All metazoan guts are subjected to immunologically unique conditions in which an efficient antimicrobial system operates to eliminate pathogens while tolerating symbiotic commensal microbiota. However, the molecular mechanisms controlling this process are only partially understood. Here, we show that bacterial-derived uracil acts as a ligand for dual oxidase (DUOX)-dependent reactive oxygen species generation in Drosophila gut and that the uracil production in bacteria causes inflammation in the gut. The acute and controlled uracil-induced immune response is required for efficient elimination of bacteria, intestinal cell repair, and host survival during infection of nonresident species. Among resident gut microbiota, uracil production is absent in symbionts, allowing harmonious colonization without DUOX activation, whereas uracil release from opportunistic pathobionts provokes chronic inflammation. These results reveal that bacteria with distinct abilities to activate uracil-induced gut inflammation, in terms of intensity and duration, act as critical factors that determine homeostasis or pathogenesis in gut-microbe interactions.

Energy homeostasis and feeding are regulated by the central nervous system. C75, a fatty acid synthase (FAS) inhibitor, causes weight loss and anorexia, implying a novel central nervous system pathway(s) for sensing energy balance. AMP-activated protein kinase (AMPK), a sensor of peripheral energy balance, is phosphorylated and activated when energy sources are low. Here, we identify a role for hypothalamic AMPK in the regulation of feeding behavior and in mediating the anorexic effects of C75. 5-Aminoimidazole-4-carboxamide-1-␤-D-ribofuranoside (AICAR), an activator of AMPK, increased food intake, whereas compound C, an inhibitor of AMPK, decreased food intake. C75 rapidly reduced the level of the phosphorylated AMPK ␣ subunit (pAMPK␣) in the hypothalamus, even in fasted mice that had elevated hypothalamic pAMPK␣ levels. Furthermore, AICAR reversed both the C75-induced anorexia and the decrease in hypothalamic pAMPK␣ levels. C75 elevated hypothalamic neuronal ATP levels, which may contribute to the mechanism by which C75 decreased AMPK activity. C75 reduced the levels of pAMPK␣ and phosphorylated cAMP response element-binding protein (pCREB) in the arcuate nucleus neurons of the hypothalamus, suggesting a mechanism for the reduction in NPY expression seen with C75 treatment. These data indicate that modulation of FAS activity in the hypothalamus can alter energy perception via AMPK, which functions as a physiological energy sensor in the hypothalamus.Despite significant advances in the understanding of appetite and satiety at molecular levels (1-3), practical therapies for weight loss remain elusive. We and others (4 -8) have demonstrated that C75, a synthetic fatty acid synthase (FAS) 1 inhibitor, caused profound weight loss and anorexia in lean, dietinduced obese (DIO) and genetically obese (ob/ob) mice. In addition to FAS inhibition, C75 also stimulates carnitine palmitoyltransferase-1 (CPT-1) activity, increasing fatty acid oxidation and ATP levels (8). Since enzymes of the fatty acid metabolic pathways are highly expressed in hypothalamic neurons that regulate feeding behavior (9), we hypothesize that C75-induced alterations in fatty acid metabolism may affect neuronal energy flux, which could signal a change in energy status, leading to changes in feeding behavior.AMPK (AMP-activated protein kinase) is activated by metabolic stresses such as nutrient starvation (10) and ischemiahypoxia (11) and by physiological processes such as vigorous exercise (12, 13). Specifically, increases in the AMP/ATP ratio, decreases in cellular pH, and increases in the creatine/phosphocreatine ratio are known to activate AMPK via allosteric activation of AMPK by AMP and by phosphorylation of AMPK by AMPKK (14 -19). Once activated, AMPK switches off ATPconsuming biosynthetic pathways such as fatty acid synthesis and switches on ATP-generating metabolic pathways such as fatty acid oxidation to preserve ATP levels (20, 21). The central roles of AMPK in both energy sensing and the control of fatty acid metabolism (16,22) and its r...

Fatty acid synthase (FAS), the enzyme responsible for the de novo synthesis of fatty acids, is highly expressed in ovarian cancers and most common human carcinomas. Inhibition of FAS and activation of AMP-activated protein kinase (AMPK) have been shown to be cytotoxic to human cancer cells in vitro and in vivo. In this report, we explore the cytotoxic mechanism of action of FAS inhibition and show that C93, a synthetic FAS inhibitor, increases the AMP/ATP ratio, activating AMPK in SKOV3 human ovarian cancer cells, which leads to cytotoxicity. As a physiologic consequence of AMPK activation, acetyl-CoA carboxylase (ACC), the rate-limiting enzyme of fatty acid synthesis, was phosphorylated and inhibited whereas glucose oxidation was increased. Despite these attempts to conserve energy, the AMP/ATP ratio increased with worsening cellular redox status. Pretreatment of SKOV3 cells with compound C, an AMPK inhibitor, substantially rescued the cells from C93 cytotoxicity, indicating its dependence on AMPK activation. 5-(Tetradecyloxy)-2-furoic acid, an ACC inhibitor, did not activate AMPK despite inhibiting fatty acid synthesis pathway activity and was not significantly cytotoxic to SKOV3 cells. This indicates that substrate accumulation from FAS inhibition triggering AMPK activation, not end-product depletion of fatty acids, is likely responsible for AMPK activation. C93 also exhibited significant antitumor activity and apoptosis against SKOV3 xenografts in athymic mice without significant weight loss or cytotoxicity to proliferating cellular compartments such as bone marrow, gastrointestinal tract, or skin. Thus, pharmacologic FAS inhibition selectively activates AMPK in ovarian cancer cells, inducing cytotoxicity while sparing most normal human tissues from the pleiotropic effects of AMPK activation. [Cancer Res 2007;67(7):2964-71]

SUMMARY mTORC1 plays a key role in autophagy as a negative regulator. The currently-known targets of mTORC1 in the autophagy pathway mainly function at early stages of autophagosome formation. Here, we identify that mTORC1 inhibits later stages of autophagy by phosphorylating UVRAG. Under nutrient-enriched conditions, mTORC1 binds and phosphorylates UVRAG. The phosphorylation positively regulates the association of UVRAG with RUBICON, thereby enhancing the antagonizing effect of RUBICON on UVRAG-mediated autophagosome maturation. Upon dephosphorylation, UVRAG is released from RUBICON to interact with the HOPS complex, a component for the late endosome and lysosome fusion machinery, and enhances autophagosome and endosome maturation. Consequently, the dephosphorylation of UVRAG facilitates the lysosomal degradation of epidermal growth factor receptor (EGFR), reduces EGFR signaling, and suppresses cancer cell proliferation and tumor growth. These results demonstrate that mTORC1 engages in late stages of autophagy and endosome maturation, defining a broader range of mTORC1 functions in the membrane-associated processes.