Caspase-9 and Apaf-1 are expressed and functionally active in human neuroblastoma tumor cell lines with 1p36 LOH and amplified MYCN.
Important roles have been suggested for caspase-8, caspase-9 and Apaf-1 in controlling tumor development and their sensitivity to chemotherapeutic agents. Methylation and deletion of Apaf-1 and CASP8 results in the loss of their expression in melanoma and neuroblastoma, respectively, while CASP9 localization to 1p36.1 suggests it is a good candidate tumor suppressor. The status of CASP9 and Apaf-1 expression in numerous neuroblastoma cell lines with/without amplified MYCN and chromosome 1p36 loss-of-heterozygosity (LOH) was therefore examined to test the hypothesis that one or both of these genes are tumor suppressors in neuroblastoma. Although CASP9 is included in the region encompassing 1p36 LOH in all neuroblastoma cell lines examined, the remaining CASP9 allele(s) express a functional caspase-9 enzyme. Apaf-1 is also expressed in all neuroblastoma tumor cell lines examined. Thus, the CASP9 or Apaf-1 genes do not appear to function as tumor suppressors in MYCN amplified neuroblastomas. However, approximately 20% of the neuroblastoma cell lines with methylated CASP8 alleles are also highly resistant to staurosporine (STS)- and radiation-induced cell death, presumably because cytochrome c is not released from mitochondria. This suggests that a second, smaller sub-group of MYCN amplified neuroblastoma tumors exists with defect(s) in apoptotic signaling components upstream of caspase-9 and Apaf-1. Since no consistent differences in Bcl-2, Bcl-x(L) or Bax expression were seen in the STS- and radiation-resistant neuroblastomas, it suggests that a unique mitochondrial signaling factor(s) is responsible for the defect in cytochrome c release in this sub-group of tumors.
Teitz
Tal
T
Department of Tumor Cell Biology, St. Jude Children's Research Hospital, Memphis, Tennessee, TN 38105, USA.
Wei
Tie
T
Liu
Dong
D
Valentine
Virginia
V
Valentine
Marcus
M
Grenet
Jose
J
Lahti
Jill M
JM
Kidd
Vincent J
VJ
D017209:Apoptosis / Q000235:genetics*; D053477:Apoptotic Protease-Activating Factor 1; D053453:Caspase 9; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D002872:Chromosome Deletion; D002878:Chromosomes, Human, Pair 1 / Q000235:genetics*; D003574:Cytochrome c Group / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005784:Gene Amplification; D016259:Genes, myc / Q000235:genetics*; D006801:Humans; D015151:Immunoblotting; D017404:In Situ Hybridization, Fluorescence; D019656:Loss of Heterozygosity; D018895:Microsatellite Repeats; D009447:Neuroblastoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019311:Staurosporine / Q000494:pharmacology; D014158:Transcription, Genetic; D014161:Transduction, Genetic; D014407:Tumor Cells, Cultured / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D051020:bcl-X Protein
C506592:APAF1 protein, human; D053477:Apoptotic Protease-Activating Factor 1; C494811:BCL2L1 protein, human; D003574:Cytochrome c Group; D017931:DNA Primers; D004791:Enzyme Inhibitors; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D051020:bcl-X Protein; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases; D019311:Staurosporine