Endocytic trafficking of laminin is controlled by dystroglycan and disrupted in cancers

Abstract

The dynamic interactions between cells and basement membranes serve as essential regulators of tissue architecture and function in metazoans, and perturbation of these interactions contributes to the progression of a wide range of human diseases, including cancers. Here, we reveal the pathway and mechanism for the endocytic trafficking of a prominent basement membrane protein, laminin-111 (referred to here as laminin), and their disruption in disease. Livecell imaging of epithelial cells revealed pronounced internalization of laminin into endocytic vesicles. Laminin internalization was receptor mediated and dynamin dependent, and laminin proceeded to the lysosome through the late endosome. Manipulation of laminin receptor expression revealed that the dominant regulator of laminin internalization is dystroglycan, a laminin receptor that is functionally perturbed in muscular dystrophies and in many cancers. Correspondingly, laminin internalization was found to be deficient in aggressive cancer cells displaying non-functional dystroglycan, and restoration of dystroglycan function strongly enhanced the endocytosis of laminin in both breast cancer and glioblastoma cells. These results establish previously unrecognized mechanisms for the modulation of cell-basement-membrane communication in normal cells and identify a profound disruption of endocytic laminin trafficking in aggressive cancer subtypes.

Lassa Virus Cell Entry via Dystroglycan Involves an Unusual Pathway of Macropinocytosis

“…Recent studies in human epithelial cells demonstrated that DG can mediate the endocytosis of its natural ligand, the ECM protein laminin, via a dynamin-dependent pathway (61). Notably, the internalization of laminin was followed by rapid delivery to late endosomes with kinetics similar to those of DG-mediated viral entry observed here.…”

“…2J). In sum, our data suggested that rLCMV-LASVGP entry via DG involves a macropinocytosis-related pathway different from the DG-mediated endocytosis of laminin (61).…”

“…However, this pathway has so far not been linked to DG, which mediates the endocytosis of laminin in a dynamin-dependent manner (61). Our data suggest that, despite striking similarities in DG recognition between LASV and laminin (23), the virus does not mimic the dynamin-dependent uptake of ECM proteins.…”

“…2B). The insensitivity of rLCMV-LASVGP entry to dynamin inhibitors suggested that the virus may not use the existing DG-associated endocytic routes described for endogenous ECM ligands (61). Since initial studies on LASV entry claimed the involvement of CME (29), we applied two well-established clathrin inhibitors, pitstop-2 (63) and chlorpromazine, which perturb the assembly of clathrincoated pits at the plasma membrane.…”

Starved epithelial cells uptake extracellular matrix for survival

“…We show that laminin, an easily accessible extracellular protein, is endocytosed and internalized into lysosomes, providing a source of EAAs that support starved epithelial cell survival. Although laminin endocytosis has previously been reported27, this process involved a distinct receptor and occurred in a different tissue context not linked to metabolism or starvation. Our study shows instead that ITGB4-mediated laminin internalization occurs under conditions of decreased PI3K/mTOR signalling, which mimic loss of nutrient uptake.…”