ECM deposition is driven by caveolin-1–dependent regulation of exosomal biogenesis and cargo sorting

Abstract

The composition and physical properties of the extracellular matrix (ECM) critically influence tumor progression, but the molecular mechanisms underlying ECM layering are poorly understood. Tumor–stroma interaction critically depends on cell communication mediated by exosomes, small vesicles generated within multivesicular bodies (MVBs). We show that caveolin-1 (Cav1) centrally regulates exosome biogenesis and exosomal protein cargo sorting through the control of cholesterol content at the endosomal compartment/MVBs. Quantitative proteomics profiling revealed that Cav1 is required for exosomal sorting of ECM protein cargo subsets, including Tenascin-C (TnC), and for fibroblast-derived exosomes to efficiently deposit ECM and promote tumor invasion. Cav1-driven exosomal ECM deposition not only promotes local stromal remodeling but also the generation of distant ECM-enriched stromal niches in vivo. Cav1 acts as a cholesterol rheostat in MVBs, determining sorting of ECM components into specific exosome pools and thus ECM deposition. This supports a model by which Cav1 is a central regulatory hub for tumor–stroma interactions through a novel exosome-dependent ECM deposition mechanism.

Extracellular Vesicles: An Emerging Mechanism Governing the Secretion and Biological Roles of Tenascin-C

“…Recent studies show that extracellular vesicles (EVs) can export ECM components to the extracellular environment ( 107 ), constituting alternative mechanisms for ECM secretion and deposition and implying specific regulatory principles for their trafficking ( 108 , 109 ). EVs are a heterogeneous group of cell-derived membranous structures that include exosomes and MVs, which defer on their intracellular origin ( 110 ).…”

“…Additionally, evidence for an ESCRT-independent mechanism for exosome biogenesis has been described ( 118 ). Specific lipid species such as ceramides (derived from sphingomyelinases-mediated hydrolysis of sphingomyelin) ( 119 ), LBPA (lyso-bis-phosphatidic acid) ( 120 ) or cholesterol, as well as proteins that modulate membrane organization, including tetraspanins ( 121 ) and caveolin-1 ( 108 , 122 , 123 ), have been recently identified as important regulators of ESCRT-independent endosome dynamics and exosome biogenesis.…”

“…Recent studies have shown that ECM proteins are exported and deposited by EVs ( 183 , 184 ) ( , ) and animal models in which exosome production has been abrogated through disruption of neutral sphingomyelinase (NSMase) activities show marked alterations in ECM deposition and architecture ( 185 , 186 ). FN is a prominent ECM cargo in EVs from different cell types, and the blockade of exosome secretion partially alters, although does not completely impair, FN fiber deposit ( 108 ). Other groups have recently described that FN is transported by EVs.…”

“…Recent studies demonstrate that exosome secretion is strictly required for appropriate extracellular TnC deposition by both tumor cells and different fibroblast types ( 108 , 122 ) ( Figure 4 ). Circulating exosomes from cancer patients frequently carry TnC ( 24 ), and several cancer cell types secrete TnC in EVs in vitro ( 183 , 184 ) ( , ).…”

“…Cav1 deficiency, exogenous cholesterol loading or pharmalogical inhibition of cholesterol trafficking from endosomes all markedly impaired exosomal secretion of TnC. Cholesterol homeostasis emerges as an as yet poorly understood mechanism by which membrane trafficking and metabolism potentially feed onto functions allocated at the endosomal compartment, including cell signalling regulation ( 206 , 207 ) and exosome secretion ( 108 ).…”