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Fatty acid oxidation (FAO) is crucial for cells to overcome metabolic stress by providing ATP and NADPH. However, the mechanism by which FAO is regulated in tumors remains elusive. Here we show that Nur77 is required for the metabolic adaptation of melanoma cells by protecting FAO. Glucose deprivation activates ERK2 to phosphorylate and induce Nur77 translocation to the mitochondria, where Nur77 binds to TPβ, a rate-limiting enzyme in FAO. Although TPβ activity is normally inhibited by oxidation under glucose deprivation, the Nur77-TPβ association results in Nur77 self-sacrifice to protect TPβ from oxidation. FAO is therefore able to maintain NADPH and ATP levels and prevent ROS increase and cell death. The Nur77-TPβ interaction further promotes melanoma metastasis by facilitating circulating melanoma cell survival. This study demonstrates a novel regulatory function of Nur77 with linkage of the FAO-NADPH-ROS pathway during metabolic stress, suggesting Nur77 as a potential therapeutic target in melanoma.

A lot of evidence indicates that cardiac fibroblasts are essential for maintaining the structure and function of heart. The present study examined whether TGFBR3 (transforming growth factor type III receptor, also known as betaglycan) could prevent hypoxia-induced injury in neonatal mice cardiac fibroblasts, if so, its possible molecular targets. MTT, electron microscopy and TUNEL assay were used to identify cell viability and apoptosis in neonatal mice cardiac fibroblasts. Results showed that hypoxia for 24 h markedly reduce cell viability by 49.8 ± 8.9%, largely via apoptosis. However, hypoxia-induced apoptosis in cardiac fibroblasts were almost completely prevented by overexpression of TGFBR3. In the present study, hypoxia also induced TGF-β1, p-Smad2/3 expression, TGFBR1-TGFBR2 complex formation and collagen production in cardiac fibroblasts, which were attenuated substantially by TGFBR3 overexpression. TGFBR3 also reversed Bax up-regulation, Bcl-2 down-regulation and Caspase-3 activation induced by hypoxia in cardiac fibroblasts. Hypoxia or TGF-β1 itself triggered an increase of [Ca(2+) ](i) in cardiac fibroblasts, which were both inhibited by TGFBR3 overexpression. Taken together, our results indicate that TGFBR3 may act as a protective factor in apoptotic process of cardiac fibroblasts by negative regulation of TGF-β signaling and represent a potential therapeutic target for heart remodeling after hypoxia injury.

Intestinal epithelial autophagy is crucial for host defense against invasive pathogens, and defects in this process occur frequently in patients with inflammatory bowel disease (IBD) and other mucosal disorders, but the exact mechanism that activates autophagy is poorly defined. Here, we investigated the role of RNA-binding protein HuR (human antigen R) in the posttranscriptional control of autophagy-related genes (ATGs) in the intestinal epithelium. We found that targeted deletion of HuR in intestinal epithelial cells (IECs) specifically decreased the levels of ATG16L1 in the intestinal mucosa. Intestinal mucosa from patients with IBD exhibited reduced levels of both HuR and ATG16L1. HuR directly interacted with Atg16l1 mRNA via its 3′ untranslated region and enhanced ATG16L1 translation, without affecting Atg16l1 mRNA stability. Circular RNA circPABPN1 blocked HuR binding to Atg16l1 mRNA and lowered ATG16L1 production. HuR silencing in cultured IECs also prevented rapamycin-induced autophagy, which was abolished by overexpressing ATG16L1. These findings indicate that HuR regulates autophagy by modulating ATG16L1 translation via interaction with circPABPN1 in the intestinal epithelium.

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Insulin resistance is a critical process in the initiation and progression of diabetic nephropathy (DN). Alprostadil (Prostaglandin E1, PGE1) had protective effects on renal function. However, it is unknown whether PGE1 inhibited insulin resistance in renal tubule epithelial cells via autophagy, which plays a protective role in DN against insulin resistance. Insulin resistance was induced by palmitic acid (PA) in human HK-2 cells, shown as the decrease of insulin-stimulated AKT phosphorylation, glucose transporter-4 (GLUT4), glucose uptake and enhanced phosphorylation of insulin receptor substrate 1(IRS-1) at site serine 307 (pIRS-1ser307) and downregulated expression of IRS-1. Along with less abundance of p62, autophagy markers LC3B and Beclin-1 significantly increased in HK-2 cells exposed to PA. Such abnormal changes were significantly reversed by PGE1, which mimicked the role of autophagy gene 7 small interfering RNA (ATG7 siRNA). Furthermore, PGE1 promoted the protein expression of autophagy-related fibroblast growth factor-21 (FGF21), which alleviated insulin resistance. Results from western blotting and immunohistochemistry indicated that PGE1 remarkably restored autophagy, insulin resistance and the FGF21 expression in rat kidney of type 2 diabetes mellitus (T2DM). Collectively, we demonstrated the potential protection of PGE1 on insulin resistance in renal tubules via autophagy-dependent FGF21 pathway in preventing the progression of DN.

