Kudchodkar Sagar B, Yu Yongjun, Maguire Tobi G, Alwine James C
Department of Cancer Biology, Abramson Family Cancer Research Institute, 421 Curie Blvd., University of Pennsylvania, Philadelphia, PA 19104-6142, USA.
J Virol. 2004 Oct;78(20):11030-9. doi: 10.1128/JVI.78.20.11030-11039.2004.
Signaling mediated by the cellular kinase mammalian target of rapamycin (mTOR) activates cap-dependent translation under normal (nonstressed) conditions. However, translation is inhibited by cellular stress responses or rapamycin treatment, which inhibit mTOR kinase activity. We show that during human cytomegalovirus (HCMV) infection, viral protein synthesis and virus production proceed relatively normally when mTOR kinase activity is inhibited due to hypoxic stress or rapamycin treatment. Using rapamycin inhibition of mTOR, we show that HCMV infection induces phosphorylation of two mTOR effectors, eucaryotic initiation factor 4E (eIF4E) binding protein (4E-BP) and eIF4G. The virally induced phosphorylation of eIF4G is both mTOR and phosphatidylinositol 3-kinase (PI3K) independent, whereas the phosphorylation of 4E-BP is mTOR independent, but PI3K dependent. HCMV infection does not induce mTOR-independent phosphorylation of a third mTOR effector, p70S6 kinase (p70S6K). We show that the HCMV-induced phosphorylation of eIF4G and 4E-BP correlates with the association of eIF4E, the cap binding protein, with eIF4G in the eIF4F translation initiation complex. Thus, HCMV induces mechanisms to maintain the integrity of the eIF4F complex even when mTOR signaling is inhibited.
在正常(无应激)条件下,由细胞激酶雷帕霉素哺乳动物靶标(mTOR)介导的信号传导可激活帽依赖性翻译。然而,细胞应激反应或雷帕霉素处理会抑制翻译,因为它们会抑制mTOR激酶活性。我们发现,在人巨细胞病毒(HCMV)感染期间,当由于缺氧应激或雷帕霉素处理导致mTOR激酶活性受到抑制时,病毒蛋白合成和病毒产生仍相对正常地进行。利用雷帕霉素对mTOR的抑制作用,我们发现HCMV感染会诱导两种mTOR效应器即真核起始因子4E(eIF4E)结合蛋白(4E-BP)和eIF4G发生磷酸化。病毒诱导的eIF4G磷酸化既不依赖于mTOR也不依赖于磷脂酰肌醇3激酶(PI3K),而4E-BP的磷酸化不依赖于mTOR,但依赖于PI3K。HCMV感染不会诱导第三种mTOR效应器p70核糖体蛋白S6激酶(p70S6K)发生不依赖于mTOR的磷酸化。我们发现,HCMV诱导的eIF4G和4E-BP磷酸化与帽结合蛋白eIF4E在eIF4F翻译起始复合物中与eIF4G的结合相关。因此,即使mTOR信号传导受到抑制,HCMV也会诱导维持eIF4F复合物完整性的机制。