ECTO-5′-NUCLEOTIDASE (ECTO-5′-NT) CAN USE IMP TO PROVIDE THE TOTAL PURINE REQUIREMENTS OF MITOGEN-STIMULATED HUMAN T CELLS AND HUMAN B LYMPHOBLASTS: 209

Abstract

The ability of mitogen-stimulated human T cells or human B lymphoblasts to derive their total purine requirements from inosine 5'-monophosphate (IMP), inosine (HxR), or hypoxanthine (Hx) was compared. Con A-stimulated T cells were treated with aminopterin (Ampt) to inhibit purine synthesis de novo; thymidine (TdR) was added as a source of pyrimidines. Under these conditions, 30 μM IMP, HxR, and Hx showed comparable abilities to support ³H-TdR incorporation into DNA or ³H-leucine incorporation into protein at rates equal to those of untreated control cultures. Similar results were found when azaserine was used to inhibit purine synthesis de novo. In parallel experiments, Ampt inhibited the growth of WI-L2 B lymphoblasts by >95% and this growth inhibition could be overcome by 30 μM IMP, HxR, or Hx (plus TdR). However, with cell line #1254, a derivative of WI-L2 lacking detectable ecto-5'-NT activity, only HxR and Hx (plus TdR), but not IMP (plus TdR), were able to restore the growth inhibition due to Ampt. Thus, the catalytic activity of ecto-5'-NT is sufficient to meet the total purine requirements of mitogen-stimulated human T cells or rapidly-dividing human B lymphoblasts, suggesting that this enzyme could play a role in purine salvage when purine synthesis de novo is limited and/or an extracellular source of purine nucleotides is available. Such conditions might exist in developing thymus, spleen and bone marrow where massive cell death occurs.

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