Downregulation of estrogen receptor β inhibits lung adenocarcinoma cell growth

Estrogen receptor β (ERβ) is an important ER subtype in lung adenocarcinoma. However, the functions and mechanisms of ERβ have not been fully elucidated. The aim of the present study was to investigate the biological effects and relevant mechanisms of ERβ in lung adenocarcinoma. The protein expression of ERβ was found to be higher in lung adenocarcinoma tissues compared with that in adjacent non‑cancerous tissues (n=75, P<0.001). Of note, ERβ protein expression was significantly correlated with tumor size (P=0.018), lymph node metastasis (P=0.041), clinical stage (P=0.041) and differentiation (P<0.001). In addition, ERβ protein expression in A549 cells was found to be higher compared with that in human bronchial epithelial cells (HBEs). Furthermore, knockdown of ERβ expression inhibited colony formation and cell invasion in vitro, whereas the number of metastatic tumors in the lungs of mice was decreased in vivo. Western blot analysis demonstrated that the expression of phosphorylated extracellular signal‑regulated kinase (pERK), matrix metalloproteinase (MMP)‑2 and MMP‑9 was decreased by downregulation of ERβ. Therefore, ERβ may play an important role in lung adenocarcinoma progression via the MEK/ERK signaling axis, and it may represent a novel therapeutic target for lung adenocarcinoma in the future.