RECOMBINANT PML ADENOVIRUS SUPPRESSES GROWTH AND TUMORIGENICITY OF HUMAN BREAST-CANCER CELLS BY INDUCING G1 CELL-CYCLE ARREST AND APOPTOSIS

Our previous studies demonstrated that the promyelocytic leukemia gene , PML which involved in the 15;17 translocation in acute promyelocytic leukemia (APL) is a growth and transformation suppressor. In this stu dy, recombinant PML adenovirus, Ad-PML was constructed and used to inf ect human breast cancer cells in vitro and in vivo, the anti-oncogenic function of PML and its mechanism of growth suppressing effect in bre ast cancer cells were examined. We showed that Ad-PML effectively infe cted the MCF-7 and SK-BR-3 cells. A high level of PML protein was expr essed within 24 h post-infection and a detectable level remained at da y 16. Ad-PML significantly suppressed the growth rate, clonogenicity, and tumorigenicity of breast cancer cells. Intratumoral injections of MCF-7-induced tumors by high titer Ad-PML suppressed tumor growth in n ude mice by about 80%. The injection sites expressed high level of PML and associated with a massive apoptotic cell death. To elucidate the molecular mechanism of PML's growth suppressing function, we examined the effect of Ad-PML on cell cycle distribution in MCF-7 and SK-BR-3 c ells. We found that Ad-PML infection caused a cell cycle arrest at the G1 phase, We further showed that G1 arrest of MCF-7 cells is associat ed with a significant decrease in cyclin DI and CDK2. An increased exp ression of p53, p21 and cyclin E was found. The Rb protein became pred ominantly hypophosphorylated 48 h post-infection. These findings indic ate that PML exerts its growth suppressing effects by modulating sever al key G1 regulatory proteins. Our study provides important insight in to the mechanism of tumor suppressing function of PML and suggests a p otential application of Ad-PML in human cancer gene therapy.