Metabolic shifts, such as loss of the mitochondrial pyruvate carrier (MPC) have prognostic value in colorectal cancer: in this case, loss of MPC predicts poorer prognosis. In publicly available datasets, we have observed that MPC1 is commonly deleted in colorectal cancers and appears to be lost early in tumorigenesis, when comparing normal tissue to adenomas and to carcinomas. Loss of MPC, a heterodimeric transporter composed of MPC1 and MPC2, uncouples glucose metabolism by preventing pyruvate, a byproduct of glucose metabolism, from entering the mitochondria to undergo oxidation, resulting in the majority of pyruvate converting to lactate. Colon stem cells, the predominant cell of origin in this cancer, normally express lower MPC than their differentiated progeny, thus suggesting a developmental mechanism for uncoupling pyruvate oxidation and glycolysis. Through studies in which we deleted MPC in non-transformed stem cells or re- express MPC in cancer cell lines, we observe an inverse causal relationship between MPC expression, proliferation capacity, and markers of stemness. This proposal is based upon the similar phenotypic findings between these stem cells and their cancerous counterparts, and we hypothesize that reinforcement of stem cell glucose metabolism confers susceptibility towards cancer initiation. Preliminary results support that loss of MPC expression is sufficient to increase susceptibility malignant transformation and to accelerate tumorigenesis in colorectal carcinoma. The following proposal tests whether MPC acts as a tumor suppressor when a stem cell is environmentally or genetically tipped towards cancer.
In AIM 1, we will utilize both loss and gain of function experiments in both the azoxymethane-dextran sodium sulfate model and the APC loss of function model of colorectal cancer induction. Each polyp has the potential to be molecularly unique as well as convergent on distinct signatures, and we assess this as a function of glucose metabolic partitioning.
In AIM 2, we will test the role and function of pyruvate oxidation on cell identity in the various proliferating cell populations of the crypt. Defining the role of metabolism in cancer initiation, from environmental exposures and from genetic risk factors, holds promise in identifying metabolic targets in treatment for the growing number of colorectal cancer patients, and ultimately utilizing metabolism to protect stem cells from transformation.
The lifetime risk for developing colorectal cancer is approximately 1 in 27 for the American patient and recently, there is a rise in incidence of colorectal cancers in patients under 30 years olds. The mitochondrial pyruvate carrier (MPC) is commonly lost in colorectal cancers, leading to the uncoupling of glycolysis and mitochondrial glucose oxidation. This study asks whether MPC1 deletion, and the subsequent metabolic partitioning, in the colon stem cells increases the susceptibility towards the initial transformation in normal colon epithelium. Certain metabolic programs may confer greater risk towards the development of polyps and thus, provide an array of preventative therapeutic targets.
| Wei, Peng; Dove, Katja K; Bensard, Claire et al. (2018) The Force Is Strong with This One: Metabolism (Over)powers Stem Cell Fate. Trends Cell Biol 28:551-559 |
