Human Cytomegalovirus Infection Maintains mTOR Activity and Its Perinuclear Localization during Amino Acid Deprivation
Human Cytomegalovirus Infection Maintains mTOR Activity and Its Perinuclear Localization during Amino Acid Deprivation
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DOI：
10.1128/jvi.05102-11
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发表时间：
2011-09-01
影响因子：
5.4
通讯作者：
Alwine, James C.
中科院分区：
文献类型：
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作者：
Clippinger, Amy J.;Maguire, Tobi G.;Alwine, James C.
哺乳动物雷帕霉素靶蛋白（mTOR）激酶存在于2种功能不同的复合物中，mTOR复合物1（mTORC 1）和复合物2（mTORC 2）。活性mTORC 1介导eIF 4 E结合蛋白（4 E-BP）和p70 S6激酶（S6 K）的磷酸化，这对维持翻译很重要。在人巨细胞病毒（HCMV）感染期间，细胞应激反应被激活，通常抑制mTOR 1;然而，以前的数据表明，HCMV感染规避应激反应，并保持mTOR激酶活性。氨基酸剥夺是一种应激反应，通常会抑制mTORC 1活性。氨基酸可以通过Rag蛋白向mTORC 1发出信号，Rag蛋白促进mTORC 1与其激活剂Rheb-GTP在核周区域的共定位，从而诱导4 E-BP和S6 K磷酸化。正如预期的那样，我们的研究结果表明，在模拟感染的细胞中的氨基酸消耗导致mTORC 1活性的丧失和核周定位的丧失;然而，在HCMV感染的细胞中没有活性或核周定位的丧失，其中Rheb-GTP和mTOR的核周定位与核周组装室（AC）相一致。这表明HCMV感染绕过了正常的Rag依赖性氨基酸信号传导。这通过Rag蛋白的短发夹RNA（shRNA）耗尽来证明，其对感染细胞中的mTORC 1活性几乎没有影响，但抑制模拟感染细胞中的活性。我们的数据表明，HCMV通过与AC形成相关的mTOR和Rheb-GTP的共定位以氨基酸和Rag非依赖性方式维持mTORC 1活性，从而绕过可能由氨基酸水平降低引起的抑制。
The mammalian target of rapamycin (mTOR) kinase is present in 2 functionally distinct complexes, mTOR complex 1 (mTORC1) and complex 2 (mTORC2). Active mTORC1 mediates phosphorylation of eIF4E-binding protein (4E-BP) and p70 S6 kinase (S6K), which is important for maintaining translation. During human cytomegalovirus (HCMV) infection, cellular stress responses are activated that normally inhibit mTORC1; however, previous data show that HCMV infection circumvents stress responses and maintains mTOR kinase activity. Amino acid deprivation is a stress response that normally inhibits mTORC1 activity. Amino acids can signal to mTORC1 through the Rag proteins, which promote the colocalization of mTORC1 with its activator Rheb-GTP in a perinuclear region, thereby inducing 4E-BP and S6K phosphorylation. As expected, our results show that amino acid depletion in mock-infected cells caused loss of mTORC1 activity and loss of the perinuclear localization; however, there was no loss of activity or perinuclear localization in HCMV-infected cells where the perinuclear localization of Rheb-GTP and mTOR coincided with the perinuclear assembly compartment (AC). This suggested that HCMV infection bypasses normal Rag-dependent amino acid signaling. This was demonstrated by short hairpin RNA (shRNA) depletion of Rag proteins, which had little effect on mTORC1 activity in infected cells but inhibited activity in mock-infected cells. Our data show that HCMV maintains mTORC1 activity in an amino acid-and Rag-independent manner through the colocalization of mTOR and Rheb-GTP, which occurs in association with the formation of the AC, thus bypassing inhibition that may result from lowered amino acid levels.