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

Abstract

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.

Cryptosporidium parvumInduces B7‐H1 Expression in Cholangiocytes by Down‐Regulating MicroRNA‐513

“…In addition, a neutralizing antibody to Fas also showed a significant inhibitory effect on the associated apoptosis (Fig. 6), consistent with our previous results demonstrating that Fas/Fas-ligand pathway is involved in the apoptosis in the co-cultured Jurkat cells [28,33]. Thus, besides the activation of the Fas/Fas-ligand pathway, miR-513-mediated expression of B7-H1 also contributes to the apoptotic cell death in T-cells induced by co-culture with C. parvum -infected cholangiocytes.…”

HIV‐1 Tat Protein Suppresses Cholangiocyte Toll‐Like Receptor 4 Expression and Defense againstCryptosporidium parvum

“…However, C. parvum biliary infection and AIDS cholangiopathy remain significant problems in individuals who lack access to or fail to respond to HAART. We have previously demonstrated that C. parvum is cytopathic to cultured uninfected bystander cholangiocytes through a paracrine Fas/FasL-dependent apoptotic mechanism [25] and that HIV-1 Tat protein sensitizes cultured cholangiocytes to C. parvum –induced Fas/FasL-dependent apoptotic cell death [45]. Thus, Tat not only sensitizes cholangiocytes, a cell type refractive to HIV-1 infection, to the cytopathic effect of biliary cryptosporidiosis, but our present results suggest that Tat also inhibits the response of cholangiocytes to this opportunistic pathogen.…”

The immunobiology of cholangiocytes

“…As suggested in other tissues, macrophage phagocytosis of apoptotic cells containing the pathogens may contribute to antigen presentation. Apoptotic cell death of cholangiocytes during microbial infection has been reported both in vivo and in vitro 67 , 68 , 69 . However, whether apoptotic cell death of cholangiocytes is involved in the antigen presenting process is unclear.…”