Increased expression of BIRC5 in non-small cell lung cancer and esophageal squamous cell carcinoma does not correlate with the expression of its inhibitors SMAC/DIABLO and PML

Abstract

Survivin (BIRC5) belongs to the family of inhibitors of apoptosis proteins (IAPs). BIRC5 is expressed in embryonic tissues and in most malignant tumors but not in fully differentiated adult tissues. BIRC5, acting as an apoptosis inhibitor, presumably plays an important part in carcinogenesis, thus providing an attractive target for antitumor therapy. The mechanisms regulating the survivin level are insufficiently understood, but a significant role is ascribed to natural survivin inhibitors, SMAC and PML. The transcription levels of BIRC5, SMAC, and PML and the levels of their protein products were assessed by RT-PCR and immunoblotting in normal and tumor human tissues in non-small cell lung cancer and esophageal squamous cell carcinoma. BIRC5 transcription was observed only in tumor tissues, whereas SMAC and PML were expressed in tumor and normal tissues at similar levels. The protein levels corresponded to the mRNA levels. Thus, increased levels of survivin in tumor tissues are not a consequence of downregulation of its inhibitors SMAC and PML, whose levels do not differ between tumor and normal cells.