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Expression of short‐form caspase 8 correlates with decreased sensitivity to Fas‐mediated apoptosis in neuroblastoma cells

Disruption of apoptotic death signal transduction pathways may be responsible for tumor formation, progression and resistance to treatment in neuroblastoma. Caspase 8, one of the initiator caspases, plays an important role in the Fas‐Fas ligand pathway. This caspase signals through the formation of a death‐inducing signaling complex in response to Fas activation by its ligand. In this study, we evaluated the sensitivity of a series of human neuroblastoma cell lines to membrane‐bound Fas ligand induced‐cell death, as well as the expression of Fas, caspase 3 and caspase 8. Sensitivity to Fas‐mediated cell death did not correlate with the expression of Fas in neuroblastoma cells, but was directly associated with the pattern of caspase 8 protein expression. We found that the majority of neuroblastoma cell lines we evaluated lacked caspase 8 expression, and these cell lines were invariably resistant to Fas‐mediated cell death. In contrast, cell lines expressing normal caspase 8 protein were quite sensitive to Fas‐mediated cell death. More interestingly, a group of cell lines expressing a distinct short form of caspase 8 with splicing out of exon 3 consistently showed moderate sensitivity to Fas‐mediated cell death. These results indicate that the profile of caspase 8 expression is an important determinant of the response of neuroblastoma cells to Fas‐mediated cell death.