Abstract
Endoplasmic reticulum (ER) stress is caused by the disturbance of ER homeostasis and leads to the activation of the unfolded protein response (UPR), which alleviates stress at an early stage and triggers apoptosis if homeostasis fails over a prolonged timeframe. Here, we report that reticulocalbin 1 (RCN1), a member of the CREC family, is transactivated by nuclear factor kappa B (NF-κB) during ER stress and inhibits ER stress-induced apoptosis. The depletion of RCN1 increases the UPR during drug-induced ER stress by activating PRKR-like ER kinase–CCAAT/enhancer-binding protein-homologous protein (PERK–CHOP) signaling, thus inducing apoptosis. Furthermore, we found that the first two EF-hand calcium-binding motifs of RCN1 specifically interact with inositol 1,4,5-trisphosphate (IP3) receptor type 1 (IP3R1) on loop 3 of its ER luminal domain and inhibit ER calcium release and apoptosis. Together, these data indicate that RCN1, a target of NF-κB, suppresses ER calcium release by binding to IP3R1 and decreases the UPR, thereby inhibiting ER stress-induced apoptosis.
Highlights
The endoplasmic reticulum (ER), a dynamic sheet and tubular organelle, has multiple functions including initial protein maturation, lipid synthesis and maintenance of intracellular calcium homeostasis.[1,2] Disturbance of the ER environment can cause ER stress and trigger the activation of a signaling network termed the unfolded protein response (UPR), which transduces information about protein folding status in the ER lumen to the cytosol and nucleus
The viability of blocked the CCAAT/enhancer-binding proteinhomologous protein (CHOP) induction caused by depletion of reticulocalbin 1 (RCN1) after TG cells was assessed by microscopy and cell proliferation assays treatment (Figure 3a)
Flow cytometry analysis showed (MTS assay), and the results indicated that depletion of RCN1 that inhibition of PRKRlike ER kinase (PERK) activation significantly alleviated the resulted in a lower number of surviving HEK293T and HepG2 cells increased ratio of early apoptotic cells in RCN1-knockdown cells after TM treatment (Figures 1a-d, Supplementary Figure S1a). after TM treatment (Figures 3b and c), whereas inhibition of inositol-requiring kinase-1 (IRE1) To further investigate whether RCN1 promotes cell survival by activation by STF88301028 resulted in no change (Supplementary inhibiting apoptosis, we performed terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) assays in TM-treated HepG2 cells
Summary
The endoplasmic reticulum (ER), a dynamic sheet and tubular organelle, has multiple functions including initial protein maturation, lipid synthesis and maintenance of intracellular calcium homeostasis.[1,2] Disturbance of the ER environment can cause ER stress and trigger the activation of a signaling network termed the unfolded protein response (UPR), which transduces information about protein folding status in the ER lumen to the cytosol and nucleus. IRE1 recruits tumor necrosis factor alpha (TNF-α) receptor associated factor 2 and apoptosis signal regulating kinase-1, culminating in activation of c-Jun N-terminal protein kinase.[8,9]
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