Transforming growth factor-beta(1) induces apoptosis in rat FaO hepatoma cells via cytochrome c release and oligomerization of Apaf-1 to form a similar to 700-kd apoptosome caspase-processing complex

In mammalian cells, non receptor-mediated apoptosis occurs via the cytochro me c-dependent assembly of a similar to 700-kd apoptotic protease-activatin g factor 1 (Apaf-1)/ caspase-9 containing apoptosome complex. This initiate s the postmitochondrial-mediated effector capase cascade. We now show that receptor mediated transforming growth factor beta(1) (TGF-beta(1))-induced apoptosis in rat hepatoma cells is accompanied by processing and activation of caspases-2, -3, -7, and -8. Furthermore, we show that caspase activatio n is mediated via the release of cytochrome c and the oligomerization of Ap af-1 into an similar to 700-kd apoptosome complex. Similarly, in vitro acti vation of hepatoma cell lysates with 2'-deoxyadenosine 5'-triphosphate (dAT P) results in the formation of the similar to 700-kd apoptosome complex, wh ich recruits and processes caspases-3 and -7. Z-VAD.FMK [benzyloxycarbonyl- Val-Ala-Asp (OMe) fluoromethylketone], the pan-caspase inhibitor totally in hibits dATP-stimulated caspase activation but does not block the assembly o f the large Apaf-1 containing apoptosome complex. However, the recruitment and subsequent processing of caspases-3 and -7 to the apoptosome is blocked , Similarly, in intact cells, although Z-VAD.FMK blocked TGF-beta(1)-induce d apoptosis, it did not prevent the oligomerization of Apaf-1 into the apop tosome. However, recruitment and processing of caspases-3 and -7 were preve nted by Z-VAD.FMK. These data show that TGF-beta(1) induces apoptosis via r elease of cytochrome c and activation of the Apaf-1 apoptosome complex, whi ch initiates the caspase cascade.