Abstract: To investigate the influence of all-trans retinoic acid (ATRA) in proliferation,migration and invasion of human hepatocellular carcinoma SMMC-7721 cells and to clarity its molecular mechanism.Methods The SMMC-7721 cells in logarithmic phase were divided into blank control group and 10,20,and 40 μmol?L-1 ATRA groups.The  proliferation ability of SMMC-7721 cells was   examined by MTS／PMS assay,and the migration and invasion abilities of SMMC-7721 cells were detected by  Wound Healing assay and Transwell assay，and the expressions of  MMP-9  mRNA and protein in SMMC-7721 cells were determined by Real-time PCR and Western blotting methods.Results Compared with blank control group,the proliferation rates in 20 and 40 μmol?L-1 ATRA groups were decreased significantly（P<0.01）.Wound Healing assay discovered that the scuffing distance of SMMC-7721 cells exposed to 20 and 40 μmol?L-1 ATRA for 24 h was significantly increased compared with blank control group（P<0.05）.Transwell assay showed that the numbers of SMMC-7721 cells migrated through the matrigel in 10,20,and 40 μmol?L-1 ATRA groups  24 h after treatment were obviously decreased compared with blank control group (P<0.05)．The Real-time PCR and Western blotting results showed that the expressions of MMP-9 mRNA and protein in SMMC-7721 cells in  20 and 40 μmol?L-1 ATRA groups 24 h after treatment were significantly decreased compared with blank control group (P<0.01)．Conclusion ATRA may inhibit the proliferation,migration and invasion of  human hepatocellular carcinoma SMMC-7721 cells,which may be related to the down-regulation of MMP-9.

Key words: all-trans retinoic acid, liver neoplasms, cell proliferation, invasion