We next investigated whether the decrease in growth rate, and particularly the acid stress sensitivity, of the AP-3 and PAN complex knockout cells resulted from increased apoptosis, as has been found for HL-60 human promyelocytic leukaemia cells under conditions of acid stress (Park et al., 1996), which occurs via Bax-mediated caspase activation and PARP cleavage (Park et al., 1999). Here, BAX is linked to acute promyelocytic leukemia.