Cell fractionation reveals mis-annotation of human microRNAs
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ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE183863 | GEO | 2025/04/23
REPOSITORIES: GEO
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Project description:MicroRNAs (miRNAs) form the sequence recognition component of the RNA-induced silencing complex (RISC), bringing Argonaute (AGO) and other RISC-associated proteins to target transcripts where they mediate post-transcriptional gene silencing. High-throughput sequencing has helped to catalogue several thousand human miRNAs, as well as a plethora of other small RNAs derived from larger transcripts. Here, we take a closer inspection of sequencing data derived from cellular fractionation and AGO-RNA immunoprecipitation and find that a subset of small RNAs, despite being denoted as miRNAs, are in fact almost exclusively nuclear and do not associate with AGO. Experimental validation of a select number of these small RNAs also fails to show endogenous miRNA-like activity, suggesting they are degradation products from larger transcripts that have been mis-annotated. Despite this, the presumed miRNA functions of almost 20 of these have collectively been the subject of several hundred publications, emphasising the need to filter unlikely miRNA candidates from sequencing data and large miRNA-sequence repositories.
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Project description:MicroRNAs (miRNAs) form the sequence recognition component of the RNA-induced silencing complex (RISC), bringing Argonaute (AGO) and other RISC-associated proteins to target transcripts where they mediate post-transcriptional gene silencing. High-throughput sequencing has helped to catalogue several thousand human miRNAs, as well as a plethora of other small RNAs derived from larger transcripts. Here, we take a closer inspection of sequencing data derived from cellular fractionation and AGO-RNA immunoprecipitation and find that a subset of small RNAs, despite being denoted as miRNAs, are in fact almost exclusively nuclear and do not associate with AGO. Experimental validation of a select number of these small RNAs also fails to show endogenous miRNA-like activity, suggesting they are degradation products from larger transcripts that have been mis-annotated. Despite this, the presumed miRNA functions of almost 20 of these have collectively been the subject of several hundred publications, emphasising the need to filter unlikely miRNA candidates from sequencing data and large miRNA-sequence repositories.
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Project description:The Argonautes (AGOs) are widely expressed, evolutionarily conserved RNA binding proteins that play an important role in gene expression regulation. The AGOs bind to small regulatory noncoding RNAs such as micro RNAs (miRNAs), short interfering RNAs (siRNAs), Piwi-interacting RNAs (piRNAs) etc. The small regulatory noncoding RNAs serve the function of guiding the AGOs to the right target RNAs by complementary base pairing. Additionally, the AGOs interact with GW182 (TNRC6A/-B/-C) proteins and together with small RNAs, they form an effector ribonucleo protein complex named, RNA Induced Silencing Complex (RISC) that regulates several aspects of transcriptional and post-transcriptional gene expression. ALG-1 (Argonaute Like Gene) and ALG-2 are the AGO proteins in C. elegans that are required for miRNA mediated gene expression regulation. Our efforts towards the characterization of the protein complexes comprised of ALG-1 led to the identification of DPF-3, a conserved protease belonging to clinically relevant Di Peptidyl Peptidase IV family, as the novel interacting partner of ALG-1. We have further explored the role of DPF-3 in AGO regulation.
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Project description:It has previously been assumed that the generally high stability of microRNAs (miRNAs) reflects their tight association with Argonaute (Ago) proteins, essential components of the RNA-induced silencing complex (RISC). However, recent data have suggested that the majority of mature miRNAs are not, in fact, Ago associated. Here, we demonstrate that endogenous human miRNAs vary widely, by >100-fold, in their level of RISC association and show that the level of Ago binding is a better indicator of inhibitory potential than is the total level of miRNA expression. While miRNAs of closely similar sequence showed comparable levels of RISC association in the same cell line, these varied between different cell types. Moreover, the level of RISC association could be modulated by overexpression of complementary target mRNAs. Together, these data indicate that the level of RISC association of a given endogenous miRNA is regulated by the available RNA targetome and predicts miRNA function. This series includes microRNA sequencing data for human cell lines 293, C8166, A549, SH-SY5Y, and an EBV-transformed LCL line. For each cell line, total small RNA isolated by TRIzol was sequenced for comparison to RISC-associated microRNAs as determined by sequencing small RNAs from an Argonaute immunoprecipitation.
