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LARP1 mRNP scaffolds mTORC1 to stimulate translation initiation of an essential class of mRNAs

ABSTRACT: The RNA biding protein, LARP1, has been proposed to function downstream of mTORC1 to positively regulate the translation of 5’TOP mRNAs such as ribosome protein (RP) mRNAs. However, its regulatory roles in mTORC1-mediated translation remain unclear. PAR-CLIP of LARP1 revealed its direct and dynamic interactions with RP mRNAs through pyrimidine-enriched sequences in the 5’UTR of RP mRNAs when mTOR activity is inhibited. Importantly, this LARP1 is a direct substrate of mTORC1 and S6K1/Akt, and phosphorylated LARP1 scaffolds mTORC1 on translation-competent mRNAs to facilitate 4EBP1 and S6K1 phosphorylation. Ablation of LARP1 causes multiple defects in the processes of translation including abnormal eIF4G1 interaction with RP mRNAs and inefficient RP mRNA elongation thereby reducing ribosome biogenesis and cell proliferation. These observations illustrate that LARP1 functions both an effector and a regulator for local mTORC1 activity, and acts as a molecular switch for ribosome biogenesis by sensing growth factor/nutrient signaling.

ORGANISM(S): Homo sapiens

PROVIDER: GSE59599 | GEO | 2014/07/31

SECONDARY ACCESSION(S): PRJNA255679

REPOSITORIES: GEO

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LARP1 mRNP scaffolds mTORC1 to stimulate translation initiation of an essential class of mRNAs

Project description:The RNA biding protein, LARP1, has been proposed to function downstream of mTORC1 to positively regulate the translation of 5M-bM-^@M-^YTOP mRNAs such as ribosome protein (RP) mRNAs. However, its regulatory roles in mTORC1-mediated translation remain unclear. PAR-CLIP of LARP1 revealed its direct and dynamic interactions with RP mRNAs through pyrimidine-enriched sequences in the 5M-bM-^@M-^YUTR of RP mRNAs when mTOR activity is inhibited. Importantly, this LARP1 is a direct substrate of mTORC1 and S6K1/Akt, and phosphorylated LARP1 scaffolds mTORC1 on translation-competent mRNAs to facilitate 4EBP1 and S6K1 phosphorylation. Ablation of LARP1 causes multiple defects in the processes of translation including abnormal eIF4G1 interaction with RP mRNAs and inefficient RP mRNA elongation thereby reducing ribosome biogenesis and cell proliferation. These observations illustrate that LARP1 functions both an effector and a regulator for local mTORC1 activity, and acts as a molecular switch for ribosome biogenesis by sensing growth factor/nutrient signaling. LARP1-bound RNA regions were sequenced from HEK293T cells under growing or mTOR-inactive conditions. In parallel, mRNA abundance was quantified, in biological duplicate, from HEK293T cells under the same conditions.

2014-07-31 | E-GEOD-59599 | biostudies-arrayexpress

The 40S-LARP1 complex reprograms the cellular translatome upon mTOR inhibition to preserve the protein synthetic capacity

Project description:Ribosomes execute the transcriptional program in every cell. Critical to sustain nearly all cellular activities, ribosome biogenesis requires the translation of ~200 factors of which 80 are ribosomal proteins (RPs). As ribosome synthesis depends on RP mRNAs translation, a priority within the translatome architecture should exist to ensure the preservation of ribosome biogenesis capacity, particularly under adverse growth conditions. Here we show that under critical metabolic constraints characterized by mTOR inhibition, LARP1 complexed with the 40S subunit protects from ribophagy the mRNAs regulon for ribosome biogenesis and protein synthesis, acutely preparing the translatome to promptly resume ribosomes production after growth conditions return permissive. Characterizing the LARP1-protected translatome revealed a set of 5’TOP transcript isoforms other than RPs involved in energy production and in mitochondrial function, among other processes, indicating that the mTOR-LARP1-5’TOP axis acts at the translational level as a primary guardian of the cellular anabolic capacity

2021-10-30 | GSE186779 | GEO

mTORC1 controls a dynamic program of TOP mRNA translation via LARP1

Project description:LARP1 has been proposed to control the translation of TOP mRNAs downstrteam of mTORC1. Here we used ribosome profiling to analyze transcriptome-wide changes in translation following mTOR inhibition in wild-type HEK-293T cells and cells where LARP1 (sgLARP1) or LARP1 and its homologue LARP1B (sgLARP1/1B) have been deleted using CRISPR/Cas9.

