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

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Abstract
The development of an effective vaccine and specific antiviral therapies against hepatitis C virus (HCV), a leading cause of liver disease, has been hampered by the lack of a convenient small animal model. With the identification of the gap junction protein occludin as the fourth and final key component of the hepatitis C virus cell-entry receptor, that elusive lab model may have come a step nearer. In addition to human occludin, viral infection of murine cells requires expression of the previously identified HCV entry factors CD81, scavenger receptor class B type I, and claudin-1. This report identifies the gap junction protein occludin as the fourth and final key component of the hepatitis C virus cell-entry receptor, paving the way towards the development of a small animal model for hepatitis C virus. 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lentiviral particles bearing HCV glycoproteins (HCVpp)3 or HCV produced in cell culture (HCVcc) (A.P., M.E. and C.M.R., unpublished observations), suggesting that there is a block at the level of entry. Here we show, using an iterative complementary DNA library screening approach, that human occludin (OCLN) is an essential HCV cell entry factor that is able to render murine cells infectable with HCVpp. Similarly, OCLN is required for the HCV-susceptibility of human cells, because its overexpression in uninfectable cells specifically enhanced HCVpp uptake, whereas 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 CD81 (ref. 4), scavenger receptor class B type I (SR-BI, also known as SCARB1)5 and claudin-1 (CLDN1)6. Although the mouse versions of SR-BI and CLDN1 function at least as well as the human proteins in promoting HCV entry, both OCLN and CD81 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 an important advance towards efforts to develop small animal models for HCV.