Human cytomegalovirus infection alters the substrate specificities and rapamycin sensitivities of raptor- and rictor-containing complexes.
Signaling mediated by the mammalian target of rapamycin kinase (mTOR) is activated during human cytomegalovirus (HCMV) infection. mTOR is found in two complexes differing by the binding partner, rictor or raptor. Activated mTOR-raptor promotes cap-dependent translation through the hyperphosphorylation of the eIF4E-binding protein (4E-BP). This activity of the raptor complex is normally inhibited by cell stress responses or the drug rapamycin. However, we previously showed that this inhibition of mTOR signaling can be circumvented during HCMV infection such that hyperphosphorylation of 4E-BP is maintained. Here we show that HCMV infection also activates the rictor complex, as indicated by increased phosphorylation of Akt S473; this phosphorylation is insensitive to rapamycin but sensitive to caffeine in both uninfected and infected cells. By using short-hairpin RNAs to deplete rictor and raptor, we find that rictor is more significant than raptor for the viral infection. Surprisingly, the inhibitory effects of rapamycin on viral growth are primarily due to the presence of rictor, not raptor. Raptor and rictor depletion experiments show that in HCMV-infected cells, both raptor- and rictor-containing complexes can mediate the hyperphosphorylation of 4E-BP and the phosphorylation of p70S6 kinase. Under these conditions, the rictor complex is rapamycin-sensitive for the hyperphosphorylation of 4E-BP, but the raptor complex is not. These data suggest that, during HCMV infection, the rictor- and raptor-containing complexes are modified such that their substrate specificities and rapamycin sensitivities are altered. Our data also suggest that the present understanding of rapamycin's inhibitory effects is incomplete.
Kudchodkar
Sagar B
SB
Department of Cancer Biology, Abramson Family Cancer Research Institute, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6142, USA.
Yu
Yongjun
Y
Maguire
Tobi G
TG
Alwine
James C
JC
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000903:Antibiotics, Antineoplastic / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D003587:Cytomegalovirus / Q000502:physiology*; D003586:Cytomegalovirus Infections / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D016086:Lentivirus / Q000235:genetics / Q000378:metabolism; D046912:Multiprotein Complexes; D009690:Nucleic Acid Conformation; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D012313:RNA / Q000737:chemistry / Q000378:metabolism; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D000076223:Regulatory-Associated Protein of mTOR; D015398:Signal Transduction / Q000502:physiology; D020123:Sirolimus / Q000378:metabolism*; D013379:Substrate Specificity; D058570:TOR Serine-Threonine Kinases
D048868:Adaptor Proteins, Signal Transducing; D000903:Antibiotics, Antineoplastic; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D011506:Proteins; C492571:RICTOR protein, human; C463659:RPTOR protein, human; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D000076223:Regulatory-Associated Protein of mTOR; D012313:RNA; D011494:Protein Kinases; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus