concanavalin-a and 5--methylthioadenosine

5'-Deoxy-5'-methylthioadenosine, a by-product of polyamine metabolism, is a potent inhibitor of cell proliferation. MTA phosphorylase cleaves MTA into adenine and 5'-methylthioribose-1-P. We studied MTA inhibition and salvage into purine compounds and methionine in concanavalin A-stimulated rat T lymphocytes and in Raji cells. When de novo purine synthesis was inhibited by azaserine (20 microM), low concentrations of MTA, (less than or equal to 20 microM), were able to completely restore cell proliferation in both types of cells. When cells were cultured in a methionine-free medium, MTA (15 microM) completely fulfilled the methionine requirement of Raji cells but only 50% of that of rat T lymphocytes. MTA displayed a dose-dependent inhibition of the proliferation of both types of cells, but in the case of MTA salvage into purines or methionine, the curves were shifted to higher MTA concentrations. In vitro studies by Backlund et al. (Backlund, P.S., Chang, C.P. and Smith, R.A. (1982) J. Biol. Chem. 257, 4196-4202) on rat liver homogenates, suggested that the last step of MTA salvage into methionine may be the transamination of 2-keto-4-methylthiobutyrate to methionine. We present evidence that this is a step physiologically efficient in intact cells.

Topics: Adenosine; Azaserine; Cell Cycle; Cell Line; Concanavalin A; Deoxyadenosines; Humans; Lymphocytes; Methionine; Purine-Nucleoside Phosphorylase; Purines; Thionucleosides

5'-Deoxy-5'-methylthioadenosine inhibits Concanavalin A induced rat T lymphocyte proliferation in a dose dependent manner (50 microM to 1000 microM). The extent of inhibition by MTA of lymphocyte proliferation was greatest when MTA was added to the cells at the same time as Concanavalin A. The determination of cyclic AMP level from 30 min to the 6th hour shows that 5'-Deoxy-5'-methylthioadenosine inhibition is correlated with an elevation of cyclic AMP at this mitogen recognition phase. 5'-Deoxy-5'-methylthioadenosine concentrations that inhibit rat T lymphocyte proliferation also inhibit phosphodiesterase activity. This biochemical mechanism could be specific to 5'-Deoxy-5'-methylthioadenosine inhibition since in an another model of inhibition of rat T lymphocyte proliferation (2'-Deoxyadenosine 10 microM, in adenosine deaminase deficiency conditions: 2'-Deoxycoformycin 10 microM), no significant modification of cyclic AMP level can be demonstrated.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Adenosine; Animals; Cell Division; Concanavalin A; Cyclic AMP; Deoxyadenosines; Dose-Response Relationship, Drug; In Vitro Techniques; Phosphodiesterase Inhibitors; Rats; T-Lymphocytes; Thionucleosides