vitamin-b-12 and Leukemia--Promyelocytic--Acute

HL60 cells were cultured for 10 days under various experimental conditions. They were then incubated with 1 mumol/l [5-3H] uridine for 2 hours and their DNA extracted. The DNA was hydrolysed to deoxyribonucleosides with phosphodiesterase and alkaline phosphatase and the hydrolysate subjected to Aminex A6 chromatography. The elution profiles showed that, when compared with control cells, DNA from cells grown in medium deficient in folate, B12 or both folate and B12 contained increased amounts of deoxyuridine (dU) and increased radioactivity in the dU peak. The data demonstrate that misincorporation of uracil into DNA occurs in a myeloid cell line cultured in growth medium deficient in folate, B12 or both folate and B12.

Topics: Chromatography, Ion Exchange; DNA, Neoplasm; Folic Acid; Humans; Leukemia, Promyelocytic, Acute; Methotrexate; Tritium; Tumor Cells, Cultured; Uracil; Vitamin B 12

Binding and uptake of transcobalamin II-bound cobalamin by HL-60 promyelocytic leukemia cells proceed through receptor-mediated endocytosis. The affinity constant of the receptor for transcobalamin II-cobalamin was found to be 6.1 liter/nmol and the maximal rate of uptake 12 pmol/10(9) cells/h. This uptake is mediated by about 3000 receptor sites per cell. Evidence is presented that the receptor recirculates from the cell surface to the lysosomes and vice versa. Upon differentiation induction of the cells by either DMSO in granulocytic direction or by 1,25-dihydroxy-vitamin D3 in monocytic direction a rapid decline in cellular uptake and cell surface binding of the protein-bound vitamin ensues. In particular the internalization of the complex decreases faster than all other observed signs of the ongoing differentiation process, such as reduction in the OKT9-reactive transferrin receptor, increase in lineage-specific surface markers, and decrease in [3H]thymidine incorporation and actual cell proliferation. The transcobalamin II receptor on the cell surface appears to be a proliferation-associated membrane component in human leukemic cells.

Topics: Calcitriol; Cell Line; Cell Transformation, Neoplastic; Cycloheximide; Dimethyl Sulfoxide; Endocytosis; Humans; Leukemia, Promyelocytic, Acute; Monensin; Receptors, Cell Surface; Transcobalamins; Tumor Cells, Cultured; Vitamin B 12