Abstract PR10: Serine biosynthesis from glucose regulates folate availability

Abstract

Abstract It has been established that de novo serine biosynthesis is important for some cancers. We have previously shown that phosphoglycerate dehydrogenase (PHGDH), the enzyme responsible for catalyzing the first step in glycolytic serine biosynthesis, is amplified in certain cancers, including breast cancer and melanoma. Knockdown of PHGDH results in decreased proliferation of PHGDH-amplified cells, demonstrating a dependence on PHDGH in these cells; however, it has not been possible to rescue this defect with exogenous serine, suggesting that glycolytic serine biosynthesis has an alternate function in cells. Here we have investigated four mutually exclusive hypotheses each consistent with the inability of serine to rescue decreased glycolytic serine biosynthesis: 1: There exists an alternative function of PHGDH; 2: Pathway activity is important for TCA cycle anapleurosis; 3: Metabolic channeling of de novo serine; and 4: A unique product of this pathway other than serine is critical for proliferation. Using a combination of genetic and biochemical approaches, we show that flux through the serine biosynthesis pathway is required for cytosolic serine-glycine conversion via serine hydroxymethyltransferase 1 (SHMT1). In many cells flux through SHMT1 occurs in the glycine-to-serine direction, including PHDGH-dependent cell lines, and loss of PHGDH activity results in wasting of folates from the one-carbon pool to make serine. This reduces availability of one-carbon units in the folate pool for nucleotide biosynthesis, resulting in S-phase arrest and eventual cell death. These data link serine biosynthesis from glucose with the regulation of one-carbon folate metabolism, and provide an explanation for why cancer cells are dependent on de novo serine production even when serine is abundant. Citation Format: Caroline A. Lewis, Brian P. Fiske, Michael E. Pacold, Aaron M. Hosios, Katherine R. Mattaini, David M. Sabatini, Matthew G. Vander Heiden. Serine biosynthesis from glucose regulates folate availability. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr PR10.