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K. Van Roosbroeck et al.
The significantly differently expressed and hub-specific microRNA signature targets are enriched in pathways involved in cancer, immunity and inflammation
To understand the biological significance of the differ- entially expressed miRNA as well as of the RS-specific miRNA hubs from the above network analyses, we per- formed ingenuity pathway analysis for the validated tar- gets (Online Supplementary Table S5A,B). Ingenuity path- way analysis of all targets of the four SDE miRNA of the restricted signature revealed the involvement of signaling pathways with a strong enrichment for pathways involved in cancer and also in immune responses (Figure 5C). We performed the same ingenuity pathway analysis on the three HUS Richter-specific miRNA (Figure 5D), and again found a strong enrichment towards cancer and autoimmune disorders/immunity-specific pathways. Interestingly, seven of the top 20 canonical pathways were common between the SDE miRNA and HUS
A
miRNA (Figure 5C,D). The connection with the p53 sig- naling pathway is compelling and can be considered as a “positive” control since this protein has a well-known role in the pathogenesis of RS, as well as aggressive CLL.14
Functional characterization of the miRNA involved in Richter transformation
In order to start the functional characterization of the miRNA, we took advantage of a well characterized CLL xenograft model that employs primary CLL cells18-20 (Figure 6A). We checked the expression levels of the eight miRNA in the Richter transformation restricted and enlarged signatures. Since human CLL cells proliferate faster after transplantation into mice18-20,31 similar to what is observed after Richter transformation in humans, we hypothesized that this model partially resembles the functional phenotype observed in Richter transformation, characterized by higher proliferation rates compared to
Figure 4. Genomic microRNA profiling in lymphoid tumors. (A) Analysis of miR-150, miR-181a/b, miR-21 and miR-26a genomic loci in a subset of 15 paired chronic lymphocytic leukemia (CLL) phase/Richter syndrome (RS) phase cases. (B) The genomic regions containing miR-21, miR-146a and miR-181a/b-1 are more often gained than lost in a set of 737 cases of
additional Information, see Online Supplementary Figure S4.
mature lymphoid tumors.17,26-29 For
B
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haematologica | 2019; 104(5)