[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 500 g/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 microg/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%, P < 0.01). 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 P < 0.01). The caspase-8 activity 6 hours after treatment of the CRL cells of Group P + T was 26.5 micromol.L(-1).h(-1).mg(-1) protein, similar to that of the HRC cells of Group P + T (27.2 micromol.L(-1).h(-1).mg(-1) protein), and significantly higher than those of the other cells (all P < 0.01). 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.