No abstract

The molecular basis for the control of energy balance by the endocannabinoid anandamide (AEA) is still unclear. Here, we show that murine 3T3-L1 fibroblasts have the machinery to bind, synthesize and degrade AEA, and that their differentiation into adipocytes increases by approximately twofold the binding efficiency of cannabinoid receptors (CBR), and by approximately twofold and approximately threefold, respectively, the catalytic efficiency of the AEA transporter and AEA hydrolase. In contrast, the activity of the AEA synthetase and the binding efficiency of vanilloid receptor were not affected by the differentiation process. In addition, we demonstrate that AEA increases by approximately twofold insulin-stimulated glucose uptake in differentiated adipocytes, according to a CB1R-dependent mechanism that involves nitric oxide synthase, but not lipoxygenase or cyclooxygenase. We also show that AEA binding to peroxisome proliferator-activated receptor-gamma, known to induce differentiation of 3T3-L1 fibroblasts into adipocytes, is not involved in the stimulation of glucose uptake.

Tumor cells activate pathways that facilitate and stimulate glycolysis even in the presence of adequate levels of oxygen in order to satisfy their continuous need of molecules, such as nucleotides, ATP and fatty acids, necessary to support their rapid proliferation. Accordingly, a variety of human tumors are characterized by elevated expression levels of the hexokinase 2 isoform (HK2). Although different molecular mechanisms, including genetic and epigenetic mechanisms, have been suggested to account for the altered expression of HK2 in tumors, the potential role of microRNAs (miRNAs) in the regulation of HK2 expression has not been evaluated. Here, we report that miR-143 inhibits HK2 expression via a conserved miR-143 recognition motif located in the 3'-untranslated region (3'UTR) of HK2 mRNA. We demonstrate that miR143 inhibits HK2 expression both in primary keratinocytes and in head and neck squamous cell carcinoma (HNSCC)-derived cell lines. Importantly, we found that miR-143 inversely correlates with HK2 expression in HNSCC-derived cell lines and in primary tumors. We also report that the miRNA-dependent regulation of hexokinase expression is not limited to HK2 as miR-138 targets HK1 via a specific recognition motif located in its 3'UTR. All these data unveil a new miRNA-dependent mechanism of regulation of hexokinase expression potentially important in the regulation of glucose metabolism of cancer cells.

The natural polyphenolic compound resveratrol (trans-3,4 H ,5-trihydroxystilbene) is shown to prevent apoptosis (programmed cell death) induced in human erythroleukemia K562 cells by hydrogen peroxide and other unrelated stimuli. Resveratrol reversed the elevation of leukotriene B 4 (from 6.40^0.65 to 2.92^0.30 pmol´mg protein 21 ) and prostaglandin E 2 (from 11.46^1.15 to 8.02^0.80 nmol´mg protein 21 ), induced by H 2 O 2 challenge in K562 cells. The reduction of leukotriene B 4 and prostaglandin E 2 correlated with the inhibition of the 5-lipoxygenase activity, and the cyclooxygenase and peroxidase activity of prostaglandin H synthase, respectively. Resveratrol also blocked lipoperoxidation induced by hydrogen peroxide in K562 cell membranes. Resveratrol was found to act as a competitive inhibitor of purified 5-lipoxygenase and 15-lipoxygenase and prostaglandin H synthase, with inhibition constants of 4.5^0.5 mm (5-lipoxygenase), 40^5.0 mm (15-lipoxygenase), 35^4.0 mm (cyclooxygenase activity of prostaglandin H synthase) and 30^3.0 mm (peroxidase activity of prostaglandin H synthase). Altogether, the results reported here suggest that the anti-apoptotic activity of resveratrol depends on the direct inhibition of the main arachidonate-metabolizing enzymes.Keywords: apoptosis; cyclooxygenase; lipoxygenase; oxidative stress; resveratrol.Resveratrol (trans-3,4 H ,5-trihydroxystilbene) occurs naturally in grapes and a variety of medicinal plants, where it functions as a phytoalexin that protects against infections and other stress factors [1]. Because of its high concentration in grape skin, a significant amount of resveratrol is present in red wine [2] and is thought to be responsible for the reduced risk of cardiovascular disease associated with moderate consumption of this beverage [2]. Resveratrol has been reported to have antiplatelet [1], anti-inflammatory [3,4] and anticarcinogenic [5] effects. Recently, it has also been reported to act as an agonist for the estrogen receptor [6] and to inhibit phorbolester-mediated activation of protein kinase C and AP-1-mediated gene expression in human mammary epithelial cells [7]. The various activities of resveratrol have been attributed to its antioxidant properties [8], which contribute to control the intracellular redox balance by inhibiting the formation of reactive oxygen species (ROS; [5]). Moreover, this polyphenolic compound interferes with the arachidonate metabolism, by reducing the levels of leukotrienes (generated by the`l ipoxygenase pathway' of the arachidonate cascade) and prostanoids (generated by the`cyclooxygenase pathway'), and this activity is also considered crucial for its biological effects [3,5,7]. Although the cyclooxygenase activity [5] and expression [7] of prostaglandin H synthase (PHS) have been shown to be reduced by resveratrol in cellular systems, a direct interaction of this compound with the enzyme has not been characterized to date. The effect of resveratrol on the other arachidonate-metabolizing enzyme, lipoxygenase, has not been inve...