Genetic dissection of the miR-17∼92 cluster of microRNAs in Myc-induced B-cell lymphomas

Abstract

The miR-17~92 cluster is frequently amplified or overexpressed in human cancers and has emerged as the prototypical oncogenic polycistron microRNA (miRNA). miR-17~92 is a direct transcriptional target of c-Myc, and experiments in a mouse model of B-cell lymphomas have shown cooperation between these two oncogenes. However, both the molecular mechanism underlying this cooperation and the individual miRNAs that are responsible for it are unknown. By using a conditional knockout allele of miR-17~92, we show here that sustained expression of endogenous miR-17~92 is required to suppress apoptosis in Myc-driven B-cell lymphomas. Furthermore, we show that among the six miRNAs that are encoded by miR-17~92, miR-19a and miR-19b are absolutely required and largely sufficient to recapitulate the oncogenic properties of the entire cluster. Finally, by combining computational target prediction, gene expression profiling, and an in vitro screening strategy, we identify a subset of miR-19 targets that mediate its prosurvival activity.Supplemental material is available at http://www.genesdev.org. The experiments presented in this study were designed to examine the role of the endogenous miR-17;92 allele in Myc-driven lymphomas, and to determine the relative contribution of each of the six constituent miRNAs to the overall oncogenic potential of the cluster.Our results show that, in the context of Myc-driven B-cell lymphomas, genetic ablation of the endogenous miR-17;92 locus leads to a dramatic reduction of tumor cell growth in vitro and suppresses tumorigenicity in vivo, two effects that are largely the consequence of increased cell death. We also demonstrate that, among the six miRNAs encoded by the miR-17;92 cluster, the members of the miR-19 family (miR-19a and miR-19b) are essential to mediate the oncogenic activity of the entire cluster, and that they do so at least in part by modulating the expression of the tumor suppressor gene Pten (phosphatase and tensin homologous). Results and DiscussionGeneration of miR-17;92 flox/flox ;Em-Myc miceTo investigate the role of miR-17;92 in Myc-induced cancers, we employed the Em-Myc mouse model of B-cell lymphomas (Adams et al. 1985). Em-Myc mice express a c-Myc transgene under the control of the B-cell-specific Em enhancer and develop B-cell lymphomas within 4-6 mo of age (Adams et al. 1985). Em-Myc mice were crossed to mice carrying a conditional miR-17;92 knockout allele (miR-17;92 fl ) ( Fig. 1B; Ventura et al. 2008). To temporally control the deletion of the floxed miR-17;92 allele, these mice were further crossed to mice carrying a 4-hydroxytamoxifen (4-OHT)-inducible Cre-recombinase estrogen receptor-T2 (Cre-ER T2 ) knock-in allele targeted to the ubiquitously expressed ROSA26 locus (R26-Cre-ER T2 mice, hereafter referred to as Cre-ER) (Ventura et al. 2007).As expected, Em-Myc; miR-17;92 fl/fl ; Cre-ER mice developed B-cell lymphomas with similar latency and phenotype as the parental Em-Myc strain (data not shown). From these mice, we derived two independent lymphoma lines (...

Dietary Manipulation of Oncogenic MicroRNA Expression in Human Rectal Mucosa: A Randomized Trial

“…Elevated miR17-92 levels have been associated with invasion and metastasis of colorectal cancer cells (32), and poorer survival (33). miR19a and miR19b in particular are key oncogenic determinants (29,30), and both were significantly elevated with the HRM diet compared with the entry diet. miR21 has similarly been classed as oncogenic, and can also induce tumorigenesis, invasion, and metastasis (34)(35)(36).…”

“…HRM intake significantly increased rectal mucosa levels of miR17-92 cluster miRNAs and miR21, which are both elevated in colorectal cancer (16,17). The miR17-92 cluster has been designated oncomir-1 (31), and can promote proliferation and angiogenesis, inhibit differentiation, and sustain cell survival (29,30). Elevated miR17-92 levels have been associated with invasion and metastasis of colorectal cancer cells (32), and poorer survival (33).…”

“…© 2014 American Association for Cancer cancerpreventionresearch.aacrjournals.org Downloaded from proliferation (18,29,30,34,35), and examination of target gene expression and cell proliferation provided preliminary evidence about the possible influence of detected miRNA changes on cellular function. The increased miR17-92 miRNA levels with the HRM diet were associated with a decrease in mRNA levels of target genes, particularly the cellcycle inhibitor CDKN1A.…”

“…[27][28][29][30]. The influence of the diet-induced changes in miR17-92 cluster miRNA levels on these target genes was investigated in the rectal biopsy samples.…”

The Inflammatory Tumor Microenvironment, Epithelial Mesenchymal Transition and Lung Carcinogenesis

“…Early studies have demonstrated that miR-17-92 cluster expression is upregulated by the protooncogene c-myc, which itself is commonly dysregulated in human malignancies [124]. In addition to being highly expressed and promoting cell proliferation and apoptosis resistance in cancer cells [125], high levels of the miR-17-92 cluster are found in embryonic stem cells. This suggests that miR-17-92 promotes the proliferation of progenitor cells and inhibits their differentiation [126].…”