Relationship of DNA methylation, mRNA transcription and protein expression of glutathione-S-transferases-P1 gene and coal-pollution-borne endemic arsenism / 中国地方病学杂志

ABSTRACT

Objective To investigate DNA methylation in the promoter region,mRNA transcription and protein expression of glutathione-S-transferases-P1 (GSTP1) gene and their relation with arsenism.Methods In endemic coal-pollution-borne arsenism area,Jiaole village of Xinren county,Guizhou province,according to the diagnostic criteria of endemic arsenism(WS/T 211-2001),123 cases with endemic arsenism were selected and divided into three groups (mild arsenism group42 cases,moderate arsenism group41 cases and severe arsenism group40 cases).Forty seven residents were selected as controls in a village about 12 km away from the endemic arsenism area.With the informed consent principle,peripheral blood of all respondents was collected in order to analyze DNA methylation and check mRNA.DNA methylation of GSTP1 gene promoter region in peripheral blood was assayed by PCR,and GSTP1 mRNA expression was assayed using real-time quantitative PCR.In addition,other cutaneous specimens originated from 53 cases with arsenism that accepted surgical treatment voluntarily were taken.Of these specimens,general pathological changes were 28 cases,precancerous 20 cases and cancerous 5 cases.Skin tissues of 15 cases of non-tumor surgery patients without abnormal pathological changes were as control group.GSTP1 protein expression in the skin tissue was detected using immunohistochemistry (IHC).Results Among different groups of arsenic poisoning,the positive rate of DNA methylation of GSTP1 gene was 28.57％(12/42) in the mild group,57.10％ (23/41) in the moderate group and 65.00％ (26/40) in the severe group.Compared with the control group (6.38％,3/47),the difference was statistically significant (x2 =7.792,26.000,33.412,all P ＜ 0.01).Among different groups of arsenic poisoning diagnosed by dermapathology,the positive rate of DNA methylation of GSTP1 gene was 21.43％(6/28) in the general pathological change group,50.00％(10/20) in the precancerous group and 80.00％(4/5) in the cancerous group.Compared with the control group(6.67％,1/15),the difference was statistically significant (x2 =3.562,7.468,10.756,all P ＜ 0.05).It showed that the positive rate of DNA methylation of GSTP1 gene increased with aggravation of the disease and dermatic lesion of arsenism (tendency x2 =38.239,x2 =13.659,all P ＜ 0.01).Compared with the control group(0.184 26),the expressions of GSTP1 mRNA in peripheral blood in moderate (0.087 77) and severe arsenic poisoning groups (0.056 93) were significantly reduced(all P ＜0.01),and that of severe group was significantly lower than that of the moderate group (P ＜ 0.01) ; compared with the control group(0.338 45) and the general lesion group(0.276 74),GSTP1 mRNA expression was significantly reduced in precancerous lesion group(0.104 81) and cancerous group(0.043 70),in which the cancerous group was significantly lower than that of the precancerous lesions.The difference of skin tissue GSTP1 protein expression rate between groups was statistically significant (x2 =20.948,P ＜ 0.05),in which the difference between the precancerous lesion group(65.00％,13/20),the cancer group (40.00％,2/5) and the control group(100.00％,15/15)was statistically significant (x2 =12.183,11.778,P ＜ 0.01).Spearman correlation analysis showed that the degree of skin lesion and the level of GSTP1 protein expression was negatively correlated (r =-0.520,P ＜ 0.05).Groups were divided according to DNA methylation of GSTP1 gene,and the mRNA and protein expression of GSTP1 in methylation group(0.038 40,57.14％) was significantly lower compared with that of unmethylated group(0.187 07,95.74％; Z =9.032,x2 =23.134,all P ＜ 0.01).Conclusions Arsenism may lead to DNA methylation of human GSTP1 gene promoter region,thereby inhibiting expression of mRNA and protein.GSTP1 gene plays an important role in arsenism or carcinogenic process.