B-cell malignancies in microRNA Eμ-miR-17∼92 transgenic mice

Significance MicroRNAs (miRs) are 21- to 22-nucleotide-long noncoding RNA molecules, which regulate the expression of several genes. miR dysregulation is associated with several cancers. The MiR-17∼92 cluster is frequently upregulated in malignancies such as diffuse large B-cell lymphoma and lung cancer. To study the role of miR-17∼92 in B-cell malignancies, we developed a transgenic mouse model overexpressing this cluster in B cells. The transgenic mice developed B-cell lymphomas, and the transcriptome analysis suggested the involvement of PI3K signaling in B lymphocytes, B-cell receptor signaling, GADD45 signaling, and IL-4 signaling pathways in these disorders. Our results provide direct experimental evidence confirming that the miR-17∼92 cluster, which is amplified in human B-cell lymphoma, also is oncogenic when overexpressed in mice. miR-17∼92 is a polycistronic microRNA (miR) cluster (consisting of miR-17, miR-18a, miR-19a, miR-19b, miR-20a, and miR-92a) which frequently is overexpressed in several solid and lymphoid malignancies. Loss- and gain-of-function studies have revealed the role of miR-17∼92 in heart, lung, and B-cell development and in Myc-induced B-cell lymphomas, respectively. Recent studies indicate that overexpression of this locus leads to lymphoproliferation, but no experimental proof that dysregulation of this cluster causes B-cell lymphomas or leukemias is available. To determine whether miR-17∼92- overexpression induces lymphomagenesis/leukemogenesis, we generated a B-cell–specific transgenic mouse model with targeted overexpression of this cluster in B cells. The miR-17∼92 overexpression was driven by the Eµ-enhancer and Ig heavy-chain promoter, and a 3′ GFP tag was added to the transgene to track the miR expression. Expression analysis using Northern Blot and quantitative RT-PCR confirmed 2.5- to 25-fold overexpression of all six miRs in the transgenic mice spleens as compared with spleens from wild-type mice. Eµ-miR-17∼92 mice developed B-cell malignancy by the age of 12–18 mo with a penetrance of ∼80% (49% splenic B-cell lymphoproliferative disease, 28% lymphoma). At this stage mice exhibited severe splenomegaly with abnormal B-cell–derived white pulp expansion and enlarged lymph nodes. Interestingly, we found three classes of B-cell lymphomas/leukemias at varying grades of differentiation. These included expansion of CD19+ and CD5+ double-positive B cells similar to the aggressive form of human B-cell chronic lymphocytic leukemia, B220+ CD43+ B1-cell proliferation, and a CD19+ aggressive diffuse large B-cell lymphoma–like disease, as assessed by flow cytometry and histopathological analysis.