Expression of DNA methyltransferases 1,3a,and 3b in retinoblastoma

Abstract

Objective To observe the expressions of DNA methyltransferases (DNMTs) 1,3a and 3b in retinoblastoma (RB).Methods Sixty-two RB samples and six normal retinas were studied,including 17 poorly differentiated and 45 well differentiated samples; 16 invasive and 46 non-invasive samples.The expressions of DNMT1,3a,and 3b,and Ki-67 were detected using immunohistochemical analysis.Brown staining of nuclei was considered to represent the positive stain for DNMT1,3a and 3b,and ki-67,blue staining as negative.The level of high expression of nuclear staining was,positive cells in DNMT1≥65 ％,in DNMT3a≥60％ and in DNMT3b≥40％.The correlations of DNMT1,3a and 3b expression in RB samples,and MIB-1 labeling index were analyzed.Results Viewed under the light microscope,negative expressions of DNMT1,3a and 3b were demonstrated in normal retinas,however,positive expression was observed in RB samples,with 100％ in DNMT1,98％ in DNMT3a and 92％ in DNMT3b.Comparing well differentiated RB samples with poorly differentiated samples,significant differences were found in high expression of DNMT1 (x2 =12.57,P＜0.05) and DNMT3a (x2 =10.54,P＜0.05) ; also in the positive cells of DNMT1 (U=179,P＜0.05) and DNMT3a (U=198,P＜0.05).No significant difference was found comparing high expression (x2=1.5,P＞0.05) and positive cells (U=307,P＞0.05) of DNMT3b.When comparing invasive tumor tissues with non-invasive tumors,significant differences were shown between high expression (x2 =4.72,P＜0.05) and positive cells comparing DNMT1 (U=236,P＜0.05).No significant difference was shown in high expression (x2=3.53,0.84; P＞0.05) in DNMT3a and DNMT3b,or in comparison with positive cells (U=338,257; P＞0.05).The expression of DNMTs was positively correlated with the MIB-1 labeling index in RB tissues (R2=0.554,0.376,0.219; P＜0.05).Conclusion There are high expressions of DNMT1,3a,and 3b in RB. Key words: Retinoblastoma/enzymology; DNA modification methylases; Tumor makers,biological