Comparative Study On The Expression Of Bmi-1, P14^ARF, Mdm2 And P53 Between Gastric Cardia Adenocarcinoma And Distal Gastric Carcinoma

Objective: Gastric carcinoma(GC) is one of the most commom malignancies, accounting for the second of all cancer death all over the world. Recent decades have witnessed a dramatic shift in the sub-site of gastric cancers. The incidence of distal gastric carcinoma(DGC) decreased while the incidence of adenocarcinoma of the proximal stomach and distal esophagus increased significantly among Western and American populations. Similar changes in the propostion of cardia and distal stomach carcinoma in southern and contral rural areas in Hebei province of China were also found. However, the causes of the above-mentioned changes remains unknown.The development and progression of cancer is an very complicated process involving several biological events such as activation of oncogenes, inactivation of tumor suppressor gene, and abnormal expression of some apoptosis-related genes, etc. The role of cell cycle regulation-related proteins in carcinogenesis, progression and prognosis of tumors has caused the concern of oncologists.p53 tumor suppressor gene is one of the most commonly mutated genes in human cancers. As we all know, that wild-type p53 gene is a tumor suppressor gene, encodes the protein that can hold the cell cycle at the G1/S regulation point or G2/M regulation point, thereby inhibiting cell proliferation. While mutant p53 gene may act as a carcinogene which encodes the protein that plays a catalytic role in cell proliferation and transformation.Mdm2(murine double minute) gene is an oncogene, expressed in variety of normal tissues, and it plays an important role in the physiological processes of cells. The overexpression of Mdm2 gene has been found in many human tumors, such as breast cancer , lung cancer, stomach cancer, prostate cancer, etc. Mdm2 functions both as an inhibitor of p53 transcriptional activation to promote cancer cell growth and a promoter of the degradation of p53 protein to block the p53-mediated cell cycle stagnation and apoptosis, and eventually cause cell immortalization and tumor formation.INK4a/ARF(Inhibitor of cyclin-Dependent Kinase 4a- Alternative Reading Frame) is the first tumor suppressor gene that may directly regulate the cell cycle and inhibit cell mitosis. INK4a/ARF gene encodes two different proteins: p14^ARF and p16INK4a, involving the regulation of cell cycle. p14^ARF can bind to Mdm2, inhibite the interaction between Mdm2 and p53, activate p53 protein and induce G1 and G2 arrests in tumor cells, which leads to cell senescence or apoptosis. Thus, it is an important inhibitor in the carcinogenesis and development of tumors. The inactivation of p14^ARF may results in disorder of cell cycle, malignant transformation and carcinogenesis.B-cell specific moloney leukemia virus insertion site 1(Bmi-1) gene is a member of polycomb group(PcG) gene family acting as transcription inhibitory factor.Bmi-l plays an important role in the regulation of self-newal in stem cells,proliferation and aging in cells. Bmi-1 may negatively regulate of the expression of p14^ARF, and prevent cell cycle arrest and apoptosis through p14^ARF-Mdm2-p53 pathway, thereby leading to tumor formation. Latest reports indicated that abnormal expression of Bmi-1 exists in various tumors.It was found that differences did exist in several aspects such as the etiology, the epidemiological features, immunohistochemical phenotypes, biological behaviors and changes in between gastric cardia cancer and distal gastric cancer. Gastric cardia cancer was widely considered as unique entity of gastric carcinomas. However, rare studies about gastric cardia cancer and distal gastric cancer are published now. Up to now, comparative studies on the differences in the field of carcinogenesis, molecular genetics changes between cardia adenocarcinoma and distal gastric adenocarcinoma are still quite few. The putative causes for the changing trend in the subsite of gastric carcinoma is not clear. Therefore, it is important to evaluate the differences in the expression of oncogene and tumor suppressor gene between gastric cardia adenocarcinoma and distal gastric carcinoma to explore the possible carcinogenesis of gastric cardia adenocarcinoma. In this study, we examined the expression of Bmi-1, p14^ARF, Mdm2 and p53 in gastric cardia adenocarcinoma and distal gastric carcinoma using immunohistochemical methods. The aim of this study is to analyze the clinical pathological significance of the afore-mentioned genes in gastric carcinoma arised from different parts of stomach, and to explore the possible differences in the carcinogenesis between gastric cardia adenocarcinoma and distal gastric carcinoma.Method: The expression of Bmi-1, p14^ARF, Mdm2 and p53 was studied in 20 cases of normal gastric mucosa(NGM), 74 cases of gastric cardia adenocarcinoma(GCA) and 41 cases of distal gastric carcinoma(DGC) with ElivisionTM plus two-step. The correlation between their expression and the clinical pathological features were analyzed. The experimental datas were anlyzed with Chi-square test, Fisher's exact test and correlation with stastics software of SPSS13.0 edition.Results1 Immunohistochemical staining results of Bmi-11.1 Expressions of Bmi-1 in GCA and DGCPositive immunoreaction was located in nucleus and/or cytoplasm. Among the 20 cases of normal gastric mucosa, 4 cases showed positive Bmi-1 expression(20.0%). The positive expression rate of Bmi-1 in GCA and DGC was 60.8% and 46.3% respectively, which were all significantly higher than that in normal gastric mucosa(P<0.05). No statistical significance was found in the difference of Bmi-1expression between GCA and DGC(P>0.05).1.2 The clinical pathological significance of Bmi-1 expression in GCA and DGCThe positive expression rate of Bmi-1 in the gastric carcinoma including GCA and DGC was reltated with tumor differentiation. The positive expression rate of Bmi-1 in well-differentiated group(46.9%) was