Faculty of Medicine at Ribeirão Preto, Department of Biochemistry and Immunology, University of São Paulo, Ribeirão Preto, SP, Brazil.
J Cell Physiol. 2010 Nov;225(2):500-5. doi: 10.1002/jcp.22229.
Eukaryotic translation initiation factor 5A (eIF5A) has a unique character: the presence of an unusual amino acid, hypusine, which is formed by post-translational modifications. Even before the identification of hypusination in eIF5A, the correlation between hypusine formation and protein synthesis, shifting cell proliferation rates, had already been observed. Embryogenesis is a complex process in which cellular proliferation and differentiation are intense. In spite of the fact that many studies have described possible functions for eIF5A, its precise role is under investigation, and to date nothing has been reported about its participation in embryonic development. In this study we show that eIF5A is expressed at all mouse embryonic post-implantation stages with increase in eIF5A mRNA and protein expression levels between embryonic days E10.5 and E13.5. Immunohistochemistry revealed the ubiquitous presence of eIF5A in embryonic tissues and organs at E13.5 day. Interestingly, stronger immunoreactivity to eIF5A was observed in the stomodeum, liver, ectoderm, heart, and eye, and the central nervous system; regions which are known to undergo active differentiation at this stage, suggesting a role of eIF5A in differentiation events. Expression analyses of MyoD, a myogenic transcription factor, revealed a significantly higher expression from day E12.5 on, both at the mRNA and the protein levels suggesting a possible correlation to eIF5A. Accordingly, we next evidenced that inhibiting eIF5A hypusination in mouse myoblast C2C12 cells impairs their differentiation into myotubes and decreases MyoD transcript levels. Those results point to a new functional role for eIF5A, relating it to embryogenesis, development, and cell differentiation.
真核翻译起始因子 5A（eIF5A）具有独特的特征：存在一种不寻常的氨基酸，即hypusine，它是通过翻译后修饰形成的。甚至在 eIF5A 中鉴定出 hypusination 之前，就已经观察到 hypusine 形成与蛋白质合成、细胞增殖率变化之间的相关性。胚胎发生是一个复杂的过程，其中细胞增殖和分化非常强烈。尽管许多研究已经描述了 eIF5A 的可能功能，但它的确切作用仍在研究中，迄今为止，尚未有报道称其参与胚胎发育。在这项研究中，我们表明 eIF5A 在所有小鼠胚胎植入后阶段都有表达，并且在胚胎第 10.5 天至 13.5 天之间，eIF5A mRNA 和蛋白表达水平增加。免疫组织化学显示，在第 13.5 天的胚胎组织和器官中，eIF5A 普遍存在。有趣的是，在口裂、肝脏、外胚层、心脏和眼睛以及中枢神经系统中观察到更强的 eIF5A 免疫反应性；这些区域在这个阶段已知经历活跃的分化，表明 eIF5A 在分化事件中起作用。肌源性转录因子 MyoD 的表达分析显示，从第 12.5 天开始，无论是在 mRNA 还是蛋白水平上，MyoD 的表达都显著增加，这表明可能与 eIF5A 相关。因此，我们接下来的证据表明，在小鼠成肌细胞 C2C12 细胞中抑制 eIF5A hypusination 会损害它们分化为肌管并降低 MyoD 转录本水平。这些结果表明 eIF5A 具有新的功能作用，与胚胎发生、发育和细胞分化有关。
