Misfolded BRICHOS SP-C mutant proteins induce apoptosis via caspase-4- and cytochrome c-related mechanisms

• Published in: American journal of physiology. Lung cellular and molecular physiology 2007-09, Vol.293 (3), p.L720-L729
• Main Authors: Mulugeta, Surafel, Maguire, Jean Ann, Newitt, Jennifer L, Russo, Scott J, Kotorashvili, Adam, Beers, Michael F
• Format: Article
• Language: English
• Subjects: Alternative Splicing - genetics; Apoptosis; Caspases, Initiator - metabolism; Cell Line; Cell Nucleus - metabolism; Cytochromes c - metabolism; Cytosol - metabolism; DNA-Binding Proteins - genetics; Endoplasmic Reticulum - pathology; Enzyme Activation; Humans; Inclusion Bodies - metabolism; Lungs; Mitochondria - metabolism; Mutant Proteins - chemistry; Mutant Proteins - metabolism; Mutation; Nuclear Proteins - genetics; Proteases; Proteasome Endopeptidase Complex - metabolism; Protein Folding; Protein Structure, Tertiary; Protein Transport; Proteins; Pulmonary Surfactant-Associated Protein C - chemistry; Pulmonary Surfactant-Associated Protein C - metabolism; Regulatory Factor X Transcription Factors; Respiratory diseases; Solubility; Transcription Factors; Ubiquitin - metabolism; X-Box Binding Protein 1
• ISSN: 1040-0605; 1522-1504
• DOI: 10.1152/ajplung.00025.2007

Pulmonary, Allergy, and Critical Care Division, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania Submitted 18 January 2007 ; accepted in final form 19 June 2007 Several mutations within the BRICHOS domain of surfactant protein C (SP-C) have been linked to interstitial lung disease. Recent studies have suggested that these mutations cause misfolding of the proprotein (proSP-C), which initiates the unfolded protein response to resolve improper folding or promote protein degradation. We have reported that in vitro expression of one of these proteins, the exon 4 deletion mutant (hSP-C exon4 ), causes endoplasmic reticulum (ER) stress, inhibits proteasome function, and activates caspase-3-mediated apoptosis. To further elucidate mechanisms and common pathways for cellular dysfunction, various assays were performed by transiently expressing two SP-C BRICHOS domain mutant (BRISPC) proteins (hSP-C exon4 , hSP-C L188Q ) and control proteins in lung epithelium-derived A549 and kidney epithelium-derived (HEK-293) GFP u -1 cell lines. Compared with controls, cells expressing either BRICHOS mutant protein consistently exhibited increased formation of insoluble aggregates, enhanced promotion of inositol-requiring enzyme 1-dependent splicing of X-box binding protein-1 (XBP-1), significant inhibition of proteasome activity, enhanced induction of mitochondrial cytochrome c release, and increased activations of caspase-4 and caspase-3, leading to apoptosis. These results suggest common cellular responses, including initiation of cell-death signaling pathways, to these lung disease-associated BRISPC proteins. surfactant protein C; misfolding proteins; protein aggregation; endoplasmic reticulum stress; proteasome inhibition Address for reprint requests and other correspondence: S. Mulugeta, Pulmonary, Allergy, and Critical Care Division, Univ. of Pennsylvania School of Medicine, Vernon & Shirley Hill Pavilion, Suite H418, 380 South Univ. Ave., Philadelphia, PA 19104 (e-mail: mulugeta{at}mail.med.upenn.edu )