Biology subjects

Sim, G.

Publications and source records attributed to Sim, G..

5 recordsLinked to original sources

bioRxiv2025

Splice-switching ASOs targeting an Alu-derived exon in the AURKA 5'UTR collapse an SRSF1-AURKA-MYC oncogenic circuit in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) remains a highly lethal malignancy, driven by oncogenic KRAS mutations and dysregulated oncogenes, such as SRSF1, MYC, and AURKA. Although KRAS-targeted therapies are in development, resistance mechanisms underscore the need to identify alternative vulnerabilities. Here, we uncover an SRSF1-AURKA-MYC oncogenic circuit, wherein SRSF1 regulates AURKA 5UTR alternative splicing, enhancing AURKA protein expression; AURKA positively regulates SRSF1 and MYC post-translationally, independently of its kinase activity; and MYC in turn transcriptionally upregulates both SRSF1 and AURKA. Elevated SRSF1 in tumor cells promotes inclusion of an exonized Alu exon in the AURKA 5UTR, resulting in splicing-dependent mRNA accumulation and exon-junction- complex deposition. Modulating 5UTR splicing with splice-switching antisense oligonucleotides (ASOs) collapses the oncogenic circuit, reducing PDAC cell viability and triggering apoptosis. Our findings identify AURKA alternative splicing as a critical regulatory node and highlight ASO-mediated splice-switching as a potential therapeutic strategy that simultaneously targets SRSF1, AURKA, and MYC oncogenes.

cancer biology↗

bioRxiv2023

Determining the defining lengths between mature microRNAs/small interfering RNAs and tinyRNAs

MicroRNAs (miRNAs) and small interfering RNAs (siRNAs) are loaded into Argonaute (AGO) proteins, forming RNA-induced silencing complexes (RISCs). The assembly process establishes the seed, central, 3' supplementary, and tail regions across the loaded guide, enabling the RISC to recognize and cleave target RNAs. This guide segmentation is caused by anchoring the 3' end at the AGO PAZ domain, but the minimum guide length required for the conformation remains to be studied because there was no method by which to do so. Using a 3'[->]5' exonuclease ISG20, we determined the lengths of AGO-associated miR-20a and let-7a with 3' ends that no longer reach the PAZ domain. Unexpectedly, miR-20a and let-7a needed different lengths, 19 and 20 nt, respectively, to maintain their RISC conformation. This difference can be explained by the low affinity of the PAZ domain for the adenosine at g19 of let-7a, suggesting that the tail-region sequence slightly alters the minimum guide length. We also present that 17-nt guides are sufficiently short enough to function as tinyRNAs (tyRNAs) whose 3 ends are not anchored at the PAZ domain. Since tyRNAs do not have the prerequisite anchoring for the standardized guide segmentation, they would recognize targets differently from miRNAs and siRNAs.

biochemistry↗

bioRxiv2022

Manganese-dependent microRNA trimming by 3'->5' exonucleases generates 14-nucleotide or shorter tiny RNAs

MicroRNAs (miRNAs) are about 22-nucleotide (nt) non-coding RNAs forming the effector complexes with Argonaute (AGO) proteins to repress gene expression. Although tiny RNAs (tyRNAs) shorter than 19 nt have been found to bind to plant and vertebrate AGOs, their biogenesis remains a long-standing question. Here, our in vivo and in vitro studies show several 3[->]5 exonucleases, such as interferon-stimulated gene 20 kDa (ISG20), three prime repair exonuclease 1 (TREX1), and ERI1 (enhanced RNAi, also known as 3hExo), capable of trimming AGO-associated full-length miRNAs to 14 nt or shorter tyRNAs. Their guide trimming occurs in a manganese-dependent manner but independently of the guide sequence and the loaded four human AGO paralogs. We also show that ISG20-mediated guide trimming makes Argonaute3 (AGO3) a slicer. Given the high Mn2+ concentrations in stressed cells, virus-infected cells, and neurodegeneration, our study sheds light on the roles of the Mn2+-dependent exonucleases in remodeling gene silencing.

molecular biology↗

bioRxiv2021

Label-free three-dimensional analyses of live cells with deep-learning-based segmentation exploiting refractive index distributions

Visualisations and analyses of cellular and subcellular organelles in biological cells is crucial for the study of cell biology. However, existing imaging methods require the use of exogenous labelling agents, which prevents the long-time assessments of live cells in their native states. Here we propose and experimentally demonstrate three-dimensional segmentation of subcellular organelles in unlabelled live cells, exploiting a 3D U-Net-based architecture. We present the high-precision three-dimensional segmentation of cell membrane, nucleus membrane, nucleoli, and lipid droplets of various cell types. Time-lapse analyses of dynamics of activated immune cells are also analysed using label-free segmentation. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/445351v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@b92093org.highwire.dtl.DTLVardef@9caa8org.highwire.dtl.DTLVardef@d81408org.highwire.dtl.DTLVardef@b3c87_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2020

Human Argonaute2 and Argonaute3 are catalytically activated by different lengths of guide RNA

RNA interfering is a eukaryote-specific gene silencing by 20[~]23 nucleotide (nt) microRNAs and small interfering RNAs that recruit Argonaute proteins to complementary RNAs for degradation. In humans, Argonaute2 (AGO2) has been known as the only slicer while Argonaute3 (AGO3) barely cleaves RNAs. Therefore, the intrinsic slicing activity of AGO3 remains controversial and a long-standing question. Here, we report 14-nt 3' end-shortened variants of let-7a, miR-27a, and specific miR-17-92 families that make AGO3 an extremely competent slicer by an [~] 82-fold increase in target cleavage. These RNAs, named cleavage-inducing tiny guide RNAs (cityRNAs), conversely lower the activity of AGO2, demonstrating that AGO2 and AGO3 have different optimum guide lengths for target cleavage. Our study sheds light on the role of tiny guide RNAs.

biochemistry↗