Lyssavirus Matrix Protein Induces Apoptosis by a TRAIL-Dependent Mechanism Involving Caspase-8 Activation

Abstract

Lyssaviruses, which are members of the Rhabdoviridae family, induce apoptosis, which plays an important role in the neuropathogenesis of rabies. However, the mechanisms by which these viruses mediate neuronal apoptosis have not been elucidated. Here we demonstrate that the early induction of apoptosis in a model of lyssavirus-infected neuroblastoma cells involves a TRAIL-dependent pathway requiring the activation of caspase-8 but not of caspase-9 or caspase-10. The activation of caspase-8 results in the activation of caspase-3 and caspase-6, as shown by an increase in the cleavage of the specific caspase substrate in lyssavirus-infected cells. However, neither caspase-1 nor caspase-2 activity was detected during the early phase of infection. Lyssavirus-mediated cell death involves an interaction between TRAIL receptors and TRAIL, as demonstrated by experiments using neutralizing antibodies and soluble decoy TRAIL-R1/R2 receptors. We also demonstrated that the decapsidation and replication of lyssavirus are essential for inducing apoptosis, as supported by UV inactivation, cycloheximide treatment, and the use of bafilomycin A1 to inhibit endosomal acidification. Transfection of cells with the matrix protein induced apoptosis using pathways similar to those described in the context of viral infection. Furthermore, our data suggest that the matrix protein of lyssaviruses plays a major role in the early induction of TRAIL-mediated apoptosis by the release of a soluble, active form of TRAIL. In our model, Fas ligand (CD95L) appears to play a limited role in lyssavirus-mediated neuroblastoma cell death. Similarly, tumor necrosis factor alpha does not appear to play an important role.

Rabies Virus-Induced Activation of Mitogen-Activated Protein Kinase and NF-κB Signaling Pathways Regulates Expression of CXC and CC Chemokine Ligands in Microglia

“…2D and E, we examined whether virion uncoating is required for the RV-induced expression of CXCL10 and CCL5 in microglia. BA1 is a selective and potent inhibitor of vacuolar H ϩ -ATPase, prevents endosomal acidification (13), and is applicable to the suppression of an acid-induced fusion of lyssaviral envelope with cell membrane (24). As shown in Fig.…”

Genetic Analysis of Phosphoprotein and Matrix Protein of Rabies Viruses Isolated in Brazil

“…In addition, the M protein is involved in viral assembly and budding, and is associated with regulating the balance between viral transcription and replication [9,10,20]. Furthermore, the M protein acts as a major inducer of apoptosis in neuronal cells [23].However, although P and M proteins have been demonstrated to have several important functions in viral infection, these investigations have all been conducted using laboratory-adapted strains. In addition, few studies on P and M proteins in wild-type RV strains have been reported to date [30,31,32,33], and no reports have genetically characterized the P and M genes in Brazilian RV isolates.…”

“…In addition, the M protein is involved in viral assembly and budding, and is associated with regulating the balance between viral transcription and replication [9,10,20]. Furthermore, the M protein acts as a major inducer of apoptosis in neuronal cells [23].…”

Mitochondrial Dysfunction in Lyssavirus-Induced Apoptosis

“…However, the molecular basis of lyssavirus-induced neuronal apoptosis is still poorly understood (16,55). The involvement of the viral glycoprotein (G) in inducing neuronal apoptosis has been extensively shown (13,38,39,45), whereas we have suggested that M is an inducer of neuronal cell death through a tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-dependent pathway (29). However, the molecular mechanism of apoptosis has not been precisely defined, and little is known about mitochondrial involvement during lyssavirus infections (46).…”