Differences in the C13orf25 miRNA Cluster in Non-Hodgkin Lymphoma and Normal B-Cell Subtypes.

Introduction Amplification of chromosome 13q31 is a frequent occurrence in lymphoma and solid tumors. The C13orf25 gene at 13q31.3 is the primary miRNA transcript for seven miRNAs. This specific cluster of miRNAs is sequentially related to the homologous miR-106a-92 cluster on chromosome X and the miR-106b-25 cluster on chromosome 7. The miR17-92 cluster has been shown to be over expressed in various non-Hodgkin Lymphoma (NHL). As a specific group of miRNAs which are derived from the same primary miRNA transcript, each miRNA in the cluster may be expected to show a similar expression level. However expression patterns vary markedly in different cancers. Aim of study To compare the expression pattern of the C13orf25 gene and the miRNAs in normal and malignant B-cells.

Methods and Materials 51 cases of Ann Abour stage I and II primary diffuse large B-cell lymphoma (DLBCL) were collected together with 29 cases of B-CLL. All samples were examined for expression of miRNA miR-18a, -19, -20a, 17-3p, -17-5p and -92 and the C13orf 25 gene. Expression levels of the mature miRNAs were determined by qRT-PCR using Taqman miRNA assays. The level of C13orf25 was also determined by qRT-PCR using random primers and a Sybergreen probe. Results were compared by using 2^−ΔCt and 2^−ΔΔCt. Normal B-cell subpopulations were isolated from fresh tonsils obtained during routine pediatric tonsillectomies. B-cell subsets were stained accordingly and sorted by FACS.

Results Comparison of the miRNA pattern (2^−ΔCt) revealed that DLBCL have the highest expression level of miR-19b and that B-CLL shows a relative high expression level of miR-92. Normal naïve, germinal center and memory B-cells all show a similar expression pattern with miR-92 having the highest expression level. Remarkably a low expression level of miR-19b is seen in all three B-cell populations in contrast to DLBCL. Comparing the relative expression levels (2^−ΔΔCt) of both NHL for each individual miRNA shows that B-CLL has a significantly higher level of expression for miR-19a. In DLBCL miR-17-5p, miR-18a and miR-20a have the highest expression levels. Currently 20 Mantle cell lymphoma are also being analyzed for the C13orf25 miRNAs cluster.

Conclusion Our results show that both of the NHL B-cell malignancies and the B-cell subsets have different expression patterns of the individual levels of the 7 miRNAs contained in the same C13orf25 cluster. The relative expression levels of certain miRNAs from the same primary transcript are different in various NHL. Although there are no marked differences in the normal B-cell subsets for the C13orf25 cluster, further profiling revealed various different expression levels of other miRNAs. These findings may point towards a difference in processing efficiency or stability of miRNAs in the C13orf25 cluster leading to differences in pathogenesis specific for each malignancy even in cells of similar origin and differentiation stage.