Objective       To investigate the bystander effect of herpes simplex virus thymidine kinase (HSV-TK) transfected by ultrasound microbubbles and ganciclovir (GCV) in SMMC-7721 hepatoma cells after the treatment of all-trans retinoic acid (ATRA).      Methods       MTT assay was used to test the proper concentration of ATRA or GCV in treatment of SMMC-7721 cells. Immunohistochemistry was used to survey the expression of Cx32 protein in SMMC-7721 cells after ATRA treatment. Fluorescence microscopy and RT-PCR were used

to detect the expression of TK in SMMC-7721 cells transfected with pIRES2-EGFP-TK with ultrasound microbubbles under ultrasound wave irradiation

and MTT assay was used to survey the changed bystander effect of SMMC-7721 on HSV-TK/GCV after ATRA treatment.       Results       The proper concentrations of ATRA and GCV were 10

-6

mol/L and 40 μg/ml respectively in the treatment of SMMC-7721 cells. After the cells exposure to 10

-6

mol/L ATRA

Cx32 protein was in high expression on the cell membrane but in low expression in the cytoplasm. HSV-TK was transfected into SMMC-7721 cells by ultrasound wave irradiation and expressed stably. ATRA treatment enhanced the bystander effect of HSV-TK/GCV on SMMC-7721 cells compared with the cells without ATRA treatment (P0.05).       Conclusion       ATRA can improve the expression of Cx32 protein and lead Cx32 protein to cell membrane

which might be involved in ATRA enhancing the bystander effect of HSV-TK/GCV on SMMC-7721 cells.