AMPK Is Essential to Balance Glycolysis and Mitochondrial Metabolism to Control T-ALL Cell Stress and Survival.

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 that 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.

MYC Disrupts the Circadian Clock and Metabolism in Cancer Cells.

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 re-expression 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.

Metabolic reprogramming of macrophages: glucose transporter 1 (GLUT1)-mediated glucose metabolism drives a proinflammatory phenotype.

Glucose is a critical component in the proinflammatory response of macrophages (MΦs). However, the contribution of glucose transporters (GLUTs) and the mechanisms regulating subsequent glucose metabolism in the inflammatory response are not well understood. Because MΦs contribute to obesity-induced inflammation, it is important to understand how substrate metabolism may alter inflammatory function. We report that GLUT1 (SLC2A1) is the primary rate-limiting glucose transporter on proinflammatory-polarized MΦs. Furthermore, in high fat diet-fed rodents, MΦs in crown-like structures and inflammatory loci in adipose and liver, respectively, stain positively for GLUT1. We hypothesized that metabolic reprogramming via increased glucose availability could modulate the MΦ inflammatory response. To increase glucose uptake, we stably overexpressed the GLUT1 transporter in RAW264.7 MΦs (GLUT1-OE MΦs). Cellular bioenergetics analysis, metabolomics, and radiotracer studies demonstrated that GLUT1 overexpression resulted in elevated glucose uptake and metabolism, increased pentose phosphate pathway intermediates, with a complimentary reduction in cellular oxygen consumption rates. Gene expression and proteome profiling analysis revealed that GLUT1-OE MΦs demonstrated a hyperinflammatory state characterized by elevated secretion of inflammatory mediators and that this effect could be blunted by pharmacologic inhibition of glycolysis. Finally, reactive oxygen species production and evidence of oxidative stress were significantly enhanced in GLUT1-OE MΦs; antioxidant treatment blunted the expression of inflammatory mediators such as PAI-1 (plasminogen activator inhibitor 1), suggesting that glucose-mediated oxidative stress was driving the proinflammatory response. Our results indicate that increased utilization of glucose induced a ROS-driven proinflammatory phenotype in MΦs, which may play an integral role in the promotion of obesity-associated insulin resistance.

Aerobic glycolysis suppresses p53 activity to provide selective protection from apoptosis upon loss of growth signals or inhibition of BCR-Abl.

Unlike the growth factor dependence of normal cells, cancer cells can maintain growth factor-independent glycolysis and survival through expression of oncogenic kinases, such as BCR-Abl. Although targeted kinase inhibition can promote cancer cell death, therapeutic resistance develops frequently, and further mechanistic understanding is needed. Cell metabolism may be central to this cell death pathway, as we have shown that growth factor deprivation leads to decreased glycolysis that promotes apoptosis via p53 activation and induction of the proapoptotic protein Puma. Here, we extend these findings to show that elevated glucose metabolism, characteristic of cancer cells, can suppress protein kinase Cδ (PKCδ)-dependent p53 activation to maintain cell survival after growth factor withdrawal. In contrast, DNA damage-induced p53 activation was PKCδ independent and was not metabolically sensitive. Both stresses required p53 Ser(18) phosphorylation for maximal activity but led to unique patterns of p53 target gene expression, showing distinct activation and response pathways for p53 that were differentially regulated by metabolism. Consistent with oncogenic kinases acting to replace growth factors, treatment of BCR-Abl-expressing cells with the kinase inhibitor imatinib led to reduced metabolism and p53- and Puma-dependent cell death. Accordingly, maintenance of glucose uptake inhibited p53 activation and promoted imatinib resistance. Furthermore, inhibition of glycolysis enhanced imatinib sensitivity in BCR-Abl-expressing cells with wild-type p53 but had little effect on p53-null cells. These data show that distinct pathways regulate p53 after DNA damage and metabolic stress and that inhibiting glucose metabolism may enhance the efficacy of and overcome resistance to targeted molecular cancer therapies.

Regulation of mTORC1 by the Rab and Arf GTPases.

The mammalian target of rapamycin (mTOR) is a key cell growth regulator, which forms two distinct functional complexes (mTORC1 and mTORC2). mTORC1, which is directly inhibited by rapamycin, promotes cell growth by stimulating protein synthesis and inhibiting autophagy. mTORC1 is regulated by a wide range of extra- and intracellular signals, including growth factors, nutrients, and energy levels. Precise regulation of mTORC1 is important for normal cellular physiology and development, and dysregulation of mTORC1 contributes to hypertrophy and tumorigenesis. In this study, we screened Drosophila small GTPases for their function in TORC1 regulation and found that TORC1 activity is regulated by members of the Rab and Arf family GTPases, which are key regulators of intracellular vesicle trafficking. In mammalian cells, uncontrolled activation of Rab5 and Arf1 strongly inhibit mTORC1 activity. Interestingly, the effect of Rab5 and Arf1 on mTORC1 is specific to amino acid stimulation, whereas glucose-induced mTORC1 activation is not blocked by Rab5 or Arf1. Similarly, active Rab5 selectively inhibits mTORC1 activation by Rag GTPases, which are involved in amino acid signaling, but does not inhibit the effect of Rheb, which directly binds and activates mTORC1. Our data demonstrate a key role of Rab and Arf family small GTPases and intracellular trafficking in mTORC1 activation, particularly in response to amino acids.

TGF-beta: a new role for an old AktTOR.

Nutrient overabundance is known to promote cellular hypertrophy, a significant pathological event in diseases like diabetes and cancer, although mechanisms have remained unclear. In this issue of Developmental Cell, Wu and Derynck provide a new model that links metabolism and cell growth by demonstrating that hyperglycemia can increase TGF-beta-dependent activation of the mTOR pathway to promote cellular hyperplasia.