TMBIM3/GRINA is a novel unfolded protein response (UPR) target gene that controls apoptosis through the modulation of ER calcium homeostasis

Abstract

Transmembrane BAX inhibitor motif-containing (TMBIM)-6, also known as BAX-inhibitor 1 (BI-1), is an anti-apoptotic protein that belongs to a putative family of highly conserved and poorly characterized genes. Here we report the function of TMBIM3/GRINA in the control of cell death by endoplasmic reticulum (ER) stress. Tmbim3 mRNA levels are strongly upregulated in cellular and animal models of ER stress, controlled by the PERK signaling branch of the unfolded protein response. TMBIM3/GRINA synergies with TMBIM6/BI-1 in the modulation of ER calcium homeostasis and apoptosis, associated with physical interactions with inositol trisphosphate receptors. Loss-of-function studies in D. melanogaster demonstrated that TMBIM3/GRINA and TMBIM6/BI-1 have synergistic activities against ER stress in vivo. Similarly, manipulation of TMBIM3/GRINA levels in zebrafish embryos revealed an essential role in the control of apoptosis during neuronal development and in experimental models of ER stress. These findings suggest the existence of a conserved group of functionally related cell death regulators across species beyond the BCL-2 family of proteins operating at the ER membrane. Cell Death and Differentiation (2012) 19, 1013-1026 doi:10.1038/cdd.2011; published online 13 January 2012Apoptosis is a conserved cell death mechanism essential for normal development and tissue homeostasis in multicellular organisms. In mammals, the BCL-2 family of proteins is a group of crucial upstream regulators of the caspase cascade, comprising both pro-and anti-apoptotic components. 1Although apoptosis is observed in most multicellular organisms, the BCL-2 family of proteins as a whole is poorly conserved in invertebrates including worms, flies, and other species.1,2 In fact, only two BCL-2 homologues are present in flies with controversial roles in programmed cell death. 3,4 A pioneering screening to identify human genes that prevents BAX toxicity in a yeast assay identified transmembrane BAX inhibitor motif-containing (TMBIM)-6, also known as BAX inhibitor-1 (BI-1), as a new mammalian gene that negatively regulates apoptosis (reviewed in Robinson KS et al. and Reimers K et al. 5,6 ). Further studies demonstrated that TMBIM6/BI-1 is a six transmembrane-spanning protein, located at the endoplasmic reticulum (ER) that has a relevant role in preventing apoptosis. 5 Remarkably, bioinformatic analysis defined a putative family of at least six highly conserved orthologs of TMBIM6/BI-1containing the consensus motif UPF0005 with unknown function, a domain encoding for six to seven transmembrane-spanning regions. 7TMBIM family of proteins includes the founder member TMBIM6/BI-1, TMBIM1/RECS1 (responsive to centrifugal force and shear stress gene 1 protein), TMBIM2/LFG (life guard), TMBIM3/GRINA (glutamate receptor ionotropic NMDA protein 1), TMBIM4/GAAP (Golgi anti-apoptoticassociated protein), and TMBIM5/GHTIM (growth hormoneinducible transmembrane protein). The TMBIM family of proteins is highly conserved in mammals, zebrafish, and flies, with homol...

Deletion of the Human Cytomegalovirus US17 Gene Increases the Ratio of Genomes per Infectious Unit and Alters Regulation of Immune and Endoplasmic Reticulum Stress Response Genes at Early and Late Times after Infection

“…We note that US12 family members share sequence similarity with the transmembrane Bax inhibitor 1 (TMBIM) family of conserved eukaryotic antiapoptotic seven-transmembrane proteins (11). These proteins localize to the membranes of various cellular organelles, where they act as rheostats that modulate apoptotic and ER stress signaling by influencing cellular calcium levels (41)(42)(43)(44)(45). Taken together, it is possible that US17 is a Bax inhibitor 1 ortholog that shapes virion composition by modulating the levels of ER stress response and apoptosis genes involved in regulation of protein folding, trafficking, and cVAC function.…”

The Protein-disulfide Isomerase ERp57 Regulates the Steady-state Levels of the Prion Protein

“…Pharmacological Induction of ER Stress-For induction of ER stress in vitro, the ER stressors tunicamycin, thapsigargin, or brefeldin A were added to the cell culture medium followed by measurement of ER stress markers by Western blot or quantitative real time PCR analysis as we reported previously (56,59). The MTT method was employed to measure cell viability according to the manufacturer's instructions (Promega).…”

Salidroside Protects Against 6-Hydroxydopamine-Induced Cytotoxicity by Attenuating ER Stress

“…ER dysfunction has been implicated in the pathological processes of many diseases [3]. In response to stress signals that disturb ER function and cellular Ca 2? homeostasis, an accumulation of misfolded proteins in the ER triggers an unfolded protein response (UPR) [4]. The UPR initially occurs as a response to the accumulation of unfolded proteins in the ER lumen to restore the protein folding ability of the ER, but a progressive UPR may trigger both protective effects and cell death [5].…”