gms | German Medical Science

Aims: The molecular mechanisms responsible for the strong resistance of renal cell carcinomas towards anticancer drug-induced apoptosis are not well understood. Since most apoptotic stimuli – extrinsic or intrinsic - converge at the mitochondria, we investigated the mitochondrial pathway of apoptosis in 4 renal carcinoma cell lines.

Methods and results: 1. RCC cell lines showed heterogeneity towards TRAIL-induced apoptosis as determined by cell counting and PARP-cleavage: two cell lines were TRAIL-sensitive and two were TRAIL-resistant. 2. Western Blot analysis revealed that sensitivity to TRAIL-induced apoptosis correlated with cleavage of initiator-caspase-8 3. Subcellular fractioning by the Digitonin method and Western Blot analysis showed that TRAIL or chemotherapeutic agents (Etoposide and Betulinic acid) targeting the mitochondrial pathway of apoptosis did not induce cytochrome C release and caspase-9 cleavage in any RCC cell line. 4. In contrast, the BCL-2 antagonist HA14-1 was able to induce cytochrome C release, caspase-9 cleavage and apoptosis with PARP-cleavage in all RCC cell lines. 5. Furthermore, in TRAIL-sensitive cell lines HA14-1-pretreatment in sublethal doses resulted in a synergistic activation of the mitochondrial pathway as measured by caspase-9- and PARP-cleavage as well as cell counting. 6. In TRAIL-resistant cell lines, however, no activation of the mitochondrial pathway could be achieved by HA14-1 pretreatment.

Conclusions: Our results demonstrate, that antiapoptotic members of the BCL-2 family are - at least in part - responsible for the apoptosis resistance of renal cell carcinomas. Thus, activation of the mitochondrial apoptosis-pathway can be achieved by inhibition of BCL-2 resulting in a synergistic enhancement of TRAIL-induced apoptosis.