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Infect. Immun. doi:10.1128/IAI.01348-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

HIV-1 Tat Protein Enhances Cryptosporidium parvum -induced Apoptosis in Cholangiocytes via a Fas Ligand-dependent Mechanism

Miles and Shirley Fiterman Center for Digestive Diseases, Division of Gastroenterology and Hepatology; Infectious Diseases Research; Mayo Clinic College of Medicine, Rochester, MN 55905

^* To whom correspondence should be addressed. Email: larusso.nicholas{at}mayo.edu.

	Abstract

While Cryptosporidium parvum infection of the intestine has been reported both in immunocompetent and immunocompromised individuals, biliary infection is seen primarily in adult AIDS patients and is associated with development of AIDS-cholangiopathy. However, the mechanisms of pathogen-induced AIDS-cholangiopathy remain unclear. Since we previously demonstrated the involvement of the Fas/FasL system in paracrine-mediated C. parvum cytopathicity in cholangiocytes, we also tested the potential synergistic effects of HIV-1 Tat-mediated FasL regulation on C. parvum-induced apoptosis in cholangiocytes by semiquantitative RT-PCR, immunoblotting, immunofluorescence, and immunogold electron microscopy. H69 cells do not express CXCR4 and CCR5, receptors required for direct HIV-1 viral infection. However, recombinant biologically active HIV-1-associated Tat protein increased FasL expression in the cytoplasm of cholangiocytes without a significant increase of apoptosis. We found that C. parvum-induced apoptosis was associated with translocation of intracellular FasL to the cell membrane surface and release of full-length FasL from infected H69 cells. Tat significantly (p < 0.05) increased C. parvum-induced apoptosis in bystander cells in a dose-dependent manner. Moreover, Tat enhanced both C. parvum-induced FasL membrane translocation and release of full-length FasL. In addition, the FasL neutralizing antibody, NOK-1, and the Caspase-8 inhibitor, Z-IETD-fmk, both blocked C. parvum-induced apoptosis in cholangiocytes. The data demonstrate synergistic effects of HIV-1 Tat on C. parvum-induced cholangiocyte apoptosis via a paracrine-mediated, FasL-dependent mechanism. Our results suggest that concurrent active HIV replication, with associated production of Tat protein, and C. parvum infection synergistically increase cholangiocyte apoptosis and thus jointly contribute to AIDS-related cholangiopathies.