Pereira Cátia M, Sattlegger Evelyn, Jiang Hao-Yuan, Longo Beatriz M, Jaqueta Carolina B, Hinnebusch Alan G, Wek Ronald C, Mello Luiz E A M, Castilho Beatriz A
Departamentos de Microbiologia, Imunologia, e Parasitologia and Fisiologia, Universidade Federal de São Paulo, São Paulo SP 04023-062, Brazil.
J Biol Chem. 2005 Aug 5;280(31):28316-23. doi: 10.1074/jbc.M408571200. Epub 2005 Jun 2.
Translational control directed by the eukaryotic translation initiation factor 2 alpha-subunit (eIF2alpha) kinase GCN2 is important for coordinating gene expression programs in response to nutritional deprivation. The GCN2 stress response, conserved from yeast to mammals, is critical for resistance to nutritional deficiencies and for the control of feeding behaviors in rodents. The mouse protein IMPACT has sequence similarities to the yeast YIH1 protein, an inhibitor of GCN2. YIH1 competes with GCN2 for binding to a positive regulator, GCN1. Here, we present evidence that IMPACT is the functional counterpart of YIH1. Overexpression of IMPACT in yeast lowered both basal and amino acid starvation-induced levels of phosphorylated eIF2alpha, as described for YIH1 (31). Overexpression of IMPACT in mouse embryonic fibroblasts inhibited phosphorylation of eIF2alpha by GCN2 under leucine starvation conditions, abolishing expression of its downstream target genes, ATF4 (CREB-2) and CHOP (GADD153). IMPACT bound to the minimal yeast GCN1 segment required for interaction with yeast GCN2 and YIH1 and to native mouse GCN1. At the protein level, IMPACT was detected mainly in the brain. IMPACT was found to be abundant in the majority of hypothalamic neurons. Scattered neurons expressing this protein at higher levels were detected in other regions such as the hippocampus and piriform cortex. The abundance of IMPACT correlated inversely with phosphorylated eIF2alpha levels in different brain areas. These results suggest that IMPACT ensures constant high levels of translation and low levels of ATF4 and CHOP in specific neuronal cells under amino acid starvation conditions.
由真核生物翻译起始因子2α亚基（eIF2α）激酶GCN2介导的翻译控制，对于协调基因表达程序以应对营养剥夺至关重要。从酵母到哺乳动物保守的GCN2应激反应，对于抵抗营养缺乏和控制啮齿动物的进食行为至关重要。小鼠蛋白IMPACT与酵母YIH1蛋白具有序列相似性，YIH1是GCN2的一种抑制剂。YIH1与GCN2竞争结合一种正向调节因子GCN1。在此，我们提供证据表明IMPACT是YIH1的功能对应物。正如YIH1的情况一样，IMPACT在酵母中的过表达降低了基础水平以及氨基酸饥饿诱导的磷酸化eIF2α水平。在小鼠胚胎成纤维细胞中IMPACT的过表达在亮氨酸饥饿条件下抑制了GCN2介导的eIF2α磷酸化，消除了其下游靶基因ATF4（CREB - 2）和CHOP（GADD153）的表达。IMPACT与酵母GCN1与酵母GCN2和YIH1相互作用所需的最小片段结合，也与天然小鼠GCN1结合。在蛋白质水平上，IMPACT主要在大脑中被检测到。发现IMPACT在大多数下丘脑神经元中丰富。在海马体和梨状皮质等其他区域检测到少量表达该蛋白水平较高的神经元。IMPACT的丰度与不同脑区中磷酸化eIF2α水平呈负相关。这些结果表明，在氨基酸饥饿条件下，IMPACT确保特定神经元细胞中翻译水平持续高水平，而ATF4和CHOP水平低。
