BNIP3Expression In Esophageal Squamous Cell Carcinoma And Its Methylation Regulation Mechanism

Background:Esophageal cancer is one of the common human malignancies in recent years, its incidence gradually increased. In China, esophageal cancer has a high incidence, the morbidity and mortality of esophageal cancer rank first in the world, and the main pathological type in China is esophageal squamous cell carcinoma, accounts for more than90%. It is a complicated process of developing esophageal cancer from normal esophageal epithelia. Abnormality of Genetics and epigenetics plays an important role on esophageal carcinogenesis. Epigenetics is a subject about gene expression, gene expression regulated by epigenetics is not involved in DNA sequence changes. Abnormal epigenetic changes are found in almost all types of human tumors. Epigenetic can lead to the expression of the tumor suppressor gene silencing, DNA methylation in primary human tumors is the most studied epigenetic, hypermethylation can be found in many tumor suppressor gene promoter region of signaling pathways in different types of tumors. The BNIP3gene is considered as a tumor suppressor in recent years, it expresses in normal tissues, but the expression is reduced in a variety of tumor. BNIP3gene expression and the mechanism of its regulation in ESCC are unclear.Objectives:1. To observe the expression of BNIP3and HIF-1α protein expression in esophageal squamous carcinoma and normal esophageal mucosa tissue, and to analyze the relationship between the expression with clinical and pathological features in esophageal squamous cell carcinoma;2. To detect the methylation state of BNIP3gene in esophageal squamous cell carcinoma and normal mucosa esophageal tissue, and to detect the expression of BNIP3protein of corresponding tissue; and to study the correlation between BNIP3protein with BNIP3gene methylation, to explore their role in the development of its clinical significance in esophageal squamous cell carcinoma.Methods:1. Tissue microarray immunohistochemical staining techniques was used to detect the expression of collected72cases of ESCC tissue samples and30cases of normal tissue mucosa samples;2. The methylation-specific PCR and immunohistochemical staining techniques wered used to detect the gene methylation status and protein expression of BNIP3of collected50pair of ESCC tissue and normal mucosa tissue samples;3. Combine clinical and pathological data with experimental results to statistically analyze with SPSS software17.0.Results:1. The positive ratio of BNIP3protein in esophageal squamous cell carcinoma tissue was37.5%(27/72), which was significantly lower than that in normal esophageal mucosa tissue60%(18/30)(P=0.037). The positive ratio of HIF-1α protein in ESCC was52.7%(38/72), which was significantly higher than that in normal esophageal mucosa tissue13.3%(4/30)(P=0.000);2. The expression of BNIP3protein was correlated with the depth of tumor invasion, TNM stage, lymph node metastasis (P-0.035, P=0.048P=0.033). The expression of HIF-la protein was also correlated with depth of tumor invasion, TNM stage, lymph node metastasis (P=0.023, P=0.004, P=0.002);3. The expression of BNIP3protein was positively correlated with HIF-1α (r=-0.274, P=0.020);4. The methylation ratio of BNIP3gene in esophageal squamous cell carcinoma tissue was60%(30/50), which was significantly higher than that in normal esophageal mucosa tissue22%(11/50)(P=0.000); the positive ratio of BNIP3protein in corresponding tissue was34%(17/50), which was significantly lower than that in normal esophageal mucosa tissue56%(28/50)(P=0.000);5. The status of methylation and expression of BNIP3was correlated with TNM stage, lymph node metastasis;6. BNIP3gene methylation and BNIP3protein expression were correlated in ESCC (P=0.000), but not in normal esophageal mucosa tissue.Conclusions:1. In ESCC the expression of BNIP3protein was in low expression, but higher in normal esophageal mucosa tissue, and the methylation ratio of BNIP3gene was higher in ESCC than in normal esophageal mucosa tissue, therefor the hypermethylation of BNIP3gene may lead to expression of BNIP3protein lower or missing in ESCC, and leading the occurrence of ESCC;2. The low expression of BNIP3was correlated with the depth of tumor invasion, TNM stage, lymph node metastasis, therefore, BNIP3plays an important role in development of ESCC;3. The expression of BNIP3protein was positively correlated with HIF-la, and they both related with the depth of tumor invasion, TNM stage, lymph node metastasis, therefor, the low expression of BNIP3may lead to the high expression of HIF-1α, promoting tumor development.