In parallel, AKT phosphorylation was completely abrogated by inhibitors to PDK, PI3K, or PKC. These data indicate that PI3K-AKT is upstream of ATP-stimulated mTOR-S6K1 signaling, whereas PDK-AKT and PKC-AKT signaling are not involved in this process. We infer that abnormal responses in Cd39-null hepatocytes resulting selleck from disordered purinergic signaling are, at least in part, mediated by way of mTOR signaling (as illustrated in Fig. 7). In this work, we show that CD39/ENTPD1 modulates crucial cell metabolic and proliferative elements in vitro and impacts

cellular transformation that is linked with development of liver cancer in vivo (as illustrated in Fig. 7). We implicate disordered purinergic signaling in the evolution of both induced and spontaneous liver cancer. The model by which disordered purinergic signaling promotes hepatocarcinogenesis may involve the following molecular mechanisms. First, heightened levels of extracellular ATP (eATP) provoke hepatocyte dysfunction, as observed in Cd39-null mice, in keeping with previous studies.4, 5, 25 eATP levels are determined by release from stressed, activated inflammatory cells or injured parenchymal elements, and by altered Galunisertib cost expression of ectonucleotidases. In turn, eATP-initiated responses are mediated by diverse hepatocellular P2 receptors. We show that these effects are blocked by a global P2 receptor

antagonist suramin (Fig. 2F) and can further implicate P2Y2 in this process (Fig. S2B). We also establish the possible role of mTOR in eATP-modulation of intracellular ATP (iATP) levels. Higher levels of eATP result in constitutive stimulation of the mTOR-S6K1 pathway in liver cells, which may incorrectly imply abundant iATP, despite these levels being decreased in these cells (Fig. 4E; Table S2). Second, we link purinergic signaling responses to deviation of cellular metabolic pathways that support rapid cell proliferation. medchemexpress Direct tyrosine phosphorylation of PKM2 by FGFR1 has been recently identified as a key mechanism promoting glycolysis and tumor growth.24 Here

we show that purinergic signaling modulates tyrosine phosphorylation as well as expression of PKM2 in proliferating hepatocytes (Fig. 4A,B). We have also previously demonstrated that inhibition of LDH-A, another essential glycolytic enzyme frequently overexpressed in cancer, limits tumor growth.20 We now show LDH-A expression to be upregulated by ATP-stimulated purinergic signaling in an mTOR-dependent manner (Figs. 4C, 6C). Cunningham et al.26 have shown that mTOR controls mitochondrial oxidative function by formation of a transcriptional complex with YY1 (Ying Yang 1)-PGC-1α (peroxisome-proliferator activated receptor coactivator-1α). Inhibition of mTOR resulted in global suppression of mitochondrial gene expression (such as PGC-1α, PGC-1β, LDH-A, NRF-1, and UCP2). We found, however, that rapamycin decreases gene expression of LDH-A and UCP2 (Fig.