During the differentiation and maturation of theymocytes, autoreactive cells are known to be deleted in thymus, but the mechanism of cell death has not been elucidated. To elucidate the mechanisms involved in mouse thymocyte apoptosis induced by
phorbol
myristate acetate(PMA0 and clacium ionophore A23187, thymocytes were treated with stimulators or stimulators plus inhibitors of protein and RNA synthesis for various times in accordance with the purpose of this research. DNA fragmentation was
analyzed
by flow cytometry(FCM) and by agarose gel electrophoresis.
Stimulation of thymocyte with PMA or A23187 for 12 hrs resulted in 50-75% fragmentation of DNA into 180-200 bp multiples, PMA-or A23187-induced DNA fragmentation was inhigited by inhibitors of RNA, protein synthesis or endonuclease. PMA-induced
DNA
fragmentation was blocked by PKC inhibitor, whereas A23187-induced DNA fragmentation was not. In adition, PMA directly inhibited A23187-induced DNA fragmentation in the isolated thymocyte nuclei. Therefore, it can be concluded that PKC and
calcium
may
play a pivotal role in the thymocyte apoptosis. The thymocytes which showed the hghest susceptibilities for in vitro exposures to PMA or A23187 belonged to the subpopulation of CD4+ CD8+ immature cells.
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