significantly lower than that in low-differentiated group(71.4%, P<0.05). No relationship between the positive expression of Bmi-1 in GCA and the age and sex of the patients, size and infiltrating depth of tumor and lymph node metastasis was found(P>0.05).In DGC, there was no relationship between the expression of Bmi-1 and the age and sex of the patients, differatiation, size and infiltrating depth of tumor and lymph node metastasis (P>0.05).Thus, the results suggestted that the significance of Bmi-1 expression be different in GCA and DGC. The positive expression of Bmi-1 in GCA was significantly related with differatiation, but no such relation was seen in DGC.2 Immunohistochemical staining results of p14^ARF2.1 Expressions of p14^ARF in GCA and DGCPositive immunohistochemical staining products were located in nucleus and/or cytoplasm as brown granule. The positive expression of p14^ARF in GCA was significantly lower than that in DGC(39.2% vs 58.5%, P<0.05), which were all significantly lower than that in normal gastric mucosa(85.0%, P<0.05).2.2 The clinical pathological significance of p14^ARF expression in GCA and DGCAmong the GCA cases, the immunohistochemical staining results exhibited significantly higher p14^ARF expression in well-differentiated group(53.1%) than that in low-differentiated group(28.6%, P<0.05). It was higher in cases without lymph node metastasis than that in cases with lymph node metastasis(54.8% vs 27.9%, P<0.05). The positive expression of p14^ARF in GCA was not related with age and sex of the patients, differatiation and size of tumor(P>0.05).No statistically significant relationship was found between p14^ARF expression and the age and sex of the patients, differatiation, size and infiltrating depth of tumor and lymph node metastasis in DGC(P>0.05).The results showed that the positive expression of p14^ARF in GCA was significantly related with differatiation and lymph node metastasis. While there was no such relation in DGC.3 Immunohistochemical staining results of Mdm23.1 Expressions of Mdm2 in GCA and DGCThe positive cytoplasmic expression rate of Mdm2 in GCA was 59.5%(44/74), which was significantly higher than that in DGC(34.1%, P<0.05).3.2 The clinical pathological significance of Mdm2 expression in GCA and DGCThe positive expression of Mdm2 was significantly related with depth of invasion in GCA. The positive expression in cases with muscle layer invasion was significantly lower than that innserous layer invasion group(40.0% vs 66.7%, P<0.05). The positive expression of Mdm2 was significantly lower in cases without lymph node metastasis than that in in cases with lymph node metastasis(45.2% vs 69.8%, P<0.05). The positive expression of Mdm2 in GCA was not associated with age and sex of the patients, differatiation and size of tumor(P>0.05).The positive expression of Mdm2 in DGC was significantly higher in well-differentiated group than that in low-differentiated group(52.9% vs 20.8%, P<0.05), while that was not related with age and sex of the patients, size and infiltrating depth of tumor and lymph node metastasis(P>0.05).The positive expression of Mdm2 in GCA was closely related with invasion depth of tumor and lymph node metastasis. While the positive expression of Mdm2 was closely related with differatiation in DGC.4 Immunohistochemical staining results of p534.1 Expressions of p53 in GCA and DGCPositive immunoreaction of p53 as brown granules was located in the nuclei of cancer cells. No positive expression cells was found in normal gastric mucosa. Immunohistochemical staining results showed that the positive expression of p53 in GCA(74.3%) was significantly higher than that in DGC(48.8%, P<0.05).4.2 The clinical pathological significance of p53 expression in GCA and DGCThe positive expression of p53 was related with depth of cancer invasion in GCA. The positive expression of p53 in cases with muscle layer invasion was significantly lower than in serous layaer invasion group(55.0% vs 81.5%, P<0.05). The positive expression of p53 in GCA was not related with age and sex of the patients, differatiation, size of tumor and lymph node metastasis(P>0.05).The positive expression of p53 in GCA was not related with age and sex of the patients, differatiation, size and infiltrating depth of tumor and lymph node metastasis(P>0.05).The positive expression of p53 in GCA was closely related with infiltrating depth of tumor in GCA. However, no relationship was observed between p53 expression and depth of invasion in DGC.5 Corelation among Bmi-1, p14^ARF, Mdm2 and p53 expressions in GCA and DGCNegative correlation could be found between Bmi-1 and p14^ARF in GCA(r=-0.263, P=0.024), but not in DGC(r=-0.211, P=0.186). There was negative correlation between expression of p14^ARF and Mdm2 in GCA and DGC(r=-0.296, P=0.011; r=-0.438, P=0.004). Positive correlation between expression of Mdm2 and p53 was found in GCA and DGC(r=0.271, P=0.020; r=0.326, P=0.037)。Conclusions1 The significantly higher expression of Bmi-1, Mdm2 and p53 was observed both in GCA and DGC as compared with that in NGM. But the expression of p14^ARF in NGM was significantly higher than that in GCA and DGC.2 No significant difference was seen in the expression of Bmi-1 between GCA and DGC, but significant differences could be found in the expression of p14^ARF, Mdm2 and p53 between the two tumors. The expression of Mdm2 and p53 in GCA was higher than that in DGC, the expression of p14^ARF in GCA was lower than that in DGC.3 In GCA cases, the expression of Bmi-1, p14^ARF, Mdm2 and p53 was respectively related with differatiation, differatiation and lymph node metastasis, depth of invasion of tumor and lymph node metastasis, and depth of invasion of tumor. While in DGC, only the expression of Mdm2 was related with differatiation.4 The differecences in Bmi-1, p14^ARF, Mdm2 and p53 expression and clinical pathological significances were found between GCA and DGC. The results suggestted that the p14^ARF-Mdm2-p53 pathway may play more important role in the carcinogenesis of GCA.