The modulating effect of proapoptotic protein Bax on the resistance of malignant lymphoma cells to tumor necrosis factor related apoptosis inducing ligand-induced apoptosis

Objective To elucidate the modulating effect of proapoptotic protein Bax on the resistance of malignant lymphoma cells to tumor necrotic factor-related apoptosis inducing ligand (TRAIL)- induced apoptosis and offer evidence for clinic work.Methods Human malignant lymphoma cells of the line CRL and normal HRC cells were cultured and treated by 500μg/L TRAIL( Group T),treated by 10 nmol/L PS-341(Group P),or pre-treated by 10 nmol/L proteasome inhibitor PS-341 for 1 hour and then treated by 500 μg/L TRAIL( Group P + T).Flow cytometry was used to detect the cell apoptosis.Western blotting was used to detect the expression of Bax protein.Caspase-8 activity was tested by fluorophotometer. Immunoprecipitation method was used to examine the conformation change of Bax protein.Results The apoptosis index 24 hours after treatment of the CRL cells of Group T was 21%,significantly lower than that of the HRC cells of Group T (32%,P0.01 ).The Bax protein expression amount 24 hours after treatment of the HRC cells of Group T was 1.8 times that of the normal cells,and the Bax protein expression amount 24 hours after treatment of the CRL cells of Group T was only 5/17 that of the normal amount.The apoptotic index 6 hours after treatment of the CRL cells of Group P + T was 54%,significantly higher than those of Groups T and P(both P0.01 ).The caspace-8 activity 6 hours after treatment of the CRL cells of Group P + T was 26.5μmol·L~(-1)·h~(-1)·mg~(-1) protein,similar to that of the HRC cells of Group P + T (27.2 μmol·L~(-1)·h~(-1)·mg~(-1)protein),and significantly higher than those of the other cells (all P0.01 ). The Bax protein expression 6 hours after treatment of the Group P HRC and CRL cells were 2.5 times and 1.2 times that of the control cells.The Bax protein expression of the HRC cells of Group P + T was 3.3 times that of the normal controls,and the Bax degradation of the CRL cells of Group P + T was significantly reduced.The combination treatment of P + T significantly increased the expression of activated Bax.Conclusion Bax degradation plays an important role in the resistance of malignant lymphoma to TRAIL-induced apoptosis.Using proteasome inhibitor can inhibit the protein degradation and overcome the drug resistance.