Spruill Laura S, McDermott Paul J
Department of Medicine, The Gazes Cardiac Research Institute, Medical University of South Carolina, Charleston, South Carolina 29403, USA.
FASEB J. 2006 Oct;20(12):2133-5. doi: 10.1096/fj.06-6245fje. Epub 2006 Aug 29.
Hypertrophic growth of adult myocardium is associated with increased expression of the early response gene c-jun. The purpose of this study was to determine whether eukaryotic initiation factor (elF) 4E (eIF4E) regulates translational efficiency of c-jun mRNA as measured by flux into polysomes. Adult feline cardiomyocytes in primary culture were treated with 0.2 microM 12-O-tetradecanoylphorbol 13-acetate (TPA), and c-jun mRNA was quantified in total, monosome, and polysome fractions by real-time polymerase chain reaction. After 1 h, TPA increased total c-jun mRNA by 10.5-fold. The corresponding flux into polysomes was significantly lower (5-fold). Adenoviral-mediated overexpression of either eIF4E or a nonphosphorylatable mutant (S209/A) did not affect total c-jun mRNA or its flux between monosomes and polysomes. Similar results were obtained following overexpression of the eIF4E kinase Mnk1. Thus, translational efficiency of c-jun mRNA was not affected by changes in activity or amount of eIF4E. In contrast, a kinase-deficient Mnk1 mutant significantly reduced total c-jun mRNA from 9.8-fold to 6.0-fold while flux between monosomes and polysomes remained constant. The decrease in total c-jun mRNA resulted from increased decay of c-jun mRNA incorporated into the polysomes. We conclude that Mnk1 activity stabilizes c-jun mRNA in polysomes independent of eIF4E phosphorylation.
成年心肌肥厚性生长与早期反应基因c-jun表达增加有关。本研究的目的是确定真核起始因子（eIF）4E（eIF4E）是否通过多核糖体通量来调节c-jun mRNA的翻译效率。对原代培养的成年猫心肌细胞用0.2 microM 12-O-十四酰佛波醇13-乙酸酯（TPA）处理，通过实时聚合酶链反应对总RNA、单核糖体和多核糖体组分中的c-jun mRNA进行定量。1小时后，TPA使总c-jun mRNA增加了10.5倍。相应的进入多核糖体的通量显著更低（5倍）。腺病毒介导的eIF4E或不可磷酸化突变体（S209/A）的过表达不影响总c-jun mRNA或其在单核糖体和多核糖体之间的通量。eIF4E激酶Mnk1过表达后也得到了类似结果。因此，c-jun mRNA的翻译效率不受eIF4E活性或量变化的影响。相反，激酶缺陷型Mnk1突变体使总c-jun mRNA从9.8倍显著降低至6.0倍，而单核糖体和多核糖体之间的通量保持恒定。总c-jun mRNA的减少是由于多核糖体中掺入的c-jun mRNA降解增加所致。我们得出结论，Mnk1活性独立于eIF4E磷酸化使多核糖体中的c-jun mRNA稳定。
