microRNAs (miRNAs) are small noncoding RNAs that regulate gene expression by targeting messenger RNA (mRNA) transcripts. Recently, a miRNA expression profile of human tumors has been characterized by an overall miRNA downregulation1–3. Explanations for this observation include a failure of miRNA post-transcriptional regulation4, transcriptional silencing associated with hypermethylation of CpG island promoters5–7 and miRNA transcriptional repression by oncogenic factors8. Another possibility is that the enzymes and cofactors involved in miRNA processing pathways may themselves be targets of genetic disruption, further enhancing cellular transformation9. However, no loss-of-function genetic alterations in the genes encoding these proteins have been reported. Here we have identified truncating mutations in TARBP2 (TAR RNA-binding protein 2), encoding an integral component of a DICER1-containing complex10,11, in sporadic and hereditary carcinomas with microsatellite instability12–14. The presence of TARBP2 frameshift mutations causes diminished TRBP protein expression and a defect in the processing of miRNAs. The reintroduction of TRBP in the deficient cells restores the efficient production of miRNAs and inhibits tumor growth. Most important, the TRBP impairment is associated with a destabilization of the DICER1 protein. These results provide, for a subset of human tumors, an explanation for the observed defects in the expression of mature miRNAs.

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Mycosis fungoide (MF) patients who develop tumors or extracutaneous involvement usually have a poor prognosis with no curative therapy available so far. In the present European Organization for Research and Treatment of Cancer (EORTC) multicenter study, the genomic profile of 41 skin biopsies from tumor stage MF (MFt) was analyzed using a high-resolution oligo-array comparative genomic hybridization platform. Seventy-six percent of cases showed genomic aberrations. The most common imbalances were gains of 7q33.3q35 followed by 17q21.1, 8q24.21, 9q34qter, and 10p14 and losses of 9p21.3 followed by 9q31.2, 17p13.1, 13q14.11, 6q21.3, 10p11.22, 16q23.2, and 16q24.3. Three specific chromosomal regions, 9p21.3, 8q24.21, and 10q26qter, were defined as prognostic markers showing a significant correlation with overall survival (OS) (P=0.042, 0.017, and 0.022, respectively). Moreover, we have established two MFt genomic subgroups distinguishing a stable group (0-5 DNA aberrations) and an unstable group (>5 DNA aberrations), showing that the genomic unstable group had a shorter OS (P=0.05). We therefore conclude that specific chromosomal abnormalities, such as gains of 8q24.21 (MYC) and losses of 9p21.3 (CDKN2A, CDKN2B, and MTAP) and 10q26qter (MGMT and EBF3) may have an important role in prognosis. In addition, we describe the MFt genomic instability profile, which, to our knowledge, has not been reported earlier.

Intrinsic and acquired resistance to chemotherapy is the fundamental reason for treatment failure for many cancer patients. The identification of molecular mechanisms involved in drug resistance or sensitization is imperative. Here we report that tribbles homologue 2 (TRIB2) ablates forkhead box O activation and disrupts the p53/MDM2 regulatory axis, conferring resistance to various chemotherapeutics. TRIB2 suppression is exerted via direct interaction with AKT a key signalling protein in cell proliferation, survival and metabolism pathways. Ectopic or intrinsic high expression of TRIB2 induces drug resistance by promoting phospho-AKT (at Ser473) via its COP1 domain. TRIB2 expression is significantly increased in tumour tissues from patients correlating with an increased phosphorylation of AKT, FOXO3a, MDM2 and an impaired therapeutic response. This culminates in an extremely poor clinical outcome. Our study reveals a novel regulatory mechanism underlying drug resistance and suggests that TRIB2 functions as a regulatory component of the PI3K network, activating AKT in cancer cells.

BackgroundLow-grade B-cell lymphomas are a very heterogeneous group of tumors, whose differential diagnosis is frequently compromised by the lack of specific cytogenetic or molecular features. Our objective was to search for genomic features that allow a better molecular identification of the different types of lymphoma studied.

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Mantle cell lymphoma (MCL) pathogenesis is still partially unexplained. We investigate the importance of microRNA (miRNA) expression as an additional feature that influences MCL pathway deregulation and may be useful for predicting patient outcome. Twenty-three MCL samples, eight cell lines and appropriate controls were screened for their miRNAs and gene expression profiles and DNA copy-number changes. MCL patients exhibit a characteristic signature that includes 117 miRNA (false discovery rate o0.05). Combined analysis of miRNAs and the gene expression profile, paired with bioinformatics target prediction (miRBase and TargetScan), revealed a series of genes and pathways potentially targeted by a small number of miRNAs, including essential pathways for lymphoma survival such as CD40, mitogen-activated protein kinase and NF-jB. Functional validation in MCL cell lines demonstrated NF-jB subunit nuclear translocation to be regulated by the expression of miR-26a. The expression of 12 selected miRNAs was studied by quantitative PCR in an additional series of 54 MCL cases. Univariate analysis identified a single miRNA, miR20b, whose lack of expression distinguished cases with a survival probability of 56% at 60 months. In summary, using a novel bioinformatics approach, this study identified miRNA changes that contribute to MCL pathogenesis and markers of potential utility in MCL diagnosis and clinical prognostication.