One-carbon metabolism in cancer

Cells require one-carbon units for nucleotide synthesis, methylation and reductive metabolism, and these pathways support the high proliferative rate of cancer cells. As such, anti-folates, drugs that target one-carbon metabolism, have long been used in the treatment of cancer. Amino acids, such as serine are a major one-carbon source, and cancer cells are particularly susceptible to deprivation of one-carbon units by serine restriction or inhibition of de novo serine synthesis. Recent work has also begun to decipher the specific pathways and sub-cellular compartments that are important for one-carbon metabolism in cancer cells. In this review we summarise the historical understanding of one-carbon metabolism in cancer, describe the recent findings regarding the generation and usage of one-carbon units and explore possible future therapeutics that could exploit the dependency of cancer cells on one-carbon metabolism

Pyruvate kinase M2 activators promote tetramer formation and suppress tumorigenesis

Cancer cells engage in a metabolic program to enhance biosynthesis and support cell proliferation. The regulatory properties of pyruvate kinase M2 (PKM2) influence altered glucose metabolism in cancer. PKM2 interaction with phosphotyrosine-containing proteins inhibits enzyme activity and increases availability of glycolytic metabolites to support cell proliferation. This suggests that high pyruvate kinase activity may suppress tumor growth. We show that expression of PKM1, the pyruvate kinase isoform with high constitutive activity, or exposure to published small molecule PKM2 activators inhibit growth of xenograft tumors. Structural studies reveal that small molecule activators bind PKM2 at the subunit interaction interface, a site distinct from that of the endogenous activator fructose-1,6-bisphosphate (FBP). However, unlike FBP, binding of activators to PKM2 promotes a constitutively active enzyme state that is resistant to inhibition by tyrosine-phosphorylated proteins. These data support the notion that small molecule activation of PKM2 can interfere with anabolic metabolism

Phosphoglycerate dehydrogenase diverts glycolytic flux and contributes to oncogenesis

Most tumors exhibit increased glucose metabolism to lactate, however, the extent to which glucose-derived metabolic fluxes are used for alternative processes is poorly understood [1, 2]. Using a metabolomics approach with isotope labeling, we found that in some cancer cells a relatively large amount of glycolytic carbon is diverted into serine and glycine metabolism through phosphoglycerate dehydrogenase (PHGDH). An analysis of human cancers showed that PHGDH is recurrently amplified in a genomic region of focal copy number gain most commonly found in melanoma. Decreasing PHGDH expression impaired proliferation in amplified cell lines. Increased expression was also associated with breast cancer subtypes, and ectopic expression of PHGDH in mammary epithelial cells disrupted acinar morphogenesis and induced other phenotypic alterations that may predispose cells to transformation. Our findings show that the diversion of glycolytic flux into a specific alternate pathway can be selected during tumor development and may contribute to the pathogenesis of human cancer.National Institutes of Health (U.S.)National Cancer Institute (U.S.)Smith Family FoundationDamon Runyon Cancer Research FoundationBurroughs Wellcome Fun

The role of phosphoglycerate dehydrogenase in cell proliferation and tumor progression

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis. Vita.Includes bibliographical references.The metabolic needs of proliferating cells are distinct from those of quiescent, terminally differentiated cells. Cancer is a disease of inappropriate cell proliferation, and tumor cells require a unique metabolic program to support proliferation. Phosphoglycerate dehydrogenase (PHGDH) catalyzes the first step in the serine biosynthesis pathway, and the gene encoding this enzyme is amplified in human cancer. PHGDH-amplified cells depend on PHGDH expression to proliferate, and upon PHGDH knockdown, supplying exogenous serine cannot restore proliferation. We hypothesized that PHGDH is an unappreciated source of the reductive currency NADPH for biosynthesis and/or redox maintenance. PHGDH can utilize NADP+ as a cofactor in vitro, and tritiated glucose tracing shows that PHGDH produces exclusively NADPH, not NADH, in cells. We therefore designed and validated mutant PHGDH enzymes with altered selectivity for NAD(P) (H) that can be used to test whether an ability of PHGDH to produce NADPH is required for cell proliferation. In the course of these experiments, we found that N-terminally tagged PHGDH exhibits structural alterations compared to the wildtype enzyme and is incapable of supporting proliferation. To enable future studies of a physiologically relevant form of PHGDH, we developed a method to purify untagged recombinant PHGDH. In order to model PHGDH-amplified cancer in vivo, we developed a doxycycline-inducible PHGDH transgenic mouse. When PHGDH expression is increased ubiquitously in mouse tissues, melanin granules are present in hair follicles at an inappropriate stage of the hair follicle cycle. This melanocyte-related abnormality is provocative, as PHGDH amplification occurs in human melanoma. When PHGDH is overexpressed in a model of melanoma driven by mutant Braf and Pten loss, tumor growth is accelerated. Mice with mutant Braf normally develop growth arrested melanocytic nevi, and when PHGDH is overexpressed in this context an increased in nevi is observed and malignant melanoma arises with incomplete penetrance. These data identify PHGDH as the first metabolic enzyme that can be overexpressed in its wild type form and promote cancer initiation and/or progression to a malignant state. We conclude that PHGDH metabolic activity is important for cancer cell proliferation and that PHGDH amplification or overexpression can promote tumorigenesis at multiple stages.by Katherine R. Mattaini.Ph. D

