Bcl-2 Expression and p38MAPK Activity in Cells Infected with Influenza A Virus

Abstract

Previous reports have shown that various steps in the influenza A virus life cycle are impaired in cells expressing the antiapoptotic protein Bcl-2 (Bcl-2؉ cells). We demonstrated a direct link between Bcl-2 and the reduced nuclear export of viral ribonucleoprotein (vRNP) complexes in these cells. However, despite its negative impact on viral replication, Bcl-2 did not prevent host cells from undergoing virally triggered apoptosis. The protein's reduced antiapoptotic capacity was related to phosphorylation of its threonine 56 and serine 87 residues by virally activated p38MAPK. In infected Bcl-2 ؉ cells, activated p38MAPK was found predominantly in the cytoplasm, colocalized with Bcl-2, and both Bcl-2 phosphorylation and virally induced apoptosis were diminished by specific inhibition of p38MAPK activity. In contrast, in Bcl-2-negative (Bcl-2 ؊ ) cells, which are fully permissive to viral infection, p38MAPK activity was predominantly nuclear, and its inhibition decreased vRNP traffic, phosphorylation of viral nucleoprotein, and virus titers in cell supernatants, suggesting that this kinase also contributes to the regulation of vRNP export and viral replication. This could explain why in Bcl-2 ؉ cells, where p38MAPK is active in the cytoplasm, phosphorylating Bcl-2, influenza viral replication is substantially reduced, whereas apoptosis proceeds at rates similar to those observed in Bcl-2 ؊ cells. Our findings suggest that the impact of p38MAPK on the influenza virus life cycle and the apoptotic response of host cells to infection depends on whether or not the cells express Bcl-2, highlighting the possibility that the pathological effects of the virus are partly determined by the cell type it targets.The influenza A virus, a widespread human pathogen, is characterized by a segmented negative strand RNA genome that encodes 11 viral proteins. Within the envelope, the eight viral RNA segments, associated with the nucleoprotein (NP) 3 and the polymerase complex, form helical ribonucleoprotein capsids (vRNP S ). After infection, the vRNP S are transported to the host cell nucleus, where they undergo transcription and replication. In the late phase of replication, newly formed RNP S are transferred from the nucleus to the cytoplasm and packaged into progeny virions (1-3). Such an essential step in the life cycle of the virus is known to be regulated in part by viral and host cell factors (4 -9), including the expression of Bcl-2, which varies widely from one cell type to another (6, 10, 11). This transmembrane protein is well known for its ability to prevent the apoptotic cell death provoked by a variety of stimuli (12), a property that is markedly diminished when Bcl-2 undergoes phosphorylation by several different cellular kinases (13-16). Several lines of evidence indicate that host cell expression of Bcl-2 is associated with impaired replication of the influenza A virus (6, 17) and significant suppression of vRNP translocation into the cytoplasm (6). We have suggested that the latter effect might be related to inte...

N-acetyl-l-cysteine (NAC) inhibits virus replication and expression of pro-inflammatory molecules in A549 cells infected with highly pathogenic H5N1 influenza A virus

“…Therefore, inhibition of H5N1 [28,34,39,40]. In MDCK cells, however, the pharmacological p38 inhibitor SB203580 was shown to inhibit RNP transport from the nucleus to the cytosol [32]. Since nuclear export of the RNP complex has been shown to be a critical step in influenza A virus replication this suggests that p38 inhibition may affect H5N1 replication in certain cell types [33].…”

Bik Mediates Caspase-Dependent Cleavage of Viral Proteins to Promote Influenza A Virus Infection

“…These observations suggest the potential for impaired shuttling of viral RNP to the cytoplasm by Bik deficiency. NPs or RNP have been shown to translocate partially to the cytoplasm after apoptotic stimuli in a caspase 3-dependent manner (16), and nuclear retention of NP caused by a lack of caspase activity has been linked to decreased titers of virus (14). Because IAV NP acts as a shuttle for viral genomic segments from the nucleus to the budding sites at the plasma membrane, localization during the virus replication cycle affects virus titers.…”

“…Although the proapoptotic proteins promote IAV replication (2,16,17,33), the prosurvival Bcl-2 members decrease viral replication rates (14,16). Therefore, we screened for changes in the expression of Bik, bad, Mcl-1, and Bcl-x L .…”

“…Bcl-2 decreases viral replication rates (14) by inhibiting IAV-induced cell death (15), because activation of caspase-3 during the cell death process is critical to the IAV life cycle (16). IAV NP acts as a shuttle for viral genomic segments from the nucleus to the budding sites at the plasma membrane, and localization during the virus replication cycle affects virus titers.…”

The PI3K/Akt pathway inhibits influenza A virus-induced Bax-mediated apoptosis by negatively regulating the JNK pathway via ASK1

“…PB1-F2, a recently discovered viral protein, makes cells more sensitive to apoptosis by localizing to the mitochondrial membranes and interacting with the ANT3 and VDAC1 proteins (Zamarin et al, 2005). In addition to the direct effects of viral pro-and anti-apoptotic factors, cellular pathways, including the Bcl-2 and p38 pathways, have been shown to be involved in influenza A virus-induced apoptosis (Nencioni et al, 2009;Olsen et al, 1996). Studies using equine influenza virus have shown that influenza virus infection induces apoptosis via a c-jun N-terminal kinase (JNK) or stress-activated protein kinase cascade (Lin et al, 2001).…”