Objective To describe the changes in cell cycle distribution during malignant transformation of human bronchial epithelial cells (16HBE) induced by cadmium chloride treatment,and to assess the relationshiP between methylation and expression of CyclinD1.
Methods Flow cytometry was used to detect the cell cycle distribution of normal 16HBE cells (control),cadmium chloride treated 16HBE cells at 5th,15th,and 35th passages,and tumorigenic cells from a nude mice model stimulated with the 35th passage 16HBE.Real-time fluorescent quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) and Western blot were used to measure the expression levels of CyclinD1 mRNA and protein in the above cells and the tumorigenic cells treated with 5-aza-2-deoxycytidine.
Results As cell passages increased,the proportions of the cadmium transformed cells and the tumorigenic cells increased in the G0/G1 phase (60.04% and 64.12% respectively),and decreased in the S (35.03% and 31.83% respectively) and G2/M phases (4.93% and 4.01% respectively),compared with the control cells (P < 0.05).The expression levels of CyclinD1 mRNA and protein also demonstrated increasing trends with the CdCl2-treated cell passages increased,and were significantly increased in the 35th passage-transformed cells (2.34-and 2.41-fold respectively) and the tumorigenic cells (2.33-and 2.35-fold respectively) compared with the controls (P < 0.05).However,the expression levels of CyclinD1 mRNA and protein of 5-Aza-2-deoxycytidine treated tumorigenic cells were decreased to 1.815-and 1.742-fold respectively of the 16HBE cells before the 5-Aza-2-deoxycytidine treatment.
Conclusion The variations in cell cycle distribution of 16HBE cells induced by cadmium may be associated with DNA methylation.
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