TOR, the """"""""target of rapamycin"""""""" is a giant protein kinase that is critical to the regulation of cell growth in response to nutrient and energy sufficiency, to growth factors (such as insulin and IGF-1) and to other developmental signals. Rapamycin inhibits a subset of TOR's actions that underlie cell growth, and in some cell backgrounds, inhibits proliferation. Rapamycin is in clinical use because of its immunosuppressant action and antiproliferative effects on vascular smooth muscle cells;it is also under evaluation as an anti-cancer agent. Two sets of recent discoveries have provided important insight into TOR function and regulation, and work supported by this award has contributed to both areas. Biochemical methods established that TOR functions in two physically independent multiprotein complexes, only one of which (called TOR complex 1;TORC1) is inhibitable by Rapamycin. The interaction of TORC1 with its known substrates through raptor has been elucidated. TOR complex 2 is resistant to rapamycin, and appears to regulate the actin cytoskeleton through unknown effectors. TORC2 also serves as a necessary activating kinase (so called PDK2) for Akt, whereas TORC1 acts as a feedback inhibitor of Akt. Independently, the molecular connection between the insulin/IGF-1 receptors/Type 1 PI-3Kinase/Akt and TORC1 was shown to be the Tuberous Sclerosis heterodimer complex (TSC1/2) and Rheb, a Ras-like GTPase, Rheb is a positive regulator of mTOR signaling to TOR complex 1, that acts in part directly on TORC1. TSC1/2 is an activator of Rheb GTPase, thereby inhibiting Rheb;insulin/IGF-1, through Akt,and other inputs through the MAPK pathway suppress TSC GAP function, thereby promoting TORC1 signaling. Depletion of amino acids, especially leucine, inhibits TORC1 signaling, mostly independent of TSC1/2, but in a manner that is rescued by overexpressed Rheb. We find that leucine withdrawal disrupts'the interaction between Rheb and TOR. We propose to carry out a structure-function analysis of Rheb so as to understand how its interactions within TOR1 control TORC1 signaling, and define the biochemical mechanism by which leucine sufficiency controls the Rheb- mTOR interaction in vivo. We will characterize the transcriptional responses to Rheb-GTP, TORC1 and TORC2 and identify and characterize additional candidate Rheb effectors. In addition, we will elucidate the operation of TORC2, by defining the physical and functional interactions among the components unique to TORC2, the regulatory inputs that control TORC2 signaling in vivo, and the identity of additional TORC2 targets/substrates. The results of these studies will provide basis for therapeutic interventions in this pathway, which is crucial to both human cancers and to diseases like Type 2 diabetes

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA073818-13
Application #
7540985
Study Section
Molecular and Cellular Endocrinology Study Section (MCE)
Program Officer
Spalholz, Barbara A
Project Start
1997-04-01
Project End
2011-11-30
Budget Start
2008-12-01
Budget End
2009-11-30
Support Year
13
Fiscal Year
2009
Total Cost
$437,500
Indirect Cost
Name
Massachusetts General Hospital
Department
Type
DUNS #
073130411
City
Boston
State
MA
Country
United States
Zip Code
02199
Papageorgiou, Angela; Rapley, Joseph; Mesirov, Jill P et al. (2015) A genome-wide siRNA screen in mammalian cells for regulators of S6 phosphorylation. PLoS One 10:e0116096
Oshiro, Noriko; Rapley, Joseph; Avruch, Joseph (2014) Amino acids activate mammalian target of rapamycin (mTOR) complex 1 without changing Rag GTPase guanyl nucleotide charging. J Biol Chem 289:2658-74
Dai, Ning; Christiansen, Jan; Nielsen, Finn C et al. (2013) mTOR complex 2 phosphorylates IMP1 cotranslationally to promote IGF2 production and the proliferation of mouse embryonic fibroblasts. Genes Dev 27:301-12
Papageorgiou, Angela; Avruch, Joseph (2012) A genome-wide RNAi screen for polypeptides that alter rpS6 phosphorylation. Methods Mol Biol 821:187-214
Rapley, Joseph; Oshiro, Noriko; Ortiz-Vega, Sara et al. (2011) The mechanism of insulin-stimulated 4E-BP protein binding to mammalian target of rapamycin (mTOR) complex 1 and its contribution to mTOR complex 1 signaling. J Biol Chem 286:38043-53
Dai, Ning; Rapley, Joseph; Angel, Matthew et al. (2011) mTOR phosphorylates IMP2 to promote IGF2 mRNA translation by internal ribosomal entry. Genes Dev 25:1159-72
Wexler, Tamara L; Durst, Ronen; McCarty, David et al. (2010) Growth hormone status predicts left ventricular mass in patients after cure of acromegaly. Growth Horm IGF Res 20:333-7
Avruch, Joseph; Long, Xiaomeng; Lin, Yenshou et al. (2009) Activation of mTORC1 in two steps: Rheb-GTP activation of catalytic function and increased binding of substrates to raptor. Biochem Soc Trans 37:223-6
Avruch, Joseph; Long, Xiaomeng; Ortiz-Vega, Sara et al. (2009) Amino acid regulation of TOR complex 1. Am J Physiol Endocrinol Metab 296:E592-602
Oshiro, Noriko; Takahashi, Rinako; Yoshino, Ken-ichi et al. (2007) The proline-rich Akt substrate of 40 kDa (PRAS40) is a physiological substrate of mammalian target of rapamycin complex 1. J Biol Chem 282:20329-39

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