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The Lupus autoantigen La prevents mis-channeling of tRNA fragments into the human microRNA pathway [miRNA-seq]

ABSTRACT: The Lupus autoantigen (La) is a single-stranded RNA-binding protein that stabilizes RNA polymerase III (pol III) transcripts and supports RNA folding. In addition, La has been implicated in different steps of the mammalian small RNA pathway. Here, we have analyzed effects of La depletion on the Argonaute (Ago)-bound small RNAs in human cells. We find that in the absence of La, distinct tRNA fragments are loaded into Ago protein complexes and our data suggests that La prevents the production and loading of such tRNA fragments. However, one specific isoleucine tRNA escapes this regulation and produces both a functional tRNA as well as a microRNA (miRNA). We demonstrate that fully complementary 5' leader and 3' trailer of the pre-tRNA-Ile form a double-stranded RNA molecule that has low affinity to La. Instead, Exportin 5 (Xpo5) recognizes it as miRNA precursor and transports it into the cytoplasm for Dicer processing and Ago loading. Thus, La functions as gatekeeper to ensure correct tRNA generation and to protect the miRNA pathway from potentially functional tRNA fragments.

ORGANISM(S): Homo sapiens

PROVIDER: GSE76676 | GEO | 2016/06/22

SECONDARY ACCESSION(S): PRJNA308305

REPOSITORIES: GEO

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The Lupus autoantigen La prevents mis-channeling of tRNA fragments into the human microRNA pathway [PAR-CLIP]

Project description:The Lupus autoantigen (La) is a single-stranded RNA-binding protein that stabilizes RNA polymerase III (pol III) transcripts and supports RNA folding. In addition, La has been implicated in different steps of the mammalian small RNA pathway. Here, we have analyzed effects of La depletion on the Argonaute (Ago)-bound small RNAs in human cells. We find that in the absence of La, distinct tRNA fragments are loaded into Ago protein complexes and our data suggests that La prevents the production and loading of such tRNA fragments. However, one specific isoleucine tRNA escapes this regulation and produces both a functional tRNA as well as a microRNA (miRNA). We demonstrate that fully complementary 5' leader and 3' trailer of the pre-tRNA-Ile form a double-stranded RNA molecule that has low affinity to La. Instead, Exportin 5 (Xpo5) recognizes it as miRNA precursor and transports it into the cytoplasm for Dicer processing and Ago loading. Thus, La functions as gatekeeper to ensure correct tRNA generation and to protect the miRNA pathway from potentially functional tRNA fragments.

2016-06-22 | GSE77897 | GEO

XPO5 is required for miRNA biogenesis and promotes primary miRNA processing independent of RanGTP

Project description:XPO5 mediates nuclear export of miRNA hairpin precursors in a RanGTP-dependent manner. However, the requirement of XPO5 for global miRNA biogenesis and mammalian development and XPO5-associated RNA species are not determined. Here we show that XPO5 is required for mouse embryonic development and morphogenesis of skin and brain. Loss of XPO5 compromises the biogenesis of most miRNAs and that leads to severe developmental defects. Surprisingly, XPO5 not only associates with miRNA hairpin precursors but also pervasively binds to double-stranded RNA (dsRNA) regions found in many cellular RNAs and some clustered pri-miRNAs. The binding of XPO5 to miR-17~92 pri-miRNAs is RanGTP-independent. Pre-incubation with XPO5 enhances the processing efficiency of the DROSHA/DGCR8 microprocessor. Together, our studies demonstrate the requirement of XPO5 for miRNA biogenesis and mouse development, reveal an unexpected role of XPO5 for recognizing and facilitating the nuclear cleavage of clustered pri-miRNAs and identify numerous cellular RNAs as novel XPO5 subtracts.

2020-02-19 | GSE111964 | GEO

Slicing-Independent RISC Activation Requires the Argonaute PAZ Domain

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

Re-evaluation of the roles of DROSHA, Exportin 5, and DICER in microRNA biogenesis

Project description:Biogenesis of canonical microRNAs (miRNAs) involves multiple steps: nuclear processing of primary miRNA (pri-miRNA) by DROSHA, nuclear export of precursor miRNA (pre-miRNA) by Exportin 5 (XPO5), and cytoplasmic processing of pre-miRNA by DICER. To gain a deeper understanding of the contribution of each of these maturation steps, we deleted DROSHA, XPO5, and DICER in the same human cell line, and analyzed their effects on miRNA biogenesis. Canonical miRNA production was completely abolished in DROSHA-deleted cells while we detected a few DROSHA-independent miRNAs including three previously unidentified noncanonical miRNAs (miR-7706, miR-3615, and miR-1254). In contrast to DROSHA knockout, many canonical miRNAs were still detected without DICER albeit at markedly reduced levels. In the absence of DICER, pre-miRNAs are loaded directly onto AGO and trimmed at the 3â² end, yielding miRNAs from the 5â² strand (5p miRNAs). Interestingly, in XPO5 knockout cells, most miRNAs are affected only modestly, suggesting that XPO5 is necessary but not critical for miRNA maturation. Our study demonstrates an essential role of DROSHA and an important contribution of DICER in the canonical miRNA pathway, and reveals that the function of XPO5 can be complemented by alternative mechanisms. Thus, this study allows us to understand differential contributions of key biogenesis factors, and provides with valuable resources for miRNA research. Two independent sequencing experiments (set 1 and set 2, respectively) were performed using 9 samples.

