ABSTRACT

We recently identified FAM134B2, which is an N-terminal truncated reticulophagy receptor highly induced by starvation such as fasting of mice and treatment of mammalian cells with a starvation medium that does not contain amino acids, glucose and growth factors. However, which starvation signal mediates the induction of FAM134B2 is still obscure. In this study, we found that amino acid deficiency (AAD) could mimic the starvation condition to induce FAM134B2 expression. Unexpectedly, EIF2AK4/GCN2-mediated integrated signal response (ISR) and MTOR (mechanistic target of rapamycin kinase) signals, which constitute two major signaling pathways that respond to AAD, did not contribute to AAD-induced FAM134B2 induction. mRNA-seq and siRNA screenings identified two ISR-independent transcription factors, MEF2D (myocyte enhancer factor 2D) and NR4A1 (nuclear receptor subfamily 4 group A member 1), involved in AAD-induced FAM134B2 expression. AAD induces MEF2D, resulting in the induction of NR4A1, which in turn induces FAM134B2-mediated reticulophagy to maintain intracellular amino acid levels. In conclusion, the MEF2D-NR4A1-FAM134B2 cascade is a critical signal in amino acid homeostasis.

Abbreviations

AAD: amino acid deficiency; APOC3: apolipoprotein C3; BACH1: BTB domain and CNC homolog 1; CEBP: CCAAT enhancer binding protein; DDIT3/CHOP: DNA damage inducible transcript 3; EBSS: Earle’s Balanced Salt Solution; EIF2AK4/GCN2: eukaryotic translation initiation factor 2 alpha kinase 4; ER: endoplasmic reticulum; HisOH: histidinol; ISR: integrated stress response; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MEF2D: myocyte enhancer factor 2D; MTOR: mechanistic target of rapamycin kinase; NR4A1: nuclear receptor subfamily 4 group A member 1; RETREG1/FAM134B: reticulophagy regulator 1; RTN2: reticulon 2, TF: transcription factor; TFEB: transcription factor EB; ZBTB10: zinc finger and BTB domain containing 10

中文翻译：

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MEF2D-NR4A1-FAM134B2 介导的网状吞噬有助于氨基酸稳态

摘要

我们最近发现了 FAM134B2，它是一种 N 端截短的网状吞噬受体，由饥饿高度诱导，例如小鼠禁食和用不含氨基酸、葡萄糖和生长因子的饥饿培养基处理哺乳动物细胞。然而，哪种饥饿信号介导 FAM134B2 的诱导仍不清楚。在这项研究中，我们发现氨基酸缺乏 (AAD) 可以模拟饥饿条件来诱导 FAM134B2 表达。出乎意料的是，构成响应 AAD 的两个主要信号通路的 EIF2AK4/GCN2 介导的综合信号反应 (ISR) 和 MTOR（雷帕霉素激酶的机械靶标）信号对 AAD 诱导的 FAM134B2 诱导没有贡献。mRNA-seq 和 siRNA 筛选确定了两个独立于 ISR 的转录因子，MEF2D（肌细胞增强因子 2D）和 NR4A1（核受体亚家族 4 A 组成员 1），参与 AAD 诱导的 FAM134B2 表达。AAD 诱导 MEF2D，导致 NR4A1 的诱导，进而诱导 FAM134B2 介导的网状吞噬以维持细胞内氨基酸水平。总之，MEF2D-NR4A1-FAM134B2 级联是氨基酸稳态的关键信号。

缩写

AAD：氨基酸缺乏；APOC3：载脂蛋白 C3；BACH1：BTB 域和 CNC 同源 1；CEBP：CCAAT增强子结合蛋白；DDIT3/CHOP：DNA 损伤诱导转录本 3；EBSS：厄尔平衡盐溶液；EIF2AK4/GCN2：真核翻译起始因子 2 α 激酶 4；ER：内质网；HisOH：组氨醇；ISR：综合压力反应；MAP1LC3/LC3：微管相关蛋白1轻链3；MEF2D：肌细胞增强因子 2D；MTOR：雷帕霉素激酶的机制靶点；NR4A1：核受体亚家族 4 A 组成员 1；RETREG1/FAM134B：网状吞噬调节剂 1；RTN2：reticulon 2，TF：转录因子；TFEB：转录因子EB；ZBTB10：锌指和 BTB 结构域包含 10