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Inhibitory effect of p15INK4B gene transfection on proliferation of human esophageal squamous cell carcinoma cell line EC109

AIM: To investigate the effect of p15^INK4B (p15) gene transfection on the proliferation of esophageal squamous cell carcinoma cell line EC109.

METHODS: The EC109 cells were divided into 3 groups: p15 transfection group, empty plasmid transfection group and non-transfection group. pCDNA3.1(+)-p15 and pCDNA3.1(+)-neo plasmid were transfected into EC109 cells using Lipofectamine2000. The expression of exogenous p15 gene and P15 protein were detected by polymerase chain reaction (PCR) and western blot, respectively. The proliferation and apoptosis of the EC109 cells were examined by MTT, colony formation assay, flow cytometry and transmission electron microscope.

RESULTS: After transfection, p15 gene cDNA was expressed in the cells of p15 transfection group, and P15 protein was expressed at a high level. The cell growth was inhibited, and the colony formation was significantly decreased in EC109-p15 cells as compared with that in the cells of empty plasmid transfection or non-transfection group (20.8±1.3% vs 54.3±3.2%, 56.8±2.3%, P<0.01). EC109-p15 cells arrested at G₁/S phase, and the population of the cells in G1 phase was significantly increased as compared with that in the cells of empty plasmid transfection group or Non-transfection group (62.45±7.08% vs 38.02±5.83%, 34.45±1.05%, P<0.01). However, the number of the cells in S phase was significantly decreased (21.12±1.31% vs 35.50±2.38%, 36.30±0.69%, P<0.01), and a Sub G₁ peak (apoptosis peak) appeared. Under electron microscope, typical features of apoptosis were observed in EC109-p15 cells.

CONCLUSION: p15 gene transfection can not only inhibit the proliferation of EC109 cells, but also induce the apoptosis of the cells in vitro.

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Mitochondrial DNA somatic mutations and germline variations in patients with esophageal cancer

AIM: To detect somatic mutations in the complete mitochondrial genome and to investigate the role of mtDNA in the tumorigenesis of esophageal cancer.

METHODS: A temporal temperature gradient gel electrophoresis (TTGE) method was used to analyze the somatic mitochondrial DNA (mtDNA) mutations in esophageal cancer. The entire mitochondrial genomes in 20 tumor samples and paired normal tissues were amplified by using 32 pairs of overlapping primers. DNA fragments showing different banding patterns between normal and tumor mtDNA were sequenced to identify the somatic mutations and germline variations.

RESULTS: Eleven out of the 20 tumors (55%) displayed at least one somatic mtDNA mutation. Total fourteen somatic mutations were found. Among them, one was in tRNA (7.1%), 4 in mRNA (28.5%), and 9 in the hypervariable D loop region (64.3%). There were two missense mutations in four novel somatic mutations. A total of 187 distinct germline variations were identified. Fourteen of these variations were novel, and 173 of them had been recorded in the Mitomap database.

CONCLUSION: The high incidence of mtDNA mutations presents in patients with esophageal cancer. mtDNA alterations may play an important role in tumorigenesis of esophageal cancer.