ECTOCELLULAR CD38-CATALYZED SYNTHESIS AND INTRACELLULAR CA2-SIGNALINGACTIVITY OF CYCLIC ADP-RIBOSE IN T-LYMPHOCYTES ARE NOT FUNCTIONALLY RELATED()

Cyclic ADP-ribose (cADPR) is a natural metabolite of beta-NAD(+) with a potent Ca2+-mobilizing activity in different cell types, including T -lymphocytes. We investigated (i) whether stimulation of T-lymphocytes with different agonists affects the intracellular concentration of cA DPR, and (ii) whether the lymphocyte antigen CD38, through its ectocel lular ADP-ribosyl cyclase and cADPR-hydrolase enzymatic activities, ca n account for the regulation of the intracellular levels of cADPR and the Ca2+-mobilizing effects of this nucleotide in Jurkat and HPB.ALL T -lymphocytes. The anti-CD3 antibody OKT3, the sphingolipid sphingosine and lysophosphatidic acid induced an increase in intracellular cADPR with concomitant increases in the intracellular Ca2+ concentration ([C a2+](i)). In contrast, activation of an ectocellular ADP-ribosyl cycla se by preincubation of cells with beta-NAD(+) led to a dose-dependent increase in cADPR, but no changes in [Ca2+](i) were observed. However, extensive washing of the cells following preincubation with NAD(+) de monstrated that the increases in cADPR were not intracellular but due to cell surface-associated nucleotide. Accordingly, measurements of AD P-ribosyl cyclase activity in intact T-cells showed ectocellular synth esis of cADPR, but no evidence was obtained for a shift of this activi ty into the cells which could account for intracellular accumulation o f cADPR, Taken together, the results indicate no direct involvement of the ADP-ribosyl cyclase activity of CD38 on the regulation of the cAD PR-mediated intracellular Ca2+-signalling in T-lymphocytes. (C) 1998 F ederation of European Biochemical Societies.