Misfolded BRICHOS SP-C mutant proteins induce apoptosis via caspase-4- and cytochrome c-related mechanisms.
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(Deltaexon4)), 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(Deltaexon4), 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.
Mulugeta
Surafel
S
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, USA. mulugeta@mail.med.upenn.edu
Maguire
Jean Ann
JA
Newitt
Jennifer L
JL
Russo
Scott J
SJ
Kotorashvili
Adam
A
Beers
Michael F
MF
D017398:Alternative Splicing / Q000235:genetics; D017209:Apoptosis; D053471:Caspases, Initiator / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000473:pathology; D004789:Enzyme Activation; D006801:Humans; D002479:Inclusion Bodies / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D037721:Pulmonary Surfactant-Associated Protein C / Q000737:chemistry* / Q000378:metabolism*; D000071701:Regulatory Factor X Transcription Factors; D012995:Solubility; D014157:Transcription Factors; D025801:Ubiquitin / Q000378:metabolism; D000071717:X-Box Binding Protein 1
D004268:DNA-Binding Proteins; D050505:Mutant Proteins; D009687:Nuclear Proteins; D037721:Pulmonary Surfactant-Associated Protein C; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D025801:Ubiquitin; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; D045304:Cytochromes c; C093516:CASP4 protein, human; D053471:Caspases, Initiator; D046988:Proteasome Endopeptidase Complex