乳腺癌APC/β-catenin信号通路变化的研究

Alterations of APC/β-catenin signal pathway in breast cancer

目的:研究乳腺癌发生、发展过程中APC/β-catenin信号通路的变化。方法:应用PCR-SSCP、微卫星标记、甲基化特异性PCR方法检测乳腺癌和癌旁正常乳腺组织中β-catenin基因外显子3和APC基因突变密集区突变、APC基因杂合缺失(LOH)和启动子1A区甲基化状态,用RT-PCR检测APC基因mRNA表达;并用免疫组织化学法检测APC和β-catenin蛋白表达。结果:乳腺癌中β-catenin异常表达率为53.9%,β-catenin异常表达与乳腺癌组织学分级、TNM分期及腋淋巴结转移呈正相关,未发现β-catenin基因突变。乳腺癌中APC蛋白表达阴性率为47.6%,APC蛋白表达阴性同TNM分期和β-catenin异常表达呈正相关,未发现APC基因突变。APC基因启动子1A区甲基化率为36.8%,甲基化与mRNA表达减少、蛋白表达缺失及TNM分期呈正相关。APC基因LOH发生率达32.6%,LOH和甲基化呈正相关。结论:在乳腺癌发生、发展过程中APC/β-catenin通路出现异常改变。β-catenin蛋白异常表达不是该基因突变所致,而是由于APC蛋白表达缺失导致破坏复合体功能障碍所致。乳腺癌中APC基因突变非常罕见,该基因LOH和启动子1A区甲基化是该基因失活的主要机制,是蛋白表达缺失的原因。

Objective：To investigate the alterations of APC/β - catenin signal pathway in tumorigenesis and development of breast cancer. Methods： Mutation in exon 3 of β - catenin gene and mutation cluster region of APC gene, loss of heterozygosity and methylation status of promoter 1 A of APC gene in breast cancer and normal tissue around tumor were detected by polymerase chain reaction - single strand conformation polymorphism, microsatellite analysis and methylation specific PCR. In addition, mRNA expression of APC gene was determined by reverse transcriptase PCR, protein expressions of APC and β - catenin gene were detected by immunohistochemistry. Results： The abnormal expression rate of β -catenin in breast cancer was 53.9%, abnormal expression was positively correlated with histological grades, TNM stages and axillary lymph node metastasis. Negative expression rate of APC in breast cancer was 47.6%, negative expression was positively correlated with abnormal expression of β - catenin and TNM stages. Although no β - catenin and APC mutations were detected, promoter methylation （36.8%） and LOH （32.6%,） of APC gene were found. Promoter methylation was positively correlated with LOH, reduction of mRNA expression, absence of protein expression and TNM stages. Conclusion： Abnormal alterations of APC/β-catenin signal pathway occur in tumorigenesis and progession of breast cancer. Reason of abnormal expression of β - catenin isn＇ t mutation of β - catenin gene, but dysfunction of destruct complex induced by absence of APC protein expresion. Although mutation of APC gene is rare in breast cancer, methylation of promoter 1A and LOH of APC gene are major mechanism of inactivation of APC gene, which results in absence of protein expression.