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Project description:Small RNAs regulate the genetic networks through a ribonucleoprotein complex called the RNA induced silencing complexes (RISC), which in mammals contains at its center one of four Argonaute proteins (Ago1-4). A key regulatory event in the RNAi and miRNA pathways is Ago loading, where double stranded small RNA duplexes are incorporated into RISC (pre-RISC) and then become single stranded (mature-RISC), a process that is not well understood. The Agos contain an evolutionary conserved PAZ (Piwi/Argonaute/Zwille) domain whose primary function is to bind the 3’-end of small RNAs. We created multiple Paz domain disrupted Ago mutant proteins and studied their biochemical properties and biological functionality in cells. We found that the Paz domain is dispensable for Ago loading of slicing-competent RISC. In contrast, in the absence of slicer activity or slicer substrate duplex RNAs, Paz-disrupted Agos bound duplex siRNAs but were unable to unwind/eject the passenger strand and form functional RISC complexes. We have discovered that the highly conserved Paz domain plays an important role in RISC activation, providing new mechanistic insights into how miRNAs regulate genes, as well as new insights for future design of miRNA and RNAi-based therapeutics. Various Argonautes associated small RNA profiles were generated by deep sequencing the Agos-IP samples in HEK293 Cells transfected with corresponding Argonaute.
2012-07-12 | E-GEOD-39146 | biostudies-arrayexpress
Project description:One goal of viral infection is to reprogram the host cell to optimize viral replication. As part of this process, viral miRNAs may compete for components of the miRNA/siRNA pathway as well as regulate cellular targets. Mouse Cytomegalovirus has been described to generate large numbers of viral miRNAs during lytic infection and was therefore used to analyze the impact of viral miRNAs on the host cell small RNA system as well as to check for sorting of viral small RNAs into specific Ago-proteins. Deep sequencing analysis of MCMV infected cells revealed that viral miRNAs represent only app. 13% of all detected miRNAs. All previously described MCMV miRNAs with the exception of miR-m88-1* were confirmed and for the MCMV miR-m01-1 hairpin an additional miRNA, designated miR-m01-1-3p, was found. Its presence was confirmed by qPCR and Northern Blot. Deep sequencing after RISC IP with antibodies specific for either Ago1 or Ago2 showed that all MCMV miRNAs are loaded into both RISC complexes. The ratio of MCMV to mouse miRNAs was not increased after immunoprecipitation of Ago-proteins. Viral miRNAs therefore do not overwhelm the host miRNA processing system nor are they preferentially incorporated into RISC. We found that 3 mouse miRNAs showed an altered expression due to MCMV infection. Down-regulation of miR-27a, as previously described, could be confirmed. In addition, miR-26a was down-regulated and an up-regulation of miR-7a dependent on viral protein expression could be observed. Examination of small RNA expression in uninfected vs. infected cells, immunoprecipitation + sequencing of Ago1 and Ago2 loaded small RNAs in infected cells
2012-06-30 | E-GEOD-36919 | biostudies-arrayexpress
Project description:It has previously been assumed that the generally high stability of microRNAs (miRNAs) reflects their tight association with Argonaute (Ago) proteins, essential components of the RNA-induced silencing complex (RISC). However, recent data have suggested that the majority of mature miRNAs are not, in fact, Ago associated. Here, we demonstrate that endogenous human miRNAs vary widely, by >100-fold, in their level of RISC association and show that the level of Ago binding is a better indicator of inhibitory potential than is the total level of miRNA expression. While miRNAs of closely similar sequence showed comparable levels of RISC association in the same cell line, these varied between different cell types. Moreover, the level of RISC association could be modulated by overexpression of complementary target mRNAs. Together, these data indicate that the level of RISC association of a given endogenous miRNA is regulated by the available RNA targetome and predicts miRNA function.
2014-05-30 | GSE58127 | GEO
Project description:One goal of viral infection is to reprogram the host cell to optimize viral replication. As part of this process, viral miRNAs may compete for components of the miRNA/siRNA pathway as well as regulate cellular targets. Mouse Cytomegalovirus has been described to generate large numbers of viral miRNAs during lytic infection and was therefore used to analyze the impact of viral miRNAs on the host cell small RNA system as well as to check for sorting of viral small RNAs into specific Ago-proteins. Deep sequencing analysis of MCMV infected cells revealed that viral miRNAs represent only app. 13% of all detected miRNAs. All previously described MCMV miRNAs with the exception of miR-m88-1* were confirmed and for the MCMV miR-m01-1 hairpin an additional miRNA, designated miR-m01-1-3p, was found. Its presence was confirmed by qPCR and Northern Blot. Deep sequencing after RISC IP with antibodies specific for either Ago1 or Ago2 showed that all MCMV miRNAs are loaded into both RISC complexes. The ratio of MCMV to mouse miRNAs was not increased after immunoprecipitation of Ago-proteins. Viral miRNAs therefore do not overwhelm the host miRNA processing system nor are they preferentially incorporated into RISC. We found that 3 mouse miRNAs showed an altered expression due to MCMV infection. Down-regulation of miR-27a, as previously described, could be confirmed. In addition, miR-26a was down-regulated and an up-regulation of miR-7a dependent on viral protein expression could be observed.
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