Estrogen promotes the metastasis of non‑small cell lung cancer via estrogen receptor β by upregulation of Toll‑like receptor 4 and activation of the myd88/NF‑κB/MMP2 pathway

: Estrogen promotes non‑small cell lung cancer (NSCLC) metastasis via estrogen receptor β (ERβ)‑mediated invasiveness‑associated matrix metalloprotease 2 (MMP2) upregulation. However, how ERβ increases the aggressiveness of NSCLC cells remains unclear. Recently, MMP2 was found to be upregulated by Toll‑like receptor 4 (TLR4) signaling activation and to promote NSCLC metastasis. Our present study aimed to examine the role of ERβ in the activation of TLR4 signaling and in tumor progression and metastasis, and to explore the synergistic metastatic effect of a combination of ERβ and TLR4 activation on human NSCLC cells in vitro and in vivo. Here, we found that ERβ is associated with TLR4 in metastatic lymph nodes. Western blot analysis and immunofluorescence revealed that ERβ overexpression upregulated TLR4 protein expression and activated downstream targets, myeloid differentiation primary response 88 (myd88)/nuclear factor (NF)‑κB/MMP2, enhancing NSCLC cell migration and invasion in vitro. A novel ERβ‑TLR4 interaction in cell plasma was identified by co‑immunoprecipitation and confocal immunofluorescence. The combination of estradiol and specific TLR4 agonist lipopolysaccharide (LPS) synergistically promoted metastatic behaviors in NSCLC cells. In cell culture and murine lung metastasis models, exposure to estradiol and LPS induced increased matrix degradation and accelerated invadopodia and metastasis formation in NSCLC cells compared with that in cells treated with estradiol or LPS alone. Together, we showed that estrogen promoted NSCLC metastasis via ERβ by upregulating TLR4 and activating its downstream signaling axis myd88/NF‑κB/MMP2. The combined targeting of ERβ and TLR4 may be a novel therapeutic strategy against advanced metastatic lung cancer.