The primary reservoir for hepatitis C virus (HCV) replication is believed to be hepatocytes, which are highly polarized with tight junctions (TJ) separating their basolateral and apical domains. HepG2 cells develop polarity over time, resulting in the formation and remodeling of bile canalicular (BC) structures. HepG2 cells expressing CD81 provide a model system to study the effects of hepatic polarity on HCV infection. We found an inverse association between HepG2-CD81 polarization and HCV pseudoparticle entry. As HepG2 cells polarize, discrete pools of claudin-1 (CLDN1) at the TJ and basal/lateral membranes develop, consistent with the pattern of receptor staining observed in liver tissue. The TJ and nonjunctional pools of CLDN1 show an altered association with CD81 and localization in response to the PKA antagonist Rp-8-Br-cyclic AMPs (cAMPs). Rp-8-Br-cAMPs reduced CLDN1 expression at the basal membrane and inhibited HCV infection, supporting a model where the nonjunctional pools of CLDN1 have a role in HCV entry. Treatment of HepG2 cells with proinflammatory cytokines, tumor necrosis factor alpha and gamma interferon, perturbed TJ integrity but had minimal effect(s) on cellular polarity and HCV infection, suggesting that TJ integrity does not limit HCV entry into polarized HepG2 cells. In contrast, activation of PKC with phorbol ester reduced TJ integrity, ablated HepG2 polarity, and stimulated HCV entry. Overall, these data show that complex hepatocyte-like polarity alters CLDN1 localization and limits HCV entry, suggesting that agents which disrupt hepatocyte polarity may promote HCV infection and transmission within the liver.Hepatitis C virus (HCV) poses a global health problem, with over 170 million infected individuals worldwide. The principal reservoir for HCV replication is believed to be hepatocytes in the liver. Innate and adaptive cellular immune responses are thought to play a critical role in controlling HCV replication. However, in the majority of cases, the virus persists and the resulting hepatitis leads to progressive liver injury, frequently culminating in fibrosis and hepatocellular carcinoma. At the present time there is no vaccine and the only established treatment is alpha interferon (IFN-ā£) in combination with ribavirin, which is only partially effective. Hence, there is an urgent need for the development of more effective therapies.The recent discovery that some strains of HCV can replicate in cell culture (HCVcc) and release infectious particles has allowed the complete viral life cycle to be studied (30,52,58). HCV initiates infection by attaching to molecules or receptors at the cell surface, and current evidence suggests that the tetraspanin CD81 (3, 10, 20, 26), scavenger receptor class B member I (SR-BI) (2, 22, 48), and the tight junction (TJ) proteins claudin-1 (CLDN1) and occludin (OCLN) (15,37,43,55,57) are required for HCV entry (reviewed in reference 50). However, the exact role(s) played by each of the receptors is unclear.Many tissues in the body contain polarized cells,...