Department of Research, Hospital Universitario Ramón y Cajal, IRYCIS, Ctra. Colmenar km 9.1, 28034 Madrid, Spain.
Department of Genetics, Physiology and Microbiology, Faculty of Biological Sciences, Universidad Complutense de Madrid, Av. Complutense, 28040 Madrid, Spain.
Int J Mol Sci. 2022 Feb 6;23(3):1830. doi: 10.3390/ijms23031830.
Ischemic strokes are caused by a reduction in cerebral blood flow and both the ischemic period and subsequent reperfusion induce brain injury, with different tissue damage depending on the severity of the ischemic insult, its duration, and the particular areas of the brain affected. In those areas vulnerable to cerebral ischemia, the inhibition of protein translation is an essential process of the cellular response leading to delayed neuronal death. In particular, translation initiation is rate-limiting for protein synthesis and the eukaryotic initiation factor (eIF) 4F complex is indispensable for cap-dependent protein translation. In the eIF4F complex, eIF4G is a scaffolding protein that provides docking sites for the assembly of eIF4A and eIF4E, binding to the cap structure of the mRNA and stabilizing all proteins of the complex. The eIF4F complex constituents, eIF4A, eIF4E, and eIF4G, participate in translation regulation by their phosphorylation at specific sites under cellular stress conditions, modulating the activity of the cap-binding complex and protein translation. This work investigates the phosphorylation of eIF4G1 involved in the eIF4E/eIF4G1 association complex, and their regulation in ischemia-reperfusion (IR) as a stress-inducing condition. IR was induced in an animal model of transient cerebral ischemia and the results were studied in the resistant cortical region and in the vulnerable hippocampal CA1 region. The presented data demonstrate the phosphorylation of eIF4G1 at Ser, Ser, and Ser in both brain regions and in control and ischemic conditions, being the phosphorylation of eIF4G1 at Ser the only one found in the eIF4E/eIF4G association complex from the cap-containing matrix (mGTP-Sepharose). In addition, our work reveals the specific modulation of the phosphorylation of eIF4G1 at Ser in the vulnerable region, with increased levels and colocalization with eIF4E in response to IR. These findings contribute to elucidate the molecular mechanism of protein translation regulation that underlies in the balance of cell survival/death during pathophysiological stress, such as cerebral ischemia.
缺血性中风是由脑血流减少引起的，缺血期和随后的再灌注都会导致脑损伤，不同的组织损伤取决于缺血损伤的严重程度、持续时间和受影响的大脑特定区域。在那些易受脑缺血影响的区域，抑制蛋白质翻译是导致迟发性神经元死亡的细胞反应的一个重要过程。特别是，翻译起始是蛋白质合成的限速步骤，真核起始因子 (eIF) 4F 复合物是帽依赖蛋白翻译所必需的。在 eIF4F 复合物中，eIF4G 是一种支架蛋白，为 eIF4A 和 eIF4E 的组装提供停靠位点，与 mRNA 的帽结构结合，并稳定复合物的所有蛋白质。eIF4F 复合物成分 eIF4A、eIF4E 和 eIF4G，通过在细胞应激条件下在特定位点磷酸化参与翻译调节，调节帽结合复合物和蛋白质翻译的活性。这项工作研究了 eIF4G1 的磷酸化，该磷酸化参与了 eIF4E/eIF4G1 结合复合物，并在缺血再灌注 (IR) 作为应激诱导条件下对其进行了调节。在短暂性脑缺血的动物模型中诱导了 IR，并在抵抗性皮质区和易损性海马 CA1 区研究了结果。所呈现的数据表明，在这两个脑区以及在对照和缺血条件下，eIF4G1 的丝氨酸、丝氨酸和丝氨酸磷酸化，而 eIF4G1 的丝氨酸磷酸化是在含有帽的基质 (mGTP-Sepharose) 中的 eIF4E/eIF4G 结合复合物中发现的唯一一种磷酸化。此外，我们的工作揭示了易损区中 eIF4G1 丝氨酸磷酸化的特定调节，IR 导致其水平增加并与 eIF4E 共定位。这些发现有助于阐明蛋白质翻译调节的分子机制，该机制是在生理病理应激（如脑缺血）下细胞存活/死亡平衡的基础。
