Biology subjects

Gibert, B.

Publications and source records attributed to Gibert, B..

5 recordsLinked to original sources

bioRxiv2024

The MYCN oncoprotein and helicases DDX17 and DDX5 have opposite effects on the production of chimeric transcripts in neuroblastoma cells

DEAD box helicases DDX17 and DDX5 control the termination of transcription and the associated cleavage of the 3 end of transcripts. Here we show that the transcriptional readthrough induced by their depletion in neuroblastoma cells also results in increased production of chimeric transcripts from tandemly oriented genes. Analysis of neuroblastoma tumours in which chimeric transcripts are abundant revealed that low expression of the DDX17 and DDX5 genes is associated with poor overall patient survival. Low DDX17 expression is also significantly associated with high-risk tumours and is inversely correlated with MYCN oncogene amplification, suggesting a link between these two factors. We demonstrate that changes in MYCN expression do not affect the expression of either helicase, but alter transcription termination leading to the production of chimeric transcripts. We provide evidence that MYCN acts on termination through its direct binding to the 3 region of genes and that it interacts with DDX17, suggesting that it may inhibit the activity of the helicase. Collectively, our work reveals a novel function of MYCN in transcription termination and suggests that the deregulation of MYCN and DDX17/DDX5 expression in neuroblastoma may lead to the expression of non-canonical and potentially harmful RNA molecules.

molecular biology↗

bioRxiv2023

Netrin signaling mediates survival of dormant epithelial ovarian cancer cells

Dormancy in cancer is a clinical state in which residual disease remains undetectable for a prolonged duration. At a cellular level, rare cancer cells cease proliferation and survive chemotherapy and disseminate disease. We created a suspension culture model of high grade serous ovarian cancer (HGSOC) dormancy and devised a novel CRISPR screening approach to identify survival genes in this context. In combination with RNA-seq, we discovered the Netrin signaling pathway as critical to dormant HGSOC cell survival. We demonstrate that Netrin-1, -3, and its receptors are essential for low level ERK activation to promote survival, and that Netrin activation of ERK is unable to induce proliferation. Deletion of all UNC5 family receptors blocks Netrin signaling in HGSOC cells and compromises viability during the dormancy step of dissemination in xenograft assays. Furthermore, we demonstrate that Netrin-1 and -3 overexpression in HGSOC correlates with poor outcome. Specifically, our experiments reveal that Netrin overexpression elevates cell survival in dormant culture conditions and contributes to greater spread of disease in a xenograft model of abdominal dissemination. This study highlights Netrin signaling as a key mediator HGSOC cancer cell dormancy and metastasis.

cancer biology↗

bioRxiv2023

Targeting the cell and non-cell autonomous regulation of 47S synthesis by GCN2 in colon cancer.

Nutrient availability is a key determinant of tumor cell behavior. While nutrient-rich conditions favor proliferation and tumor growth, scarcity, and particularly glutamine starvation, promotes cell dedifferentiation and chemoresistance. Here, linking ribosome biogenesis plasticity with tumor cell fate, we uncover that the amino acid sensor GCN2 represses the expression of the precursor of ribosomal RNA, 47S, under metabolic stress. We show that blockade of GCN2 triggers cell death by an irremediable nucleolar stress and subsequent TP53-mediated apoptosis in patient-derived models of colon adenocarcinoma (COAD). In nutrient-rich conditions, GCN2 activity supports cell proliferation through the transcription stimulation of 47S rRNA, independently of the canonical ISR axis. However, impairment of GCN2 activity prevents nuclear translocation of the methionyl tRNA synthetase (MetRS) underlying the generation of a nucleolar stress, mTORC1 inhibition and autophagy induction. Inhibition of the GCN2-MetRS axis drastically improves the cytotoxicity of RNA pol I inhibitors, including the first-line chemotherapy oxaliplatin, on patient-derived COAD tumoroids. Our data thus reveal that GCN2 differentially controls the ribosome biogenesis according the nutritional context. Furthermore, pharmacological co-inhibition of the two GCN2 branches and the RNA pol I activity may represent a valuable strategy for elimination of proliferative and metabolically-stressed COAD cell.

cancer biology↗

bioRxiv2022

RAS-induced transformation of mammary epithelial cells relies on ZEB1-dependent cellular reprogramming via a paracrine process

While uncommon in breast cancers, oncogenic activation of the RAS/MAPK signalling pathway is frequent in claudin-low (CL) tumours, a subtype of breast malignancies enriched in features of epithelial-mesenchymal transition (EMT), suggesting an interplay between RAS activation and EMT. Using inducible models of human mammary epithelial cells, we show that RAS-mediated transformation relies on cellular reprogramming governed by the EMT-inducing transcription factor ZEB1. The path to ZEB1 induction involves a paracrine process: cells entering a senescent state following RAS activation release proinflammatory cytokines, notably IL-6 and IL-1 which promote ZEB1 expression and activity in neighbouring cells, thereby fostering their malignant transformation. Collectively, our findings unveil a previously unprecedented role for senescence in bridging RAS activation and EMT over the course of malignant transformation of human mammary epithelial cells.

cancer biology↗

bioRxiv2020

The comprehensive roadmaps of reprogramming and transformation unveiled antagonistic roles for bHLH transcription factors in the control of cellular plasticity

Coordinated changes of cellular identity and plasticity are critical for pluripotent reprogramming (PR) and malignant transformation (MT). However, the molecular circuitries orchestrating these modifications, as well as their degree of analogy during reprogramming and transformation, remain unknown. To address this question, we generated "repro-transformable" mice models and dissected comparatively the early events underpinning PR - mediated by Oct4, Sox2, Klf4, c-Myc - and MT - triggered by oncogenic Ras and c-Myc. Transcriptomic analyses allowed the identification of a unique set of markers - the cell surface glycoprotein Thy1 and the transcription factor (TF) Bcl11b - that are commonly downregulated during PR and MT and delineate cellular intermediates (CI) highly amenable to generate pluripotent or malignant derivatives. Comprehensive transcriptomic, epigenomic and functional analyses of different CI, prone or refractory to PR/MT, unveiled that cellular plasticity acquisition precedes the broad extinction of cellular identity. It also demonstrated the existence of specific and shared molecular features of PR and MT while ensuring the identification of broad-range regulators of cellular plasticity. As a proof-of-concept, we revealed that the basic helix-loop-helix (bHLH) class A TF Atoh8 constrains rodent and human iPS cells generation as well as MT and direct neuron conversion. Mechanistically, this TF hampers the reactivation of the pluripotent network during PR and limits the acquisition of phenotypic plasticity during MT. Furthermore, an integrated analysis of Atoh8 genome-wide binding, alongside the other bHLH TFs c-Myc, Ascl1 and MyoD promoting reprogramming/transdifferentiation, unveiled how Atoh8 constrains cellular plasticity by occupying a specific subset of MEF enhancers and by finetuning WNT signalling activity. Collectively, by deconvoluting the early steps of the reprogramming and transformation roadmaps, this integrated study uncoupled changes of cellular plasticity and identity to shed light on novel insights into reprogramming and cancer biology. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=161 SRC="FIGDIR/small/424606v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@1718383org.highwire.dtl.DTLVardef@1714ab8org.highwire.dtl.DTLVardef@e0958borg.highwire.dtl.DTLVardef@7a0643_HPS_FORMAT_FIGEXP M_FIG C_FIG One-sentence summaryComparative roadmaps of cellular plasticity acquisition during pluripotent reprogramming and malignant transformation.

cell biology↗