Multiple ways to die: delineation of the unfolded protein response and apoptosis induced by Surfactant Protein C BRICHOS mutants.
Epithelial cell dysfunction is now recognized as an important mechanism in the pathogenesis of interstitial lung diseases. Surfactant Protein C (SP-C), an alveolar type II cell specific protein, has contributed to this concept with the observation that heterozygous expression of SFTPC gene mutations are associated with chronic interstitial lung disease. We have shown that transient expression of aggregation prone mutant SP-C isoforms (SP-C BRICHOS) destabilize ER quality control mechanisms resulting in the intracellular accumulation of aggregating propeptide, inhibition of the ubiquitin/proteasome system, and activation of apoptosis. The goal of the present study was to define signaling pathways linking the unfolded protein response (UPR) and subsequent ER stress with intrinsic apoptosis events observed following mutant SP-C expression. In vitro expression of the SP-C BRICHOS mutant, SP-C(Δexon4), was used as a model system. Here we show stimulation of a broad ER stress response in both transfected A549 and HEK293 cells with activation of all 3 canonical sensing pathways, IRE1/XBP-1, ATF6, and PERK/eIF2α. SP-C(Δexon4) expression also resulted in activation of caspase 3, but failed to stimulate expression of the apoptosis mediating transcription factors ATF4/CHOP. However, inhibition of either caspase 4 or c-jun kinase (JNK) each blocked caspase 3 mediated cell death. Taken together, these results suggest that expression of SP-C BRICHOS mutants induce apoptosis through multiple UPR signaling pathways, and provide new therapeutic targets for the amelioration of ER stress induced cytotoxicity observed in fibrotic lung remodeling.
Pulmonary and Critical Care Division, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-4539, United States.
Jean Ann
JA
Maguire
Surafel
S
Mulugeta
Michael F
MF
Beers
D051701:Activating Transcription Factor 4 / Q000378:metabolism; D051702:Activating Transcription Factor 6 / Q000378:metabolism; D017209:Apoptosis / Q000235:genetics*; D048708:Cell Growth Processes / Q000235:genetics; D059865:Endoplasmic Reticulum Stress / Q000235:genetics / Q000502:physiology; D004722:Endoribonucleases / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D017563:Lung Diseases, Interstitial / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D009154:Mutation; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D037721:Pulmonary Surfactant-Associated Protein C / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D051742:Transcription Factor CHOP / Q000378:metabolism; D014162:Transfection; D056811:Unfolded Protein Response / Q000235:genetics; D019892:eIF-2 Kinase / Q000378:metabolism
D051701:Activating Transcription Factor 4; D051702:Activating Transcription Factor 6; D004722:Endoribonucleases; D048670:MAP Kinase Kinase 4; D008565:Membrane Proteins; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases; D037721:Pulmonary Surfactant-Associated Protein C; D051742:Transcription Factor CHOP; D019892:eIF-2 Kinase; C497109:ATF4 protein, human; C497111:ATF6 protein, human; C497249:DDIT3 protein, human; C403982:ERN2 protein, human