Fig. 2: NOXA expression determines apoptosis sensitivity (caspase activation) to sorafenib/TRAIL in Huh7 cells and human HCC tissues.
A Expression of pro- (NOXA, PUMA, BIM, and BAX) and anti-apoptotic (MCL-1, BCL-XL) Bcl-2 proteins in the HCC cell lines Huh7 and Hep3B as detected by Western blotting. In contrast to Huh7 cells, NOXA expression was undetectable in Hep3B cells. B HCC tissues from different patients (n = 14) were treated for 8 h with sorafenib (7.5 µg/ml) and TRAIL (50 ng/ml; left panel). In contrast to apoptosis-resistant HCC tissues (n = 7), in apoptosis-sensitive tissues (n = 7) treatment with sorafenib and TRAIL resulted in caspase-3/-7 activation. HCC tissues from the same patients were treated for 8 h with sorafenib (right panel). Sorafenib induced a stronger upregulation of transcripts encoding the BH3-only protein NOXA (assessed by real-time PCR) in HCC tissues sensitive to sorafenib/TRAIL-induced apoptosis (n = 7), compared to HCC tissues resistant to this treatment combination (n = 7). C Effective siRNA-mediated NOXA downregulation in Huh7 cells as determined by Western blotting (left panel). Downregulation of NOXA by siRNA (12.5 nM) did not affect caspase activation in Huh-7 cells treated for 8 h with sorafenib or TRAIL alone. In contrast, caspase activation induced by the combination of sorafenib and TRAIL was significantly reduced in Huh7 cells with NOXA downregulation as compared to the respective control cells. The results of five independent experiments are shown. *p < 0.05.
