Inosine 5'-monophosphate vs inosine and hypoxanthine as substrates for purine salvage in human lymphoid cells.
The ability of inosine 5'-monophosphate vs inosine or hypoxanthine to supply the total purine requirements of mitogen-stimulated human T cells or rapidly dividing human B lymphoblastoid cells was evaluated. Mitogen-stimulated human peripheral blood T cells were treated with aminopterin to inhibit purine synthesis de novo and make the cells dependent upon an exogenous purine source. Thymidine was added as a source of pyrimidines. Under these conditions, 25 microM inosine 5'-monophosphate, inosine, and hypoxanthine showed comparable abilities to support [3H]thymidine incorporation into DNA at rates equal to that of untreated control cultures. In parallel experiments with the rapidly dividing human B lymphoblastoid cell line, WI-L2, treatment with aminopterin (plus thymidine) inhibited the growth rate by greater than 95%. The normal growth rate was restored by the addition of 30 microM inosine 5'-monophosphate, inosine, or hypoxanthine to the medium. However, in similar experiments with cell line No. 1254, a derivative of WI-L2 which lacks detectable ecto-5'-nucleotidase activity, only inosine and hypoxanthine (plus thymidine), but not inosine 5'-monophosphate (and thymidine) were able to restore the growth inhibition due to aminopterin. These results show that the catalytic activity of ecto-5'-nucleotidase is sufficient to meet the total purine requirements of mitogen-stimulated human T cells or rapidly dividing human B lymphoblastoid cells and suggest that this enzyme may have functional significance when rates of purine synthesis de novo are limited and/or an extracellular source of purine nucleotides is available.
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D015720:5'-Nucleotidase; D000630:Aminopterin / Q000494:pharmacology; D002455:Cell Division; D002460:Cell Line; D002478:Cells, Cultured; D006801:Humans; D019271:Hypoxanthine; D007042:Hypoxanthines / Q000378:metabolism*; D007288:Inosine / Q000378:metabolism*; D007291:Inosine Monophosphate / Q000378:metabolism*; D007292:Inosine Nucleotides / Q000378:metabolism*; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000378:metabolism*; D009708:Nucleotidases / Q000378:metabolism*; D011687:Purines / Q000378:metabolism*
D007042:Hypoxanthines; D007292:Inosine Nucleotides; D011687:Purines; D007291:Inosine Monophosphate; D019271:Hypoxanthine; D007288:Inosine; D009708:Nucleotidases; D015720:5'-Nucleotidase; D000630:Aminopterin