title: DNA demethylation in the PTEN gene promoter induced by 5-azacytidine activates PTEN expression in the MG-63 human osteosarcoma cell line.
abstract: This study used the MG-63 osteosarcoma cell line to investigate the demethylation of the phosphate and tension homolog (PTEN) gene promoter and the change in PTEN gene expression levels, which are caused by the methylation inhibitor 5-azacytidine (5-Zac), and the association between the two. Different concentrations of 5-Zac (0, 5 and 10 μmol/l) were added into the MG-63 cell culture medium and the cells were cultured for 72 h. The following techniques were performed on the cells: Western blot analysis to detect the PTEN protein; reverse transcription-polymerase chain reaction (PCR) to detect the mRNA transcription levels of the PTEN gene; flow cytometry to detect the cell apoptotic rate; and sodium bisulfate to deal with the DNA of each group. The genes of the PTEN promoter and the transcription factors specificity protein 1 (Sp1) and Myc were PCR amplified and transformed intoEscherichia coli, then a number of clones were selected for sequencing and the methylation status of the amplified PTEN promoter fragment was detected. Following culture of the MG-63 cells with 5-Zac at concentrations of 0, 5 and 10 μmol/l for 72 h, the expression levels of PTEN protein in each group were gradually increased, presenting a concentration-dependent effect: Group 0 μmol/l compared with groups 5 and 10 μmol/l, P<0.05; and group 5 μmol/l compared with group 10 μmol/l, P=0.007. The mRNA expression levels of thePTENgene significantly increased. The apoptotic rates of groups 0, 5 and 10 μmol/l were 0.69±0.42, 2.50±0.30 and 6.59±0.62%, and significant differences (P<0.01) were observed between every two groups. The bisulfate DNA sequencing results of three groups showed that, following the treatment with 5-Zac, the binding of the CG site to transcription factors was affected by demethylation. The average rate of demethylation indicated a statistical difference among the three groups. In conclusion, the methylation inhibitor 5-Zac leads to a significant increase in the expression levels of the tumor suppressor gene PTEN in the MG-63 osteosarcoma cell linein vitro. The expression levels of mRNA and the cellular apoptotic rate were also increased. The elevated activation and expression levels of the PTEN gene may be associated with the low methylation levels of the CG site that binds to the transcription factors Sp1 and Myc in the PTEN gene promoter, and they promote the combination of the transcription factors and the gene promoter.
authors.affiliation: Department of Orthopaedics, The Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, P.R. China.
authors.forename: Deye
authors.initials: D
authors.lastname: Song
authors.affiliation: Department of Orthopaedics, The Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, P.R. China.
authors.forename: Jiangdong
authors.initials: J
authors.lastname: Ni
authors.affiliation: Department of Orthopaedics, The Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, P.R. China.
authors.forename: Hongming
authors.initials: H
authors.lastname: Xie
authors.affiliation: Department of Orthopaedics, The Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, P.R. China.
authors.forename: Muliang
authors.initials: M
authors.lastname: Ding
authors.affiliation: Department of Orthopaedics, The Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, P.R. China.
authors.forename: Jun
authors.initials: J
authors.lastname: Wang
keywords: 5-azacytidine; DNA demethylation; MG-63 human osteosarcoma cell line; PTEN expression; PTEN gene