Abstract: Objective:To study the effects of speci fic inhibi tion to proteasome inhibi tor REG γ gene expres-sion by small interfering RNAs (siRNA) on the apoptosis of human medullary thyroid carcinoma TT cell line. Methods:An eukaryotic expression vector carrying human pREG γ-shRNA and a negative control plasmid pNeg-shRNA were constructed. The vector carrying pREG γ-shRNA or the negative control plasmid was trans-fected respectively into human medullary thyroid carcinoma TT cells by Lipofectamine 2000. REG γ expres-sion in TT cel ls transfected wi th pREG γ-shRNA and TT cel ls transfected wi th pNeg-shRNA was detected by RT- PCR and Western blot. TUNEL was employed to detect the apoptosis rate and Western blot was used to detect caspase-3 expression in TT cel ls transfected wi th pREG γ-shRNA and TT cel ls transfected wi th pNeg-shRNA.Results: The expression of REG γ mRNA and REG γ protein in TT cel ls transfected wi th pREG γ-shRNA was lower than that in TT cel ls transfected wi th pNeg-shRNA (P<0.05). The apoptosis rate was high -er in TT cel ls transfected wi th pREG γ-shRNA than in those transfected wi th pNeg-shRNA (P<0.05). Conclusion:siRNA targeting REG γ mRNA can speci fical ly suppress REG γ gene expression and can signi ficantly pro-mote apoptosis of TT cel ls, suggesting that REG can prevent apoptosis and is helpful for developing new methods of cancer biotherapy.