Es. It is known that GLUT1 exerts its glucose transporter function only when exposed on the outer cell membrane. Consistent with mRNA expression data, PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/1986172 flow cytometry analysis of permeabilized cells indicated that the two subsets contained comparable total amounts of GLUT1 protein. However, CD44+CD117+ cells expressed much higher levels of GLUT1 protein on the cell surface. This finding was corroborated by analysis of fluorescent glucose uptake: CD44+CD117+ cells bound FITC-labelled glucose much more avidly, compared to CD44+CD117- cells. Oncotarget from an EOCbearing Varlitinib biological activity patient.This observation may recall what has been reported in senescence, where cells undergo a pseudo-hypoxic state in the absence of reduced oxygen tension, mostly driven by mTOR. In a sense, single-positive EOC cells look like cells undergoing “chronological senescence” , as suggested by a sustained Warburg effect and lack of OXPHOS respiration in the absence of hypoxia. On the contrary, ovarian CSC show intact respiratory activity, suggesting a nonsenescent phenotype, which is conceivably essential for the maintenance of a self-renewing reservoir. It has been reported that the balance between the PKM1 and PKM2 isoforms of PKM may be critical in directing pyruvate to either lactate production or mitochondrial utilization. Indeed, in models of enforced expression or silencing of these enzymes in malignant cell lines, PKM2 expression is associated with the Warburg effect. Although we observed a significant elevation in total PKM in the CSC subset, we did not observe any difference in the relative proportion of PKM1 and PKM2 between CD44+CD117+ and CD44+CD117- cells. However, molecular and biochemical data on PKM2 may be misleading and may not reflect its actual enzymatic activity, as PKM2 function depends on the formation of dimers/tetramers, detection of which is possible under controlled conditions in established cell lines, but unfeasible in our setting. Our data clearly indicate that EOC CD44+CD117+ cells are much less dependent on glucose than the CD44+CD117- population. This finding is in line with recent observations on in vitro resistance of glioblastoma CSC to glucose deprivation. Intriguingly, although the metabolic profile of their CD133+ population was not characterized, these investigators observed pronounced expression of the glucose transporter GLUT3. Our finding of strong surface expression of GLUT1 in ovarian CSC leads us to ask why these relatively quiescent OXPHOSdriven cells should manifest high glucose avidity compared to the bulk tumor cells, and how limiting the Warburg effect might be advantageous to ovarian CSC. We found that ovarian CSC are characterized by high PPP activity, a finding consistent with their high glucose Oncotarget PG 490 web uptake and HKII expression. One key function of the PPP is to maintain high levels of NADPH, which in turn is essential for recharging ROS-scavenging enzymes. Thus, the finding of higher PPP activity, along with high OXPHOS and mitochondrial ROS production, might point to differences in ROS homeostasis between CSC and the bulk tumor cell population, in order to preserve the integrity of the former, and avoid further DNA damage or irreversible opening of mitochondrial pores. In addition, the higher expression of fatty acid -oxidation enzymes by CD44+CD117+ cells could indicate that these metabolites also play an important role within the CSC energy economy, probably to produce intermediates for the Krebs cycle. In this re.Es. It is known that GLUT1 exerts its glucose transporter function only when exposed on the outer cell membrane. Consistent with mRNA expression data, PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/1986172 flow cytometry analysis of permeabilized cells indicated that the two subsets contained comparable total amounts of GLUT1 protein. However, CD44+CD117+ cells expressed much higher levels of GLUT1 protein on the cell surface. This finding was corroborated by analysis of fluorescent glucose uptake: CD44+CD117+ cells bound FITC-labelled glucose much more avidly, compared to CD44+CD117- cells. Oncotarget from an EOCbearing patient.This observation may recall what has been reported in senescence, where cells undergo a pseudo-hypoxic state in the absence of reduced oxygen tension, mostly driven by mTOR. In a sense, single-positive EOC cells look like cells undergoing “chronological senescence” , as suggested by a sustained Warburg effect and lack of OXPHOS respiration in the absence of hypoxia. On the contrary, ovarian CSC show intact respiratory activity, suggesting a nonsenescent phenotype, which is conceivably essential for the maintenance of a self-renewing reservoir. It has been reported that the balance between the PKM1 and PKM2 isoforms of PKM may be critical in directing pyruvate to either lactate production or mitochondrial utilization. Indeed, in models of enforced expression or silencing of these enzymes in malignant cell lines, PKM2 expression is associated with the Warburg effect. Although we observed a significant elevation in total PKM in the CSC subset, we did not observe any difference in the relative proportion of PKM1 and PKM2 between CD44+CD117+ and CD44+CD117- cells. However, molecular and biochemical data on PKM2 may be misleading and may not reflect its actual enzymatic activity, as PKM2 function depends on the formation of dimers/tetramers, detection of which is possible under controlled conditions in established cell lines, but unfeasible in our setting. Our data clearly indicate that EOC CD44+CD117+ cells are much less dependent on glucose than the CD44+CD117- population. This finding is in line with recent observations on in vitro resistance of glioblastoma CSC to glucose deprivation. Intriguingly, although the metabolic profile of their CD133+ population was not characterized, these investigators observed pronounced expression of the glucose transporter GLUT3. Our finding of strong surface expression of GLUT1 in ovarian CSC leads us to ask why these relatively quiescent OXPHOSdriven cells should manifest high glucose avidity compared to the bulk tumor cells, and how limiting the Warburg effect might be advantageous to ovarian CSC. We found that ovarian CSC are characterized by high PPP activity, a finding consistent with their high glucose Oncotarget uptake and HKII expression. One key function of the PPP is to maintain high levels of NADPH, which in turn is essential for recharging ROS-scavenging enzymes. Thus, the finding of higher PPP activity, along with high OXPHOS and mitochondrial ROS production, might point to differences in ROS homeostasis between CSC and the bulk tumor cell population, in order to preserve the integrity of the former, and avoid further DNA damage or irreversible opening of mitochondrial pores. In addition, the higher expression of fatty acid -oxidation enzymes by CD44+CD117+ cells could indicate that these metabolites also play an important role within the CSC energy economy, probably to produce intermediates for the Krebs cycle. In this re.