2020-02-12 | GSE132703 | GEO

eIF4A1 enhances LARP1-mediated translational repression during mTORC1 inhibition

Project description:Eukaryotic translation initiation factor (eIF) 4A — a DEAD-box RNA-binding protein — plays an essential role in translation initiation. Recent reports have suggested helicase-dependent and helicase-independent functions for eIF4A, but the multifaceted roles of eIF4A have not been fully explored. Here, we show that eIF4A1 enhances translational repression during the inhibition of mechanistic target of rapamycin complex 1 (mTORC1), an essential kinase complex controlling cell proliferation. RNA pulldown followed by sequencing revealed that eIF4A1 preferentially binds to mRNAs containing terminal oligopyrimidine (TOP) motifs (TOP mRNAs), whose translation is rapidly repressed upon mTORC1 inhibition. This selective interaction depends on a La-related RNA-binding protein, LARP1. Ribosome profiling revealed that deletion of EIF4A1 attenuated the translational repression of TOP mRNAs upon mTORC1 inactivation. Moreover, eIF4A1 increases the affinity between TOP mRNAs and LARP1 and thus ensures stronger translational repression upon mTORC1 inhibition. Our data show the multimodality of eIF4A1 in modulating protein synthesis through an inhibitory binding partner and provide a unique example of the repressive role of a universal translational activator.

2024-02-13 | GSE184247 | GEO

TMT quantitative proteomics of a) protrusions and cells bodies of a panel of cell lines, b) protrusions and cells bodies of MDA-MB231 cells collected after 1 h, 2 h, 4 h, 8 h post- induction of protrusions, c) non-transfected (nt) or LARP6 siRNAs MDA-MB231 cells grown on either close or open collagen coated transwells and d) protrusions and cells bodies of a panel of breast cell lines.

Project description:Translation of Ribosomal Protein coding mRNAs (RP-mRNAs) constitutes a key step in regulation of ribosome biogenesis in human cells, but the exact mechanisms which modulate RP-mRNAs translation under various cellular and environmental conditions remain poorly understood. Here we show that the subcellular localisation of RP-mRNAs acts as a key regulator of their translation in mesenchymal-like migratory cells. As cells invade into their surroundings, RP-mRNAs localise to the actin-rich protrusions at the front of the cells. This localisation is mediated by La related protein-6 (LARP6), an RNA Binding Protein (RBP) that is enriched in protrusions. Importantly, translation initiation and elongation factors are also enriched in protrusions. LARP6 dependent localisation of RP-mRNAs enhances their translation, leading to up-regulation of ribosome biogenesis and increased overall protein synthesis. In breast carcinomas, enhanced expression of LARP6 is associated with Epithelial to Mesenchymal Transition (EMT), and can be therapeutically targeted by a small molecule inhibitor which interferes with LARP6 RNA binding. These findings reveal an RNA localisation based post-transcriptional mechanism that governs ribosome biogenesis in migratory cells, and implicate a role for this process in cancer progression downstream of EMT.

2021-09-08 | PXD015808 | Pride

GCN2 suppresses TOP mRNA translation via LARP1

Project description:La-related protein 1 (LARP1) has been identified as a key translational inhibitor of terminal oligopyrimidine tract (TOP) mRNAs downstream of the nutrient sensing protein kinase complex, mTORC1. LARP1 exerts this inhibitory effect on TOP mRNA translation by binding to the mRNA cap and the adjacent 5’TOP motif, resulting in the displacement of the eIF4E complex from TOP mRNAs. In the present study, we identify a second nutrient sensing kinase GCN2 that converges on LARP1 to control TOP mRNA translation. GCN2 inhibits TOP mRNA translation via ATF4-dependent transcriptional induction of LARP1 mRNAs and GCN1-mediated recruitment of LARP1 to stalled ribosomes. We performed ATF4 ChIP-seq experiments in both WT and GCN2 KO MEFs with or without leucine deprivation.

