TORC1 (Target of rapamycin complex 1) has a critical role in the regulation of cell growth and cell size. A wide range of signals, including amino acids, is known to activate TORC1. Here, we report the identification of Rag GTPases as novel activators of TORC1 in response to amino acid signals. Knockdown of Rag gene expression suppressed the stimulatory effect of amino acids on TORC1 in Drosophila S2 cells. Expression of constitutively active (GTP-bound) Rag in mammalian cells enhances TORC1 in the absence of amino acids while expression of dominant negative Rag blocks the stimulatory effects of amino acids on TORC1. Drosophila genetic studies also show that the Rag GTPases regulate cell growth, autophagy, and animal viability under starvation. Together, our studies establish a novel function of Rag GTPases in TORC1 activation in response to amino acid signals.

Background: GLUT1 is the main glucose transporter in certain immune cells. Results: Overexpressing GLUT1 in macrophages results in increased glucose uptake and glucose utilization. Conclusion: Driving glucose uptake and metabolism through GLUT1 induces a proinflammatory response that is dependent upon glycolysis and reactive oxygen species. Significance: Understanding how macrophage substrate metabolism impacts inflammation is crucial to develop novel therapeutics for obesity and diabetes.

Summary The MYC oncogene encodes MYC, a transcription factor that binds the genome through sites termed E-boxes (5′-CACGTG-3′), which are identical to the binding sites of the heterodimeric CLOCK-BMAL1 master circadian transcription factor. Hence, we hypothesized that ectopic MYC expression perturbs the clock by deregulating E-box-driven components of the circadian network in cancer cells. We report here that deregulated expression of MYC or N-MYC disrupts the molecular clock in vitro by directly inducing REV-ERBα to dampen expression and oscillation of BMAL1, and this could be rescued by knockdown of REV-ERB. REV-ERBα expression predicts poor clinical outcome for N-MYC-driven human neuroblastomas that have diminished BMAL1 expression, and reexpression of ectopic BMAL1 in neuroblastoma cell lines suppresses their clonogenicity. Further, ectopic MYC profoundly alters oscillation of glucose metabolism and perturbs glutaminolysis. Our results demonstrate an unsuspected link between oncogenic transformation and circadian and metabolic dysrhythmia, which we surmise to be advantageous for cancer.

Summary T cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy associated with Notch pathway mutations. While both normal activated and leukemic T cells can utilize aerobic glycolysis to support proliferation, it is unclear to what extent these cell populations are metabolically similar and if differences reveal T-ALL vulnerabilities. Here we show that aerobic glycolysis is surprisingly less active in T-ALL cells than proliferating normal T cells and T-ALL cells are metabolically distinct. Oncogenic Notch promoted glycolysis but also induced metabolic stress that activated 5′ AMP activated kinase (AMPK). Unlike stimulated T cells, AMPK actively restrained aerobic glycolysis in T-ALL cells through inhibition of mTORC1 while promoting oxidative metabolism and mitochondrial Complex I activity. Importantly, AMPK-deficiency or inhibition of Complex I led to T-ALL cell death and reduced disease burden. Thus AMPK simultaneously inhibits anabolic growth signaling and is essential to promote mitochondrial pathways that mitigate metabolic stress and apoptosis in T-ALL.

In response to nutrient deficiency, eukaryotic cells activate macroautophagy, a degradative process in which proteins, organelles and cytoplasm are engulfed within unique vesicles called autophagosomes. Fusion of these vesicles with the endolysosomal compartment leads to breakdown of the sequestered material into amino acids and other simple molecules, which can be used as nutrient sources during periods of starvation. This process is driven by a group of autophagy-related (Atg) proteins, and is suppressed by TOR (target of rapamycin) signalling under favourable conditions. Several distinct kinase complexes have been implicated in autophagic signalling downstream of TOR. In yeast, TOR is known to control autophagosome formation in part through a multiprotein complex containing the serine/threonine protein kinase Atg1. Recent work in Drosophila and mammalian systems suggests that this complex and its regulation by TOR are conserved in higher eukaryotes, and that Atg1 has accrued additional functions including feedback regulation of TOR itself. TOR and Atg1 also control the activity of a second kinase complex containing Atg6/Beclin 1, Vps (vacuolar protein sorting) 15 and the class III PI3K (phosphoinositide 3-kinase) Vps34. During autophagy induction, Vps34 activity is mobilized from an early endosomal compartment to nascent autophagic membranes, in a TOR- and Atg1-responsive manner. Finally, the well-known TOR substrate S6K (p70 ribosomal protein S6 kinase) has been shown to play a positive role in autophagy, which may serve to limit levels of autophagy under conditions of continuously low TOR activity. Further insight into these TOR-dependent control mechanisms may support development of autophagy-based therapies for a number of pathological conditions.