Constitutive expression of misfolded surfactant protein C

Mutations in the gene encoding surfactant protein C (SFTPC) have been linked to interstitial lung disease in children and adults. Expression of the index mutation, SP-Cdeltaexon4, in transiently transfected cells and type II cells of transgenic mice resulted in misfolding of the proprotein, activation of ER stress pathways and cytotoxicity. In the current study we show that stably transfected cells adapted to chronic ER stress imposed by constitutive expression of SP-Cdeltaexon4 via an NF-kB-dependent pathway. However, infection of cells expressing SP-Cdeltaexon4 with respiratory syncytial virus resulted in significantly enhanced cytotoxicity associated with accumulation of the mutant proprotein, pronounced activation of the unfolded protein response and cell death. Adaptation to chronic ER stress imposed by misfolded SP-C was associated with increased susceptibility to viral-induced cell death. The wide variability in the age of onset of ILD in patients with SFTPC mutations may be related to exposure to an environmental insult that ultimately overwhelms the homeostatic, cytoprotective response. Keywords: transcriptional response to misfolded protein due to genetic modification samples consisted of HEK293 cells stably transfected with wild-type SP-C (WT), the delta exon4 mutant of SP-C (Exon4) or empty vector (EVcontrol). Groups were performed in triplicate.