Characterization of the 40S-LARP1 complex in a model of ribosome biogenesis-addicted tumors
[eng] In the process of neoplastic transformation, hyperactivation of proliferative signaling and the deregulation of cellular metabolism are required to ensure uncontrolled cellular growth and proliferation as well as high levels of energy production. To do so, hyperactivation of key oncogenes like...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2024 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/215954 |
| Acceso en línea: | https://hdl.handle.net/2445/215954 http://hdl.handle.net/10803/692365 |
| Access Level: | acceso abierto |
| Palabra clave: | Oncologia Càncer colorectal Ribosomes Ciències de la salut Oncology Colorectal cancer Medical sciences |
| Sumario: | [eng] In the process of neoplastic transformation, hyperactivation of proliferative signaling and the deregulation of cellular metabolism are required to ensure uncontrolled cellular growth and proliferation as well as high levels of energy production. To do so, hyperactivation of key oncogenes like MYC and oncogenic pathways such as mTOR, PI3K/AKT, Ras/MEK and WNT/β-catenin are essential to maintain high levels of protein synthesis and to sustain the production of ribosomes, the proteins factories of the cell. Ribosomes are ribonucleoprotein complexes composed by 80 ribosomal proteins (RPs) and 4 rRNA. The generation of new ribosomes is a multi-step and high energy- demanding process that requires a tight regulation from transcription to translation and beyond. In this regard, the production of RP is coordinated at the post-transcriptional level through a cis-element, termed Terminal Oligopyrimidine (TOP) motif, present at the transcriptional start site of their cognate transcripts. mTOR, which senses the external and internal metabolic cues in the cell, acts as a translational switch of this family of 5'TOP mRNAs accordingly. Our group has discovered that 5'TOP mRNAs are stabilized and preserved in a biochemical complex composed by the RNA-binding protein LARP1 and the small ribosomal subunit 40S, and that mTOR inhibition triggers the formation of the 40S-LARP1-5'TOP complex. Importantly, we recently described that the 40S-LARP1-5'TOPs complex acts as an anabolic storage in the form of stable pools of translationally-inactive mRNAs upon restrained metabolic limitations characterized by mTOR inhibition such as treatment with pharmacological inhibitors or by amino acid or serum deprivation. This reservoir of anabolic capacity can be rapidly spent by the cells to generate new ribosomes when conditions return permissive and mTOR is reactivated, suggesting that the mTOR / 40S-LARP1 axis could constitute a cell instrinsic mechanism of metabolic resistance to adverse growth conditions. This might have important implications in the process of tumorigenesis and in the treatment of cancers addicted to ribosome biogenesis. However, little is known regarding the formation of this biochemical complex and its molecular makeup in response to limiting metabolic constraints. To this end, we have characterized the 40S-LARP1 complex interactome in 1 normal growing conditions and under different mTOR inhibiting conditions by Mass Spectrometry. This characterization has shown that the 40S-LARP1 complex interacts with proteins involved in multiple steps of RNA regulation and translation as well as ribosome biogenesis, mitochondrial translation or intracellular organization. An initial analysis on the functional role of the 40S-LARP1 complex(es) interactors has revealed that the RNA binding protein ILF3 and the mitochondrial protein PHB1 are new players in the regulation of 5'TOP mRNAs. Of note, the interaction of the 40S-LARP1 complex with these two partners does not appear to be concomitant, pointing to a model of different 40S-LARP1 complexes co-existing in the cell at the same time. Indeed, LARP1 colocalizes with PHB1 in the mitochondria, which might confer specific functions to the 40S-LARP1 complex confined to such subcellular compartment and distinct of other 40S- LARP1 complexes. Intriguingly, ILF3 and PHB1 have been already described as negative prognostic markers in cancer and chemoresistance, respectively, suggesting a potential role of the 40S-LARP1 anabolic reservoir in those contexts. Furthermore, we have evaluated the subcellular localization of LARP1 protein, which we have proved to be widespread and mainly cytoplasmic but sensitive to the mTOR pathway. We have observed that LARP1 increases its co-localization with markers of the endoplasmic reticulum and the mitochondria upon mTOR inhibition. Understanding this will shed light on the metabolic pathways fed by the anabolic storage, and consequently on new potential targets in RiBi-addicted cancers. |
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