Human DICER1 hotspot mutation induces both loss and gain of miRNA function

Area of Science:

• Molecular Biology
• Genetics
• Cancer Biology

Background:

• The enzyme DICER1 is crucial for microRNA (miRNA) biogenesis, processing precursor miRNAs into mature strands.
• Recurrent DICER1 mutations in cancer often affect its RNase IIIb domain, impairing its function.
• Understanding the precise molecular consequences of these mutations is limited by the lack of appropriate models.

Purpose of the Study:

• To investigate the functional impact of DICER1 mutations on miRNA biogenesis and function using human embryonic stem cell models.
• To elucidate the molecular mechanisms by which DICER1 mutations alter miRNA strand selection and gene repression.

Main Methods:

• Generation of DICER1-knockout and DICER1(S1344L) mutant human embryonic stem cells (homozygous and hemizygous).
• Analysis of miRNA profiles using RNA-sequencing.
• In vitro assays to assess pre-miRNA processing and Argonaute loading.
• Assessment of gene repression capacity.

Main Results:

• DICER1 knockout cells lack canonical miRNAs.
• The DICER1(S1344L) mutation leads to ablation of miRNA-5p strands and selective changes in miRNA-3p strands.
• A directional upregulation of miRNA-3p passenger strands was observed, indicating a strand switch.
• 3p-arm-nicked pre-miRNAs preferentially load miRNA-3p species into Argonaute, enhancing gene repression capacity.

Conclusions:

• DICER1 hotspot mutations in cancer induce a significant strand switch in miRNA biogenesis, favoring the loading of miRNA-3p strands.
• This altered miRNA loading enhances the gene repression capacity of the DICER1 mutant cells.
• These findings expand the understanding of the molecular consequences of DICER1 mutations in cancer.