Study of the mechanism underlying the inhibitory effects of transglutaminase II on apoptosis in the osteosarcoma MG-63 cell line under hypoxic conditions

The aim of the present study was to investigate the association between the apoptosis phenomenon in the MG-63 osteosarcoma cell line, and transglutaminase II (TG2) expression. The relationship between the anti-apoptotic mechanism of TG2 and the expression of cytochrome c as well as caspase-3 under hypoxic conditions was also verified. A hypoxic culture of MG-63 cells was prepared. The hypoxia and TG2 siRNA hypoxia groups were established, and the cultures were incubated for 12 h under hypoxic conditions. TG2 activity, TG2 protein expression and its mRNA level were investigated. Cytochrome c and caspase-3 protein levels in the TG2 nucleus and cytoplasm were measured. The apoptotic rate was also monitored. The results showed that TG2 activity, TG2 protein expression and its mRNA level in the hypoxia group were significantly higher than those of the siRNA hypoxia group. The results showed statistically insignificant differences (P<0.05). By contrast, a comparison of the two groups in the cytoplasm yielded no statistically significant differences (P>0.05). Cytochrome c and caspase-3 protein levels in the hypoxia group were significantly higher than those of the TG2 siRNA hypoxia group. The results showed statistically significant differences (P<0.05). By contrast, the protein levels in the cytoplasm were significantly lower than those of the TG2 siRNA hypoxia group, with differences being statistically significant (P<0.05). The differences in apoptotic rates between the hypoxia and TG2 siRNA hypoxia groups were also statistically significant (P<0.05). Under hypoxic conditions, a high TG2 expression inhibited the apoptosis of the MG-63 osteosarcoma cell line. This effect was probably associated with its suppressive activity on the transportation of cytochrome c and caspase-3 from nucleus to cytoplasm.