Tumors and tumor cells exhibit a unique metabolism referred to as the Warburg Effect characterized by high rates of glucose transport and glycolysis. Glycolysis is an inefficient means by which to generate ATP, however since this change is almost universal in its appearance it must provide a selective advantage to tumor cells. Tumor cells must transport large amounts of glucose to generate the needed ATP. Most tumor cells have elevated levels of the glucose transporter GLUT1 which is thought to be responsible for the increased glucose transport needed to drive the synthesis of ATP by glycolysis. The use of glucose by tumor cells is highly leveraged because it is a critical substrate. The overall goal of this proposal is to determine whether glucose transported into tumor cells via hexose transporters represents the major metabolic event that supports altered tumor metabolism in vivo. We hypothesize that glucose is the major metabolic precursor that supports the Warburg Effect, and therefore loss of hexose transporters will suppress tumor cell proliferation in vivo. Furthermore failure to meet the metabolic needs of the tumor due to loss of GLUT1 expression will result in cell death by either apoptosis or induction of autophagy which in turn leads to cell death. It may be possible that tumor cells escape this fate by mutation of oncogenes that modulate tumor metabolism or altering the expression of metabolic genes that compensate for the loss of glucose as a carbon source for bioenergetic and biosynthetic processes and we will characterize these compensatory pathways. Preliminary data shows that knockdown of GLUT1 reduces glucose uptake and consumption, lactate generation, and proliferation in vitro and in vivo. Overexpression of GLUT1 enhances glucose uptake and consumption, lactate generation, suppresses apoptosis, and stimulates tumor growth in vivo. We propose three aims: 1) Determine what hexose transporters are functional in cells lacking GLUT1, determine how loss of these additional hexose transporters affects tumor cell proliferation in vitro and in vivo, and determine the contributions of other metabolic pathways (fatty acid oxidation and glutaminolysis) to tumor cell metabolism;2) Identify genes that support the proliferation of tumor cells lacking GLUT1 using a synthetic lethal screen;and 3) Determine whether elimination of GLUT1 from mammary epithelial cells in vivo alters mammary tumorigenesis induced by ErbB2. Gene expression profiling and deep sequencing will identify genetic changes that support tumor growth in the absence of GLUT1.
These specific aims will provide insight into the critical molecules that regulate glucose uptake, how tumor cells compensate for the loss of glucose as a metabolite, whether the metabolic environment stimulates genetic changes in tumors, and whether GLUT1 is required for induction of mammary tumorigenesis. Given the current interest in developing therapies that attack the metabolism of tumor cells, these studies are timely and will provide important insight into the plasticity of tumor metabolism and the genetic changes that underlie tumor adaption to the metabolic challenges it faces.
Tumor cells grow and divide quickly and thus require abundant energy;however, tumor cells frequently generate energy from sugar (specifically glucose), which is less efficient than burning fat. As a result they consume high amounts of glucose, and rely on one cell surface transporter to bring in the fuel they need. We wish to determine how limiting glucose entry into tumor cells affects their growth, and identify how cancer cells compensate for the lack of glucose when they continue to survive and grow. These insights may provide new means to kill tumor cells by blocking the different chemical ways they use to make energy.
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