基因甲基化抑制鼻咽癌组织SCCA1的表达

Gene methylation inhibits the expression of squamous cell carcinoma antigen 1 in nasopharyngeal carcinoma tissues

背景与目的:鳞状细胞癌抗原1(squamous cell carcinoma antigen 1,SCCA1)与鳞状细胞癌的生长、分化及转移密切相关,鼻咽癌(nasopharyngeal carcinoma,NPC)组织SCCA1表达水平低于鼻咽黏膜上皮组织,其表达降低的机制不清楚。本研究初步探讨NPC组织SCA1表达水平降低是否由基因甲基化所致。方法:收集75例NPC活检组织(NPC组)和25例慢性鼻咽炎鼻咽黏膜活检组织(对照组),采用甲基化特异性聚合酶链式反应检测SCCA1基因甲基化状态,PCR检测SCCA1 mRNA表达水平,免疫组织化学染色和Western blot检测SCCA1蛋白表达情况。结果:NPC组SCCA1基因完全甲基化、不完全甲基化和未甲基化的例数分别为38例、27例和10例,对照组不完全甲基化和未甲基化的例数分别为5例和120例,NPC组甲基化频率显著高于对照组(65/75vs 5/25,x^2=39.7,P<0.01)。SCCA1基因不完全甲基化导致mRNA和蛋白表达降低,SCCA1基因完全甲基化导致mRNA和蛋白表达缺失。在NPC组,SCCA1不完全甲基化标本mRNA表达水平和蛋白表达水平显著低于SCCA1未甲基化病例(0.22±0.05 vs 0.37±0.07和0.14±0.05 vs 0.31±0.04,P<0.01);等级相关分析显示SCCA1基因甲基化程度与NPC组织免疫组织化学染色积分呈负相关(P<0.01),与NPC淋巴结转移分期呈正相关(P<0.01)。结论:NPC组织SCCA1蛋白质表达降低主要是由基因甲基化所致,SCCA1表达降低可能对NPC淋巴结转移具有促进作用。

Background and purpose：Squamous cell carcinoma antigen 1（SCCA1） is associated with growth,differentiation and metastasis of squamous cell carcinoma.The expression of SCCA1 in nasopharyngeal carcinoma（NPC） tissue is down-regulated when compared with that of nasopharyngeal mucosal epithelia although the mechanism is unclear.This study aimed to investigate whether the down-regulation of SCCA 1 expression in NPC tissue is caused by gene methylation.Methods：Biopsy specimens of 75 NPC tissues and 25 chronic nasopharyngitis nasopharyngeal mucosal tissues were harvested.Then the methylation status of SCCA1 gene was revealed by methylation specific PCR and the expression level of SCCA1 mRNA was evaluated by reverse transcriptional PCR. Protein expression was evaluated by immunohistochernistry as well as Western blot.Results：The SCCAl gene was exhaustively methylated in 38 cases,partially methylated in 27 cases,and unmethylated in 10 cases in NPC tissues. In control nasopharyngeal mucosal tissues,5 cases were methylated and 20 cases were unmethylated.The frequency of SCCA1 gene methylation for NPC tissues was higher than that for the control nasopharyngeal mucosal tissues （65/75 vs 5/25,X^2=39.7,P0.01）.Partial methylation of SCCA1 gene led to decreased mRNA and protein expression. Exhaustive methylation of SCCA1 gene led to absent mRNA and protein expression.In regards to NPC tissues, the expression levels of SCCA1 mRNA and SCCA1 protein in partially methylated cases were significantly lower than those in unmethylated cases（RT-PCR：0.22±0.05 vs 0.37±0.07,P0.01;Western-blot：0.14±0.05 vs 0.31±0.04, P0.01）.Graded correlation analysis discovered that SCCA1 gene methylation degree was reversely correlated with immunohistochemical score（P0.01）,and positively correlated with NPC lymphoid node metastasis staging（P0.01）. Conclusion：SCCA1 protein expression in NPC tissue is down-regulated and this is mainly due to gene methylation. Decreased SCCAl expression in NPC perhaps promotes lymph node metastasis.