Vitamin B12-dependent replication of L1210 mouse leukemia cells. A model system for cobalamin-folate inter-relationships.
L1210 mouse leukemia cells were made cobalamin-deficient by propagation in a medium from which cyanocobalamin was omitted and fetal bovine serum (containing protein-bound cobalamins) was replaced by bovine serum albumin. These cobalamin-deficient cells exhibited a normal replication time of 12 h, provided that the medium contained excess folate or 5-formyltetrahydrofolate. The cells responded poorly, however, to 5-methyltetrahydrofolate unless exogenous cobalamin was added. A cobalamin dependency was also observed when low levels of folate or 5-formyltetrahydrofolate were used. With 5-methyltetrahydrofolate, optimal stimulation of growth was observed with free and transcobalamin-II-bound cobalamin at 4,000 pM and 2 pM, respectively. Under cobalamin-replete conditions, cells contained 2,000 to 4,000 molecules of cobalamin/cell, and in the deficient state, this value declined to less than 10 molecules/cell; optimal replication on 5-methyltetrahydrofolate required approximately 180 molecules/cell. Cobalamin-deficient cells cultured in the absence of folate reached an arrested state from which limited replication could be induced by the addition of aquacobalamin; normal replication was induced by aquacobalamin plus 5-methyltetrahydrofolate. Results of this investigation are interpreted in terms of the requirement for tetrahydrofolate in cell replication and the production of this compound from folate and 5-formyltetrahydrofolate (via cobalamin-independent pathways) and from 5-methyltetrahydrofolate (via the cobalamin-dependent methionine synthetase).
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D005492:Folic Acid / Q000494:pharmacology*; D007700:Kinetics; D002955:Leucovorin / Q000494:pharmacology; D007939:Leukemia L1210 / Q000503:physiopathology*; D008715:Methionine / Q000378:metabolism; D051379:Mice; D013329:Structure-Activity Relationship; D014805:Vitamin B 12 / Q000494:pharmacology*
D005492:Folic Acid; D008715:Methionine; D014805:Vitamin B 12; D002955:Leucovorin