Aggressive childhood neuroblastomas do not express caspase-8: an importantcomponent of programmed cell death

Neuroblastomas that overexpress N-Myc due to amplification of the MYCN onco gene are aggressive tumors that become very resistant to treatment by chemo therapy and irradiation. to identify tumor suppressor genes in this group o f neuroblastomas we analyzed the expression and function of both apoptosis- related cell cycle regulatory genes in cell lines and patient tumor samples . We found that in a high percentage of neuroblastoma cell lines and patien t samples with amplified MYCN, caspase-8 mRNA is not expressed. The caspase -8 gene, CASP8, was deleted or silenced by methylation in the neuroblastoma cell lines while methylation of its promoter region was the predominant me chanism for its inactivation in the patient tumor samples. Reintroduction o f caspase-8 into the neuroblastoma cell lines resensitized these cells to d rug-induced and survival factor dependent apoptosis. Subsequently others ha ve also shown that caspase-8 is silenced by methylation in neuroblastoma an d peripheral neural ectodermal tumors, and that the caspase-9 regulator Apa f-1 is silenced by methylation in melanoma cell lines and patient samples. We conclude that caspase-8 acts as a tumor suppressor gene in neuroblastoma s, that its silencing provides a permissive environment for MYCN gene ampli fication once the tumors are treated with chemotherapeutic drugs/irradiatio n, and that expression of this gene in these tumor cells may be of clinical benefit. We also discuss the possible significance of the neural crest cel l progenitor cell origin and the silencing, of important apoptotic regulato rs via methylation in both neuroblastoma and melanoma tumors.