A human IAP-family gene, apollon, expressed in human brain cancer cells.

IAP is a family of protein that has baculovirus IAP repeat (BIR) domains and inhibits apoptosis. We found a human IAP family gene, which we named Apollon, encoding a huge protein (530 kDa) that contains a single BIR domain and a ubiquitin-conjugating enzyme domain, that is a human homolog of BRUCE. Apollon protein was expressed in four of six brain cancers (gliomas), and one of five ovarian cancers in 38 human cancer cell lines that we examined. Among the brain cancer cell lines, SNB-78 expressed a high level of Apollon, and this cell line shows resistance against various anticancer drugs. Treating SNB-78 cells with antisense oligonucleotide against Apollon reduced the expression of Apollon protein, and significantly sensitized the cells to apoptosis induced by cisplatin and camptothecin. These results suggest that Apollon protects SNB-78 cells from undergoing apoptosis and, at least in part, plays a role in tumorigenesis and drug resistance of this cell line.