Biology subjects

Bard, F.

Publications and source records attributed to Bard, F..

4 recordsLinked to original sources

bioRxiv2021

The extracellular matrix promotes breast cancer cell growth under amino acid starvation by promoting tyrosine catabolism

Breast and pancreatic tumours are embedded in a collagen I-rich extracellular matrix (ECM) network, where nutrients are scarce due to limited blood flow and elevated tumour growth. Metabolic adaptation is required for cancer cells to endure these conditions. Here, we demonstrated that the presence of ECM supported the growth of invasive breast cancer cells, but not non-transformed mammary epithelial cells, and pancreatic cancer cells under amino acid starvation, through a mechanism that required macropinocytosis-dependent ECM uptake. Importantly, we showed that this behaviour was acquired during carcinoma progression. ECM internalisation, followed by lysosomal degradation, contributed to the upregulation of the intracellular levels of several amino acids, most notably tyrosine and phenylalanine. This resulted in elevated tyrosine catabolism on ECM under starvation, leading to increased fumarate levels, potentially feeding into the tricarboxylic acid cycle. Interestingly, this pathway was required for ECM-dependent cell growth under amino acid starvation, as the knockdown of p-hydroxyphenylpyruvate hydroxylase-like protein (HPDL), the third enzyme of the pathway, opposed cell growth on ECM in both 2D and 3D systems, without affecting cell proliferation on plastic. Finally, high HPDL expression correlated with poor prognosis in breast and pancreatic cancer patients. Collectively, our results highlight that the ECM in the tumour microenvironment represents an alternative source of nutrients to support cancer cell growth, by regulating phenylalanine and tyrosine metabolism.

cancer biology↗

bioRxiv2020

Src activates retrograde membrane traffic through phosphorylation of GBF1

The Src tyrosine kinase controls cancer-critical protein glycosylation through Golgi to ER relocation of GALNTs enzymes. How Src induces this trafficking event is unknown. Golgi to ER transport depends on the GTP Exchange factor (GEF) GBF1 and small GTPase Arf1. Here we show that Src induces the formation of tubular transport carriers containing GALNTs through promotion of a GBF1-Arf1 complex. The complex is initiated by phosphorylation on GBF1 on 10 tyrosine residues; two of them, Y876 and Y898 are located near the C-terminus of the Sec7 GEF domain. Their phosphorylation promotes partial melting of the Sec7 domain, favoring binding to the GTPase. Perturbation of these rearrangements prevent GALNTs relocation. In sum, Src promotes GALNTs relocation by favoring binding of GBF1 to Arf1. Regulation of a GEF-Arf axis by tyrosine phosphorylation appears to be a highly conserved and wide-spread mechanism.

cell biology↗

bioRxiv2020

Targeting c-Myc with a novel Peptide Nuclear Delivery Device

Biologics such as peptides and antibodies are a well-established class of therapeutics. However, their intracellular delivery remains problematic. In particular, methods to efficiently inhibit intra-nuclear targets are lacking. We previously described that Pseudomonas Exotoxin A reaches the nucleoplasm via the endosomes-to-nucleus trafficking pathway. Here, we show that a non-toxic truncated form of PE can be coupled to peptides and efficiently reach the nucleoplasm. It can be used as a Peptide Nuclear Delivery Device (PNDD) to deliver polypeptidic cargos as large as Glutathione-S-transferase (GST) to the nucleus. PNDD1 is a fusion of PNDD to the c-myc inhibitor peptide H1. PNDD1 is able to inhibit c-Myc dependent transcription at nanomolar concentration. In contrast, H1 fused to various cell-penetrating peptides are active only in the micromolar range. PNDD1 attenuates cell proliferation and induces cell death in various tumor cell lines. In particular, several patient-derived Diffuse Large B-Cell Lymphomas cell lines die after exposure to PNDD1, while normal B-cells survive. Altogether, our data indicate that PNDD is a powerful tool to bring active cargo to the nucleus and PNDD1 could be the basis of a new therapy against lymphoma.

cell biology↗

bioRxiv2018

The GalNAc-T Activation (GALA) Pathway: Drivers and Markers

The enzymes GALNTs add GalNAc sugar to Ser and Thr residues, forming the Tn glycan. GALNTs are activated by trafficking from Golgi to ER, a process driven by the Src kinase and negatively regulated by ERK8. This GALNTs activation (aka GALA) pathway induces high Tn levels and is a key driver of liver tumor growth. Recently, Tabak and colleagues have contested our previous data that EGF stimulation can induce GALNTs relocation. Here, we show that relocation induced by EGF is actually detectable in the images acquired by Tabak et al. Furthermore, we show that expression of EGFR enhances relocation and appears required to drive relocation induced by ERK8 depletion. We also propose that quantification of O-glycosylation of the ER resident protein PDIA4 provides an alternative measure of GALA. In sum, we demonstrate that non-reproducibility was due to experimental errors, that EGFR is indeed a driver of GALA and propose additional markers to facilitate the study of this pathway.

cell biology↗