Phospholipase D-mTOR requirement for the Warburg effect in human cancer cells
Introduction
A hallmark of cancer cells is aerobic glycolysis whereby there is an increased utilization of glucose and glycolysis for energy and the raw materials needed for cell growth [1]. This effect is commonly referred to as the Warburg effect after its discoverer [2], [3]. Glycolysis generates the precursors needed for the synthesis of lipids and nucleotides for generating membranes and nucleic acids [4]. A shift away from mitochondrial respiration also occurs as a response to the stress of hypoxia where oxidative phosphorylation is not an option [5]. Much of the response to hypoxia is due to elevated expression of hypoxia-inducible factor-α (HIFα) – a family of transcription factors that stimulate the expression glycolytic and angiogenic genes [5]. HIFα expression is elevated in a significant percentage of human cancers [6].
The expression of the α subunits for both HIF1 and HIF2 is dependent upon phospholipase D (PLD) in human kidney and breast cancer cells [7], [8]. Elevated PLD activity in human cancer cells provides both survival and migration signals [8], [9]. The primary metabolite of PLD is phosphatidic acid (PA) and it is required for the activation of the mammalian target of rapamycin (mTOR) [10], [11], [12], which has also been implicated in survival signals and HIFα expression [13], [14], [15]. mTOR has been implicated as a sensor of nutritional sufficiency and elevated mTOR promotes cell cycle progression when there is sufficient nutrition for cells to double their mass and divide [16], [17]. Thus, there is a connection between PLD-mTOR survival signals and the Warburg effect in cancer cells. We have investigated whether the Warburg effect is dependent on PLD-mTOR signaling in human cancer cells.
Section snippets
Cells, cell culture conditions and transfection
The 786-O, MDA-MB-231, MCF-7, and HEK293 cells used in this study were obtained from the American Type Culture Collection. All cells were maintained in Dulbecco’s modified Eagle’s medium (DMEM) with 10% fetal bovine serum. Transfections were performed using Lipofectamine LTX (Invitrogen) according to the vendor’s instructions.
Materials
Antibodies against mTOR, Rictor, Raptor, HIF2α, GLUT1, Actin, and hemagglutinin (HA) were obtained from Santa Cruz Biotechnology; antibodies against Akt1, Akt2, GLUT3 and
Elevated glucose uptake in human cancer cells is dependent on PLD activity
Glucose uptake was examined in four human cell lines – two breast cancer cell lines (MCF-7 and MDA-MB-231), a kidney cancer cell line (786-O), and HEK293 human embryonic kidney cells. These cells have been analyzed previously for their PLD activity with MDA-MB-231 cells having high levels of PLD activity relative to the MCF-7 cells, and 786-O cells having high levels of PLD activity relative to the HEK293 cells [7], [22], [23]. This is shown graphically in Fig. 1A. The level of glucose uptake
Discussion
The “metabolic transformation” [1] that takes place in most cancer cells has attracted renewed attention as it has become apparent that the altered metabolism is closely integrated with oncogenic transformation. The metabolic changes that occur in cancer cells confer several advantages that allow cells to survive in an emerging tumor mass where there is inconsistent vascularization. We reported previously that elevated PLD activity in renal cancer cells is required for the expression of both
Conflict of interest
There are no conflicts of interest regarding this paper.
Acknowledgments
We thank Michael Frohman (SUNY, Stony Brook) for the PLD genes used in this study. This work was supported by grant from the National Cancer Institute (CA46677) (DAF), and grants from the Canadian Cancer Society of the National Cancer Institute of Canada (MO). Research Centers in Minority Institutions (RCMI) award RR-03037 from the National Center for Research Resources of the National Institutes of Health, which supports infrastructure and instrumentation in the Biological Sciences Department
References (41)
- et al.
The biology of cancer: metabolic reprogramming fuels cell growth and proliferation
Cell Metab.
(2008) - et al.
Brick by brick: metabolism and tumor cell growth
Curr. Opin. Genet. Dev.
(2008) - et al.
Regulation of angiogenesis by hypoxia and hypoxia-inducible factors
Curr. Top. Dev. Biol.
(2006) - et al.
Hypoxia-inducible factors: central regulators of the tumor phenotype
Curr. Opin. Genet. Dev.
(2007) - et al.
Phospholipase D couples survival and migration signals in response to stress in human breast cancer cells
J. Biol. Chem.
(2006) Phosphatidic acid signaling to mTOR: signals for the survival of human cancer cells
Biochem. Biophys. Acta
(2009)Will mTOR inhibitors make it as cancer drugs?
Cancer Cell
(2003)- et al.
TOR signaling in growth and metabolism
Cell
(2006) - et al.
Differential dependence of HIF1 and HIF2 on mTORC1 and mTORC2
J. Biol. Chem.
(1999) - et al.
Elevated phospholipase D induces apoptosis in normal rat fibroblasts
Biochem. Biophys. Res. Commun.
(2002)
Ubiquitin pathway in VHL cancer syndrome
Neoplasia
The von Hippel-Lindau tumor suppressor protein is required for proper assembly of an extracellular fibronectin matrix
Mol. Cell
C. elegans EGL-9 and mammalian homologs define a family of dioxygenases that regulate HIF by prolyl hydroxylation
Cell
HIF-1-mediated expression of pyruvate dehydrogenase kinase: a metabolic switch required for cellular adaptation to hypoxia
Cell Metab.
Cancer’s sweet tooth
Cancer Cell
Defining the role of mTOR in cancer
Cancer Cell
AKT/PKB signaling: navigating downstream
Cell
Attenuation of LDH-A expression uncovers a link between glycolysis, mitochondrial physiology, and tumor maintenance
Cancer Cell
Tumor cell metabolism: cancer’s Achilles’ heel
Cancer Cell
On the origin of cancer cells
Science
Cited by (0)
- 1
Present address: New York University Cancer Institute, New York University School of Medicine, New York, NY 10016, United States.
- 2
Present address: Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.