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Activation of Early Enzyme Production in Small Lymphocytes in Response to High, Nonmitogenic Concentrations of Concanavalin A
Jay L. Degen and David R. Morris
Proceedings of the National Academy of Sciences of the United States of America
Vol. 77, No. 6, [Part 2: Biological Sciences] (Jun., 1980), pp. 3479-3483
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/8913
Page Count: 5
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Lymphocyte mitogenesis is generally assessed by measuring the incorporation of [3H]thymidine into DNA. By this criterion, small lymphocytes, which are activated by relatively low doses of concanavalin A, are either unresponsive to or inhibited by higher concentrations. Because lymphocytes begin to synthesize DNA about 24 hr after addition of mitogen, the response is far removed temporally from the initial stimulus. We have chosen to use the induction of S-adenosylmethionine decarboxylase (S-adenosyl-L-methionine carboxy-lyase, EC 18.104.22.168) to assess early activation events in bovine lymphocytes. Adenosylmethionine decarboxylase induction is bimodal, with an initial phase beginning 3 hr after addition of concanavalin A and a second wave coinciding with the onset of DNA synthesis. The initial accumulation of the decarboxylase (0-9 hr) in cultures treated with ``nonmitogenic'' levels of concanavalin A (108 μ g/ml) was similar to that observed in cultures stimulated with optimally mitogenic doses (18 μ g/ml). The early induction of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 22.214.171.124) was also similar under these two culture conditions. However, the second phase of adenosylmethionine decarboxylase accumulation, the induction of thymidine kinase (ATP: thymidine 5′-phosphotransferase, EC 126.96.36.199), and DNA replication were blocked at the higher concentrations of concanavalin A. The inhibition of late events by high doses of concanavalin A was reversible. Cells treated with α -methyl-D-mannopyranoside 25 hr after addition of a high dose of lectin responded with a second period of adenosylmethionine decarboxylase accumulation, induction of thymidine kinase, and progression through S phase. These results suggest that initial lymphocyte activation occurs normally at high doses of concanavalin A, but that the cells are reversibly blocked prior to induction of ``late'' enzymes and progression through S phase.
Proceedings of the National Academy of Sciences of the United States of America © 1980 National Academy of Sciences