The role of death receptor in tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis in medullary thyroid cancer TT cell line

Objective To study the role of death receptors death receptor 4 (DR4) and DR5 in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in medullary thyroid cancer TT cell line.Methods The growth inhibition of TT cells was measured by methyl thiazol tetrazolium(MTT) assay.Annexin V/PI double staining was used to analyze the apoptosis rate of TT cells by flow cytometry.The mRNA expression of DR4 and DR5 was detected by using semiquantitative real-time quantitative polymerase chain reaction (Real-time PCR).The protein expression of DR4,DR5 and Caspase-8 was detected by using Western blotting.Results (1) The growth inhibition ratio of TT cells induced by TRAIL at the concentration of 1 000 μg/L and 2 000 μg/L was (7.51 ± 1.57) ％ and (12.76 ± 3.23) ％ respectively,suggesting a significant resistance of TT cells to TRAIL; (2) The apoptosis rate of combination group after treatment for 48 h was (21.92 ± 1.35) ％,which was significantly higher than TRAIL [(4.32 ±0.83)％] and celecoxib [(14.29 ± 2.15)％] treatment alone (P ＜0.01) ; (3) The expression of DR5 was low in control group and TRAIL group,but there was no significant difference between the two groups (P ＞ 0.05).The co-administration of TRAIL and celecoxib and administration of celecoxib alone could up-regulate the transcripts and translation of DR5 (P ＞ 0.05),but not DR4.The cleavage of Caspase-8 could be augmented by the combined treatment of TRAIL and celecoxib.Conclusion The low expression of DR5 was involved in the resistance of TT cells to TRAIL,which could be reversed by celecoxib through the up-regulation of DR5 and cleavage of Caspase-8. Key words: Death receptor;  Tumor necrosis factor-related apoptosis-inducing ligand;  Celecoxib;  Medullary thyroid cancer