The Expression And Significance Of P53 And Upstream Gene ATM, Downstream Gene PUMA In Colorectal Cancer

Objective: Colorectal cancer is a common malignant tumor of digestive tract, the formation and development of which is a multi-factor, multi-step process. DNA methylation, DNA damage and multiple change under the action of oncogene and tumor suppressor genes lead to the formation of cancer. Tumor suppressor genes mutation or loss is a major molecular genetic change occurrence in development of colorectal cancer. Thereinto, tumor suppressor gene p53 gene and its upstream gene ATM, downstream gene PUMA play important roles in the development of colorectal cancer. p53 gene contains wild-type p53 and mutant-type p53. Wild-type p53(wtp53) gene can prevent tumors from forming and suppress their growth by blocking the cell cycle, promoting apoptosis, repairing the damaged DNA, restraining carcinoma angiogenesis. By negatively controlling the wild-type p53 and making chromosome instability, Mutant-type p53(mtp53) can promote the development of tumor. The half-life of wild-type p53 protein is too short to test by immunohistochemical detection. But the half-life of mutant p53 protein is longer, which can be detected by using immunohistochemical detection. Therefore, when higher expression of p53 detected in organizations, actually, the gene is the mutant p53 gene. ATM gene is the upstream gene of p53, which plays a vital role by perceiving the DNA damage especially radiation caused by DNA double- strand break(DSB) and repairing the damaged DNA、regulating cell cycle and promoting apoptosis. PUMA is the downstream gene of p53, which plays a key role in a variety of stress-induced cell apoptosis by p53-dependent and p53-independent. The effects of p53 on colorectal cancer has been reported, but the effect of ATM and PUMA on the colorectal cancer have been seldom reported, Investigation on combined test for p53 gene and its upstream gene ATM, downstream gene PUMA in colorectal cancer have not been reported before. This study intends to investigate the expression of p53, ATM and PUMA in colorectal cancer, explore mechanisms in the development of colorectal cancer, provide theoretical basis for mechanisms, diagnosis and treatment in colorectal cancer.Methods: 60 cases of colorectal cancer were collected in Sichuan Provincial People’s Hospital with surgical excision specimens from 2013~2014. 20 cases of normal control were taken from the colorectal mucosa beyond 5cm to the end of colorectal cancer. Use Envision two-step immunohistochemical method to detect the expressions of p53, ATM and PUMA in normal colorectal tissue and colorectal carcinoma,and analyze their relationship with clinical pathology.Statistical Methods: The analysis of data is performed by statistical software SPSS19.0, and with α=0.05 as the inspection level。x2 test was used for comparing the expressions rate; The Spearman test was used for testing the correlation of expressions among p53, ATM and PUMA.Results:1. The positive expression rate of p53 in colorectal cancerous tissue is 61.67%, and in normal tissues is 25%. The positive expression rate of p53 in colorectal cancer is higher than the normal tissue’s, and the difference is statistically significant(P < 0.05). The expression of p53 in colorectal cancer has no relation to patients’ age, sex and tumor size(P> 0.05);The expression of p53 is related to tumor location, clinical TNM staging, depth of tumor invasion, pathologic differentiation degree and lymphatic metastasis(P < 0.05).2. The positive expression rate of ATM in colorectal cancerous tissue is 35%, and in normal tissue’s is 60%, The positive expression rate of ATM in colorectal cancerous tissue is lower than the normal tissue’s, and the difference is statistically significant(P < 0.05). The expression of ATM in colorectal cancer has no significant differences with patients’ age, sex,depth of tumor invasion, the degree of tumor pathologic differentiation and lymphatic metastasis(P>0.05), but it has relation to clinical TNM staging.3. The positive expression rate of PUMA in colorectal cancer is 36.67%, and in normal tissue’s is 65%. The positive expression rate of PUMA in colorectal cancer is higher than the normal tissue’s, and the difference is statistically significant(P < 0.05). The expression of PUMA in colorectal cancer has no significant differences with patients’ age, sex and lymphatic metastasis(P> 0.05).The expression of PUMA is related to tumor size, clinical pathologic staging, pathologic differentiation degree and tumor location.4. The expression of P53 shows a negative correlation with ATM and PUMA(r=0.363, x 2=7.904,P<0.05; r=0.315, x 2=5.967, P<0.05)。The expression of ATM has no correlation with PUMA(r=0.167, x 2=1.669, P>0.05)。Conclusion:1. The expression of mt-p53 is up-regulated in colorectal tumor, suggesting that mt-p53 promote colorectal tumor genesis by promoting cell proliferation and inhibiting the apoptosis. The expression of ATM is down-regulated in colorectal cancer,suggesting that ATM gene mutations can lead to protein expression reduced, thereby reduce the protective function to colorectal cancer, It might be one of the reasons for the occurrence of colorectal cancer. The expression of PUMA is down-regulated in colorectal cancer,suggesting that Overexpression of mt-p53 inhibit the expression of PUMA, Thus promoting apoptosis function is inhibited. ATM and PUMA expression reducing promote colorectal tumor genesis.2. The positive expression rate of p53 increasing in the group of poor differentiation,advanced TNM,lymph node metastasis and invasion of serosa of colorectal cancer, The positive expression rate of ATM reducing in advanced TNM group,The positive expression rate of PUMA reducing in poor differentiation,advanced TNM,and invasion of serosa of colorectal cancer, suggest that they may be associated with treatment and prognosis of colorectal cancer, and may be have certain help in evaluating the prognosis of patients with colorectal cancer.3. There is a negative correlation between the ATM and p53 in colorectal cancer, p53 and PUMA also negatively correlated, suggesting that because ATM gene mutation, ATM protein expression was reduced, leading to wtp53 downregulation and mtp53 increased expression, mtp53 will inhibit the expression of PUMA, PUMA’s pro-apoptotic function is suppressed. All these indicate that ATM-p53-PUMA pathway plays an important role in occurrence and development of colorectal cancer. Combined detection of ATM, p53, PUMA could provide new ideas to the occurrence and development of colorectal cancer from the molecular level. And it may be have certain help in choosing the right treatment and assessing the prognosis in colorectal cancer.