Increased PHGDH expression promotes aberrant melanin accumulation

Background: Copy number gain of the D-3-phosphoglycerate dehydrogenase (PHGDH) gene, which encodes the first enzyme in serine biosynthesis, is found in some human cancers including a subset of melanomas. Methods: In order to study the effect of increased PHGDH expression in tissues in vivo, we generated mice harboring a PHGDH tetO allele that allows tissue-specific, doxycycline-inducible PHGDH expression, and we analyzed the phenotype of mice with a ubiquitous increase in PHGDH expression. Results: Tissues and cells derived from PHGDH tetO mice exhibit increased serine biosynthesis. Histological examination of skin tissue from PHGDH tetO mice reveals the presence of melanin granules in early anagen hair follicles, despite the fact that melanin synthesis is closely coupled to the hair follicle cycle and does not normally begin until later in the cycle. This phenotype occurs in the absence of any global change in hair follicle cycle timing. The aberrant presence of melanin early in the hair follicle cycle following PHGDH expression is also accompanied by increased melanocyte abundance in early anagen skin. Conclusions: These data suggest increased PHGDH expression impacts normal melanocyte biology, but PHGDH expression alone is not sufficient to cause cancer.Koch Institute for Integrative Cancer Research (Grant (P30-CA14051)National Science Foundation (U.S.). Graduate Research Fellowship Program (DGE-1122374)Damon Runyon Cancer Research Foundation (Grant DRG-2241-15)Ludwig Center for Molecular Oncology at MIT (Grant 21-CA198028)Ludwig Center for Molecular Oncology at MIT (Grant R01-CA168653

Human Phosphoglycerate Dehydrogenase Produces the Oncometabolite d‑2-Hydroxyglutarate

Human d-3-phosphoglycerate dehydrogenase (PHGDH), the first enzyme in the serine biosynthetic pathway, is genomically amplified in tumors including breast cancer and melanoma. In <i>PHGDH</i>-amplified cancer cells, knockdown of PHGDH is not fully rescued by exogenous serine, suggesting possible additional growth-promoting roles for the enzyme. Here we show that, in addition to catalyzing oxidation of 3-phosphoglycerate, PHGDH catalyzes NADH-dependent reduction of α-ketoglutarate (AKG) to the oncometabolite d-2-hydroxyglutarate (d-2HG). Knockdown of PHGDH decreased cellular 2HG by approximately 50% in the <i>PHGDH</i>-amplified breast cancer cell lines MDA-MB-468 (normal concentration 93 μM) and BT-20 (normal concentration 35 μM) and overexpression of PHGDH increased cellular 2HG by over 2-fold in non-<i>PHGDH</i>-amplified MDA-MB-231 breast cancer cells, which normally display very low PHGDH expression. The reduced 2HG level in PHGDH knockdown cell lines can be rescued by PHGDH re-expression, but not by a catalytically inactive PHGDH mutant. The initial connection between cancer and d-2HG involved production of high levels of d-2HG by mutant isocitrate dehydrogenase. More recently, however, elevated d-2HG has been observed in breast cancer tumors without isocitrate dehydrogenase mutation. Our results suggest that PHGDH is one source of this d-2HG

The importance of serine metabolism in cancer

Serine metabolism is frequently dysregulated in cancers; however, the benefit that this confers to tumors remains controversial. In many cases, extracellular serine alone is sufficient to support cancer cell proliferation, whereas some cancer cells increase serine synthesis from glucose and require de novo serine synthesis even in the presence of abundant extracellular serine. Recent studies cast new light on the role of serine metabolism in cancer, suggesting that active serine synthesis might be required to facilitate amino acid transport, nucleotide synthesis, folate metabolism, and redox homeostasis in a manner that impacts cancer.American Association for Cancer ResearchBurroughs Wellcome FundDavid H. Koch Institute for Integrative Cancer Research at MITLudwig Center for Molecular Oncology at MITStand Up To CancerNational Science Foundation (U.S.) (NSF Graduate Research Fellowship Program)National Institutes of Health (U.S.) (NIH grant R21 CA198028

BRD4 Short Isoform Interacts with RRP1B, SIPA1 and Components of the LINC Complex at the Inner Face of the Nuclear Membrane

<div><p>Recent studies suggest that BET inhibitors are effective anti-cancer therapeutics. Here we show that BET inhibitors are effective against murine primary mammary tumors, but not pulmonary metastases. <i>BRD4</i>, a target of BET inhibitors, encodes two isoforms with opposite effects on tumor progression. To gain insights into why BET inhibition was ineffective against metastases the pro-metastatic short isoform of BRD4 was characterized using mass spectrometry and cellular fractionation. Our data show that the pro-metastatic short isoform interacts with the LINC complex and the metastasis-associated proteins RRP1B and SIPA1 at the inner face of the nuclear membrane. Furthermore, histone binding arrays revealed that the short isoform has a broader acetylated histone binding pattern relative to the long isoform. These differential biochemical and nuclear localization properties revealed in our study provide novel insights into the opposing roles of BRD4 isoforms in metastatic breast cancer progression.</p> </div