Epigenetic regulation of epithelial-to-mesenchymal transition as a captain of journey of cancer from lung to brain

Abstract

Background: There have been many studies for epithelial-to-mesenchymal transition (EMT) of the cancer, especially focused on the important transcriptional factors. Recently epigenetic mechanisms, including histone modification have been comprehensively studied for establishing the role on the prohibiting metastasis of cancer cell. The objective of presenting study is to investigate the epigenetic role of histone lysine methylation/demethylation on the regulating expression of the transcriptional factors of EMT in lung cancer and brain metastasis.

Material and Methods: The paired samples of NSCLC and brain metastasis were analyzed in 23 individual patients. Both samples were obtained by surgical resection or biopsy of the lung and brain. The paraffin-fixed formalin embedded (FFPE) samples was obtained at the pathological archives in our institute. The medical record (age, gender, performance status, interval of metastasis, site of extracranial metastasis, survival after diagnosis of NSCLC, and survival after diagnosis of brain metastasis) was reviewed retrospectively. In both samples of NSCLC and brain metastasis, immunohistochemical staining was performed for epithelial markers, mesenchymal markers, transcriptional factors of EMT factors, histone lysine methyltransferase, and histone lysine demethylase.

Results: The epithelial markers such as E-cadherin (24.6% vs 12.6%, p = 0.037), Desmoplakin (15.6% vs 2.3%, p = 0.007), α-caterin (41.3% vs 28.3%, p = 0.042), and β-caterin (38.6% vs 16.9%, p = 0.029) were significantly decreased in brain metastasis samples compared with NSCLC sample. The mesenchymal markers such as N-cadherin (20.6% vs 43.2%, p = 0.028), Vimentin (15.3% vs 51.6%, p = 0.004), and Fibronectin (7.6% vs 39.4%, p = 0.002) were significantly increased in brain metastasis samples compared with NSCLC sample. The immunoreactivity of transcriptional factors such as Slug (15.6% vs 42.6%, p = 0.005), Twist (23.6% vs 45.9%, p = 0.010) and ZEB1 (15.0% vs 55.9%, p = 0.002) was also increased in brain metastasis samples compared with NSCLC sample. Epigenetic inducers such as MLL4 (H3K4 methyltransferase) and UTX (H3K36 demethylase) were statistically increased and epigenetic repressor such as EZH2 (H3K27 methyltransferase) was statistically decreased in brain metastasis samples compared with NSCLC sample. The expression of UTX-ZEB1 (R2 linear = 1.204) and MLL4-Slug (R2 linear = 0.987) was increased in direct proportion and EZH2-Twist (R2 linear = − 2.723) was decreased in reverse proportion.

Conclusion. This study suggested that MLL4 and UTX should epigenetically induce the expression of EMT transcriptional factor such as Slug and ZEB1 respectively, and EZH2 should epigenetically reduce the expression of EMT transcription factor such as Twist in the process of NSCLC metastasis to the brain.