DNA Fragmentation Factor 45 (DFF45) gene at 1p36.2 is homozygously deleted and encodes variant transcripts in neuroblastoma cell line

Recently, loss of heterozygosity (LOH) studies suggest that more than two tumor suppressor genes lie on the short arm of chromosome 1 (Ip) in neuroblastoma (NB). To identify candidate tumor suppressor genes in NE, we searched for homozygous deletions in 20 NE cell lines using a high-density STS map spanning chromosome 1p36, a common LOH region in NE. We found that the 45-kDa subunit of the DNA fragmentation factor (DFF45) gene was homozygously deleted in an NE cell line, NB-I, DFF45 is the chaperon of DFF90, and both molecules are necessary for caspase 3 to induce apoptosis, DFF35, a splicing variant of DFF45, is an inhibitor of DFF40. We examined 20 NE cell lines for expression and mutation of DFF45 gene by reverse transcription (RT)-polymerase chain reaction (PCR) and RT-PCR-single-strand conformation polymorphism. Some novel variant transcripts of the DFF45 gene were found in NE cell lines, but not in normal adrenal gland and peripheral blood. These variants may not serve as chaperons of DFF40, but as inhibitors like DFF35, thus disrupting the balance between DFF45 and DFF40, No mutations of the DFF45 gene were found in any NE cell line, suggesting that the DFF45 is not a tumor suppressor gene for NE. However? homozygous deletion of the DFF45 gene in the NB-I cell line may imply the presence of unknown tumor suppressor genes in this region.