Search

Borna disease virus (BDV) is a noncytolytic, neurotropic RNA virus that has a broad host range in warmblooded animals, probably including humans. Recently, it was demonstrated that a 24-kDa phosphoprotein (P) of BDV directly binds to a multifunctional protein, amphoterin-HMGB1, and inhibits its function in cultured neural cells (W. Kamitani, Y. Shoya, T. Kobayashi, M. Watanabe, B. J. Lee, G. Zhang, K. Tomonaga, and K. Ikuta, J. Virol. 75:8742-8751, 2001). This observation suggested that expression of BDV P may cause deleterious effects in cellular functions by interference with HMGB1. In this study, we further investigated the significance of the binding between P and HMGB1. We demonstrated that P directly binds to the A-box domain on HMGB1, which is also responsible for interaction with a tumor suppression factor, p53. Recent works have demonstrated that binding between HMGB1 and p53 enhances p53-mediated transcriptional activity. Thus, we examined whether BDV P affects the transcriptional activity of p53 by interference with HMGB1. Mammalian two-hybrid analysis revealed that p53 and P competitively interfere with the binding of each protein to HMGB1 in a p53-deficient cell line, NCI-H1299. In addition, P was able to significantly decrease p53-mediated transcriptional activation of the cyclin G promoter. Furthermore, we showed that activation of p21[sup waf1] expression was repressed in cyclosporine-treated BDV-infected cells, as well as p53-transduced NCI-H1299 cells. These results suggested that BDV P may be a unique inhibitor of p53 activity via binding to HMGB1. [ABSTRACT FROM AUTHOR]

In this study, we show that the highly pathogenic H5N1 avian influenza virus (AIV) (A/crow/Kyoto/53/04 and A/chicken/Egypt/CL6/07) induced apoptosis in duck embryonic fibroblasts (DEF). In contrast, apoptosis was reduced among cells infected with low-pathogenic AIVs (A/duck/HK/342/78 [H5N2], A/duck/HK/820/80 [H5N3], A/wigeon/Osaka/1/01 [H7N7], and A/turkey/Wisconsin/1/66 [H9N2]). Thus, we investigated the molecular mechanisms of apoptosis induced by H5N1-AIV infection. Caspase-dependent and -independent pathways contributed to the cytopathic effects. We further showed that, in the induction of apoptosis, the hemagglutinin of H5N1-AIV played a major role and its cleavage sequence was not critical. We also observed outer membrane permeabilization and loss of the transmembrane potential of the mitochondria of infected DEF, indicating that mitochondrial dysfunction was caused by the H5N1-AIV infection. We then analyzed Ca2+ dynamics in the infected cells and demonstrated an increase in the concentration of Ca2+ in the cytosol ([Ca2+]i) and mitochondria ([Ca2+]m) after H5N1-AIV infection. Regardless, gene expression important for regulating Ca2+ efflux from the endoplasmic reticulum did not significantly change after H5N1-AIV infection. These results suggest that extracellular Ca2+ may enter H5N1-AIV-infected cells. Indeed, EGTA, which chelates extracellular free Ca2+, significantly reduced the [Ca2+]i, [Ca2+]m, and apoptosis induced by H5N1-AIV infection. In conclusion, we identified a novel mechanism for influenza A virus-mediated cell death, which involved the acceleration of extracellular Ca2+ influx, leading to mitochondrial dysfunction and apoptosis. These findings may be useful for understanding the pathogenesis of H5N1-AIV in avian species as well as the impact of Ca2+ homeostasis on influenza A virus infection. [ABSTRACT FROM AUTHOR]

In this study, we show that the highly pathogenic H5N1 avian influenza virus (AIV) (A/crow/Kyoto/53/04 and A/chicken/Egypt/CL6/07) induced apoptosis in duck embryonic fibroblasts (DEF). In contrast, apoptosis was reduced among cells infected with low-pathogenic AIVs (A/duck/HK/342/78 [H5N2], A/duck/HK/820/80 [H5N3], A/wigeon/Osaka/1/01 [H7N7], and A/turkey/Wisconsin/1/66 [H9N2]). Thus, we investigated the molecular mechanisms of apoptosis induced by H5N1-AIV infection. Caspase-dependent and -independent pathways contributed to the cytopathic effects. We further showed that, in the induction of apoptosis, the hemagglutinin of H5N1-AIV played a major role and its cleavage sequence was not critical. We also observed outer membrane permeabilization and loss of the transmembrane potential of the mitochondria of infected DEF, indicating that mitochondrial dysfunction was caused by the H5N1-AIV infection. We then analyzed Ca(2+) dynamics in the infected cells and demonstrated an increase in the concentration of Ca(2+) in the cytosol ([Ca(2+)](i)) and mitochondria ([Ca(2+)](m)) after H5N1-AIV infection. Regardless, gene expression important for regulating Ca(2+) efflux from the endoplasmic reticulum did not significantly change after H5N1-AIV infection. These results suggest that extracellular Ca(2+) may enter H5N1-AIV-infected cells. Indeed, EGTA, which chelates extracellular free Ca(2+), significantly reduced the [Ca(2+)](i), [Ca(2+)](m), and apoptosis induced by H5N1-AIV infection. In conclusion, we identified a novel mechanism for influenza A virus-mediated cell death, which involved the acceleration of extracellular Ca(2+) influx, leading to mitochondrial dysfunction and apoptosis. These findings may be useful for understanding the pathogenesis of H5N1-AIV in avian species as well as the impact of Ca(2+) homeostasis on influenza A virus infection.

Previous data revealed that primary cultures of peripheral blood mononuclear cells (PBMCs) were killed by apoptosis at higher rates after infection with two CRF01_AE primary isolates of human immunodeficiency virus type 1 (HIV-1) than after infection with five other CRF01_AE primary isolates, five subtype B primary isolates, and two subtype B laboratory strains. Here, we show evidence that mutations at the vpu gene which were exclusively identified only in the two CRF01_AE isolates mentioned above are involved in their abilities to induce massive apoptosis in primary CD4(+) T lymphocytes. The rates of virus production by these two isolates in the culture media of infected PBMCs were lower (the same as those of the other CRF01_AE isolates) than those of the subtype B isolates. To confirm the correlation between the higher apoptosis-inducing abilities and the mutations at the vpu gene, infectious molecular clone pNL4-3-based vpu mutants were constructed and examined for their apoptosis induction levels. The apoptosis induction levels after introduction of the vpu mutations were greatly increased in primary CD4(+) T lymphocytes. In contrast, the apoptosis induction abilities of these vpu mutants were lower in human T-cell line MT-4. Thus, the Vpu protein of HIV-1 could play a protective role against virus-induced apoptosis in primary CD4(+) T lymphocytes.