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-glycerophosphorylcholine), 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.

25-Hydroxycholesterol Activates the Integrated Stress Response to Reprogram Transcription and Translation in Macrophages

“…Atf4, Chop/Ddit3, Chac1, Trib3, and asparagine synthetase (Asns) are up-regulated during cellular responses to stress and were among the most highly induced genes by 25OHC ( Fig. 1C and supplemental Dataset S1) (13,34). Q-PCR assays in BMDMs confirmed that stress response genes were induced by 25OHC in a concentration-and time-dependent manner ( Fig.…”

Mammalian proapoptotic factor ChaC1 and its homologues function as γ‐glutamyl cyclotransferases acting specifically on glutathione

“…When the homology models of these proteins were superimposed on the g-GCT (C7orf24) structure they revealed very high structural similarity, despite no sequence similarity in their primary sequences (Fig 1A; supplementary Fig S2A online). Moreover, 39 YGSL 42 and E 116 residues of ChaC1, and 13 YGSL 16 and E 115 residues of YER163c are equivalent to the critical 22 YGSN 25 and E 98 residues of g-GCT that are involved in substrate binding and catalysis and superimposed very well on the corresponding residues of g-GCT (Fig 1B; supplementary Fig S2B online).…”

“…Glutathione depletion is an important factor for apoptosis initiation and execution. Moreover, ChaC1 has been shown as a proapototic factor in mammals [1,16]. To examine if the ChaC family proteins caused glutathione depletion in vivo and g-GACT, g-glutamylamine cyclotransferase; g-GCG, g-glutamylcyclotransferase-glutathione-specific; g-GCT, g-glutamyl cyclotransferase.…”

Discovery and characterization of nutritionally regulated genes associated with muscle growth in Atlantic salmon

“…This situation is likely to occur during the transition from a fasted state to that of satiation feeding where increased protein synthesis occurs through activation of the AKT/ mTOR pathway. Stimulation of the UPR leads to the activation of several transcription factors, resulting in the expression of DNAJ, HSPA1B, HSP90, and CHAC1 (52). There are three different UPR response pathways, regulated by PERK, ATF-6, and IRE-1.…”