E-cadherin promoter hypermethylation may contribute to protein inactivation in pterygia

Abstract

Purpose: Our recent reports indicated that the molecular changes of pterygia are similar to tumor cells. We believe that pterygia may have a similar mechanism in oncogenesis. Many studies have revealed that E-cadherin associated protein expression decreases in many tumors and pterygia. E-cadherin may be a marker for both tumor metastasis and prognosis. However, no studies have examined the reason for E-cadherin protein inactivation in pterygia. Therefore, this study aimed to analyze the association of E-cadherin promoter hypermethylation with protein inactivation in pterygial tissues.

Methods: E-cadherin methylation-status and the expression of E-cadherin and beta-catenin protein were studied using methylation-specific PCR and immunohistochemistry, respectively, on 120 pterygial specimens and 30 normal conjunctivas.

Results: Hypermethylation of E-cadherin gene promoter was detected in 32 (26.7%) of the 120 pterygial specimens. A total of 79 (65.8%) pterygial specimens tested positive for E-cadherin protein expression and 41 (34.2%) specimens tested negative. The E-cadherin staining was limited to the membrane of the epithelial layer. There was a reverse correlation between E-cadherin gene promoter hypermethylation and E-cadherin protein expression (p<0.0001). Aberrant localization of beta-catenin was higher in the E-cadherin negative group than in E-cadherin positive group.

Conclusions: Our study demonstrates E-cadherin gene promoter hypermethylation were associated with low or absent expression of E-cadherin. Moreover, loss of E-cadherin protein may contribute to aberrant localization of beta-catenin. These data provide evidence that methylation exists in pterygia and may play a role in their development.

Figure 1

Representative immunostaining results for E-cadherin associated protein expression. A: The first antibody replaced with IgG was used as the negative control. B: The representative positive β-catenin immunostaining in conjunctival tissue was used as the positive control. C: E-cadherin protein expression detected in the membrane (400×). D: β-Catenin protein expression detected in the membrane (400×). In addition, aberrant localization of β-catenin was also detected in the cytoplasm/nuclei (E) and nucleus (F) (400×).