1. Center for the Study of Hepatitis C, The Rockefeller University, 1230 York Ave, New York 10021, USA
2. Aaron Diamond AIDS Research Center, The Rockefeller University, 455 First Avenue, New York 10016, USA
3. Present address: Division of Immunity and Infection, Institute of Biomedical Research, Medical School, University of Birmingham, Birmingham B15 2TT, UK.
4. These authors contributed equally to this work.

Correspondence to: Charles M. Rice¹ Correspondence and requests for materials should be addressed to C.M.R. (Email: ricec@mail.rockefeller.edu).

Abstract

Hepatitis C virus (HCV) is a leading cause of cirrhosis and liver cancer worldwide. A better understanding of the viral life cycle, including the mechanisms of entry into host cells, is needed to identify novel therapeutic targets. Although HCV entry requires the CD81 co-receptor, and other host molecules have been implicated, at least one factor critical to this process remains unknown (reviewed in refs 1–3). Using an iterative expression cloning approach we identified claudin-1 (CLDN1), a tight junction component that is highly expressed in the liver⁴, as essential for HCV entry. CLDN1 is required for HCV infection of human hepatoma cell lines and is the first factor to confer susceptibility to HCV when ectopically expressed in non-hepatic cells. Discrete residues within the first extracellular loop (EL1) of CLDN1, but not protein interaction motifs in intracellular domains, are critical for HCV entry. Moreover, antibodies directed against an epitope inserted in the CLDN1 EL1 block HCV infection. The kinetics of this inhibition indicate that CLDN1 acts late in the entry process, after virus binding and interaction with the HCV co-receptor CD81. With CLDN1 we have identified a novel key factor for HCV entry and a new target for antiviral drug development.

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