LAUSR

Introduction MiRNAs are short non coding RNAs involved in post-transcriptional regulation of gene expression that can acquire oncogenic properties in consequence of overexpression or mutations. Tumour genomes undergo global demethylation that triggers genetic instability and activates transcription of sequences normally silenced by methylation. These include the overexpression of tumour specific miRNAs that can deregulate various processes in the malignant cell. Therefore, the aim of the study was to identify aberrantly activated miRNAs in classical Hodgkin lymphoma (cHL). Material and methods We have screened NGS small RNA reads (HiSeq 4000 (Illumina); single-end 50 bp seq) of cHL cell lines (n=7) and compared them to non-HL cell lines (n=10) and germinal centre B cell pools (GCB)(n=10) to find yet undescribed miRNAs. High quality reads validated using FastQC and CAP-miRSeq software mapping to the reference genome (GRCh37) (using Bowtie software) not reported as miRNAs before were identified. In order to find miRNAs expressed exclusively in cHL we have moreover compared the sequences in respect to sequence-derived gene expression data from 143 malignant lymphomas generated by the ICGC MMML-Seq consortium (www.icgc.org). Last, the expression of novel miRNAs seemingly specific for cHL was validated by real-time qPCR using custom designed molecular probes (Thermo Fisher Scientific). Results and discussions Seven novel miRNAs expressed in at least 3/7 cHL cell lines but neither in the non-HL cell lines nor in the GCB cells and observed with a frequency <1% in the ICGC MMML-Seq cohort were identified. As a proof of principle we intended to confirm the expression of miRNA #1 and #7 using real-time qPCR. In concordance with the NGS data expression of miRNA #7 (chr2:213543512–213543573) was observed in 4/7 cHL cell lines exclusively. In silico analyses of potential target mRNAs has shown enrichment in gene ontologies including regulation of signalling (p<0.001) (GO:0023051) or regulation of actin cytoskeleton organisation (p<0.05) (GO:0032956) - processes deregulated in human neoplasms. The expression of miRNA #1 was not confirmed and the validation of the further 5 novel miRNAs is ongoing. Conclusion Our data provide evidence for aberrant activation of miRNAs in neoplastic cells probably not expressed under physiologic conditions in the same cell type. The identified miRNA #7 and potentially the currently tested 5 further candidates contribute to the unique cHL miRNAome.