ISHL10 Abstract P030

The lymphoid cell specific transcription factor ELF-1 is transcriptionally downregulated and recurrently deleted in classical Hodgkin lymphoma (cHL)

ELF-1 and ELF-2 belong to the ETS-family of transcription activators or repressors implicated in processes recurrently deregulated in human neoplasms. Recently, we have shown that genes hypermethylated in cHL are enriched for binding sites of ETS-family members ETS-1 (1.28 fold), ELF-1 (1.07 fold) and ELF-2 (1.91 fold). We hypothesized that hypermethylation of genes in cHL might be secondary towards genomic alterations of these B-cell related transcription factors. In line, we have recently reported recurrent alterations and significant downregulation of ETS-1 expression in cHL. Encouraged by this finding, here we analyzed the two other ETS family members in cHL. We show significant downregulation of ELF-1 (8.82 fold, p<0.0001, tag 40067_at) and 1.36 fold of ELF-2 (tag 507_s_at) in cHL cell lines (n=4) compared to GCB pools (n=20) (U95 microarray). This was further validated for ELF-1 in primary biopsies where using immunohistochemistry (AB99401) we observed loss or downregulation of the protein in HRS cells in 26/35 (74%) cases but not in no-tumor bystander cells. In case of ELF-2 no reduction of protein abundance was observed. To identify the underlying mechanism we sequenced the ELF-1 coding region in 7 cHL cell lines but no mutations were identified. In contrast, we analyzed copy number (CN) alterations of the ELF-1 locus in primary biopsies using combined immunophenotyping and in situ hybridization (FICTION) and identified deletions in 5/11 (45%) analyzed cases. Similarly, deletions or LOH were found in 4/7 (57%) cHL cell lines (Affymetrix SNP 6.0 array). Also epigenetic mechanism may contribute to ELF-1 downregulation as using next-generation miRnome sequencing we observed 3.26 fold overexpression (p=0.0018) of the hsa-miR-330-3p in cHL cell lines (n=7) compared to non-Hodgkin lymphomas (n=10). Hsa-miR-330-3p shows significant affinity (p=0.0013) towards the 3’UTR region of ELF-1 basing on in silico analysis (miRWalk). In conclusion, we show recurrent loss of ELF-1 expression in HRS cells that at least in part is attributable to the genomic deletions and overexpressed hsa-miR-330-3p. Moreover, our data support the concept, that downregulation of the ELF-1 transcription factor may lead to consequent hypermethylation and silencing of its target genes contributing to the loss of B-cell phenotype of HRS cells.