Figure 5

Protein degradation was a mechanism for decreased MICA/B protein expression during UPR activation. (A) Increased expression level of MICA/B mRNA in SMMC7721 cells after the treatment with TM for 24 h and 36 h. Bars represented the relative quantities of MICA/B mRNA in SMMC7721 cells (mean and S.D.). *P < 0.05. (B) The proteasome inhibitor MG132 reversed the downregulation of MICA in hepatoma cells during UPR. SMMC7721 cells with or without pretreatment with the proteasome inhibitor MG132 (10 mM) for 1 h were treated with TM (3 mM) for 24 h. Total protein from whole-cell lysates was then subjected to western blot analysis for MICA/B and GAPDH (as a loading control). The data shown are representative of three individual experiments. (C) UPR accelerated the turnover rate of MICA/B in hepatoma cells. SMMC7721 cells were treated with the protein synthesis inhibitor cycloheximide (CHX; 10 mg/ml) with or without the addition of TM (3 mM) for the indicated periods. Total protein from whole-cell lysates was then subjected to western blot analysis for MICA/B and GAPDH (as a loading control). The data shown are representative of three individual experiments.