Clinicopathological Significance Of Bmi-1 Expression In Gastric Carcinoma And Their Precancerous Lesions

Bmi-1(B-cell-specific Moloney murine leukemia virus insertion site 1) is a transcriptional repressor belonging to the Polycomb group gene(PcG) family,and a potent negative regulator of the Ink4a/Arf locus and regulates cell proliferation and apoptosis,as well as overexpressed in several human tumors.Reinisch et al reported that Bmi-1 was a protein expressed in stem cells,specialized cells and tumors of gastrointestinal tract.In present study,the expression of Bmi-1,ki-67 and Bcl-2 were detected immunohistochemically,the distribution of Bcl-2~+/ki-6T cells were observed in gastric carcinoma and their matched normal mucosa as well as precancerous lesions. The significance of the relationship between Bmi-1 expression and clinicopathological features of gastric carcinoma was explored.ObjectiveImmunohistochemistry staining and immunohistochemical double-labelling staining methods were used to display the expression of Bmi-1,ki-67 and Bcl-2 in normal gastric mucosa,gastric carcinoma and precancerous lesions.The correlation between Bmi-1,ki-67 and Bcl-2 and the distribution of Bcl-2~+/ki-67~- cells was analyzed objectively.Furthermore,the correlation and significance with clinicopathological features of gastric carcinoma have been explored.Material and methodsClinical material:One hundred and sixty-two cases of surgically resected gastric carcinoma specimens and matched normal gastric mucosa,82 cases of intestinal metaplasia(IM) as well as 52 cases of dysplasia(DYS),were collectted from the first Affiliated Hospital of China Medical University from August 2006 to May 2008.The age of the patients ranges from 30 to 80 years old,According to WHO's histological classification of gastric cancer,the cases were classified as 4 cases of papillary adenocarcinoma(papi ade),12 well-differentiated adenocarcinoma(well ade),50 moderately-differentiated adencarcinoma(mod ade),75 poorly-differentiated adenocarcinoma(poor ade),10 mucinous adenocarcinoma(mucin ade),9 signet ring cell carcinoma(SRC) and 2 undifferentiated adenocarcinoma(undiff ade).The samples were fixed in 10%formalin,embedded in paraffin,cut into 4μm-thick sections and constructed in four blocks of tissue microarray(TMA).All the specimens were diagnosed by two experienced pathologists.Grading of immunostaining results:Two hundred cells from two selected representative fields of each sample were counted by two independent observers.The staining intensity was classified as 0(negative),1(weak),2(moderate),and 3(strong). Positive cells were half quantified as a percentage of the total number of the same kind of cells counted in 2 high power field(×400),and assigned to one of five categories:0:＜5%,1:5～25%,2:26～50%,3:51～75%and 4:＞75%.According to the product of intensity of immunostaining and percentage of positive cells,immunostaining results were divided into:negative(-),0;weakly positive(+),1～4;moderately positive(++), 5～8;strongly positive(+++),9～12.BCIP/NBT (5-bromo-4-chloro-3-indolyl-phosphate/nitro-bule tetrazolium,dark blue granules) and AEC(3-amino-9-ethylcarbozole,red granules) double staining system was used to display Bcl-2~+/ki-67~- cell,and clearly red fine granules in cytoplasm and unstained nuclei within one cell was defined as Bcl-2~+/ki-67~- cell.The images were captured through a digital camera(Olympus AX70,Japan).Statistical analysis:Statistical evaluation was performed by SPSS 11.5 statistical software,using chi-square test to differentiate the rates of different groups and Kendall's tau-b rank correlation.P＜0.05 was considered as statistically significant.ResultsThe expression of Bmi-1 in normal gastric mucosa,gastric carcinoma and precancerous lesions:The posilive rates of Bmi-1 expression in gastric carcinoma (52.5%),intestinal metaplasia(79.3%) and dysplasia(80.8%) were significantly higher than that in normal gastric mucosa(21.6%),respectively,all P＜0.05(X~2=33.088, 74.844,59.819).The immunoreactivity to Bmi-1 protein was located in cytoplasm. There was a close relationship between the Bmi-1 expression in gastric carcinomas and Lauren's classification,Borrmann's classification and clinical stage(X~2=4.400,6.122 and 11.190,respectively;P＜0.05).The immunoreactivity to Bcl-2 was located in cytoplasm(red fine granules),while the immunoreactivity to ki-67 located in nuclei (dark blue fine granules).The distribution of Bcl-2~+/ki-67~- cells is mostly in proliferative zone of gastric mucosa.The expression of ki-67 is related to Borrmann's classification(X~2=13.380,P＜0.05).The expression of Bcl-2 was related to Lauren's classification(X~2=5.552,P＜0.05).The relationship among the expressions of Bmi-1, ki-67 and Bcl-2 in gastric carcinoma and their precancerous lesions:There were a positive relationship between Bmi-1 and Bcl-2 expression in gastric carcinomas (r_k=0.157,P=0.043),in intestinal metaplasia(r_k=0.270,P=0.038) and dysplasia (r_k=0.499,P=0.019),and a positive relationship between Bcl-2 and ki-67 expression in gastric carcinomas(r_k=0.225,P=0.005) and intestinal metaplasia(r_k=0.309,P=0.035).ConclusionsThe abnormality of Bmi-1 expression in gastric carcinomas might be involved in cell proliferation,apoptosis and cancerization,and hopefully as an objective marker indicating clinicopathological characteristics of gastric carcinomas,especially intestinal type of gastric carcinoma.