Research
| Title： | Deficiency in the membrane protein Tmbim3a/Grinaa initiates cold-induced ER stress and cell death by activating an intrinsic apoptotic pathway in zebrafish |
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| First author： | Chen, Kai; Li, Xixi; Song, Guili; Zhou, Tong; Long, Yong; Li, Qing; Zhong, Shan; Cui, Zongbin |
| Journal： | JOURNAL OF BIOLOGICAL CHEMISTRY |
| Years： | 2019 |
| DOI： | 10.1074/jbc.RA119.007813 |
| Abstract： | Most members of the family of proteins containing a transmembrane BAX inhibitor motif (TMBIM) have anti-apoptotic activity, but their in vivo functions and intracellular mechanisms remain obscure. Here, we report that zebrafish Tmbim3a/Grinaa functions in the prevention of cold-induced endoplasmic reticulum (ER) stress and apoptosis. Using a gene-trapping approach, we obtained a mutant zebrafish line in which the expression of the tmbim3a/grinaa gene is disrupted by a Tol2 transposon insertion. Homozygous tmbim3a/grinaa mutant larvae exhibited time-dependently increased mortality and apoptosis under cold exposure (at 16 degrees C). Mechanistically, using immunofluorescence, fluorescence-based assessments of intracellular/mitochondrial Ca2+ levels, mitochondrial membrane potential measurements, and Ca2+-ATPase assays, we found that cold exposure suppresses sarcoplasmic/ER Ca2+-ATPase (SERCA) activity and induces the unfolded protein response (UPR) and ER stress. We also found that the cold-induced ER stress is increased in homozygous tmbim3a/grinaa mutant embryos. The cold-stress hypersensitivity of the tmbim3a/grinaa mutants was tightly associated with disrupted intracellular Ca2+ homeostasis, followed by mitochondrial Ca2+ overload and cytochrome c release, leading to the activation of caspase 9- and caspase-3-mediated intrinsic apoptotic pathways. Treatment of zebrafish larvae with the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N ',N '-tetraacetate-acetoxymethyl ester (BAPTA-AM) or with 2-aminoethoxydiphenyl borate (2-APB), an inhibitor of the calcium-releasing protein inositol 1,4,5-trisphosphate receptor (IP3R), alleviated cold-induced cell death. Together, these findings unveil a key role of Tmbim3a/Grinaa in relieving cold-induced ER stress and in protecting cells against caspase 9- and caspase 3-mediated apoptosis during zebrafish development. |
