BACKGROUND: The second mitochondria-derived activator of caspase/direct inhibitor of apoptosis-binding protein with low pI (Smac/DIABLO) was recently identified as a protein that is released from mitochondria in response to apoptotic stimuli and promotes apoptosis by antagonizing inhibitor of apoptosis proteins. Furthermore, Smac/DIABLO plays an important regulatory role in the sensitization of cancer cells to both immune- and drug-induced apoptosis. However, little is known about the clinical significance of Smac/DIABLO in various cancers including hepatocellular carcinoma (HCC). This study was undertaken to investigate the expression of Smac and Survivin and their relationship with the apoptosis in primary HCC.
METHODS: The expression of Smac and Survivin proteins was evaluated by immunohistochemistry. The mRNA expression of Smac and Survivin was evaluated by reverse transcription-polymerase chain reaction (RT-PCR) in HCC tissues of 50 patients, para-carcinoma tissues of 20 patients, and normal liver tissues of 15 patients.
RESULTS: Smac mRNA was detected by RT-PCR in HCC tissues of 21 (42.0%) of the 50 patients, para-carcinoma tissues of 19 (95.0%) of the 20 patients, and normal liver tissues of 15 (100%) of the 15 patients. Survivin mRNA was found in HCC tissues of 46 of the 50 patients, para-carcinoma tissues of 2 of the 20 patients, and normal liver tissues of 0 of 15 patients. Immunohistochemistry revealed Smac protein in HCC tissues of 20 patients (40.0%), in para-carcinoma tissues of 18 patients (90.0%), and normal liver tissues of 15 patients (100.0%). The expression of Smac was significantly different in HCC tissues and non-HCC tissues. Survivin protein was found in HCC tissues in 45 patients, para-carcinoma tissues in 2 patients, and  normal liver tissues in none of the patients. The expression of Survivin was significantly different in HCC tissues and non-HCC tissues.
CONCLUSION: Smac inhibits apoptosis of HCC cells by suppression of Survivin, and the two genes probably form an important link in the signal pathway of HCC cells.