2022-08-31 | GSE166590 | GEO

p70 S6 Kinase 1-dependent alterations in cortical mRNA translation in fragile X syndrome mice

Project description:Fragile X syndrome (FXS) is caused by loss of the fragile X mental retardation protein (FMRP). The mechanism by which FMRP regulates messenger RNA (mRNA) translation remains disputed. We observed reduced ribosome footprint abundance in the majority of differentially translated genes in cortices of FXS mice, which was correlated with an increased rate of ribosome translocation that was normalized by inhibition of p70 S6 Kinase 1 (S6K1). We also show that alterations in translation efficiencies across mRNAs in FXS mouse cortices exhibit a positive to negative gradation with coding sequence length, which is prevented by the genetic reduction of S6K1. Our findings reveal the identity of dysregulated mRNAs and a molecular mechanism by which reduction of S6K1 prevents altered translation in FXS.

2020-10-31 | GSE143659 | GEO

Small and large ribosomal subunit deficiencies lead to distinct gene expression signatures that reflect cellular growth rate

Project description:Levels of the ribosome, the conserved molecular machine that mediates translation, are tightly linked to cellular growth rate. In humans, ribosomopathies are diseases associated with cell-type-specific pathologies and reduced ribosomal protein (RP) levels. Because gene expression defects resulting from ribosome deficiency have not yet been experimentally defined, we systematically probed mRNA, translation, and protein signatures that were either unlinked or linked to cellular growth rate in RP-deficient yeast cells. Ribosome concentration was seen to be associated with translation of gene sub-classes, and profound general secondary effects of RP loss on the spectrum of cellular mRNAs were seen. Among these effects, growth-defective 60S mutants increased synthesis of proteins involved in proteasome-mediated degradation, whereas 40S mutants accumulated mature 60S subunits and increased translation of ribosome biogenesis genes. These distinct signatures of protein synthesis suggest intriguing and currently mysterious differences in the cellular consequences of deficiency for small and large ribosomal subunits.

2018-11-29 | GSE121189 | GEO

LARP1 senses free ribosomes to coordinate supply and demand of ribosomal proteins

Project description:Terminal oligopyrimidine motif-containing (TOP) mRNAs encode all ribosomal proteins in mammals and are regulated to tune ribosome synthesis to cell state. Previous studies implicate LARP1 in 40S- or 80S-ribosome complexes that repress and stabilize TOP mRNAs. However, a mechanistic understanding of how LARP1 and TOP mRNAs interact with ribosomes to coordinate TOP mRNA outcomes is lacking. Here, we show that LARP1 senses the cellular supply of ribosomes by directly binding non-translating 80S ribosomes. Cryo-EM structures reveal a previously uncharacterized domain of LARP1 bound to and occluding the 40S mRNA channel and mutations at the LARP1-ribosome interface block formation of the 40S/80S-LARP1-TOP complexes. Free cytosolic ribosomes induce sequestration of TOP mRNAs in repressed 80S-LARP1-TOP complexes independent of alterations in mTOR signaling. Together, this work demonstrates a ribosome-sensing function of LARP1 that allows it to tune ribosome protein synthesis to the availability of free ribosomes.

2023-10-28 | GSE246077 | GEO

Parallel global profiling of plant TOR dynamics reveals a conserved role for LARP1 in protein translation

Project description:TARGET OF RAPAMYCIN (TOR) is a deeply conserved protein kinase that coordinates eukaryotic metabolism with nutrient availability. In mammals, TOR specifically promotes translation of ribosomal protein mRNAs when amino acids are available to support protein synthesis. The mechanisms controlling translation downstream from TOR remain contested, however, and are largely unexplored in plants. Here, we took parallel global profiling approaches to define the in planta TOR-regulated proteome, and phosphoproteome. We found that TOR regulates ribosome biogenesis in plants at multiple levels. To investigate this further, we focused on a putative TOR substrate identified in our phosphoproteome: LARP1, a eukaryotic RNA-binding protein that is proposed to mediate TOR translational control of 5′TOP mRNAs in humans.

2021-01-05 | PXD019942 | Pride

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