The Correlation Study Between Smad4 Abnormal Expression And Colorectal Cancer

Objective : To study the association between Smad4 gene expression levels change,abnormal methylation of CpG islands in colorectal cancer and its clinical and pathological features,and explore the effect of Smad4 protein express on the development and progression in colorectal tumor.Method : All cases are from the patients who have received surgery in our hospital.The samples from biopsy with endoscopy or surgery resection are confirmed colorectal adenocarcinoma or adenoma, the colorectal cancer is sporadic excluding Hereditary Non-Polyposis Colorectal Cancer(HNPCC) and Familial Adenomatous Polyposis(FAP). Recording patient's age, sex, susceptive factors to colorectal cancer in details. Tissue sample acquitted from patients were divided into four groups, colorectal adenocarcinoma group (n=43), tumour adjacent tissues (n=43) ,adenoma group (n=32) and healthy person's mucosa group (n=12) respectively. By RT-PCR and sequencing,semi-quantitative RT-PCR was used to detect Smad4 mRNA expression level changes;Methylation-specific PCR (MSP) for gene promoter methylation level and Immunohistochemical detection methods for Smad4 protein levels. Finally, the above results were tested byχ2,t-test and Fisher exact probabilities statistical analysis.Result:1. The frequencies of the Smad4 mRNA (25/43, 58.14%) in colorectal adenocarcinoma patients was detected by RT-PCR method, its positive rate was lower than those in tumour adjacent tissues (38/43, 88.37%), colorectal adenoma (29/32, 90.63%) and normal mucosa (12/12, 100.00%) (P <0.05).2. The expression levels of the Smad4 mRNA (0.73±0.25) in colorectal adenocarcinoma patients was detected by semi-quantitative RT-PCR method,the expression levels (0.63±0.25), its positive rate and expression levels were lower than those in corresponding adjacent tissues (0.95±0.29), colorectal adenoma (1.01±0.37) and normal mucosa (1.18±0.33) (P <0.05).3.MSP showed the positive rates of Smad4 gene promoter methylation were 60.52%, 27.03%, 25.00% and 16.77% respectively, colorectal cancer was significantly higher than that in normal mucosa group and the adjacent tissues (P <0 .05).4.Immunohistochemistry showed that positive rates of Smad4 protein expression were 44.19% (19/43), 76.74% (33/43), 87.50% (28/32), 91.67% (11/12) respectively (P <0.05), with deep invasion and lymph node metastasis, the positive rate also will be dropped.Conclusion:Down-regulation of Smad4 expression may be associated with the biological behavior and prognosis of colorectal cancer,and which may be used as an important biological marker and one of the signs of disease Assessment.