Serine-associated one-carbon metabolic reprogramming: a new anti-cancer therapeutic strategy

Tumour metabolism is a major focus of cancer research, and metabolic reprogramming is an important feature of malignant tumours. Serine is an important non-essential amino acid, which is a main resource of one-carbon units in tumours. Cancer cells proliferate more than normal cells and require more serine for proliferation. The cancer-related genes that are involved in serine metabolism also show changes corresponding to metabolic alterations. Here, we reviewed the serine-associated one-carbon metabolism and its potential as a target for anti-tumour therapeutic strategies.

HLA-DRB1 Amino Acid Positions and Residues Associated with Antibody-positive Rheumatoid Arthritis in Black South Africans

OBJECTIVE

To investigate the association of specific amino acid positions, residues, and haplotypes of HLA-DRB1 in black South Africans with autoantibody-positive rheumatoid arthritis (RA).

METHODS

High-resolution HLA-DRB1 genotyping was performed in 266 black South Africans with autoantibody-positive RA and 362 ethnically and geographically matched controls. The alleles were converted to specific amino acid residues at polymorphic sites for downstream analyses. Logistic regression models were used to test whether variability at site, specific amino acid residues, and haplotypes (constructed from positions 11, 71, and 74) were associated with RA.

RESULTS

Of the 29 amino acid positions examined, positions 11, 13, and 33 (permutation p = 3.4^e-26, 1.2^e-27, and 2.1^e-28, respectively) showed the strongest association with RA. Univariate analyses of individual amino acid residues showed valine at position 11 (OR 5.1, 95% CI 3.7-7.0) and histidine at position 13 (OR 6.1, 95% CI 4.2-8.6) conferred the highest risk. The valine containing haplotypes of position 11, 71, 74, V_K_A conferred the most risk (OR 4.52, 95% CI 2.68-7.61) and conversely the haplotype with serine at this position, S_K_R, conferred the most protection (OR 0.83, 95% CI 0.61-1.15).

CONCLUSION

Autoantibody-positive RA in black South Africans is associated with histidine at position 13 and valine at position 11 of HLA-DRB1, and haplotypes with valine at position 11 conferred the highest risk; conversely, serine at position 11 conveyed protection.

Pharmacological responses of thiamine-deficient rat tissues

Rats were rendered deficient in thiamine by feeding a synthetic diet free of the vitamin. Responses of the isolated heart to acetylcholine, adrenaline, noradrenaline and isoprenaline, and of the phrenic nerve-diaphragm preparation to tubocurarine, gallamine and eserine, were compared with responses of tissues obtained from littermate rats pair-fed an identical diet with the addition of 25 mug of thiamine hydrochloride per day. In thiamine-deficient tissues eserine failed to produce sustained potentiation of the twitch response of the phrenic nerve-diaphragm preparation to single supramaximal nerve stimuli. The perfused thiamine-deficient heart was more sensitive to acetylcholine, adrenaline, noradrenaline and isoprenaline, which produced greater negative or lesser positive chronotropic and inotropic effects. There was no significant difference in the response of the phrenic nerve-diaphragm preparation to tubocurarine and gallamine, or to eserine with faradic stimulation.

HOMOCYSTINURIA: ABSENCE OF CYSTATHIONINE IN THE BRAIN

Cystathionine was absent in the cerebrum of a patient with homocystinuria. This supports the theory that the enzymatic defect in homocystinuria is deficiency of cystathionine synthetase.

RELATIONSHIP OF PNH3 OF TUBULAR CELLS TO RENAL PRODUCTION OF AMMONIA

Renal excretion of ammonia, addition of ammonia to renal venous blood, and total renal production of ammonia were measured in acidotic dogs before and during the intravenous infusion of ammonium chloride at rates of 0.5 and 1.0 mmole/min. Infusion of ammonium chloride increased urinary excretion of ammonia, reversed the direction of diffusion of ammonia between tubular cells and blood, i.e., induced the extraction of ammonia from blood, and reduced cellular production of ammonia. Production of ammonia was an inverse function of pNH3 of tubular cells. The infusion of ammonium lactate-N15 into one renal artery increased total ammonia excretion but decreased production of ammonia-N14 from normal blood-borne precursors. The intravenous infusion of ammonium chloride reduced extraction of glutamine from renal blood, yet increased the concentration of free glutamine in renal cortical cells. Our data suggest that an increase in pNH3 of tubular cells results in competitive inhibition of the glutaminase-1 reaction. We further suggest that the pNH3 of tubular cells is one factor governing renal production of ammonia; i e., the higher the cellular pNH3, the lower is the renal production of ammonia.

