Activation of the intrinsic mitochondrial apoptotic pathway in swine influenza virus-mediated cell death

Young Ki Choi,Chul-Joong Kim,Tae-Kyung Kim,Seungkwon You,Ki-Chang Hong,Se-Young Oh,Joong-Seob Lee,Douglas N Foster,Hyunggee Kim,Han Soo Joo

doi:10.1038/emm.2006.2

Young Ki Choi, Chul-Joong Kim + Show 8 more

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https://doi.org/10.1038/emm.2006.2

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Abstract

The mitochondrial pathway of swine influenza virus (SIV)-induced apoptosis was investigated using porcine kidney (PK-15) cells, swine testicle (ST) cells, and HeLa cervical carcinoma cells which are known not to support viral replication. As judged by cell morphology, annexin V staining, and DNA fragmentation, PK-15 and ST cells infected with three different subtypes of SIV (H1N1, H3N2, and H1N2) were obviously killed by apoptosis, not necrosis. SIV infection in PK-15 and HeLa cells was shown to decrease the cellular levels of Bcl-2 protein compared to that of mock-infected control cells at 24 h post-infection, whereas expression levels of Bax protein increased in the PK-15 cells, but did not increase in HeLa cells by SIV infection. Cytochrome c upregulation was also observed in cytosolic fractions of the PK-15 and HeLa cells infected with SIV. Apoptosome (a multi-protein complex consisting of cytochrome c, Apaf-1, caspase-9, and ATP) formation was confirmed by immunoprecipitation using cytochrome c antibody. Furthermore, SIV infection increased the cellular levels of TAJ, an activator of the JNK- stressing pathway, and the c-Jun protein in the PK-15 and HeLa cells. Taken together, these results suggest that the mitochondrial pathway should be implicated in the apoptosis of PK-15 cells induced by SIV infection.

Highlights

Programmed cell death, or apoptosis, is central to many physiological processes, including tissue atrophy, development of the immune system, and tumor biology (Majno and Joris, 1995; Jacobson et al, 1997)
These results suggest that swine influenza virus (SIV)-induced apoptosis in porcine kidney-15 cell (PK-15) and swine testicle (ST) cells might be accompanied by replication of live virus, not by just attachment of the virus to cells, as judged by the lack of Cytopathic effects (CPE) and apoptotic effects in the cells inoculated with UV-irradiated
The death receptor-mediated apoptosis pathway induced by influenza infection has been extensively studied (Takizawa et al, 1995; Wada et al, 1995; Fujimoto et al, 1998), little is known about the potential participation of the mitochondriamediated apoptosis pathway during influenza-induced cell death

Summary

Introduction

Programmed cell death, or apoptosis, is central to many physiological processes, including tissue atrophy, development of the immune system, and tumor biology (Majno and Joris, 1995; Jacobson et al, 1997). There is no obvious advantage for apoptosis induction by a cytopathogenic virus, the influenza virus induces apoptosis in numerous cell types, both in vivo (Mori et al, 1995) and in vitro (Morris et al, 1999; SchultzCherry et al, 2001). Two primary pathways induce apoptosis in mam malian cells (Hengartner, 2000). Binding of CD95 ligand to CD95 induces receptor clustering and formation of a death-inducing signal complex. This complex recruits multiple procaspase molecules into close proximity via the adaptor molecule FADD (fas-associated death domain protein), which results in caspase-8 activation through proximity. The second apoptosis pathway is induced by mitochondria in response to extracellular cues

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