 additional paired samples (n=10) confirmed the changed expression of all 6 previously identified miRNAs (3 down-, 3 up-regulated). The most constantly up-regulated was miR-34a, which was previously shown to be regulated by p53 (He et al., 2005; Mraz et al., 2009). To test the importance of miR-34a in vivo, we collected samples from CLL pts. (n=51) treated with F, cyclophosphamide and rituximab (FCR) regimen. miR-34a was induced in all samples after F administration (day 2, p