Induction of 2,3-bisphosphoglycerate synthase in Friend leukemia cells

Bisphosphoglycerate mutase controls serine pathway flux via 3-phosphoglycerate

Lower glycolysis involves a series of reversible reactions, which interconvert intermediates that also feed anabolic pathways. 3-phosphoglycerate (3-PG) is an abundant lower glycolytic intermediate that feeds serine biosynthesis via the enzyme phosphoglycerate dehydrogenase, which is genomically amplified in several cancers. Phosphoglycerate mutase (PGAM1) catalyzes the isomerization of 3-PG into the downstream glycolytic intermediate 2-phosphoglycerate (2-PG). Catalytic activity of PGAM1 requires its histidine phosphorylation. We show that the primary PGAM1 histidine phosphate donor is 2,3-bisphosphoglycerate (2,3-BPG), which is made from the glycolytic intermediate 1,3-bisphosphoglycerate (1,3-BPG) by bisphosphoglycerate mutase (BPGM). When BPGM is knocked out, 1,3-BPG can directly phosphorylate PGAM1. In this case, PGAM1 phosphorylation and activity are decreased, but nevertheless sufficient to maintain normal glycolytic flux and cellular growth rate. 3-PG, however, accumulates, leading to increased serine synthesis. Thus, one biological function of BPGM is to control glycolytic intermediate levels and thereby serine biosynthetic flux.

The phosphoglycerate mutases

The phosphoglycerate mutase family is generally very well documented with respect to structure, evolution, and mode of action. However, a few individuals in the family remain relatively poorly characterized and will clearly require more detailed study. Furthermore, certain aspects of the detailed behavior of these enzymes are, as yet, incompletely understood and require further investigation. Cofactor-dependent monophosphoglycerate mutase and bisphosphoglycerate mutase are undoubtedly very closely related. Their amino acid sequences are strongly similar, they can form active heterodimers, and they catalyze the same three reactions, albeit at substantially different relative rates. Both enzymes catalyze a ping-pong type of reaction with a phosphohistidine intermediate. The presence of an additional phospho ligand at the active site of monophosphoglycerate mutase helps to explain why this enzyme is better at retaining the 2,3-bisphosphoglycerate intermediate and why it is thus more efficient (by a factor of about 10(3)) at catalyzing the interconversion of 3- and 2-phosphoglycerates. The reason why 1,3-bisphosphoglycerate is a better substrate for bisphosphoglycerate mutase than for monophosphoglycerate mutase (by a factor of about 30) is not yet apparent but presumably relates to the relative positioning of the two phospho-binding sites. Both enzymes are equally good as phosphatases when the reaction is activated by 2-phosphoglycollate. Available evidence indicates that these mutases are similar in many respects to the much smaller, cofactor-dependent monophosphoglycerate mutase from Schizosaccharomyces pombe, but further information is required to define the relationship more precisely. Cofactor-independent monophosphoglycerate mutase belongs to a quite distinct branch of the phosphoglycerate mutase family. It is not known at present whether this branch is related divergently or convergently to the cofactor-dependent monophosphoglycerate mutase/bisphosphoglycerate mutase branch. Existing evidence can be argued both ways. For example, the kinetic evidence shows a ping-pong type of reaction and would be consistent with a phosphohistidine intermediate as encountered in the other mutases. Thus the cofactor-independent enzyme may also have arisen by gene duplication--but, in this case, yielding an enzyme of about twice the size, with slightly different residues at the active site and C-terminal tail. An alternative possibility, of course, is that the two branches of the phosphoglycerate mutase family are quite unrelated in a divergent sense and are little more similar structurally than is, for example, the catalytically similar enzyme phosphoglucomutase.(ABSTRACT TRUNCATED AT 400 WORDS)

Apoptotic changes precede mitochondrial dysfunction in red cell-type pyruvate kinase mutant mouse erythroleukemia cell lines

Two erythroleukemia cell lines have been established from the splenic lesions of red blood cell-type pyruvate kinase (R-PK) activity-deficient mice of CBA/N origin infected with a polycythemic strain of Friend leukemia virus complex (FVp). Ten to 30% of the cells of these cell lines undergo apoptotic changes in routine passage, as shown by nuclear fragmentation, DNA laddering, DNA content (propidium iodide (PI) staining), and annexin V binding assay. In these cells, however, although adenosine 5'-triphosphate (ATP) levels were lower than in the control cells, the mitochondrial inner transmembrane potential (delta psi m), detected by rhodamine 123 (R123) and diSC3(5) staining, remained unchanged until the final stage of apoptosis. No evidence was obtained to relate this finding to R-PK mutation due to difficulty in cloning stable, conditionally inducible R-PK gene transfectants. However, low delta psi m in the apoptotic cell population of the control T3-K-1 (K-1) and T3-CI-2-0 (2-0) Friend erythroleukemia cells supports a possible relationship, as do results obtained in two Friend erythroleukemia cells recently isolated from normal CBA/N mice. These cell lines are expected to be useful for clarifying both the primary apoptotic changes independent of mitochondrial dysfunction and the PK-isozyme changes during erythrodifferentiation, for example, the decreased muscle type 2 (M2) PK level. Modification of growth signals in these cell lines may modulate differentiation and/or apoptosis and allow further elucidation of the signaling networks.

