Stage-dependent expression and nuclear localization of EZH2 in endometrial carcinogenesis: evidence from cell lines...

Enhancer of zeste homolog 2 (EZH2) is a key epigenetic regulator implicated in tumor progression; however, its expression pattern and subcellular localization across different stages of endometrial carcinogenesis remain incompletely characterized. This study evaluated EZH2 expression in two biologically distinct endometrial carcinoma cell lines (Ishikawa and MFE-319) and in archived human endometrial tissues representing proliferative and secretory endometrium, hyperplasia, and Type I and Type II endometrial carcinomas. Histopathological evaluation was performed using hematoxylin and eosin staining. EZH2 expression was assessed by immunocytochemistry and Western blot analysis in the cell lines and by immunohistochemistry in tissue specimens, while apoptosis was evaluated by TUNEL assay in tissue samples. MFE-319 cells demonstrated significantly higher EZH2 expression than Ishikawa cells (H-score: 352.9 ± 78.9 vs. 137.6 ± 31.5, p < 0.0001), and Western blot analysis confirmed the same direction of change. Among tissue specimens, the highest EZH2 immunoreactivity was observed in Type II endometrial carcinoma (366.0 ± 63.7), with significantly higher expression than proliferative endometrium (231.5 ± 59.3), secretory endometrium (190.5 ± 52.4), and hyperplasia without atypia (261.0 ± 56.9), whereas no significant differences were detected among several intermediate histopathological groups. Nuclear localization of EZH2 became more prominent in atypical hyperplasia and carcinoma tissues. Apoptotic indices were significantly higher in both Type I and Type II carcinomas than in normal endometrium and hyperplasia groups, representing an association with increased EZH2 expression rather than evidence of a direct mechanistic relationship. These findings demonstrate that EZH2 expression differs across histopathological categories of endometrial lesions, with the highest expression observed in Type II endometrial carcinoma. The observed predominance of nuclear EZH2 in atypical hyperplasia and carcinoma further supports its association with aggressive tumor biology, although additional functional and clinicopathological studies are required to establish its clinical and biological significance.