INVITRO MODELS FOR BIOCHEMICAL INVESTIGATIONS ON PROGRAMMED CELL-DEATH

Isolated rat thymocytes treated with methylprednisolone (MPS), cultured human synovial (McCoy's) cells exposed to cold shock and human mammary adenocarcinoma (BT-20) cells treated with Tumour Necrosis Factor (TNF), all showed DNA fragmentation and the morphological and biochemical features of cell death characteristic of a process known as apoptosis. DNA fragmentation in MPS-treated thymocytes and in cold shock-exposed McCoy's cells was preceded by a marked increase in cytosolic free Ca2+ concentration resulting either from a sustained influx of Ca2+ from the extracellular medium or from the release of Ca2+ from intracellular pools. On the other hand, in TNF-treated BT-20 cells, DNA fragmentation was not associated with any early, marked increase in the cytosolic free Ca2+ level. In all three models, however, DNA fragmentation was efficiently prevented by intracellular Ca2+ chelators, calmodulin inhibitors and activators of protein kinase C (PKC). These results suggest that the activation of common mechanisms involving Ca2+ and PKC may be essential for the development of apoptosis.