Human occludin is a hepatitis C virus entry factor required for infection of mouse cells

Abstract

Hepatitis C virus (HCV) is a leading cause of liver disease worldwide. The development of much needed specific antiviral therapies and an effective vaccine has been hampered by the lack of a convenient small animal model. The determinants restricting HCV tropism to human and chimpanzee hosts are unknown. Replication of the viral RNA has been demonstrated in mouse cells1,2, but these cells are not infectable with either lentiviral particles bearing HCV glycoproteins (HCVpp)3 or HCV produced in cell culture (HCVcc)(unpublished data), suggesting a block at the level of entry. Through an iterative cDNA library screening approach we have identified human occludin (OCLN) as an essential HCV cell entry factor that is able to render murine cells infectable with HCVpp. Similarly, OCLN is required for HCV-susceptibility of human cells, since its overexpression in uninfectable cells specifically enhanced HCVpp uptake while its silencing in permissive cells impaired both HCVpp and HCVcc infection. In addition to OCLN, HCVpp infection of murine cells required expression of the previously identified HCV entry factors, CD814, scavenger receptor class B type I (SR-BI)5, and claudin-1 (CLDN1)6. While the mouse versions of SR-BI and CLDN1 function at least as well as the human proteins for promoting HCV entry; both OCLN and CD81, however, must be of human origin to allow efficient infection. The species-specific determinants of OCLN were mapped to its second extracellular loop. The identification of OCLN as a new HCV entry factor further highlights the importance of the tight junction complex in the viral entry process and provides a major advance towards efforts to develop small animal models for HCV.

Characterization of the inhibition of hepatitis C virus entry by In vitro –generated and patient-derived oxidized low-density lipoprotein

“…6 Cell-surface factors essential for HCV entry, but not directly involved in lipid trafficking, include the tetraspanin, CD81, 7 and the tight-junction components, claudin-1 8 and occludin. 9 SR-BI is a 509-amino-acid protein with two transmembrane domains and a single large extracellular loop that is highly expressed in the liver and in tissues producing steroid hormones. 10 It is the key highdensity lipoprotein (HDL) receptor and mediates a flux of free cholesterol from the lipoprotein into the cellular membrane.…”

“…10,[12][13][14][15] First proposed as an HCV receptor because of its interaction with the viral glycoprotein, E2, 16 SR-BI was subsequently shown to be essential for HCV entry in numerous studies. 5,9,17,18 Animal data indicate that SR-BI is also important for HCV infection in vivo, 19 and an inhibitor of HCV/SR-BI interaction is the only HCVentry inhibitor currently in clinical trials. 20 Recent work has suggested that SR-BI fulfils at least two distinct functions during viral entry: one related to initial attachment and another during post-binding.…”

Experimental models for hepatitis C viral infection #

“…Most recently, human occludin was identified as a crucial factor for HCV entry. 37 The involvement of these diverse molecules was first demonstrated using HCV pseudoparticles, but has now been verified in the infectious HCV cell culture system.…”

“…A better understanding of the essential host cell factors required for productive HCV infection by, for instance, genomewide RNA interference screening and microRNA profiling, may allow the manipulation of small laboratory animals as hosts of HCV infection. In this endeavor, the combined expression of human occludin and CD81, which makes mouse cells infectable by HCV, 37 and the expression of the liver-specific microRNA miR-122, which promotes viral replication in nonhepatocyte cells, 38 may hold promise for the future.…”

“…It has been reported that mice transgenic for human CD81 are not susceptible to HCV, 84 but the possibility that a combination of multiple human HCV receptors may make hepatocytes permissive to HCV infection is tantalizing. 37 One has to keep in mind that the characteristics of modified mouse hepatocytes may differ from human hepatocytes. A major downside of the uPA/SCID mouse model is that the chimeric animals are genetically immunodeficient.…”