Caspase-dependent cleavage of BAG3 in proteasome inhibitors-induced apoptosis in thyroid cancer cells

OBJECTIVE:To investigate the role of BAG3 in proteasome inhibitor-mediated apoptosis in thyroid cancer cells.METHODS:ARO(proteasome inhibitor-insensitive) and FRO(proteasome inhibitor-sensitive) cells were treated with vehicle,MG132,pancaspase inhibitor Z-VAD-FMK or combination of Z-VAD-FMK and MG132.BAG3 mRNA and protein levels were analyzed by using real-time PCR and Western blot,respectively.Apoptotic cells were analyzed by using flow cytometry(FCM).RESULTS:Compared with the blank group,BAG3 mRNA(s) in the other groups were time-dependently(ARO:F=198.67,P=0.000;FRO:F=174.43,P=0.000) and concentration-dependently(ARO:F=278.93,P=0.000;FRO:F=410.56,P=0.000) induced by MG132 with a similar extent in ARO and FRO cells.ARO cells demonstrated a significant increase in BAG3 proteins without marked apoptosis(P0.05).In FRO cells,accompanied with apoptosis,MG132 dose-dependently induced 40×103 cleavage product of BAG3.Cotreatment with MG132,Z-VAD-FMK completely prohibited the appearance of 40×103 cleavage product of BAG3,and the full length of BAG3 was increased.CONCLUSIONS:Proteasome inhibitor MG132 induces the expression of BAG3 in ARO and FRO cells.In proteasome inhibitor sensitive thyroid cancer cells,accompanied with apoptosis,BAG3 is cleaved in a Caspase-dependent manner.