P21对胃癌细胞MGC-803的增殖抑制及对POLD1基因表达的调控

Effect of Smilax china L.-containing serum on the expression of POLD1 mRNA in human hepatocarcinoma SMMC-7721 cells

Bock greenbrier rhizome, also known as Smilax china L. rhizome, induces heat clearing and detoxification and dispels wind dampness. Additionally, this Chinese medicine has been shown to function as an anticancer compound in various types of cancer. The aim of the present study was to investigate the mechanism by which Smilax china L.-containing serum suppresses SMMC-7721 human hepatocellular carcinoma (HCC) cell growth as well as to determine its effect on the expression of DNA polymerase δ catalytic subunit gene 1 (POLD1). SMMC-7721 human HCC cells were cultured with serum containing various amounts of Smilax china L. for 24 h. The cells were also cultured in blank serum or serum containing a drug used in Western medicine (cyclophosphamide; CTX) as a positive control. HCC cell growth and proliferation were determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cell cycle distribution and apoptosis were analyzed by flow cytometry, and the expression of POLD1 mRNA was detected by quantitative polymerase chain reaction (PCR). The number of cells following culture with Smilax china L.-containing serum was observed to be decreased. There was significant growth inhibition in the Smilax china L.-treated cells (shown in the high concentration serum group, volume fraction 30%), which was significantly different from the inhibition observed in the control group (P<0.05). Among the various cell cycle phases following culture, the percentage of cells in the S phase was significantly increased, and the percentage of cells in the G0/G1 phase was decreased; these percentages were significantly different from the percentages of the control cells (P<0.05). The results obtained following quantitative PCR showed a significant reduction in POLD1 expression. Smilax china L.-containing serum directly suppressed cell growth and induced the apoptosis of human HCC cells. However, the number of cells in the S phase was reduced. This mechanism is suggested to be associated with the suppression of POLD1 expression.

Transfection of a eukaryotic vector expressing a mutant CDK4 up-regulates POLD1 expression in SMMC-7702 cells

AIM: To construct a eukaryotic expression vector encoding a mutant CDK4 protein and to investigate the effect of transfection of this vector on POLD1 expression in SMMC-7702 cells.

METHODS: The mutant CDK4 gene was amplified by RT-PCR from total RNA isolated from the human hepatocarcinoma cell line SMMC-7721, digested, and inserted into the eukaryotic expression vector pEGFP-C1. The resultant recombinant plasmid was confirmed by sequencing. After the recombinant plasmid was transfected into SMMC-7702 cells using Lipofectamine 2000, the expression of fusion protein was observed by fluorescence microscopy, and expression of CDK4 and POLD1 mRNAs was detected by real-time PCR.

RESULTS: The eukaryotic expression plasmid GFP-CDK4 was successfully constructed. The mutant CDK4 gene contained 5 base mutation sites, 4 base insertions and 2 deletions, which caused 7 amino acids to change. Compared to non-tranfected cells or cells transfected with the pEGFP-C1 vector, cell proliferation was significantly higher in cells transfected with the recombinant vector (0.826 ± 0.08 vs 0.596 ± 0.06, 0.609 ± 0.10, F = 7.033, P < 0.05). The expression levels of CDK4 and POLD1 genes in cells transfected with the recombinant vector was significantly higher than those in the two control groups (1.94 ± 0 .11 vs 1.01 ± 0.00, 1.05 ± 0.12, F = 54.046, P < 0.01; 0.54 ± 0.04 vs 0.30 ± 0.07, 0.25 ± 0.06, F = 11.788, P < 0.05). Similar results were also obtained for the protein expression levels of CDK4 (0.65 ± 0.03 vs 0.41 ± 0.03, 0.39 ± 0.05, F = 14.665, P < 0.05) and P125 (0.54 ± 0.04 vs 0.30 ± 0.07, 0.25 ± 0.06, F = 11.788, P < 0.05).

CONCLUSION: Tranfection of the eukaryotic expression plasmid GFP-CDK4 significantly increases the proliferation and invasion of SMMC-7702 cells possibly by up-regulating POLD1 expression.