Modulation of the unfolded protein response pathway as an antiviral approach in airway epithelial cells

Abstract

Introduction: Rhinovirus (RV) infection is a major cause of cystic fibrosis (CF) lung morbidity with limited therapeutic options. Various diseases involving chronic inflammatory response and infection are associated with endoplasmic reticulum (ER) stress and subsequent activation of the unfolded protein response (UPR), an adaptive response to maintain cellular homeostasis. Recent evidence suggests impaired ER stress response in CF airway epithelial cells, this might be a reason for recurrent viral infection in CF. Therefore, assuming that ER stress inducing drugs have antiviral properties, we evaluated the activation of the UPR by selected ER stress inducers as an approach to control virus replication in the CF bronchial epithelium.

Methods: We assessed the levels of UPR markers, namely the glucose-regulated protein 78 (Grp78) and the C/EBP homologous protein (CHOP), in primary CF and control bronchial epithelial cells and in a CF and control bronchial epithelial cell line before and after infection with RV. The cells were also pretreated with ER stress-inducing drugs and RV replication and shedding was measured by quantitative RT-PCR and by a TCID₅₀ assay, respectively. Cell death was assessed by a lactate dehydrogenate (LDH) activity test in supernatants.

Results: We observed a significantly impaired induction of Grp78 and CHOP in CF compare to control cells following RV infection. The ER stress response could be significantly induced in CF cells by pharmacological ER stress inducers Brefeldin A, Tunicamycin, and Thapsigargin. The chemical induction of the UPR pathway prior to RV infection of CF and control cells reduced viral replication and shedding by up to two orders of magnitude and protected cells from RV-induced cell death.

Conclusion: RV infection causes an impaired activation of the UPR in CF cells. Rescue of the ER stress response by chemical ER stress inducers reduced significantly RV replication in CF cells. Thus, pharmacological modulation of the UPR might represent a strategy to control respiratory virus replication in the CF bronchial epithelium.

Keywords: Cystic fibrosis; Endoplasmic reticulum stress; Rhinovirus; Unfolded protein response.