BIOSYNTHESIS OF SERINE IN ESCHERICHIA COLI AND SALMONELLA TYPHIMURIUM

Umbarger, H. E. (Long Island Biological Association, Cold Spring Harbor, N.Y.), Merle A. Umbarger, and Patrick M. L. Siu. Biosynthesis of serine in Escherichia coli and Salmonella typhimurium. J. Bacteriol. 85:1431-1439. 1963.-Evidence for the operation in extracts of Escherichia coli of a pathway from glucose to serine involving 3-phosphoglycerate, phosphohydroxypyruvate, and phosphoserine as intermediates was obtained by the technique of isotopic competition. The steps of the pathway were demonstrated in extracts of E. coli and Salmonella typhimurium. The first reaction was studied in the reverse of the biosynthetic direction by observing the disappearance of reduced nicotinamide adenine dinucleotide in the presence of phosphohydroxypyruvate. The enzyme catalyzing this reaction was missing in two E. coli mutants that required serine or glycine for growth and in a representative of one of two genetically distinct classes of S. typhimurium serine-glycine auxotrophs. The second reaction, the amination of phosphohydroxypyruvate, was also studied in the reverse of the biosynthetic direction using alpha-ketoglutarate as the amino acceptor in a transamination reaction with phosphoserine. The final step, the cleavage of phosphoserine, could not be catalyzed by extracts prepared from cells of S. typhimurium serine-glycine auxotrophs of the second genetic class. It has been concluded that these three reactions provide the only significant pathway to serine in these organisms.

AEROBIC DEGRADATION OF CHOLINE. I. FERMENTATION OF CHOLINE BY A MARINE BACTERIUM, ACHROMOBACTER CHOLINOPHAGUM N. SP

A marine bacterium, isolated by an enrichment technique, is able to utilize choline as the sole carbon and nitrogen source in a medium containing various salts. The morphological and biochemical characteristics of the organism indicate that it is a new species. Substrate feeding coupled with culture filtrate analyses indicate that choline is metabolized as follows: choline → betaine → dimethylglycine + formaldehyde → sarcosine + formaldehyde → serine → pyruvate + ammonia without transmethylation being involved. This pathway has not previously been reported for other bacteria or for animal tissues.

THE PERIODATE OXIDATION OF AMINO ACIDS WITH REFERENCE TO STUDIES ON GLYCOPROTEINS

1. All alpha-amino acids are oxidized by periodate, but at different rates. 2. The rates of oxidation of individual alpha-amino acids vary with pH. In general, oxidation proceeds more rapidly at alkaline pH. 3. Serine, threonine, cysteine, cystine, methionine, proline, hydroxyproline, tryptophan, tyrosine and histidine are rapidly and extensively oxidized by periodate. 4. Cysteine, cystine, methionine, tryptophan, tyrosine and histidine are oxidized by periodate when they are substituted in the carboxyl and amino groups, as in a polypeptide chain.

ACID INACTIVATION OF AND INCORPORATION OF PHOSPHATE INTO ALKALINE PHOSPHATASE FROM ESCHERICHIA COLI

1. Alkaline phosphatase of Escherichia coli undergoes below pH 6.0 a reversible acid inactivation that has been studied and related to the extent of uptake of inorganic phosphate occurring below pH 6.0. 2. The rate of inactivation is rapid in the first few minutes but later it decreases markedly. Temperature, pH, composition of buffer and other factors have an important effect on the inactivation. 3. About 60% of the activity lost at pH values above 3.5 is rapidly recovered when the enzyme is taken back to pH 8.0, independently (within certain limits) of the extent of the inactivation. 4. Phosphate and Zn(2+), although very good protectors of the inactivation by acid, are not by themselves able to reverse the acid inactivation. 5. Inorganic phosphate seems not to be incorporated into the acid-inactivated enzyme. 6. Incorporation of more than one mole of phosphate/mole of enzyme has been obtained, but the phosphate residues seem to be incorporated to serine residues with a common sequence, suggesting two identical active serine residues/molecule of active enzyme.

