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1.  The mTORC1 pathway stimulates glutamine metabolism and cell proliferation by repressing SIRT4 
Cell  2013;153(4):840-854.
Summary
Proliferating mammalian cells use glutamine as a source of nitrogen and as a key anaplerotic source to provide metabolites to the tricarboxylic acid cycle (TCA) for biosynthesis. Recently, mTORC1 activation has been correlated with increased nutrient uptake and metabolism, but no molecular connection to glutaminolysis has been reported. Here, we show that mTORC1 promotes glutamine anaplerosis by activating glutamate dehydrogenase (GDH). This regulation requires transcriptional repression of SIRT4, the mitochondrial-localized sirtuin that inhibits GDH. Mechanistically, mTORC1 represses SIRT4 by promoting the proteasome-mediated destabilization of cAMP response element binding-2 (CREB2). Thus, a relationship between mTORC1, SIRT4 and cancer is suggested by our findings. Indeed, SIRT4 expression is reduced in human cancer, and its overexpression reduces cell proliferation, transformation and tumor development. Finally, our data indicate that targeting nutrient metabolism in energy-addicted cancers with high mTORC1 signaling may be an effective therapeutic approach.
doi:10.1016/j.cell.2013.04.023
PMCID: PMC3684628  PMID: 23663782
2.  Autophagy 
Autophagy  2011;7(11):1400-1401.
Mammalian target of rapamycin (mTOR) complex 1 (mTORC1), which is activated in tuberous sclerosis complex (TSC) and lymphangioleiomyomatosis (LAM), is a master regulator of cell growth, cellular metabolism and autophagy. Treatment of TSC and LAM patients with mTORC1 inhibitors partially decreases the size of brain and kidney tumors, and stabilizes pulmonary function. However, the tumors regrow and lung function continues to decline when treatment is discontinued. We hypothesized that dysregulation of autophagy plays a critical role in the pathogenesis of tumors with mTORC1 hyperactivation and in their response to mTORC1-targeted therapy. We found that cells lacking TSC2 have low levels of autophagy under basal and cellular stress conditions. Using genetic and pharmacological approaches, we discovered that the survival of Tsc2-deficient tumor cells is dependent on autophagy induction. Thus, autophagy inhibitors may have therapeutic potential in TSC and LAM, either as single agent therapy or in combination with mTORC1 inhibitors.
doi:10.4161/auto.7.11.17652
PMCID: PMC3242802  PMID: 21997371
autophagy; p62/sequestosome 1; tuberin; sirolimus; mTOR; chloroquine; tuberous sclerosis complex; lymphangioleiomyomatosis; metabolism
3.  Mammalian Target of Rapamycin Signaling and Autophagy 
The pace of progress in lymphangioleiomyomatosis (LAM) is remarkable. In the year 2000, TSC2 gene mutations were found in LAM cells; in 2001 the tuberous sclerosis complex (TSC) genes were discovered to regulate cell size in Drosophila via the kinase TOR (target of rapamycin); and in 2008 the results were published of a clinical trial of rapamycin, a specific inhibitor of TOR, in patients with TSC and LAM with renal angiomyolipomas. This interval of just 8 years between a genetic discovery for which the relevant signaling pathway was as yet unknown, to the initiation, completion, and publication of a clinical trial, is an almost unparalleled accomplishment in modern biomedical research. This robust foundation of basic, translational, and clinical research in TOR, TSC, and LAM is now poised to optimize and validate effective therapeutic strategies for LAM. An immediate challenge is to deduce the mechanisms underlying the partial response of renal angiomyolipomas to rapamycin, and thereby guide the design of combinatorial approaches. TOR complex 1 (TORC1), which is known to be active in LAM cells, is a key inhibitor of autophagy. One hypothesis, which will be explored here, is that low levels of autophagy in TSC2-null LAM cells limits their survival under conditions of bioenergetic stress. A corollary of this hypothesis is that rapamycin, by inducing autophagy, promotes the survival of LAM cells, while simultaneously arresting their growth. If this hypothesis proves to be correct, then combining TORC1 inhibition with autophagy inhibition may represent an effective clinical strategy for LAM.
doi:10.1513/pats.200909-104JS
PMCID: PMC3137149  PMID: 20160148
tuberin; rapamycin; chloroquine; Rheb; tuberous sclerosis

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