[5-aza-2'-deoxycytidine-induced inhibition of CDH13 expression and its inhibitory effect on methylation status in human colon cancer cells in vitro and on growth of xenograft in nude mice].

OBJECTIVE: To determine the inhibitory effect of 5-aza-2'-deoxycytidine (5-Aza-CdR) on the growth of human colon carcinoma cells and xenografts in nude mice, to observe its effect on CDH13 gene expression and methylation in the xenografts, and to explore the possible mechanisms. METHODS: Human colon carcinoma cell line HCT116 cells were treated with 5-Aza-CdR, and the cell morphology was observe by phase contrast microscopy. The cell growth was assessed by MTT assay. A tumor-bearing mouse model was generated by subcutaneous inoculation of human colon carcinoma HCT116 cells into nude mice. The tumor growth in the nude mice was observed, the CDH13 gene expression and its methylation status in the tumors were detected using methylation specific PCR (MSP), RT-PCR, Western blotting and immunohistochemistry. RESULTS: After treatment with 5-Aza-CdR, the inhibition rate of the growth of cultured HCT116 cells was increased as the concentration was increasing. The growth of the xenografts in nude mice was significantly inhibited, and the methylated CDH13 gene was reactivated. After 4 weeks of 5-Aza-CdR treatment, no significant difference was found between the body weights of nude mice in the 5-Aza-CdR group [(18.06 ± 1.29) g] and control group [(17.07 ± 0.84) g], (P > 0.10), and the average volume of xenografts of the 5-Aza-CdR group was (907.00 ± 87.29) mm(3), significantly smaller than the (1370.93 ± 130.20) mm(3) in the control group (P < 0.005). No expression of CDH13 gene was found in the control group. The expression of CDH13 gene in the 5-Aza-CdR group was increased along with the increasing concentration of 5-Aza-CdR. CONCLUSIONS: 5-Aza-CdR inhibits the growth of human colon cancer cells in culture and in nude mice, and induces the cancer cells to re-express CDH13 in nude mice. Its mechanism may be that demethylation of the methylated CDH13 promoter induced by 5-Aza-CdR restores CDH13 expression and thus inhibits the tumor growth in nude mice.

Correlation between T-cadherin gene expression and aberrant methylation of T-cadherin promoter in human colon carcinoma cells.

Previous researches showed T-cadherin (CDH13) expression was downregulated in colon cancer tissues and was associated with increase of invasive and metastatic potential. This research was to observe the mechanisms responsible for inactivation of T-cadherin gene in colon carcinoma; we investigated the methylation status around the 5' promoter region of T-cadherin gene of Hct116 colon cancer cell line by methylation-specific polymerase chain reaction (MSP), also detected the expression change of T-cadherin mRNA and protein in Hct116 cell line after 5-Aza-CdR treatment by reverse transcriptase polymerase chain reaction and Western blotting, and compared the T-cadherin methylation status with T-cadherin mRNA and protein expression. We found that hypermethylation of T-cadherin was involved in Hct116 cell line, while T-cadherin mRNA and protein expression was almost lost or downregulated in Hct116 cell line. Therefore, methylation of the T-cadherin promoter region was correlated with the loss or downregulation of T-cadherin mRNA and protein expression in Hct116 colon cancer cell line. Treatment of T-cadherin-negative carcinoma cells with the demethylating agent, 5-aza-2'-deoxycytidine, induced re-expression of this gene. Our findings demonstrate that 5' CpG island methylation is common in colon carcinoma and may play an important role in the inaction of T-cadherin. Our results also suggest that demethylation of the T-cadherin gene may be a potential therapeutic strategy for colon carcinoma.

[Effect of 5-Aza-CdR on expression and methylation of E-cadherin gene in human colon carcinoma cells].

BACKGROUND AND OBJECTIVE: Colon cancer is one of the most common malignant tumors, and its pathogenesis is not fully understood. Transcriptional silencing by DNA methylation is believed to be an important mechanism of carcinogenesis. E-cadherin can suppress tumor cell invasion and metastasis, and is considered as an invasion/metastasis suppressor gene. Inactivation of E-cadherin gene often occurs in colon carcinoma. This study was to investigate the correlation between E-cadherin gene expression and the methylation status of E-cadherin 5' CpG islands in human colon carcinoma cell line HT-29, and to explore the mechanism of carcinogenesis of colon cancer. METHODS: Immunocytochemical dicho-step method and reverse transcription-polymerase chain reaction (RT-PCR) were used to detect the expression of E-cadherin protein and mRNA in HT-29 cells after 5-Aza-CdR treatment; methylation specific PCR was used to analyze the methylation status at promoter of E-cadherin gene. RESULTS: The expression of E-cadherin gene could be restored by 5-Aza-CdR treatment, immunocytochemical staining showed the positive expression ratio of E-cadherin increased from (21+/-7)% (1 micromol/L) to (39+/-13)% (5 micromol/L); E-cadherin genes were methylated and not expressed in HT-29 cells in the colon carcinoma. CONCLUSIONS: E-cadherin methylation plays an important role in the carcinogenesis of colon carcinoma cells and can re-express after the treatment with 5-Aza-CdR.