Objective To investigate the effects of aquaporin-8 (AQP-8) on the expression of multidrug resistance factors by overexpression of AQP-8 in human colon cancer HT-29 cells in vitro.Methods Human colon cancer HT-29 cells in logarithm growth period were used.AQP-8 eukaryotic expression vector was constructed and transfected into HT-29 cells.Western blotting was used to detect the transfection efficiency.Methyl thiazol tetrazolium (MTT) assay was used to measure the cell growth inhibition rate.Fluorescence real-time quantitative polymerase chain reaction (FQ-PCR) and Western blotting were used to determine the mRNA and protein expression of multidrug resistance factors:permeability glycoprotein (P-gp),glutathione S-transferase-π (GST-πr),and topoisomerase Ⅱ (Topo Ⅱ).Results Western blotting showed that the expression of AQP-8 was up-regulated in colon cancer HT-29 cells in GFP-AQP-8transfection group [(0.976 ± 0.086)] as compared with GFP-N1 control group [(0.140 ± 0.024),P ＜0.05].MTT revealed that as compared with GFP-N1 control group [(1.12 ± 0.17) ％],the proliferation inhibition rate was increased significantly in GFP-AQP-8 transfection group [(22.86 ± 3.75) ％ (P ＜0.05)].The apoptosis rate was increased significantly in GFP-AQP-8 transfection group [(14.08 ±2.37) ％] as compared with GFP-N 1 control group [(4.95 ± 0.58) ％,(P ＜ 0.05)].Fluorescence realtime quantitative RT-PCR demonstrated that the mRNA levels of P-gp,GST-π and Topo Ⅱ were lower in GFP-AQP-8 transfection group (0.44 ±0.05,0.34 ±0.03,and 0.38 ±0.05 respectively) than in GFP-N1 control group (0.99 ±0.12,1.02 ±0.12,0.96 ±0.14 respectively).The protein levels of P-gp and GST-π were significantly down-regulated by AQP-8 overexpression in GFP-AQP-8 transfection group (0.28 ± 0.04,0.37 ±0.05 respectively) as compared with GFP-N1 control group (0.83 ±0.08,0.75 ±0.10 respectively)(P ＜ 0.05).However,the protein expression of Topo Ⅱ had no significant change in GFP-AQP-8 transfection group (0.60 ± 0.08) and GFP-N1 control group (0.62 ± 0.07) (P ＞ 0.05).Conclusion Overexpression of AQP-8 inhibited growth of HT-29 cells probably by down-regulating the expression of P-gp,GST-π,and Topo Ⅱ.