Caspase 6 activity initiates caspase 3 activation in cerebellar granule cell apoptosis

Using a well documented ex vivo system consisting of rodent cerebellar gran ule cells (CGCs) the activation of caspases 3 and 6 during apoptosis induce d by withdrawal of trophic support was analyzed, At the time of deprivation , the addition of the irreversible, broad-spectrum caspase inhibitor zVADfm k or the cell permeable, caspase 6 inhibitor CP-VEID-cho can transiently su ppress the appearance of apoptosis, including the early appearance of DNA f ragmentation. Using immunoblotting and fluorogenic peptide assays we observ e deprivation-induced activation of caspases 3 and 6, but not caspase 9, Fu rthermore, active caspase 6 is capable of processing and activating procasp ase 3 in cellular extracts prepared from non-apoptotic CGCs, whereas caspas e 3 failed to activate caspase 6, In consonant with this, the cell permeabl e caspase 6 inhibitor prevented deprivation induced caspase 3 activation wh ereas a cell permeable caspase 3 inhibitor, CP-DEVD-cho, had no effect on c aspase 6 activation. This would indicate that caspase 6 is a significant in ducer of the early caspase 3 activity in apoptotic CGCs.