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Human Dicer hotspot mutation induces both loss and gain of miRNA function [iCLIP]

ABSTRACT: The core miRNA biogenesis enzyme Dicer sustains recurrent mutations in cancer, which specifically compromise catalysis by its RNase IIIb domain. These are proposed to act as selective hypomorphs, since Dicer-RNase IIIb cleaves the 5p arms of pre-miRNA hairpins. However, the lack of knockin models has hindered a full understanding of the consequences of Dicer hotspot mutations for miRNA biogenesis. Here, we generated Dicer-KO and Dicer-S1344L (homozygous and hemizygous) hESCs; the latter is a non-catalytic mutation in RNase IIIa that impairs RNase IIIb activity. Consistent with our previous work, Dicer-KO is cell lethal in hESCs. However, in contrast to the expectation that Dicer hotspot mutations confer cell advantages, Dicer-S1344L knockin hESCs were subviable and also required a conditional genetic strategy for isolation. Small RNA sequencing using spike-in normalization reveals two broad trends: ablation of miRNA-5p species, and selective changes in miRNA-3p species. Curiously, we recognized a directional upregulation of miRNA-3p passenger strands, indicating a broad strand switch. Activity assays and Argonaute profiling of the transcriptome confirm that these confer increased repression capacity. Finally, we used in vitro assays to show 3p arm-nicked pre-miRNAs preferentially load miRNA-3p species into Argonaute, compared to corresponding miRNA/passenger duplexes. Overall, Dicer hotspot mutations have unexpected neomorphic consequences on miRNAs, including both loss- and gain-of-function.

ORGANISM(S): Homo sapiens

PROVIDER: GSE274851 | GEO | 2025/08/13

REPOSITORIES: GEO

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Human Dicer hotspot mutation induces both loss and gain of miRNA function [RNA-seq]

Project description:The core miRNA biogenesis enzyme Dicer sustains recurrent mutations in cancer, which specifically compromise catalysis by its RNase IIIb domain. These are proposed to act as selective hypomorphs, since Dicer-RNase IIIb cleaves the 5p arms of pre-miRNA hairpins. However, the lack of knockin models has hindered a full understanding of the consequences of Dicer hotspot mutations for miRNA biogenesis. Here, we generated Dicer-KO and Dicer-S1344L (homozygous and hemizygous) hESCs; the latter is a non-catalytic mutation in RNase IIIa that impairs RNase IIIb activity. Consistent with our previous work, Dicer-KO is cell lethal in hESCs. However, in contrast to the expectation that Dicer hotspot mutations confer cell advantages, Dicer-S1344L knockin hESCs were subviable and also required a conditional genetic strategy for isolation. Small RNA sequencing using spike-in normalization reveals two broad trends: ablation of miRNA-5p species, and selective changes in miRNA-3p species. Curiously, we recognized a directional upregulation of miRNA-3p passenger strands, indicating a broad strand switch. Activity assays and Argonaute profiling of the transcriptome confirm that these confer increased repression capacity. Finally, we used in vitro assays to show 3p arm-nicked pre-miRNAs preferentially load miRNA-3p species into Argonaute, compared to corresponding miRNA/passenger duplexes. Overall, Dicer hotspot mutations have unexpected neomorphic consequences on miRNAs, including both loss- and gain-of-function.

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DICER1 hotspot mutations cause defective miRNA processing

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In vivo structure-function analysis of human Dicer reveals directional processing of precursor miRNAs

2012-07-13 | E-GEOD-36978 | biostudies-arrayexpress

Gene expression profiles of DKO172 cells expressing DICER1 wildtype or hotspot mutants

Project description:DICER1 plays a critical role in microRNA (miRNA) biogenesis. Recurrent somatic “hotspot” mutations at four mental binding sites within the RNase IIIb domain of DICER1, were identified in ovarian sex cord-stromal tumors and have since been described in other pediatric tumors. In this study, we identified and characterized DICER1 hotspot mutations in endometrial cancers derived from The Cancer Genome Atlas (TCGA) and our local tumor bank. DICER1 hotspot mutations are found in ~2% of endometrial tumors. Using Illumina and Sanger targeted resequencing we observed biallelic DICER1 mutations in more than 50% of cases with hotspot mutations and identified an additional recurrent mutation G1809R in 2 cases. Through small RNA deep sequencing and real-time PCR, we demonstrated mutations that add a positively charged side chain to residue 1809 have similar detrimental effects on 5p miRNA production as mutations at metal binding sites. In one case G1809R was compound heterozygous with a germline S839F mutation, which contributes to loss of DICER1 expression by promoting protein degradation. As expected, 5p miRNAs are globally reduced in tumors and cell lines with hotspot mutations. Pathway analysis of gene expression profiles indicated that genes derepressed due to loss of 5p miRNAs are strongly associated with cell cycle related pathways. Using a Dicer null cell line model, we demonstrated that DICER1 hotspot mutants abolished the inhibitory effects of wildtype DICER1 on cell proliferation upon re-expression. Furthermore, targets of let-7 family miRNAs are enriched among the upregulated genes, suggesting loss of let-7 may be impacting downstream pathways.

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