Although the mechanisms controlling skeletal muscle homeostasis have been identified, there is a lack of knowledge of the integrated dynamic processes occurring during myogenesis and their regulation. Here, metabolism, autophagy and differentiation were concomitantly analyzed in mouse muscle satellite cell (MSC)-derived myoblasts and their cross-talk addressed by drug and genetic manipulation. We show that increased mitochondrial biogenesis and activation of mammalian target of rapamycin complex 1 inactivation-independent basal autophagy characterize the conversion of myoblasts into myotubes. Notably, inhibition of autophagic flux halts cell fusion in the latest stages of differentiation and, conversely, when the fusion step of myocytes is impaired the biogenesis of autophagosomes is also impaired. By using myoblasts derived from p53 null mice, we show that in the absence of p53 glycolysis prevails and mitochondrial biogenesis is strongly impaired. P53 null myoblasts show defective terminal differentiation and attenuated basal autophagy when switched into differentiating culture conditions. In conclusion, we demonstrate that basal autophagy contributes to a correct execution of myogenesis and that physiological p53 activity is required for muscle homeostasis by regulating metabolism and by affecting autophagy and differentiation.

Interleukin-6 (IL-6), a pro-inflammatory cytokine released by cancer-associated fibroblasts, has been linked to the invasive and metastatic behavior of ovarian cancer cells. Resveratrol is a naturally occurring polyphenol with the potential to inhibit cancer cell migration. Here we show that Resveratrol and IL-6 affect in an opposite manner the expression of RNA messengers and of microRNAs involved in cell locomotion and extracellular matrix remodeling associated with the invasive properties of ovarian cancer cells. Among the several potential candidates responsible for the anti-invasive effect promoted by Resveratrol, here we focused our attention on ARH-I (DIRAS3), that encodes a Ras homolog GTPase of 26-kDa. This protein is known to inhibit cell motility, and it has been shown to regulate autophagy by interacting with BECLIN 1. IL-6 down-regulated the expression of ARH-I and inhibited the formation of LC3-positive autophagic vacuoles, while promoting cell migration. On opposite, Resveratrol could counteract the IL-6 induction of cell migration in ovarian cancer cells through induction of autophagy in the cells at the migration front, which was paralleled by up-regulation of ARH-I and down-regulation of STAT3 expression. Spautin 1-mediated disruption of BECLIN 1-dependent autophagy abrogated the effects of Resveratrol, while promoting cell migration. The present data indicate that Resveratrol elicits its anti-tumor effect through epigenetic mechanisms and support its inclusion in the chemotherapy regimen for highly aggressive ovarian cancers. © 2016 Wiley Periodicals, Inc.

GLUT1 is the facilitative transporter playing the major role in the internalization of glucose. Basally, GLUT1 resides on vesicles located in a para-golgian area, and is translocated onto the plasmamembrane upon activation of the PI3KC1-AKT pathway. In proliferating cancer cells, which demand a high quantity of glucose for their metabolism, GLUT1 is permanently expressed on the plasmamembrane. This is associated with the abnormal activation of the PI3KC1-AKT pathway, consequent to the mutational activation of PI3KC1 and/or the loss of PTEN. The latter, in fact, could antagonize the phosphorylation of AKT by limiting the availability of Phosphatidylinositol (3,4,5)-trisphosphate. Here, we asked whether PTEN could control the plasmamembrane expression of GLUT1 also through its protein-phosphatase activity on AKT. Experiments of co-immunoprecipitation and in vitro de-phosphorylation assay with homogenates of cells transgenically expressing the wild type or knocked-down mutants (lipid-phosphatase, protein-phosphatase, or both) isoforms demonstrated that indeed PTEN physically interacts with AKT and drives its dephosphorylation, and so limiting the expression of GLUT1 at the plasmamembrane. We also show that growth factors limit the ability of PTEN to dephosphorylate AKT. Our data emphasize the fact that PTEN acts in two distinct steps of the PI3k/AKT pathway to control the expression of GLUT1 at the plasmamembrane and, further, add AKT to the list of the protein substrates of PTEN.

Glucose represents an important source of energy for the cells. Proliferating cancer cells consume elevated quantity of glucose, which is converted into lactate regardless of the presence of oxygen. This phenomenon, known as the Warburg effect, has been proven to be useful for imaging metabolically active tumours in cancer patients by 18 F-fluorodeoxyglucose positron emission tomography (FDG-PET). Glucose is internalised in the cells by glucose transporters (GLUTs) belonging to the GLUT family. GLUT1 (SLC2A1) is the most prevalent isoform in more aggressive and less differentiated thyroid cancer histotypes. In a previous work, we found that loss of expression of PTEN was associated with increased expression of GLUT1 on the plasma membrane (PM) and probability of detecting thyroid incidentalomas by FDG-PET. Herein, we investigated the molecular pathways that govern the expression of GLUT1 on the PM and the glucose uptake in WRO (expressing WT PTEN) and FTC133 (PTEN null) follicular thyroid cancer cells cultured under glucose-depleted conditions. The membrane expression of GLUT1 was enhanced in glucose-deprived cells. Through genetic manipulations of PTEN expression, we could demonstrate that the lack of this oncosuppressor has a dominant effect on the membrane expression of GLUT1 and glucose uptake. We conclude that loss of function of PTEN increases the probability of cancer detection by FDG-PET or other glucose-based imaging diagnosis.

Proliferating cancer cells oxidize glucose through the glycolytic pathway. Since this metabolism is less profitable in terms of ATP production, cancer cells consume large quantity of glucose, and those that experience insufficient blood supply become glucose-addicted. We have analyzed the response to glucose depletion in WRO and FTC133 follicular thyroid cancer cells, which differ in the expression of two key regulators of the glucose metabolism. WRO cells, which express wild type p53 and PTEN, showed a higher rate of cell proliferation and were much less sensitive to glucose-depletion than FTC133 cells, which are PTEN null and express mutant p53. Glucose depletion slowed-down the autophagy flux in FTC133 cells, not in WRO cells. In a wound-healing assay, WRO cells were shown to migrate faster than FTC133 cells. Glucose depletion slowed down the cell migration rate, and these effects were more evident in FTC133 cells. Genetic silencing of either wild-type PTEN or p53 in WRO cells resulted in increased uptake of glucose, whereas the ectopic expression of PTEN in FTC133 cells resulted in diminished glucose uptake. In conclusion, compared to WRO, FTC133 cells were higher glucose up-taker and consumer. These data do not support the general contention that cancer cells lacking PTEN or expressing the mutant p53R273H are more aggressive and prone to better face glucose depletion. We propose that concurrent PTEN deficiency and mutant p53 leads to a glucose-addiction state that renders the cancer cell more sensitive to glucose restriction. The present observation substantiates the view that glucose-restriction may be an adjuvant strategy to combat these tumours.