AMINO ACID COMPOSITION AND C-TERMINAL RESIDUES OF ALGAL BILIPROTEINS

1. R-phycoerythrin from Ceramium rubrum and C-phycocyanin from Nostoc muscorum have been obtained in purified form by fractional crystallization, followed by chromatography and gel-filtration. 2. The amino acid composition of both chromoproteins was determined; 85% of the total weight of both was recovered as amino acids. 3. Alanine was identified as the only C-terminal amino acid of R-phycoerythrin, each molecule of which contained about 12 terminal groups. 4. Serine was identified as the only C-terminal group of C-phycocyanin.

METABOLIC ACTIVITY IN COXIELLA BURNETII

Ormsbee, Richard A. (Rocky Mountain Laboratory, Hamilton, Mont.), and Marius G. Peacock. Metabolic activity in Coxiella burnetii. J. Bacteriol. 88:1205-1210. 1964.-Purified suspensions of Coxiella burnetii were shown to utilize alpha-ketoglutarate, succinate, fumarate, malate, oxaloacetate, pyruvate, glutamate, and serine. The addition of nicotinamide adenine dinucleotide(+) was necessary to elicit the maximal rate of oxygen uptake with l-glutamate as substrate, but was unnecessary when other substrates were employed. It was concluded that the Krebs cycle of intermediary carbohydrate metabolism probably operates within C. burnetii, and that pyruvate is the chief energy source.

SUCCINIC ESTER AND AMIDE OF HOMOSERINE: SOME SPONTANEOUS AND ENZYMATIC REACTIONS

O-Succinylhomoserine and N-succinylhomoserine have been synthesized. The first is rapidly transformed into the second by alkali. In acid, the second undergoes ring closure to the lactone, rather than the reverse acyl transfer. Neither supports the growth of methionine auxotrophs of Neurospora or Salmonella. However, bacterial extracts rapidly catalyze formation of a compound, chromatographically identical with cystathionine, from cysteine and O-succinylhomoserine. In the absence of cysteine the O-succinylhomoserine is converted to alpha-ketobutyrate. Both these reactions are absent from the same Salmonella mutant, and therefore are probably catalyzed by a single enzyme which is needed for methionine synthesis. Both reactions require pyridoxal phosphate. N-succinylhomoserine does not undergo either reaction.

THE SYNTHESIS OF PHOSVITIN IN VITRO BY SLICES OF LIVER FROM THE LAYING HEN

1. Slices of liver from laying hens incorporated Na(2) (14)CO(3) and NaH(2) (32)PO(4) into phosvitin. Slices of liver from immature birds did not do so to any appreciable extent. The (32)P was incorporated into O-phosphorylserine in the phosvitin molecule. 2. Kidney, spleen, muscle, large and small intestine, ovary and oviduct from laying birds did not incorporate Na(2) (14)CO(3) into phosvitin. 3. Slices of liver from laying hens carried out a net synthesis of phosphoprotein under the standard conditions of incubation. Slices from the livers of immature pullets did not do so. 4. Liver from the laying hen incorporated [2-(14)C]glycine, [3-(14)C]serine and [2-(14)C]glutamic acid into phosvitin. Part of the glycine was shown to be present as serine in the final product. 5. Slices of liver from immature birds treated with oestradiol synthesized phosvitin from [2-(14)C]glycine, but the addition of oestrogens in vitro to slices from untreated immature birds did not promote synthesis during a 3 hr. incubation period.

THE IMPORTANCE OF GLYOXYLATE IN AMINO ACID BIOSYNTHESIS IN PLANTS

1. [(14)C(2)]Glyoxylate was rapidly metabolized by carrot storage tissues, pea leaves, pea cotyledons, sunflower cotyledons, corn coleoptiles, corn roots and pea roots. In many tissues over 70% of the supplied [(14)C(2)]glyoxylate was utilized during the 6hr. experimental periods. 2. In all tissues, the chief products of [(14)C(2)]-glyoxylate metabolism were carbon dioxide, glycine and serine. In several of the tissues, there was also a considerable incorporation of the label into the organic acids, particularly into glycollate. 3. Degradations of the labelled serine produced during [(14)C(2)]glyoxylate metabolism showed that glyoxylate carbon was incorporated into all three positions of the serine molecule. 4. The results are interpreted as indicating that glyoxylate is utilized by the tissues by pathways involving transamination, transmethylation, reduction and oxidative decarboxylation of the supplied glyoxylate.