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Bardin, S.

Publications and source records attributed to Bardin, S..

6 recordsLinked to original sources

Mechanical forces stimulate Golgi export

Cells face diverse mechanical stimuli that vary with cell type, state, and pathological conditions. Mechanobiology investigates how cells sense and respond to these forces. While most work has focused on the cell surface and nucleus as primary mechanosensors, how intracellular organelles adapt to extracellular mechanical forces remains largely unknown. Here, we show that extracellular mechanical signals influence the secretory function of the Golgi apparatus. By subjecting adherent cells to mechanical challenges -cell spreading on different ligands, altered substrate stiffness, or equibiaxial strain-, we reveal that extracellular forces modulate Golgi-to-cell surface carrier biogenesis, thereby regulating exocytosis. Together with changes in Golgi membrane tension, we identify molecular determinants of the mechanotransduction pathway, including microtubule acetylation, diacylglycerol production, and protein kinase D activity. In turn, inhibition of Golgi export suppresses this mechanoresponse and causes impaired cell spreading. These findings uncover a bidirectional mechanotransduction axis in which extracellular mechanics tune Golgi secretory output, providing a framework for investigating organelle-based mechanoadaptation in physiology and disease.

cell biology↗

The recycling endosome biogenesis machinery coordinates BACE1 endosomal sorting and amyloid-Beta production

Alzheimers disease (AD) is the most common form of dementia worldwide. One of ADs main pathological hallmarks is the cerebral plaque deposits of {beta}-amyloid (A{beta}). A{beta} is generated through sequential enzymatic cleavage of the amyloid precursor protein (APP). The {beta}-secretase or {beta}-site APP-cleaving enzyme 1 (BACE1) initiates this cleavage and is thus key to regulate A{beta} formation. Both APP and BACE1 transit through the endolysosomal system but the exact nature of the compartment(s) where APP cleavage occurs as well as the molecular mechanisms that govern their endosomal sorting remain poorly known. Here we show that RAB11 not only regulates BACE1 transport from early/sorting endosomes (EEs/SEs) and drives the exocytosis of BACE1-containing recycling carriers. Moreover, recycling endosome-associated KIF13A, as well as its closely related homolog KIF13B, which are known RAB11 effectors involved in the biogenesis of recycling endosome (RE) from EEs/SEs, also participate in BACE1 endosomal sorting. Importantly, depletion of KIF13A or KIF13B leads to an increase in A{beta} generation. Depletion of the BLOC-1 complex, previously described as an essential partner for KIF13A-dependent RE biogenesis, also induces increased amount of A{beta}. Altogether, our findings support a model where the EEs/SEs represent a major organelle for A{beta} formation and identify the recycling endosome biogenesis machinery as a master coordinator of BACE1 endosomal sorting and transport.

cell biology↗

A phosphorylation switch regulates RAB6 function during mitosis

RAB GTPases are key regulators of membrane trafficking in eukaryotic cells. In addition to their role in interphase, several RAB proteins, including Golgi-associated RAB6, have mitotic functions. The aim of this study was to investigate how the interphasic and mitotic functions of RAB6 could be regulated. Since phosphorylation is a key regulatory process in mitosis, we looked for specific mitotic phosphorylation of RAB6 using a phospho-proteomic approach. We found that RAB6 is phosphorylated at position S52 by the mitotic kinase Pololike kinase 1 (Plk1) in mitosis. Phosphorylated RAB6 localizes at the spindle poles from prophase to anaphase. In metaphase, we observed RAB6A-positive structures containing Mad1 and Mad2 moving along the mitotic spindle via the dynein-dynactin complex. We provide evidence that phosphorylation impairs RAB6A binding to some of its known partners, including p150Glued and Bicaudal-D2. In addition, the overexpression of RAB6A phospho-mutants lead to mitosis and cytokinesis defects. Our results suggest that a cycle of RAB6 phosphorylation/dephosphorylation is required for cell division.

cell biology↗

Regulation of neuronal progenitor delamination by dynein-driven post-Golgi apical transport

Radial glial (RG) cells are the neural stem cells of the developing neocortex. Apical RG (aRG) cells can delaminate to generate basal RG (bRG) cells, a cell type associated with human brain expansion. Here, we report that this delamination is regulated by the post-Golgi secretory pathway. Using in situ subcellular live imaging, we show that post-Golgi transport of RAB6+ vesicles occurs toward the minus ends of microtubules and depends on dynein. We demonstrate that the apical determinant Crumbs3 (CRB3) is also transported by dynein. Double knockout of RAB6A/A and RAB6B impairs apical localization of CRB3, and induces a retraction of aRG cell apical process, leading to delamination and ectopic division. These defects are phenocopied by knock-out of the dynein activator LIS1. Overall, our results identify a RAB6-dynein-LIS1 complex for Golgi to apical surface transport in aRG cells, and highlights the role of this pathway in the maintenance of neuroepithelial integrity.

cell biology↗

RAB6 GTPase is a crucial regulator of the mammary secretory function controlling STAT5 activation

The Golgi-associated RAB GTPases, RAB6A and RAB6A, regulate anterograde and retrograde transport pathways from and to the Golgi. In vitro, RAB6A/A have been reported to be involved in several cellular functions, including, in addition to transport, cell division, migration, adhesion and polarity. However, their role remains poorly described in vivo, in particular in epithelial tissues. Here, we generated BlgCre; Rab6aF/F mouse presenting a specific deletion of Rab6a in the mammary luminal secretory lineage during gestation and lactation. Rab6a loss severely impaired the differentiation, maturation and maintenance of the secretory tissue, compromising lactation. It led to a decreased activation of STAT5, a key regulator of the lactogenic process primarily governed by prolactin. Data obtained with a human mammary epithelial cell line suggested that defective STAT5 activation might originate from a perturbed transport of the prolactin receptor, altering its membrane expression and signaling cascade. Despite the major functional defects observed upon Rab6a deletion, the polarized organization of the mammary epithelial bilayer was preserved. Altogether, our data reveal a crucial role for RAB6A/A in the lactogenic function of the mammary gland. They also suggest that the trafficking pathways controlled by RAB6A/A depend on cell type specialization and tissue context. SUMMARY STATEMENTThis study reveals a role for the Golgi-associated RAB GTPases, RAB6A/A, in the lactogenic function of the mammary gland.

developmental biology↗

RAB6 and microtubules restrict secretion to focal adhesions

To ensure their homeostasis and sustain differentiated functions, cells continuously transport diverse cargos to various cell compartments and in particular to the cell surface. Secreted proteins are transported along intracellular routes from the endoplasmic reticulum through the Golgi complex before reaching the plasma membrane along microtubule tracks. Using a synchronized secretion assay, we report here that exocytosis does not occur randomly at the cell surface but on localized hotspots juxtaposed to focal adhesions. Although microtubules are involved, the RAB6-dependent machinery plays an essential role. We observed that, irrespective of the transported cargos, most post-Golgi carriers are positive for RAB6 and that its inactivation leads to a broad reduction of protein secretion. RAB6 may thus be a general regulator of post-Golgi secretion.

cell biology↗