Biology subjects

Cherqui, S.

Publications and source records attributed to Cherqui, S..

4 recordsLinked to original sources

bioRxiv2026

The molecular architecture of tunneling nanotubes

Tunneling nanotubes (TNTs) are thin intercellular bridges that mediate the exchange of proteins, organelles, and nucleic acids between neighboring cells. They are enriched in tumor cells, implicated in chemotherapy resistance, induced in models of aggregation-based diseases, and their formation is stimulated by viruses that use TNTs to enhance infection. Despite their broad relevance and therapeutic potential, TNT morphology and function remain poorly understood, owing to the absence of clear morphological criteria and the limitations of light microscopy. Here, we establish two complementary systems to study TNT formation and function: stimulation with the pseudorabies viral kinase US3 to model viral transmission, and treatment of acute monocytic leukemia THP-1 cells with daunorubicin to model chemotherapy resistance. Using live-cell imaging, we characterize cytoskeletal organization and bidirectional lysosome transport in both contexts, and apply cryo-correlative light and electron microscopy (cryo-CLEM) with cryogenic electron tomography (cryo-ET) to visualize TNTs in their native state at molecular resolution. We show that TNTs display a rich molecular architecture, comprising actin filaments, microtubules, intermediate filaments, active ribosomes, and diverse organelles including multivesicular bodies, autophagosomes, and lysosomes. Sub-nanometer microtubule reconstructions reveal mixed polarity within individual TNTs, suggesting that both connected cells actively contribute to TNT formation and cargo trafficking. This organization is conserved across both systems, implying that TNT biogenesis reflects a shared cellular program rather than a context-specific response. Our findings provide the first structural framework for TNTs, revealing an unexpectedly rich molecular architecture and laying the groundwork for understanding how TNTs orchestrate intercellular communication in disease.

cell biology↗

bioRxiv2025

Cystinosin is involved in Na+/H+ Exchanger 3 trafficking in the proximal tubular cells: new insights in the renal Fanconi syndrome in cystinosis

Cystinosis is a systemic lysosomal storage disease resulting from a defective CTNS gene, leading to the accumulation of cystine in all organs. Despite the ubiquitous expression of cystinosin, the renal Fanconi syndrome (FS) is the first manifestation of cystinosis that presents early in life of the patients while other complications appear years later. Additionally, the cystine reduction therapy, cysteamine, does not prevent the FS. While the matter is still unresolved, it is apparent that specific function(s) of cystinosin in the proximal tubular cells (PTCs) beyond cystine transport explain the early tubular defects in cystinosis. Here, we report a novel interaction of cystinosin with the sodium/hydrogen (Na+/H+) exchanger proteins in the endosomes in both yeast and mammalian cells. One isoform of Na+/H+ exchanger, NHE3, is a major absorptive sodium transporter at the apical membrane of the proximal tubules. Cystinosin was found to play a significant role in NHE3 subcellular localization, trafficking, and resulting sodium uptake in PTCs. Interestingly, introduction of CTNS successfully rescued these defects in CTNS-deficient PTCs, whereas CTNS-LKG, the lysosomal and plasma membrane isoform of cystinosin, did not. NHE3 mislocalization was confirmed in Ctns-/- mice and cystinosis patient kidney. Interestingly, transplantation of wild-type hematopoietic stem and progenitor cells in Ctns-/- mice restored NHE3 expression at the brush border membrane. This study uncovers a new role of cystinosin in the trafficking of NHE3 in the PTCs that is evolutionary conserved, offering new insights in the pathogenesis of the renal FS in cystinosis and potential new therapeutic avenue for this pathology. SignificanceThis study reveals a new role of cystinosin in the trafficking of NHE3, the Na+/H+ exchanger in the proximal tubular cells (PTCs) in the kidney. NHE3 contributes to the majority of renal sodium absorption and is essential for maintaining the homeostasis of the PTCs. Thus, this study offers new molecular insights in the endosomal trafficking of NHE3 and provides a new mechanism that may explain the underlying pathogenesis and early onset of the renal Fanconi syndrome in cystinosis. Additionally, these findings provide potential new drug targets for this pathology and are also relevant to our ongoing stem cell gene therapy clinical trial for cystinosis, offering valuable information on the potential impact of hematopoietic stem cell transplantation on renal Fanconi syndrome.

molecular biology↗

bioRxiv2020

DYNC1LI2 regulates localization of the chaperone-mediated autophagy-receptor LAMP2A and improves cellular homeostasis in cystinosis

The dynein motor protein complex is required for retrograde transport but the functions of the intermediate-light chains that form the cargo-binding complex are not elucidated and the importance of individual subunits in the maintenance of cellular homeostasis is unknown. Here, using mRNA arrays and protein analysis, we show that the dynein subunit, intermediate chain 2 (DYNC1LI2) is downregulated in cystinosis, a lysosomal storage disorder caused by genetic defects in the lysosomal cystine transporter, cystinosin. Reconstitution of the expression of DYNC1LI2 in Ctns-/- cells re-established endolysosomal dynamics. Defective vesicular trafficking in cystinotic cells was rescued by DYNC1LI2 expression which correlated with decreased endoplasmic reticulum stress manifested as decreased expression levels of the chaperone Grp78. Mitochondrial fragmentation in cystinotic fibroblasts was also rescued by DYNC1LI2. Survival of cystinotic cells to oxidative stress insult was increased by DYNC1LI2 reconstitution but not by its paralog DYNC1LI1, which also failed to decrease ER stress levels and mitochondrial fragmentation. Restoring DYNC1LI2 expression rescued the localization of the chaperone-mediated autophagy receptor, LAMP2A, and restored cellular homeostasis of cystinotic proximal tubule cells, the primary cell type affected in cystinosis. DYNC1LI2 failed to rescue phenotypes in cystinotic cells when LAMP2A was downregulated or when co-expressed with dominant negative (DN) RAB7 or DN-RAB11, which impair LAMP2A trafficking. DYNC1LI2 emerges as a new target to repair underlying trafficking and CMA defects in cystinosis, a mechanism that is not restored by currently used lysosomal depletion therapies.

cell biology↗

bioRxiv2018

Cystinosin regulates kidney inflammation through its interaction with galectin-3

Inflammation is implicated in the pathogenesis of many disorders. Here, we show that cystinosin, protein defective in the lysosomal storage disorder cystinosis, is a critical regulator of galectin-3 during inflammation. Cystinosis is a lysosomal storage disorder and despite ubiquitous expression of cystinosin, kidney is the primary organ to be impacted by the disease. Here, we show that cystinosin interacts with galectin-3 and enhances its lysosomal localization and degradation. Galectin-3 is also found overexpressed in the kidney of the mouse model of cystinosis, Ctns-/-mice. Absence of galectin-3 in Ctns-/- mice led to a better renal function and structure, and decreased macrophage/monocyte infiltration in the kidney. Finally, galectin-3 interacts with a protein implicated in the recruitment of monocytes and macrophages during inflammation, Monocyte Chemoattractant Protein-1 (MCP1), that was found increased in the serum of Ctns-/- mice. These findings highlight a new role of cystinosin and galectin-3 interaction in inflammation, providing a mechanistic explanation for kidney disease pathogenesis in cystinosis, which may lead to the identification of new drug targets to delay its progression.

molecular biology↗