Hepatitis C virus infection propagates through interactions between Syndecan-1 and CD81 and impacts the hepatocyte glycocalyx.

The hepatitis C virus (HCV) infects hepatocytes after binding to heparan sulfate proteoglycans, in particular Syndecan-1, followed by recognition of the tetraspanin CD81 and other receptors. Heparan sulfate proteoglycans are found in a specific microenvironment coating the hepatocyte surface called the glycocalyx and are receptors for extracellular matrix proteins, cytokines, growth factors, lipoproteins, and infectious agents. We investigated the mutual influence of HCV infection on the glycocalyx and revealed new links between Syndecan-1 and CD81. Hepatocyte infection by HCV was inhibited after knocking down Syndecan-1 or Xylosyltransferase 2, a key enzyme of Syndecan-1 biosynthesis. Simultaneous knockdown of Syndecan-1 and CD81 strongly inhibited infection, suggesting their cooperative action. At early infection stages, Syndecan-1 and virions colocalized at the plasma membrane and were internalized in endosomes. Direct interactions between Syndecan-1 and CD81 were revealed in primary and transformed hepatocytes by immunoprecipitation and proximity ligation assays. Expression of Syndecan-1 and Xylosyltransferase 2 was altered within days post-infection, and the remaining Syndecan-1 pool colocalized poorly with CD81. The data indicate a profound reshuffling of the hepatocyte glycocalyx during HCV infection, possibly required for establishing optimal conditions of viral propagation.

Unraveling the distinct distributions of VE- and N-cadherins in endothelial cells: a key role for p120-catenin.

Endothelial cells express two different classical cadherins, vascular endothelial (VE) cadherin and neural (N) cadherin, having distinct functions in the vascular system. VE-cadherin is specific to endothelial adherens junctions and is strictly necessary for vascular morphogenesis. On the contrary, N-cadherin shows diffuse localization on the cell surface and interacts with mural cells for vessel stabilization. In this study, we sought to clarify the cellular mechanisms leading to the distinct cellular locations and functions of the two cadherins in the endothelium. VE-cadherin has been shown to be responsible for the junctional exclusion of N-cadherin. Using several endothelial models, we demonstrate that this property is dependent on VE-cadherin binding to p120 catenin (p120(ctn)). Moreover, although in the absence of VE-cadherin N-cadherin can localize to cell contacts, angiogenesis remains impaired, demonstrating that endothelial junction formation is not sufficient for normal vessel development. Interestingly, we show that VE-cadherin, but not N-cadherin, is partially associated with cholesterol-enriched microdomains. Lipid raft-associated-VE-cadherin is characterized by a very high level of p120(ctn) association, and this association is necessary for VE-cadherin recruitment into lipid rafts. Altogether, our results indicate a critical role for p120(ctn) in regulating the membrane distribution of endothelial cadherins with functional consequences in terms of cadherin stabilization and intracellular signaling.