Abstract: Objective To investigate the effect of let-7a on proliferation of HCCLM3 cells under hypoxia by regulating autophagy in vitro. Methods The HCCLM3 cells from human hepatocellular carcinoma were divided into three groups,e.g. the normoxia group:5×10⁶/mL HCCLM3 cells in 10% fetal bovine DMEM medium were cultured in 37 ℃,5% CO₂,20% O₂,hypoxia group:in 37 ℃,5% CO₂,2% O₂,93%N₂ and hypoxia let-7a group:in 37 ℃,5% CO₂,2% O₂,93%N₂. Six parallel samples were prepared in each group and cultured for 72 h. After incubation,the autophagy of HCCLM3 cells was detected by acridine orange staining,the activity of HCCLM3 cells was detected by MTT,the HCCLM3 cell cycle analysis G1 was detected by flow cytometry,and the let-7a,cyc D1 and vascular endothelial growth factor （VEGF） levels in supernatant were determined by ELISA. Results The cell survival rate in oxygen let -7 group was（49.7±9.5） %,significantly lower than in normal oxygen or hypoxia group [（100.0±0.0） % or （119.1±13.1） %,P<0.05],the cell survival rate in hypoxia group was significantly higher than that in the normal oxygen group （P<0.05）;the cell cycle G1 phase and the rate of autophagy in oxygen let -7a group were （89.6±16.1） % and （49.3±7.4） %,significantly higher than those in normal oxygen or hypoxia group [（56.3±11.0）% and（13.2±8.1）% or（69.7±14.1）% and（23.5±5.5）%（P<0.05）;the let-7a level in the supernatant in the oxygen let -7a group was（96.1±9.3） μmol/L,much higher than in the normal oxygen or hypoxia group [（33.4±7.1）μmol/L or （65.3±5.2）μmol/L,P<0.05],cyc D1 and VEGF levels were（72.3±8.8）μmol/L and（56.3±6.3）μmol/L,much lower than in the normal oxygen or hypoxia group [（124.1±7.2）μmol/L and（114.1±5.2） μmol/L or （98.2±6.7） μmol/L and （85.2±8.1）μmol/L,P<0.05]. Conclusion The upregulation of let-7a expression in hepatocellular carcinoma HCCLM3 cells in vitro can induce cell autophagy,make the transformation disorder of the cells in G1 phase to S phase,inhibit the proliferation of cells in hypoxia,and the mechanism might be the decreased CYC D1 and VEGF expression.

Key words: Hepatocellular carcinoma, HCCLM3 cells, Let-7a, Autophagy, Hypoxia.