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      Identification of a multienzyme complex for glucose metabolism in living cells

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          Abstract

          <p class="first" id="d9038921e208">Sequential metabolic enzymes in glucose metabolism have long been hypothesized to form multienzyme complexes that regulate glucose flux in living cells. However, it has been challenging to directly observe these complexes and their functional roles in living systems. In this work, we have used wide-field and confocal fluorescence microscopy to investigate the spatial organization of metabolic enzymes participating in glucose metabolism in human cells. We provide compelling evidence that human liver-type phosphofructokinase 1 (PFKL), which catalyzes a bottleneck step of glycolysis, forms various sizes of cytoplasmic clusters in human cancer cells, independent of protein expression levels and of the choice of fluorescent tags. We also report that these PFKL clusters colocalize with other rate-limiting enzymes in both glycolysis and gluconeogenesis, supporting the formation of multienzyme complexes. Subsequent biophysical characterizations with fluorescence recovery after photobleaching and FRET corroborate the formation of multienzyme metabolic complexes in living cells, which appears to be controlled by post-translational acetylation on PFKL. Importantly, quantitative high-content imaging assays indicated that the direction of glucose flux between glycolysis, the pentose phosphate pathway, and serine biosynthesis seems to be spatially regulated by the multienzyme complexes in a cluster-size-dependent manner. Collectively, our results reveal a functionally relevant, multienzyme metabolic complex for glucose metabolism in living human cells. </p>

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          Partitioning of lipid-modified monomeric GFPs into membrane microdomains of live cells.

          Many proteins associated with the plasma membrane are known to partition into submicroscopic sphingolipid- and cholesterol-rich domains called lipid rafts, but the determinants dictating this segregation of proteins in the membrane are poorly understood. We suppressed the tendency of Aequorea fluorescent proteins to dimerize and targeted these variants to the plasma membrane using several different types of lipid anchors. Fluorescence resonance energy transfer measurements in living cells revealed that acyl but not prenyl modifications promote clustering in lipid rafts. Thus the nature of the lipid anchor on a protein is sufficient to determine submicroscopic localization within the plasma membrane.
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            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. 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.
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              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.
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                Author and article information

                Journal
                Journal of Biological Chemistry
                J. Biol. Chem.
                American Society for Biochemistry & Molecular Biology (ASBMB)
                0021-9258
                1083-351X
                June 02 2017
                June 02 2017
                : 292
                : 22
                : 9191-9203
                Article
                10.1074/jbc.M117.783050
                5454101
                28424264
                996ecd9d-779b-47bf-b3f1-8057dd31196f
                © 2017
                History

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