title: CHAC1/MGC4504 is a novel proapoptotic component of the unfolded protein response, downstream of the ATF4-ATF3-CHOP cascade.
abstract: To understand pathways mediating the inflammatory responses of human aortic endothelial cells to oxidized phospholipids, we previously used a combination of genetics and genomics to model a coexpression network encompassing >1000 genes. CHAC1 (cation transport regulator-like protein 1), a novel gene regulated by ox-PAPC (oxidized 1-palmitoyl-2-arachidonyl-sn-3-glycero-phosphorylcholine), was identified in a co-regulated group of genes enriched for components of the ATF4 (activating transcription factor 4) arm of the unfolded protein response pathway. Herein, we characterize the role of CHAC1 and validate the network model. We first define the activation of CHAC1 mRNA by chemical unfolded protein response-inducers, but not other cell stressors. We then define activation of CHAC1 by the ATF4-ATF3-CHOP (C/EBP homologous protein), and not parallel XBP1 (X box-binding protein 1) or ATF6 pathways, using siRNA and/or overexpression plasmids. To examine the subset of genes downstream of CHAC1, we used expression microarray analysis to identify a list of 227 differentially regulated genes. We validated the activation of TNFRSF6B (tumor necrosis factor receptor superfamily, member 6b), a FASL decoy receptor, in cells treated with CHAC1 small interfering RNA. Finally, we showed that CHAC1 overexpression enhanced apoptosis, while CHAC1 small interfering RNA suppressed apoptosis, as determined by TUNEL, PARP (poly(ADP-ribose) polymerase) cleavage, and AIF (apoptosis-inducing factor) nuclear translocation.
authors.affiliation: Department of Medicine, University of California at Los Angeles, CA 90095, USA. imungrue@yahoo.com
authors.forename: Imran N
authors.initials: IN
authors.lastname: Mungrue
authors.forename: Joanne
authors.initials: J
authors.lastname: Pagnon
authors.forename: Omid
authors.initials: O
authors.lastname: Kohannim
authors.forename: Peter S
authors.initials: PS
authors.lastname: Gargalovic
authors.forename: Aldons J
authors.initials: AJ
authors.lastname: Lusis
mesh_terms: D051700:Activating Transcription Factor 3 / Q000737:chemistry* / Q000235:genetics; D051701:Activating Transcription Factor 4 / Q000737:chemistry*; D051033:Apoptosis Inducing Factor / Q000502:physiology; D051017:Apoptosis Regulatory Proteins / Q000737:chemistry* / Q000502:physiology; D004229:Dithiothreitol / Q000494:pharmacology; D020869:Gene Expression Profiling; D006367:HeLa Cells; D006801:Humans; D020411:Oligonucleotide Array Sequence Analysis; D010713:Phosphatidylcholines / Q000494:pharmacology; D011065:Poly(ADP-ribose) Polymerases / Q000502:physiology; D017510:Protein Folding; D015398:Signal Transduction / Q000187:drug effects* / Q000276:immunology*; D051742:Transcription Factor CHOP / Q000737:chemistry* / Q000235:genetics; D014415:Tunicamycin / Q000494:pharmacology; D033921:Vesicular Transport Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000502:physiology
chemical_list: C494829:AIFM1 protein, human; C490449:ATF3 protein, human; C497109:ATF4 protein, human; D051700:Activating Transcription Factor 3; D051033:Apoptosis Inducing Factor; D051017:Apoptosis Regulatory Proteins; C497249:DDIT3 protein, human; D010713:Phosphatidylcholines; C429654:VPS13A protein, human; D033921:Vesicular Transport Proteins; C472349:oxidized-L-alpha-1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine; D014415:Tunicamycin; D051701:Activating Transcription Factor 4; D051742:Transcription Factor CHOP; D011065:Poly(ADP-ribose) Polymerases; D004229:Dithiothreitol