Mps1 contributes to tamoxifen resistance in Breast Cancer through phosphorylation of ERα

Overexpression of mitotic kinase monopolar spindle 1 (Mps1) has been identified in many tumor types and targeting Mps1 for tumor therapy has been shown great promise in multiple preclinical cancer models. However, the role of Mps1 in tamoxifen resistance in breast cancer has never been reported. Here in this study, we report that Mps1 determined the sensitivity of breast cancer cells to tamoxifen treatment. Mps1 overexpression rendered breast cancer cells more resistant to tamoxifen, while Mps1 inhibitor or siMps1 oligos could overcome tamoxifen resistance. Mechanistically, Mps1 interacted with ERα and stimulated its transcriptional activity in kinase activity-dependent manner. Mps1 was responsible for ERα phosphorylation at S559 and T224 sites. Importantly, Mps1 failed to enhance the transcriptional activity of ERα in the presence of ERα S559A or T224A mutant. Collectively, our findings suggest that Mps1 contributes to tamoxifen resistance in breast cancer and is a potential therapeutic to overcome tamoxifen resistance in breast cancer.