Expression of PRMT5 in lung adenocarcinoma and its significance in epithelial-mesenchymal transition

Although protein arginine methyltransferase 5 (PRMT5) has been implicated in various cancers, its expression pattern in lung adenocarcinoma cell lines and tissues has not been elucidated enough. In this study, microarray analysis of 40 non-small-cell lung carcinoma cell lines showed that PRMT5 was a candidate histone methyltransferase gene that correlated with epithelial-mesenchymal transition. Immunocytochemical analysis of these cell lines indicated that the expression of PRMT5 was localized to the cytoplasm of E-cadherin-low and vimentin-high cell lines, whereas it was predominant in the nucleus and faint in the cytoplasm of E-cadherin-high and vimentin-low cell lines. Immunohistochemical analysis of lung adenocarcinoma cases (n = 130) revealed that the expression of PRMT5 was high in the cytoplasm of 47 cases (36%) and the nuclei of 34 cases (26%). The marked cytoplasmic expression of PRMT5 was frequently observed in high-grade subtypes (1 of 17 low grade, 21 of 81 intermediate grade, and 25 of 32 high grade; P <.0001) such as solid adenocarcinoma with the low expression of thyroid transcription factor 1 (the master regulator of lung) and low expression of cytokeratin 7 and E-cadherin (2 markers for bronchial epithelial differentiation), whereas the high nuclear expression of PRMT5 was frequently noted in adenocarcinoma in situ, a low-grade subtype (6 of 17 low grade, 25 of 81 intermediate grade, and 3 of 32 high grade; P =.0444). The cytoplasmic expression of PRMT5 correlated with a poor prognosis (P =.0089). We herein highlighted the importance of PRMT5 expression, especially its cytoplasmic expression, in the process of epithelial-mesenchymal transition and loss of the bronchial epithelial phenotype of lung adenocarcinoma.