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

Recently, loss of heterozygosity (LOH) studies suggest that more than two t umor suppressor genes lie on the short arm of chromosome 1 (Ip) in neurobla stoma (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-k Da subunit of the DNA fragmentation factor (DFF45) gene was homozygously de leted in an NE cell line, NB-I, DFF45 is the chaperon of DFF90, and both mo lecules 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 fo r expression and mutation of DFF45 gene by reverse transcription (RT)-polym erase chain reaction (PCR) and RT-PCR-single-strand conformation polymorphi sm. 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 di srupting the balance between DFF45 and DFF40, No mutations of the DFF45 gen e 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 t he NB-I cell line may imply the presence of unknown tumor suppressor genes in this region.