Rubella Virus-Induced Apoptosis Varies among Cell Lines and Is Modulated by Bcl-XLand Caspase Inhibitors

Abstract

Rubella virus (RV) causes multisystem birth defects in the fetuses of infected women. To investigate the cellular basis of this pathology, we examined the cytopathic effect of RV in three permissive cell lines: Vero 76, RK13, and BHK21. Electron microscopy and the TUNEL assay showed that the cytopathic effect resulted from RV-induced programmed cell death (apoptosis) in all three cell lines, but the extent of apoptosis varied among these cells. At 48 h postinfection, the RK13 cell line showed the greatest number of apoptotic cells, the Vero 76 cell line was approximately 3-fold less, and BHK21 had very few. An increased multiplicity of infection and longer time postinfection were required for the BHK21 cell line to reach the level of apoptotic cells in Vero 76 at 48 h. Purified RV induced apoptosis in a dose-dependent fashion, but not UV-inactivated RV or virus-depleted culture supernatant. Specific inhibitors of the apoptosis-specific proteases caspases reduced RV-induced apoptosis and led to higher levels of RV components in infected cells. To address the role of regulatory proteins in RV-induced apoptosis, the antiapoptotic gene Bcl-2 or Bcl-XL was transfected into RK13 cells. Although a high level of Bcl-2 family proteins was expressed, no protection was observed from apoptosis induced by RV, Sindbis virus, or staurosporine in RK13 cells. In BHK21 cells, however, increased expression of Bcl-XL protected cells from apoptosis. The observed variability in apoptotic response to RV of these cell lines demonstrates that programmed cell death is dependent on the unique properties of each cell and may be indicative of how selective organ damage occurs in a congenital rubella syndrome fetus.

Time-course induction of apoptosis by wild-type and attenuated strains of rubella virus

“…This is the first report of the time-course of early biochemical apoptotic events during RV-induced apoptosis. The induction of apoptotic cascades in RV-infected RK13 cells occurred as early as 12 h p.i., with both wt (RN) and attenuated (Cendehill) strains, and is much earlier than suggested by previous studies (Duncan et al, 1999). This rapid activation of apoptotic mechanisms is in agreement with current knowledge on the apoptotic cascade, with caspase activation as the leading event (Au et al, 1999).…”

“…RV-induced apoptosis was first described in 1998 (Pugachev & Frey, 1998). This and other studies have demonstrated that RV cytopathic effect (CPE) is due to caspase-dependent apoptosis and that RV replication is required for this process (Duncan et al, 1999(Duncan et al, , 2000Hofmann et al, 1999;Megyeri et al, 1999). These studies were carried out in susceptible cell lines, as animal models have not proved sufficiently reliable for the study of symptomatic RV infection and pathogenesis (Chantler et al, 2000).…”

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

“…Since the Bcl-2 family is associated with apoptosis in a variety of viral infections (Conti et al, 1998;Duncan et al, 1999;Lewis et al, 1999;Mastrangelo et al, 2000;Hong and Wu, 2002), and because expression of Bcl-2, an anti-apoptosis gene, in MDCK cells blocks influenza virus-induced apoptosis and DNA fragmentation (Hinshaw et al, 1994), we determined the expression of Bcl-2 and Bax proteins to investigate whether members of the Bcl-2 family are implicated in SIV-mediated apoptosis of PK-15 and HeLa cells. As shown in Figure 3, the cellular level of Bcl-2 protein was remarkably downregulated following SIV infection in both cell lines compared to mock-infected control cells at 24 h post-infection, whereas expression of Bax protein, a pro-apoptosis gene, was upregulated in SIV-infected PK-15 cells, but was not upregulated in SIV-infected HeLa cells.…”

“…Although influenza virus-induced apoptosis is inhibited by Bcl-2 (Olsen et al, 1996), v-FLIP, and crmA (Takizawa et al, 1999), the best characterized pathway of influenzainduced apoptosis is that activation of receptor-mediated signaling is associated with the activation of caspase-8 (death receptor pathway) Fujimoto et al, 1998). However, although the Bcl-2 family is associated with apoptosis in various viral infections (Conti et al, 1998;Duncan et al, 1999;Lewis et al, 1999), there have been few reports regarding the activation of members of the Bcl-2 family by the influenza virus. Hence, we examined expression mitochondrial pathway-associated gene regulation in the porcine kidney cell line (PK-15) and HeLa cells infected with three subtypes of swine influenza viruses (SIV).…”

Coxsackievirus B3-induced apoptosis and Caspase-3

“…Upon receipt of a death signal, a cascade of proteolytic cleavages results in activation of preexisting inactive caspases, which cleave specific substrates such as DNA fragmentation factor (DFF) and poly (ADP-ribose) polymerase (PARP), resulting in apoptosis and corresponding cell morphological & structural changes [10]. Several apoptosis-inducing signals including virus infection have been shown to activate caspases [11][12][13][14]. However, various recent reports indicated the existence of caspase-independent apoptosis [15][16][17][18].…”