Molecular cloning and nucleotide sequence of murine 2,3-bisphosphoglycerate mutase cDNA

Cloning and sequencing of a murine cDNA with the entire coding region of 2,3-bisphosphoglycerate mutase is reported, as a prerequisite for further expression studies of this erythroid specific enzyme in Friend mouse erythroleukemia cells. A comparison between species of the deduced amino acid sequences of these proteins shows 20 substitutions between mouse and human and 21 between mouse and rabbit: none of these substitutions are in positions assumed to be in the active site. Amino acid alignment with the other related enzymes, the phosphoglycerate mutases, in combination with crystallographic data from yeast phosphoglycerate mutase, gives some insight into the structure/function correlation for this protein family. Amino acid residues which are most likely critical for either 2,3-bisphosphoglycerate mutase or phosphoglycerate mutase function are pointed out. Concerning the phylogenetic analysis, phosphoglycerate mutases B and M from mammalians appear to have diverged with the yeast enzyme from a common ancestor, before the emergence of the 2,3-bisphosphoglycerate mutases.

Erythropoietin receptor of a human leukemic cell line with erythroid characteristics

A new cell line of human erythroleukemia cells differentiates spontaneously so that 30% of the cells are always hemoglobinized. Erythropoietin did not affect the percentage of such cells but stimulated the cell growth, indicating that the cells have functioning receptors. Binding of human recombinant radioiodinated erythropoietin to the receptors was specific. The bound ligand was internalized into cells at 37 degrees C but not at 15 degrees C. Scatchard analysis showed two classes of binding sites. Covalent binding of erythropoietin to its receptors yielded two products detected on sodium dodecyl sulfate-polyacrylamide gels electrophoresed under reducing conditions. Under non-reducing conditions, these species disappeared and larger products appeared.

Characterization of erythropoietin receptor of murine erythroid cells

Radioiodinated or biologically tritiated recombinant human erythropoietin was used to characterize receptors for this hormone on the surface of Friend erythroleukemic cells (745A and TSA8) and cells from mouse erythropoietic tissues (liver from fetus and spleen from animals made anemic by injection of Friend virus or phenylhydrazine). Specific binding of erythropoietin to these cells was time-dependent and dose-dependent. Binding studies at 37 degrees C showed that dissociation constants of erythropoietin-receptor complexes were in the range of 100-300 pM. The number of receptors on erythroleukemic cells increased after treatment with dimethylsulfoxide. Covalent binding of 125I-erythropoietin to its receptors with a cross-linking reagent, disuccinimidyl suberate or glutaraldehyde, resulted in the formation of two major radiolabeled products that migrated as 120-kDa and 140-kDa species on sodium dodecyl sulfate/polyacrylamide electrophoresis gels under reducing conditions. Under non-reducing conditions, both 120-kDa and 140-kDa species disappeared and two cross-linked products, a minor product with a molecular mass of 250 kDa and a major product of high molecular mass that kept it from migration into the separating gels, appeared. The relationship of the cross-linked products found under non-reducing conditions with those under reducing conditions remains to be clarified.

Isolation and characterization of cDNA encoding rabbit reticulocyte 2,3-bisphosphoglycerate synthase

We have isolated and sequenced a cDNA clone containing the entire coding region of rabbit reticulocyte 2,3-bisphosphoglycerate (DPG) synthase. The cDNA was verified by translation of the hybridization-selected RNA and by demonstrating identity of the deduced amino acid (aa) sequence to the sequences of CNBr peptides of the purified enzyme. The aa sequence of the enzyme was homologous to the reported sequence of the human enzyme [Haggarty et al., EMBO J. 2 (1983) 1213-1220], especially in the N-terminal half (aa 1-142). Northern blot analysis of rabbit reticulocyte poly(A)+ RNA revealed a single species of mRNA with about 1700 nucleotides.

Role and induction of 2,3-bisphosphoglycerate synthase

2,3-Bisphosphoglycerate accumulates in mammalian erythrocytes, where it facilitates the supply of oxygen to the tissues by binding to hemoglobin. Regulatory properties of 2,3-bisphosphoglycerate synthase and phosphatase are discussed. The 2,3-bisphosphoglycerate concentration was shown to rise linearly along with the hemoglobin level during erythroid differentiation. The accumulation of 2,3-bisphosphoglycerate was primarily attributable to an increase in 2,3-bisphosphoglycerate synthase. Antibody-binding studies showed that the increased activity is achieved solely through an increase in the amount of enzyme. It was shown that 2,3-bisphosphoglycerate synthase was synthesized in nucleated erythroid precursor cells and also in anucleated reticulocytes. The mRNA of this protein appears to be fairly stable in reticulocytes. Coordinate expression of hemoglobin and 2,3-bisphosphoglycerate synthase was found during dimethylsulfoxide-induced differentiation of Friend erythroleukemia cells. 2,3-Bisphosphoglycerate rose concomitantly.