Matrix detachment induces caspase-dependent cytochrome c release from mitochondria: inhibition by PKB/Akt but not Raf signalling

Detachment of epithelial cells from extracellular matrix results in inducti on of apoptosis ('anoikis') which can be blocked by expression of activated Pas or PKB/Akt. Here we show that detachment causes release of cytochrome c from mitochondria in MDCK cells, This is blocked by caspase inhibitors, s uggesting a role for caspases upstream of mitochondria in the initiation of anoikis, in accord with the ability of dominant negative FADD to inhibit t his form of cell death, Bulk activation of caspase-8 following detachment l ags behind cytochrome c release, and is likely the result of a mitochondria l positive feed back loop. Matrix detachment also induces Bar translocation to mitochondria in a caspase-dependent manner. Expression of activated Ras or PKB/Akt blocks all the detectable events on the detachment-induced apop tosis signalling pathway, suggesting that PKB/Akt acts at an early point in the pathway, providing the signal normally generated by matrix attachment. Strong activation of Raf can also protect MDCK cells from detachment induc ed apoptosis, but this occurs at a point downstream of cytochrome c release from mitochondria, and is clearly distinct from the effect of PKB/Akt.