The Promoter Methylation Of ASPP Gene Family In Lung Cancer And Relationship With P53 Apoptosis Pathway

Objective:In order to research the relation between ASPP gene family and incidence of lung carcinoma, the article examined the promoter methylation statut of the ASPP1 and ASPP2 from lever of DNA in lung carcinoma, and the expression of ASPP1,ASPP2 and p53 from lever of protein, and the apoptosis index of the lung cancer tissues.Metholds:To construct tissue microarray of lung cancers,we collected 90 cases lung carcinoma tissues as experimental group and 25 normal adjacent lung tissue as control group. The expression state of ASPP1,ASPP2 and p53 protion were determined by immunohistochemical staining combined with tissue microarray of lung cancer, Terminal deoxynucleotidyl transferase dUTP nick end labeling(TUNEL) was applied to detect the apoptosis in the tissue microarray, The apoptosis index(AI) were defined. The methylations of ASPPl and ASPP2 promoter region CpG island were analysised by methylation-specific PCR (MSP). Furthermore, We analysis the relationship among expression of ASPP1,ASPP2 protein, promoter region methylation,AI,and p53 apoptosis pathway.Results: 1.The position rate of ASPP1 in 90 cases lung cancer tissues was 27.8%, and the position rate of ASPP2 was 11.1%; the positive rate of ASPP1 in 25 normal adjacent lung tissues was 52.0%, and the ASPP2 positive rate was 16.0%; Significant difference was found between the expression of ASPP1 in cancer tissue and their normal adjacent tissues (x2=5.188,P<0.05); while the expression of ASPP2 has no significant difference (x2=0.437,P>0.05).2. The expression of ASPP1 in 90 cases lung cancer had positive relation with the differentiation, TNM stage and lymph node metastasis of the disease (x2:=4.680,6.330,6.045, P<0.05),but not related to sex, age,and histological type. Significant difference was not found between the expression of ASPP2 and clinical pathologic characteristic(P>0.05).3. The positive expression of ASPP1 was 16 cases in 39 cases that negative expression of p53,and 9 cases in 51cases that mutation p53 cancer tissues. The Spearman's method was used, and the result was that there was negative correlation between the expression of ASPP1 and mutation p53 in lung cancer (r=-0.259,P<0.01),but the positive expression of ASPP2 was 6 cases in 39 cases that nagetive expression of p53 cancer tissues, and 4 cases in 51 cases mutation p53 tissues, the expression of ASPP2 was not associated with p53 state by used Spearman's method(r=-0.119,P>0.05).4. The AI in the group of ASPP1 positive expression was significantly higher than in the group of ASPP 1 negative expression, this showed that there was close relationship between the expression of ASPP1 and cell apoptosis in lung carcinoma (t=2.337,P<0.05); but no significant different was found between the group of ASPP2 positive expression and the group of negative expression, so the expression of ASPP2 may has no relation with cell apoptosis in lung carcinoma(t=1.083,P>0.05)5. The positive rate of ASPP 1 methylation in lung tumor tissues was significantly higher than that in the adjacent lung tissues{42.22%(38/90) vs 16.00%(4/25), P =0.019}.The methylation state of ASPP 1 had close relation with TNM stage and lymphnode metastasis of the disease (x2=6.919,5.213,P=<0.05),but not related to age,sex, histological type and differentiation(x2=1.l29,1.488,1.126,4.555,P >0.05).The group with promoter methylation showed lower expression of ASPP 1 than that with unmethylation state (x2=5.188,P<0.05); Methylation in the promoter region of ASPP2 gene was not detected in lung cancer (n=90) or side-carcinoma tissues (n=25);Conclutions: 1. The lower expression of ASPP1 was correlation with TNM stage and lymph node metastasis in lung cancer, that shows the loss expression of ASPP1 may participate in lung carcinogenesis and development.2. There was no significant difference in expression of ASPP2 between lung cancer tissue and the paracarcinomatous tissues, it indicated that ASPP2 may not be as a tumor suppressor gene in lung carcinomas.3. ASPP1 can induce AI, and the expression of ASPP1 has a negative correlationship with mutation p53; ASPP1 may be as a key factor of p53 apoptosis pathway in lung cancer tissue;but ASPP2 may be independent of the p53 apoptosis pathway.4. The hypermethylation of ASPP1 gene might lead to the abnormal expression of ASPP1 protein; and it is respected of the aggressive clinical behavior and advanced tumor stage; while the ASPP2 gene promoter methylation may not be the cause of the abnormal expression of ASPP2 protein in tumorgenesis.