Tumorigenesis requires not only loss of proliferative control, but also a metabolic shift towards increased glucose and glutamine consumption required for increased energy production and to drive the de novo biosynthesis of nucleotides, amino acids, and lipids essential for cell division. These processes are primarily driven through oncogenes or loss of tumor suppressors, which act to circumvent normal regulatory pathways. The retinoblastoma (Rb) protein, the first described tumor suppressor, is extensively involved in cell cycle regulation, and perturbations within the Rb pathway are found in most tumor types. Beyond cell cycle control, Rb has been implicated in multiple additional biochemical pathways known to be involved in tumor progression, such as metastasis and angiogenesis. However, little is known about the role of Rb in regulating the unique changes in metabolism that have been observed in human cancers. Using stable 13C-glucose isotopomer NMR analysis, we found that triple knock-out (TKO) of all three Rb family members in mouse embryonic fibroblasts (MEFs) resulted in increased glucose uptake and flux to lactate, and simultaneously decreased glucose-derived carbon incorporation into Krebs' cycle intermediates relative to wild-type (WT) MEFs. To supplement this loss of glucose carbons for anaplerosis within the Krebs' cycle, we speculated that the Rb TKO MEFs may increase glutamine uptake for both bioenergetic and anabolic precursors. We observed that loss of Rb caused increased 13C-glutamine uptake and flux into glutamate and Krebs' cycle intermediates using isotopomer NMR analyses. Importantly, this shift towards glutamine utilization was essential for the survival of Rb TKO MEFs and not for the WT MEFs. Preliminary studies of the precise downstream metabolic enzymes that may in part mediate these global changes in metabolism then demonstrated that the expression of distinct regulatory metabolic enzymes, including glucose transporters, hexokinase 2, and glutaminase 1, are simultaneously increased in the Rb TKO MEFs compared to WT MEFs. Combined, these studies suggest that inactivation of the Rb protein in human cancers leads to a global metabolic shift towards enhanced glycolysis and glutamine utilization, which in turn is required for neoplastic immortalization and transformation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr PR-12.