TRAIL Dependent Fratricidal Killing of gp120 Primed Hepatocytes by HCV Core Expressing Hepatocytes Stacey A. Rizza, Kishore B. Challagundla¤, Sekar Natesampillai, Gary D. Bren, Jaromir Sykora, Henning Walczak, Andrew D. Badley* Division of Infectious Diseases, Mayo Clinic, Rochester, Minnesota, United States of America Abstract The mechanism by which HIV and HCV cooperatively accelerate hepatocyte damage is not clearly understood; however, each virus affects the TRAIL: TRAIL- receptor system. We, therefore, questioned whether the independent effects of HCV and HIV combine to synergistically result in TRAIL dependent hepatocyte killing. We describe that Huh7 hepatocytes treated with HIV gp120 results in both increase TRAIL-R2 expression and an acquired sensitivity to TRAIL mediated killing. Moreover HCV infection and HCV core expression alone in Huh7 cells upregulates TRAIL. Co-incubation of HIV gp120 primed hepatocytes with HCV core expressing hepatocytes results in the selective death of the HIV gp120 primed hepatocytes that is selectively blocked by TRAIL–R2-Fc fusion protein. Liver biopsies from HIV mono-infected patients have increased TRAIL- R2; biopsies from HCV infected patients have increased TRAIL, while co-infected liver biopsies have increased PARP cleavage within hepatocytes indicating enhanced apoptosis. These findings suggest a pathogenic model to understand why HIV/HCV co-infection accelerates liver injury. Citation: Rizza SA, Challagundla KB, Natesampillai S, Bren GD, Sykora J, et al. (2011) TRAIL Dependent Fratricidal Killing of gp120 Primed Hepatocytes by HCV Core Expressing Hepatocytes. PLoS ONE 6(11): e27171. doi:10.1371/journal.pone.0027171 Editor: Naglaa H. Shoukry, University of Montreal, Canada Received June 6, 2011; Accepted October 11, 2011; Published November 14, 2011 Copyright: 2011 Rizza et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Dr. Andrew Badley is supported by a grant from the National Institutes of Health (NIH) (R01 AI62261). Dr. Stacey Rizza’s work was supported by a grant from the NIH (R21DK 77575-1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: badley.andrew@mayo.edu ¤ Current address: Department of Molecular and Medical Genetics, School of Medicine, and OHSU Knight Cancer Institute, Oregon Health and Science University, Portland, Oregon, United States of America Introduction HCV and HIV infections are frequent worldwide; in the USA more than four million people are infected with HCV, which can cause liver fibrosis, cirrhosis, end-stage liver disease, and hepatocellular carcinoma. Approximately 30% of HIV- infected individuals are co-infected with Hepatitis C Virus (HCV) due to their similar modes of transmission [1], as evidenced by the fact that 80% of intravenous drug users (IVDU) infected with HIV are co-infected with HCV. HIV/HCV co-infection results in an increase in morbidity and mortality than occurs with either HIV or HCV mono-infection [2,3]. The pathologic mechanism(s) underlying the accelerated liver disease associated with HCV during HIV co-infection are not clearly understood, but have been proposed to be due to a loss of HCV- specific CD4+ T cells[4]. Such a model accounts for improvements in liver disease which occurs after highly active antiretroviral therapy (HAART)-induced immune reconstitution [5], and lower CD4+ T cell counts being associated with worsened liver function [6]. Alternative models include HIV infection altering the host cytokine response to HCV [7], enhancing the ability of HCV to infect target cells [8], or HIV exacerbating the cytotoxicity of HCV [9]. It also has been suggested that HIV and HCV may cooperatively induce hepatocyte injury through apoptosis [10]. Hepatocyte apoptosis in turn leads to liver fibrogenesis and ultimately cirrhosis [11]. Apoptosis contributes to many liver diseases, including viral hepatitis. Activation of the TNF super-family of death inducing receptors results in hepatocyte apoptosis in several models of liver disease [12]. Hepatocytes express Fas (CD95), TRAIL-R1 and – R2 (TNF-related apoptosis-inducing ligand receptor -1 and -2) (DR5/CD262) and TNF-R1 (TNF receptor type 1) on the cell surface [13,14,15]. After ligation by their respective ligands, these death receptors aggregate and form the death inducing signaling complex (DISC) which causes caspase 8 activation that ultimately results in mitochondrial membrane permeabilization, formation of the apoptosome, which in turn activates effector proteases and nucleases, resulting in the phenotypic changes of apoptosis [16]. There is increasing evidence that liver damage caused by HCV is due to hepatocyte apoptosis, with more hepatocyte apoptosis being present in livers from HCV-infected compared to non- infected individuals [17,18]. Using antibodies specific for active caspase-3 and -7, as well as the cleaved form of PARP, caspase activation and PARP cleavage is increased in livers infected with HCV compared to non-infected livers and caspase activation, as well as hepatocyte apoptosis are directly correlated with the grade of necro-inflammatory injury (reviewed in [18,19]). Hepatocyte apoptosis may be caused by both immune mechanisms and direct cytopathic effects of HCV [20]. Fas (CD95) has been the most thoroughly investigated death inducing ligand during HCV infection. Fas is expressed on hepatocytes during HCV infection and levels correlate with the severity of liver inflammation. Cell surface associated Fas and FasL levels are also associated with increased hepatocyte apoptosis during HIV/HCV infection [15,17]. Of note, several recent reports indicate that hepatocytes PLoS ONE | www.plosone.org 1 November 2011 | Volume 6 | Issue 11 | e27171