Biallelic DICER1 mutations occur in Wilms tumours

Abstract

DICER1 is an endoribonuclease central to the generation of microRNAs (miRNAs) and short interfering RNAs (siRNAs). Germline mutations in DICER1 have been associated with a pleiotropic tumour predisposition syndrome and Wilms tumour (WT) is a rare manifestation of this syndrome. Three WTs, each in a child with a deleterious germline DICER1 mutation, were screened for somatic DICER1 mutations and were found to bear specific mutations in either the RNase IIIa (n = 1) or the RNase IIIb domain (n = 2). In the two latter cases, we demonstrate that the germline and somatic DICER1 mutations were in trans, suggesting that the two-hit hypothesis of tumour formation applies for these examples of WT. Among 191 apparently sporadic WTs, we identified five different missense or deletion somatic DICER1 mutations (2.6%) in four individual WTs; one tumour had two very likely deleterious somatic mutations in trans in the RNase IIIb domain (c.5438A>G and c.5452G>A). In vitro studies of two somatic single-base substitutions (c.5429A>G and c.5438A>G) demonstrated exon 25 skipping from the transcript, a phenomenon not previously reported in DICER1. Further we show that DICER1 transcripts lacking exon 25 can be translated in vitro. This study has demonstrated that a subset of WTs exhibits two 'hits' in DICER1, suggesting that these mutations could be key events in the pathogenesis of these tumours.No conflicts of interest were declared. pleuropulmonary blastoma (PPB) syndrome (OMIM 601200) [7,8]. Several genes have been identified as being somatically mutated in WT, including WT1 , CTNNB1 , IGF2 , TP53 , WTX , DIS3L2 , FBXW7 and MYCN [5,9]. There are overlapping distributions of molecular abnormalities at 11p15, WTX , WT1 and CTNNB1 in WT [9,10], but other genes could be contributing to the aetiology of WT [3,[11][12][13]. WT histopathology is heterogeneous and tumours associated with different types of nephrogenic rests and histologies tend to show different underlying genetic changes [14,15]. A revised model for WT ontogeny takes into account genetic data (WT1 status, 11p15 imprint control region 1 methylation status, gene expression patterns of other genes) and histological data [14]. Nevertheless, each WT is thought to be of monoclonal origin [16].

Recurrent DICER1 hotspot mutations in endometrial tumours and their impact on microRNA biogenesis

“…In sample D, the E1813G mutation was identified by initial genomic DNA (gDNA) sequencing, and subsequent cDNA sequencing of an amplicon spanning the RNase IIIb domain revealed two products, a long one containing the canonical DICER1 sequence and a shorter one with a 163 nt deletion missing exon 25 ( Figure 2B). This result agreed with a previous observation that the c.5438A > G (E1813G) mutation in DICER1 promotes inefficient exon 25 exclusion, producing both a full-length transcript with c.5438A > G and an exon-25-depleted transcript [13]. Interestingly, when the longer cDNA amplicon was sequenced, only c.5438A > G but no wild-type (WT) sequence was detected ( Figure 2B), suggesting that the expression of WT DICER1 is lost, probably due to either a cryptic genomic aberration or epigenetic silencing.…”

“…This is consistent across both the TCGA dataset (7/304) and our own local tumour bank (6/290; see supplementary material, Tables S1, S7). DICER1 hotspot mutations, although rare, were also identified in brain, colorectal and thyroid cancers (see supplementary material, TableDICER1 hotspot mutations in endometrial cancer 223 tumourigenesis beyond the spectrum of rare paediatric cancers [8][9][10][11][12][13][15][16][17][18]. DICER1 hotspot mutations and subsequent miRNA/mRNA dysregulation may therefore constitute a common oncogenic pathway in a small subset of endometrial tumours.…”

“…The two-hit hypothesis for DICER1 was initially proposed after identification of DICER1 hotspot mutations in tumours from PPB and PPB-FTDS patients with germline DICER1 mutations [11,13,29]. More recently, frequent biallelic DICER1 mutations were identified in sporadic (8/11) and germline PPB (12/12) from two independent studies [16,28].…”

“…Subsequent studies have shown that hotspot mutations at the four metal-binding sites in the RNase IIIb domain (E1705, D1709, D1810 and E1813) impair DICER1's ability to generate mature 5p miRNAs [4,11,12]. More recently, DICER1 hotspot mutations were identified in tumours from PPB and PPB-FTDS cases possessing germline DICER1 mutations, suggesting a two-hit hypothesis of tumourigenesis [11,[13][14][15][16].…”

“…The mutational analyses of DICER1 have previously focused on rare paediatric cancers [6][7][8][9][10][11][13][14][15][16]. In this study, we investigated the prevalence of DICER1 mutations in a spectrum of more common malignancies.…”