The 2-chlorodeoxyadenosine-induced cell death signalling pathway in human thymocytes is different from that induced by 2-chloroadenosine.

2-chloroadenosine induced DNA fragmentation and cell death in human thymocytes primarily by Ca(2+)-dependent mechanisms. Incubation of human thymocytes with 2-chlorodeoxyadenosine (5-1000 nM) also induced cell death (apoptosis) which was dependent on macromolecule synthesis and involved activation of an endonuclease which was inhibited by Zn2+. The effect of 2-chlorodeoxyadenosine was prevented by addition of dipyridamole, a strong nucleoside transport inhibitor, or of deoxycytidine, previously shown to compete for uptake by deoxycytidine kinase. 2-Chlorodeoxyadenosine-induced apoptosis did not involve increases in the cytosolic Ca2+ concentration, but required the presence of intracellular Ca2+. It was not inhibited by activators of protein kinase C previously shown to inhibit Ca(2+)-dependent cell death. Addition of 2-chlorodeoxyadenosine induced an increase in the amount of p53 in human thymocytes, while 2-chloroadenosine had no effect. These data suggest that 2-chloroadenosine and 2-chlorodeoxyadenosine induce cell death in human thymocytes via different signalling pathways.