2016-03-17 | E-GEOD-77989 | biostudies-arrayexpress

Slicing-Independent RISC Activation Requires the Argonaute PAZ Domain

2012-07-12 | GSE39146 | GEO

Re-evaluation of the roles of DROSHA, Exportin 5, and DICER in microRNA biogenesis

Project description:Biogenesis of canonical microRNAs (miRNAs) involves multiple steps: nuclear processing of primary miRNA (pri-miRNA) by DROSHA, nuclear export of precursor miRNA (pre-miRNA) by Exportin 5 (XPO5), and cytoplasmic processing of pre-miRNA by DICER. To gain a deeper understanding of the contribution of each of these maturation steps, we deleted DROSHA, XPO5, and DICER in the same human cell line, and analyzed their effects on miRNA biogenesis. Canonical miRNA production was completely abolished in DROSHA-deleted cells while we detected a few DROSHA-independent miRNAs including three previously unidentified noncanonical miRNAs (miR-7706, miR-3615, and miR-1254). In contrast to DROSHA knockout, many canonical miRNAs were still detected without DICER albeit at markedly reduced levels. In the absence of DICER, pre-miRNAs are loaded directly onto AGO and trimmed at the 3′ end, yielding miRNAs from the 5′ strand (5p miRNAs). Interestingly, in XPO5 knockout cells, most miRNAs are affected only modestly, suggesting that XPO5 is necessary but not critical for miRNA maturation. Our study demonstrates an essential role of DROSHA and an important contribution of DICER in the canonical miRNA pathway, and reveals that the function of XPO5 can be complemented by alternative mechanisms. Thus, this study allows us to understand differential contributions of key biogenesis factors, and provides with valuable resources for miRNA research.

2016-03-17 | GSE77989 | GEO

An altered basis of tRNA processing is linked to a distinct La protein in T. thermophila

Project description:La proteins bind the UUU-3’OH sequence found at the 3’-end of nascent RNA polymerase III transcripts, including pre-tRNAs, using a tandem arrangement of a winged-helix fold La motif (LaM) and an adjacent RNA recognition motif (RRM). La binding in diverse species results in protection of the 3’-end from exonucleases, stabilization of the pre-tRNA species and promotion of pre-tRNA folding until the UUU-3’OH containing trailer is endonucleolytically cleaved. Based on sequence conservation in the LaM, the Tetrahymena thermophila protein MLP1 (and related factors in other alveolates) has been hypothesized to function as a genuine La protein, despite the absence of the adjacent RRM found in La proteins of all prior investigated species. We show that MLP1 functions as a genuine La protein in that it binds and affects the processing of pre-tRNAs in T. thermophila and when expressed as a heterologous factor in fission yeast, however, unlike in other examined eukaryotes, depletion of MLP1 results in 3’-trailer stabilization. We also observed that 3’-trailers in T. thermophila are uniquely shortened relative to other examined eukaryotes, and that 5’-leaders in this species have evolved to disfavour pre-tRNA leader/trailer pairing. Our data suggest that the variant MLP1 architecture relative to other genuine La proteins is linked to an altered mechanism of tRNA processing in T. thermophila.

2022-09-13 | GSE199642 | GEO

A Tetrahymena Piwi Bound to Mature tRNA 3' Fragments Activates the Exonuclease Xrn2 for RNA Processing in the Nucleus

Project description:Emerging evidence suggests that Ago/Piwi proteins function in the nucleus as well as the cytoplasm to control gene expression, but the mechanisms they employ in the nucleus remain poorly defined. The Tetrahymena thermophila Ago/Piwi protein Twi12 is essential for growth and functions in the nucleus. We show that Twi12 interacts with the exonuclease Xrn2. Twi12 functions to stabilize and localize Xrn2 in vivo, as well as activate its exonuclease activity in vitro. When Twi12 or Xrn2 are depleted, pre-rRNA processing intermediates accumulate and mature rRNA levels decline. RNA polymerase I and II (RNAP I and II) transcripts also accumulate. Twi12 function depends on small RNA (sRNA) binding, which is required for its nuclear import. Twi12-bound sRNAs are Dicer-independent 3' tRNA fragments that we propose may not be involved in sequence-specific base pairing to targets. Our findings suggest a role for tRNA fragments and an Ago/Piwi protein in global control of gene expression through interaction with a conserved exonuclease.

2012-08-31 | GSE38507 | GEO

Amyotrophic Lateral Sclerosis-associated Mutants of SOD1 Modulate miRNA Biogenesis through Aberrant Interactions with Exportin 5

Project description:Mutations in SOD1 (Superoxide Dismutase 1) gene are associated with amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease. By employing ascorbate peroxidase (APEX)-based proximity labeling, coupled with LC-MS/MS analysis, we uncovered 37 and 28 proteins exhibiting higher abundance in the proximity proteomes of SOD1G85R and SOD1G93A, respectively, than that of the wild-type SOD1. Immunoprecipitation followed by western blot analysis confirmed the preferential binding of one of these proteins, exportin 5 (XPO5), toward the two mutants of SOD1 over its wild-type counterpart. In line with the established function of XPO5 in pre-miRNA transport, we observed diminished nucleocytoplasmic transport of pre-miRNAs in cells with ectopic expression of the two SOD1 mutants over those expressing the wild-type counterpart. On the other hand, RT-qPCR results revealed significant elevations in mature miRNA in cells expressing the two SOD1 mutants, which are attributed to diminished inhibitory effect of XPO5 on Dicer-mediated cleavage of pre-miRNA to mature miRNA. Together, our chemoproteomic approach led to the revelation of a novel mechanism through which ALS-associated mutants of SOD1 perturb miRNA biogenesis, i.e., through aberrant binding toward XPO5.

2024-01-26 | PXD035452 | Pride

A Tetrahymena Piwi protein and the exonuclease Xrn2 form a complex that is essential for ribosome biogenesis

2012-08-31 | E-GEOD-38507 | biostudies-arrayexpress

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