Kim Steven K, Srivastava Meera
Department of Anatomy, Physiology and Genetics, and Institute for Molecular Medicine, Uniformed Services University School of Medicine (USUHS), Bethesda, Maryland 20814, USA.
DNA Cell Biol. 2003 Mar;22(3):171-8. doi: 10.1089/104454903321655792.
Nucleolin is a nucleolar phosphoprotein that plays a direct role in ribosome biogenesis. Our aim was to determine how its activity as a growth-promoting factor is coordinated with, if not regulated by, the cell cycle machinery. In serum starting and then rescuing these cells with serum, we found that the protein level did not drop in the same way that the mRNA level did. In addition, although the mRNA level rises during the immediate period during serum rescue, the protein level remained the same. We found that the protein level was maintained after serum starvation as a result of high stability. There was no selective enhanced translation of the remaining amount of Nucleolin mRNA. With regard to the constancy in protein level despite the rise in mRNA level during serum rescue, there is no concomitant degradation of newly synthesized or old protein and synthesis of new protein. Because Nucleolin has been documented to bind mRNA, APP mRNA being one among them, we propose a autoregulatory model in which Nucleolin regulates the translation of Nucleolin mRNA, such that during a period of excess protein, translation is inhibited through direct binding of Nucleolin protein to its mRNA.
核仁素是一种核仁磷蛋白，在核糖体生物合成中起直接作用。我们的目的是确定其作为生长促进因子的活性如何与细胞周期机制协调（即便不受其调控）。在血清起始培养然后用血清挽救这些细胞的过程中，我们发现蛋白质水平下降的方式与mRNA水平不同。此外，虽然在血清挽救的即刻期间mRNA水平升高，但蛋白质水平保持不变。我们发现血清饥饿后由于高稳定性蛋白质水平得以维持。剩余的核仁素mRNA没有选择性增强翻译。关于血清挽救期间mRNA水平升高但蛋白质水平恒定的情况，新合成或旧蛋白质没有伴随降解，也没有新蛋白质合成。由于已证明核仁素可结合mRNA，APP mRNA就是其中之一，我们提出一种自调节模型，其中核仁素调节核仁素mRNA的翻译，使得在蛋白质过量的时期，通过核仁素蛋白直接结合其mRNA来抑制翻译。
