Human Immunodeficiency Virus Type 1 Tat Protein Enhances Cryptosporidium parvum-Induced Apoptosis in Cholangiocytes via a Fas Ligand-Dependent Mechanism

• Published in: Infection and Immunity Vol. 75; no. 2; pp. 684 - 696
• Main Authors: O'Hara, Steven P, Small, Aaron J, Nelson, Jeremy B, Badley, Andrew D, Chen, Xian-Ming, Gores, Gregory J, LaRusso, Nicholas F
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.02.2007
• Subjects: Animals; Antibodies, Monoclonal - metabolism; Apoptosis; Bile Ducts - cytology; Bile Ducts - parasitology; Biological and medical sciences; Blotting, Western; Cell Line, Transformed; Cell Membrane - chemistry; Cryptosporidium parvum; Cryptosporidium parvum - pathogenicity; Cytoplasm - chemistry; Enzyme Inhibitors - pharmacology; Epithelial Cells - cytology; Epithelial Cells - parasitology; Fas Ligand Protein - antagonists & inhibitors; Fas Ligand Protein - metabolism; Fluorescent Antibody Technique; Fundamental and applied biological sciences. Psychology; Fungal and Parasitic Infections; Gene Expression Regulation; Gene Products, tat - physiology; Human immunodeficiency virus 1; Human viral diseases; Humans; Infectious diseases; Medical sciences; Microbiology; Microscopy, Immunoelectron; Miscellaneous; Oligopeptides - pharmacology; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - analysis; Viral diseases; Viral diseases of the lymphoid tissue and the blood. Aids; Virology; Immunopathology; Protozoa; Fas ligand; Apicomplexa; Microbiology; HIV-1 virus; Cytokine; Retroviridae; AIDS; Immune deficiency; Lentivirus; Immunity; Mechanism; Infection; Virus; Cryptosporidium parvum; Cell death; Viral disease; Human immunodeficiency virus; Apoptosis
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.01348-06

While Cryptosporidium parvum infection of the intestine has been reported in both 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 that the Fas/Fas ligand (FasL) system is involved in paracrine-mediated C. parvum cytopathicity in cholangiocytes, we also tested the potential synergistic effects of human immunodeficiency virus type 1 (HIV-1) transactivator of transcription (Tat)-mediated FasL regulation on C. parvum-induced apoptosis in cholangiocytes by semiquantitative reverse transcription-PCR, immunoblotting, immunofluorescence analysis, and immunogold electron microscopy. H69 cells do not express CXCR4 and CCR5, which are 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 in 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 demonstrated that HIV-1 Tat enhances 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.