Background: Breast cancer (BC) is the most common malignancy worldwide. ERα36 (ERα66 variant) is expressed in many breast cancer cells, especially highly expressed in tamoxifen (TAM)-resistant cell lines and triple-negative...

Purpose: This study is to investigate the effect and mechanism of curcumol on ERα36 positive breast cancer cells, and the relationship between curcumol’s target protein nucleolin (NCL) and ERα36. Methods: The anti-tumor effect of curcumol were quantified via MTT assay, colony formation and cycle arrest respectively. The expression of ERα36, NCL and the proteins involved in PI3K/AKT signaling were evaluated by western blotting. The interaction between two proteins were detected using co-immunoprecipitation (Co-IP) and immunofluorescence assay. Mouse xenograft model was established to verify the role of ERα36 in breast cancer cells and curcumol’s effect on ERα36 positive cancer cells. Results: Curcumol inhibited the cell growth, caused cell cycle arrest, decreased cell cycle related-proteins and inactivated PI3K/AKT pathway in ERα36 positive breast cancer cells. There is a positive correlation between NCL and ERα36 in breast cancer cells. In addition, ERα36 bound to NCL, the two proteins were distributed in the nucleus, cytoplasm and on the plasma membrane, where their expression were obviously decreased by curcumol. Moreover, NCL silenced by NCL siRNA blocked the cell cycle progress and inhibited the activation of PI3K/AKT in MDA-MB-231 cells, while overexpressed ERα36 increased the expression of NCL, promoted cell cycle progress and enhanced the activity of PI3K/AKT in MCF-7 cells. NCL knockdown or ERα36 overexpressed all attenuated the effect of curcumol on breast cancer cells. Conclusion: Curcumol reduced the proliferation of breast cancer cells by targeting NCL/ERα36 and inactivated PI3K/AKT pathway.