Respiratory Syncytial Virus Decreases p53 Protein to Prolong Survival of Airway Epithelial Cells

Abstract

Respiratory syncytial virus (RSV) is a clinically important pathogen. It preferentially infects airway epithelial cells causing bronchiolitis in infants, exacerbations in patients with obstructive lung disease, and life-threatening pneumonia in the immunosuppressed. The p53 protein is a tumor suppressor protein that promotes apoptosis and is tightly regulated for optimal cell growth and survival. A critical negative regulator of p53 is murine double minute 2 (Mdm2), an E3 ubiquitin ligase that targets p53 for proteasome degradation. Mdm2 is activated by phospho-Akt, and we previously showed that RSV activates Akt and delays apoptosis in primary human airway epithelial cells. In this study, we explore further the mechanism by which RSV regulates p53 to delay apoptosis but paradoxically enhance inflammation. We found that RSV activates Mdm2 1–6 h after infection resulting in a decrease in p53 6–24 h after infection. The p53 down-regulation correlates with increased airway epithelial cell longevity. Importantly, inhibition of the PI3K/Akt pathway blocks the activation of Mdm2 by RSV and preserves the p53 response. The effects of RSV infection are antagonized by Nutlin-3, a specific chemical inhibitor that prevents the Mdm2/p53 association. Nutlin-3 treatment increases endogenous p53 expression in RSV infected cells, causing earlier cell death. This same increase in p53 enhances viral replication and limits the inflammatory response as measured by IL-6 protein. These findings reveal that RSV decreases p53 by enhancing Akt/Mdm2-mediated p53 degradation, thereby delaying apoptosis and prolonging survival of airway epithelial cells.

Inflammation and p53: A Tale of Two Stresses

“…In fact, Nutlin-3A administration significantly increased the survival of mice following LPS-induced septic shock (E. A. Komarova, L. Vassilev, and A. V. Gudkov, in preparation). These results are consistent with earlier reports by Liu et al 81 and Groskreutz et al, 101 who showed anti-inflammatory effects of Nutlin-3A in models of LPS-induced and respiratory syncytial virus-induced lung injury, respectively. It was shown previously in vitro that Nutlin-3A can down-regulate TNFα-and IL-1-induced activation of NF-κB-dependent reporter gene expression and inhibit the expression of proteins encoded by the NF-κB target genes ICAM-1 and MCP-1, which are known to be critical for cancer cell invasion.…”

Proapoptotic signaling induced by RIG-I and MDA-5 results in type I interferon–independent apoptosis in human melanoma cells

“…Thus, viral RNA mimetics are advantageous for analyzing the basic principles of antiviral responses as revealed in our study. It is important to note that RIG-I and MDA-5 are capable to induce apoptosis independently of two key antiviral proapoptotic pathways, the type I IFN system and p53 (37,38). As a consequence, apoptosis induction by RIG-I and MDA-5 remains functional even in situations where the virus applies strategies to downregulate type I IFN (11,39) or p53 (38).…”

Fusogenic membrane glycoproteins induce syncytia formation and death in vitro and in vivo: a potential therapy agent for lung cancer

“…Thus, our results suggest that induction of apoptosis in these syncytia is FMG-and cell line-dependent and is certainly not the unique mechanism involved in syncytial death. It has been shown that Respiratory Syncytial Virus can block early apoptosis of infected cells through a p53-dependent pathway and phosphatidyl inositol-3kinase/AKT activation, 38 while its F fusogenic protein is capable of inducing p53-dependent apoptosis. 39 The presence or absence of the p53 tumorsuppressor protein may thus contribute to explaining the differences we observed between the two NSCLC cell lines A549 (P53 WT) and H322 (p53À/À) in response to GALV-induced syncytia death.…”