Inhibitor of apoptosis protein-1 promotes tumor cell survival in mesothelioma

Malignant pleural mesothelioma (MPM) is a highly lethal pleural neoplasm that is often resistant to chemotherapeutic drugs, including cisplatin, and for which little is known regarding carcinogenic pathways. We used differential display to compare gene expression patterns in mesothelioma, normal pleura and normal lung, in order to better understand MPM pathobiology, and to search for genes that may facilitate drug resistance in this cancer. The human inhibitor of apoptosis protein-1 gene (IAP-1/MIHC/cIAP2) was discovered to be highly expressed in MPM. We confirmed overexpression of IAP-1 mRNA and protein in 39 additional human MPM tumor specimens and 3/5 (60%) MPM cell lines by multiple methods, including real time quantitative reverse transcription-PCR and western blot analysis. Using an antisense targeting approach, we found that attenuation of IAP-1 mRNA levels decreases baseline cell viability and increases the sensitivity of MPM cell lines to cisplatin by nearly 20-fold. Reduced IAP-1 gene expression also results in a concordant increase of the pro-apoptotic cleavage product of caspase 9 and a reduction in the number of viable tumor cells. Our observations strongly suggest that IAP-1 is at least partly responsible for promoting carcinogenesis and mediating resistance to cisplatin in many MPM tumors and that further study of this apoptotic pathway is warranted.