Biology subjects

Berquez, M.

Publications and source records attributed to Berquez, M..

3 recordsLinked to original sources

bioRxiv2025

A Drosophila model for Dent disease reveals impaired ER export of Cubilin as pathogenic mechanism

Mutations in the CLCN5 gene encoding the chloride-hydrogen exchanger ClC-5 cause Dents disease, a genetic disorder of the endolysosomal pathway in the proximal tubules of the kidneys. Many patients also develop glomerular lesions, but the underlying mechanism is unclear. We have established an in vivo model for Dents disease using Drosophila nephrocytes that share similarities with podocytes and proximal tubular cells. Upon depletion of ClC-c, the fly homologue of CLCN5, the endocytic receptor Cubilin was lost from the cortex of nephrocytes, which led to a strong decrease in albumin uptake and slit diaphragm (SD) turnover. Moreover, the actin and microtubular cytoskeleton as well as Rab11-marked recycling endosomes showed a strong cortical accumulation, whereas cholesterol-enriched autophagic compartments emerged in the perinuclear area. Cubilin exhibited a mild mislocalization to cortical early and late endosomal compartments and, in addition, strongly accumulated in the endoplasmic reticulum (ER). This was accompanied by a fragmentation of the ER morphology and an increase in ER exit sites and associated Golgi stacks. These secretory pathway phenotypes were also observed upon silencing of a subunit of the vacuolar H+-ATPase (V-ATPase) suggesting that they depend on acidification. Therefore, we speculate that ClC-c and the V-ATPase together acidify the Golgi to allow proper glycosylation and surface trafficking of Cubilin (or its binding partner Amnionless). Interestingly, ER retention of Cubilin was confirmed in ClC-5 knockout mice, underscoring the relevance of this pathomechanism for Dents disease. Translational statementIn this work, we study the function of the fly ortholog of CLCN5 whose mutations cause Dents disease, a devastating hereditary kidney disease. By demonstrating that the protein uptake receptor Cubilin is retained in the ER upon ClC-c/ClC-5 depletion in flies and mice, we provide an unexpected new disease mechanism for this disease. Future therapeutic strategies may be directed at improving ER export through acidification of the Golgi apparatus.

cell biology↗

bioRxiv2024

A multi-subunit autophagic capture complex facilitates degradation of ER stalled MHC-I in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDA) evades immune detection partly via autophagic capture and lysosomal degradation of major histocompatibility complex class I (MHC-I). Why MHC-I is susceptible to capture via autophagy remains unclear. By synchronizing exit of proteins from the endoplasmic reticulum (ER), we show that PDAC cells display prolonged retention of MHC-I in the ER and fail to efficiently route it to the plasma membrane. A capture-complex composed of NBR1 and the ER-phagy receptor TEX264 facilitates targeting of MHC-I for autophagic degradation, and suppression of either receptor is sufficient to increase total levels and re-route MHC-I to the plasma membrane. Binding of MHC-I to the capture complex is linked to antigen presentation efficiency, as inhibiting antigen loading via knockdown of TAP1 or beta 2-Microglobulin led to increased binding between MHC-I and the TEX264-NBR1 capture complex. Conversely, expression of ER directed high affinity antigenic peptides led to increased MHC-I at the cell surface and reduced lysosomal degradation. A genome-wide CRISPRi screen identified NFXL1, as an ER-resident E3 ligase that binds to MHC-I and mediates its autophagic capture. High levels of NFXL1 are negatively correlated with MHC-I protein expression and predicts poor patient prognosis. These data highlight an ER resident capture complex tasked with sequestration and degradation of non-conformational MHC-I in PDAC cells, and targeting this complex has the potential to increase PDAC immunogenicity.

cancer biology↗

bioRxiv2022

Lysosomal cystine export regulates mTORC1 signaling to guide kidney epithelial cell fate specialization

Differentiation is critical for cell fate decisions, but the signals involved remain unclear. The kidney proximal tubule (PT) cells reabsorb disulphide-rich proteins through endocytosis, generating cystine via lysosomal proteolysis. Here we report that defective cystine mobilization from lysosomes through cystinosin (CTNS), which is mutated in cystinosis, diverts PT cells towards growth and proliferation, disrupting their functions. Mechanistically, cystine storage stimulates Ragulator-Rag GTPase-dependent recruitment of mechanistic target of rapamycin complex 1 (mTORC1) and its constitutive activation. Re-introduction of CTNS restores nutrient-dependent regulation of mTORC1 in knockout cells, whereas cell-permeant analogues of L-cystine, accumulating within lysosomes, render wild-type cells resistant to nutrient withdrawal. Therapeutic mTORC1 inhibition corrects lysosome and differentiation downstream of cystine storage, and phenotypes in a zebrafish model of cystinosis. Thus, cystine serves as a lysosomal signal that tailors mTORC1 and metabolism to direct epithelial cell fate decisions. These results identify mechanisms and therapeutic targets for dysregulated homeostasis in cystinosis.

cell biology↗