Leptin, an anorexigenic hormone in the hypothalamus, suppresses food intake and increases energy expenditure. Failure to respond to leptin will lead to obesity. Here, we discovered that nuclear receptor Nur77 expression is lower in the hypothalamus of obese mice compared with normal mice. Injection of leptin results in significant reduction in body weight in wild-type mice but not in Nur77 knockout (KO) littermates or mice with specific Nur77 knockdown in the hypothalamus. Hypothalamic Nur77 not only participates in leptin central control of food intake but also expands leptin's reach to liver and adipose tissues to regulate lipid metabolism. Nur77 facilitates signal transducer and activator of transcription 3 (STAT3) acetylation by recruiting acetylase p300 and disassociating deacetylase histone deacetylase 1 (HDAC1) to enhance the transcriptional activity of STAT3 and consequently modulates the expression of downstream gene Pomc in the hypothalamus. Nur77 deficiency compromises response to leptin in mice fed a high-fat diet. Severe leptin resistance in Nur77 KO mice with increased appetite, lower energy expenditure, and hyperleptinemia contributes to aginginduced obesity. Our study opens a new avenue for regulating metabolism with Nur77 as the positive modulator in the leptin-driven antiobesity in the hypothalamus.The hypothalamus is the major center for regulating energy homeostasis by sensing and responding to input from hormonal and nutrient-related signals (1). Among various signals sensed by the hypothalamus, leptin is an important hormone derived from adipocytes with a key role in representing nutritional status to the hypothalamus for the regulation of energy balance (2). This regulation is mostly mediated by several well-structured nuclei in the hypothalamus, especially in arcuate nucleus (ARC) (3). Two distinct populations of neurons in ARC, proopiomelanocortin (Pomc) neurons and agouti-related protein (AgRp) neurons, are regulated by leptin in completely different fashions. Leptin suppresses the expression of orexigenic neuropeptide AgRp and neuropeptide Y (NPY) in AgRp neurons but upregulates the expression of anorexigenic neuropeptide Pomc in Pomc neurons (3). Leptin's function in these neurons is critical to normal food intake and body weight, and its dysregulation would break energy homeostasis. Leptin signaling ablation from the mutations of db or ob genes in mice would result in severe obesity and diabetes (4). Administration of leptin greatly reduces body weight and food intake in normal mice but not in obese mice. This phenomenon, together with higher circulating leptin level in the obese, is the so-called leptin resistance.Signal transducer and activator of transcription 3 (STAT3) is an important downstream component in leptin signaling on energy balance for the regulation of body weight and food intake (5). Mouse models with neural deletion of STAT3 develop hyperphagia and obesity, as well as severe diabetes (6). As Tyr 1138 of OB-Rb (the long form of leptin receptor) is specific for STAT3 ...

Activation of NAD(P)H oxidase has been reported to produce superoxide (O2 ·-) extracellularly as an autocrine/paracrine regulator or intracellularly as a signaling messenger in a variety of mammalian cells. However, it remains unknown how the activity of NAD(P)H oxidase is regulated in arterial myocytes. Recently, CD38-associated ADP-ribosylcyclase has been reported to use NAD(P)H oxidase product, NAD+ or NADP+ to produce cyclic ADP-ribose (cADPR) or nicotinic acid adenine dinucleotide phosphate (NAADP), which mediates intracellular Ca2+ signaling. The present study was designed to test a hypothesis that CD38/cADPR pathway as a downstream event exerts feedback regulatory action on the NAD(P)H oxidase activity in production of extra- or intracellular O2 ·-in mouse coronary arterial myocytes (CAMs). By fluorescent microscopic imaging, we simultaneously monitored extra- and intracellular O2 ·-production in wild-type (CD38+/+) and CD38 knockout (CD38-/-) CAMs in response to oxotremorine (OXO), a muscarinic type 1 (M1) receptor agonist. It was found that CD38 deficiency prevented OXO-induced intracellular but not extracellular O2 ·-production in CAMs. Consistently, the OXO-induced intracellular O2 ·-production was markedly inhibited by CD38 shRNA or CD38 inhibitor nicotinamide in CD38+/+ CAMs. Further, Nox4 siRNA inhibited OXO-induced intracellular but not extracellular O2 ·- production, whereas Nox1 siRNA attenuated both intracellular and extracellular O2 ·-production in CD38+/+ CAMs. Direct delivery of exogenous cADPR into CAMs markedly elevated intracellular Ca2+ concentration and restored intracellular O2 ·-production in CD38-/- CAMs. Functionally, CD38 deficiency or Nox1 siRNA and Nox4 siRNA prevented OXO-induced contraction in isolated perfused coronary arteries in CD38 WT mice. These results provide direct evidence that CD38/cADPR pathway importantly controls Nox4-mediated intracellular O2 ·-production and that CD38-dependent intracellular O2 ·-production is augmented via an autocrine manner of CD38-independent Nox1-derived extracellular O2 ·-production in CAMs.