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The effect of folate analogues and vitamin B12 on provision of thymine nucleotides for DNA synthesis in megaloblastic anemia 总被引:2,自引:0,他引:2
The role of vitamin B12 in the folate dependent biosynthesis of thymidine nucleotides is controversial. In an attempt to clarify this, three methods have been used to assess the relative efficacy of vitamin B12 (hydroxocobalamin) and various folate analogues in titrated concentrations at correcting 'de novo' thymidylate synthesis by megaloblastic human marrow cells: (1) The deoxyuridine (dU) suppression test which analyses the reduction in (3H)-thymidine labeling of DNA by unlabeled dU. Marrow cells were also labeled with (6-3H)-dU with assessment of (2) its incorporation into DNA and (3) the accumulation of (6-3H)-deoxyuridine monophosphate (3H-dUMP). The three methods gave similar results. In both, N6-formyl tetrahydrofolate (formyl-FH4) was the most effective agent at correcting thymidylate synthesis in megaloblastic anemia due to vitamin B12 or folate deficiency. Vitamin B12 corrected the lesion in vitamin B12 deficiency but not in folate deficiency. Tetrahydrofolate (FH4) and folic acid were effective in deficiency of vitamin B12 or folate, although in both deficiencies they were less effective than formyl-FH4. Methyl-FH4 was effective in folate deficiency but not in vitamin B12 deficiency. These results confirm the failure of methyl-FH4 utilisation in vitamin B12 deficiency. They suggest that if vitamin B12 is needed in the formylation of FH4, this is a minor role in provision of the correct coenzyme for thymidylate synthesis compared with its major role of provision of FH4 from methyl- FH4. 相似文献
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Role of ADP-ribosyl transferase in differentiation of human granulocyte- macrophage progenitors to the macrophage lineage 总被引:6,自引:0,他引:6
Nuclear adenosine diphosphate-ribosyl (ADP-ribosyl) transferase is a chromatin-bound enzyme catalyzing the transfer of ADP-ribose from NAD+ to chromatin proteins. The physiologic function of this covalent modification of chromatin has not been fully established, but roles in both DNA repair and in differentiation have been proposed. We demonstrate that three specific inhibitors of ADP-ribosyl transferase (5-methylnicotinamide, 3-methoxybenzamide, 3-aminobenzamide) inhibit differentiation of human granulocyte-macrophage progenitor cells to the macrophage lineage. Differentiation to the neutrophil-granulocyte lineage is much less affected. The inhibition of macrophage differentiation seems to relate to the ability of these compounds to inhibit ADP-ribosyl transferase. A structural analogue (3- methoxybenzoic acid), which is not inhibitory for the enzyme, did not inhibit macrophage differentiation. Additional evidence for a role of ADP-ribosyl transferase in the differentiation of granulocyte- macrophage progenitors was obtained from experiments in which enzyme activity levels were measured in permeabilized marrow cells. Marrow cell ADP-ribosyl transferase activity increased after 3-hr stimulation by the differentiation/proliferation stimulus--granulocyte-macrophage colony-stimulating activity (GM-CSA). Unstimulated marrow cells showed low or undetectable levels of enzyme activity. 相似文献
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Estrogen-induced microsatellite DNA alterations are associated with Syrian hamster kidney tumorigenesis 总被引:4,自引:0,他引:4
Exposure to estrogens is associated with an increase in cancers, including
malignancies of the breast and uterus in humans, and of the kidney in
hamsters. DNA damage induced by metabolic activation of estrogen has been
postulated to result in gene mutations critical for the development of
estrogen-induced kidney tumors in hamsters. As part of our examination of
the genetic consequences of estrogen-induced DNA damage, we searched for
estrogen-induced alterations in microsatellite DNA, a frequent site of
mutation in tumors. Genomic DNA isolated from kidney of hamsters treated
with estradiol, from estrogen-induced kidney tumors and from untreated
age-matched controls, was examined by Southern blot analysis with three
multi-locus oligonucleotide probes: (GACA)4, (CAC)6 and (CAG)6. Alterations
in DNA fragments containing GACA and CAC tandem repeats were detected in
kidney DNA of hamsters treated with hormone for 3 and 4 months, whereas no
such effects were seen in control animals. In estrogen-induced tumors,
microsatellite alterations were observed in fragments that contain these
same two repeat sequences and also CAG repeat sequences. The induction of
microsatellite alterations by estradiol in kidney DNA preceding
estrogen-induced renal malignancy may play a role in hormone-induced
tumorigenesis.
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