Recombinant PML adenovirus suppresses growth and tumorigenicity of human breast cancer cells by inducing G1 cell cycle arrest and apoptosis

Abstract

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 study, recombinant PML adenovirus, Ad-PML was constructed and used to infect human breast cancer cells in vitro and in vivo, the anti-oncogenic function of PML and its mechanism of growth suppressing e ect in breast cancer cells were examined. We showed that Ad-PML e ectively infected the MCF-7 and SK-BR-3 cells. A high level of PML protein was expressed within 24 h postinfection and a detectable level remained at day 16. Ad-PML signi®cantly 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 nude 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 e ect of Ad-PML on cell cycle distribution in MCF-7 and SK-BR-3 cells. 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 associated with a signi®cant decrease in cyclin D1 and CDK2. An increased expression of p53, p21 and cyclin E was found. The Rb protein became predominantly hypophosphorylated 48 h post-infection. These ®ndings indicate that PML exerts its growth suppressing e ects by modulating several key G1 regulatory proteins. Our study provides important insight into the mechanism of tumor suppressing function of PML and suggests a potential application of Ad-PML in human cancer gene therapy.

The promyelocytic leukemia (PML) protein suppresses cyclin D1 protein production by altering the nuclear cytoplasmic distribution of cyclin D1 mRNA

“…Blots were probed with the actin antibody to indicate the quantity of protein loaded into each lane. Consistent with these ®ndings, previous reports indicated that cyclin D1 protein levels were reduced by PML overexpression in breast cancer cells but provided no mechanism for this observation (Le et al, 1998). Our data indicate that this suppression is mediated at least in part through eIF-4E.…”

HER2 signaling modulates the equilibrium between pro- and antiangiogenic factors via distinct pathways: implications for HER2-targeted antibody therapy

“…All mice were maintained under specific pathogen-free conditions and given sterile food and water. A 17b-estradiol pellet (Innovative Research of America, Sarasota, FL, USA) was implanted as described previously (Le et al, 1998). Once the tumors became palpable (mean size of 0.2-0.3 mm 3 at day 12 after injection), mice were divided into two groups and treated i.p.…”

“…Tumor sizes and body weights were measured twice a week by the same observer. The tumor volume in mm 3 was calculated as described previously (Le et al, 1998). Experiments with nude mice were repeated three times with similar results.…”

Adenovirus-mediated N5 gene transfer inhibits tumor cell proliferation by induction of apoptosis

“…14 -17 For example, in contrast to AdN5, cells containing wt p53 are less sensitive to Adp53 than cells lacking wt p53. 18 Furthermore, Adp53 and AdPML infection induces G 1 cell cycle arrest and subsequent apoptosis, 15,19 whereas AdE2F-1 infection induces premature entry into S phase. 20 In contrast, AdN5 causes a G 2 /M cell cycle arrest followed by apoptosis (J. Doostzadeh-Cizeron, unpublished observations).…”