Vol.:(0123456789) 1 3 Breast Cancer https://doi.org/10.1007/s12282-020-01166-0 ORIGINAL ARTICLE EZH2 knockdown in tamoxifen‑resistant MCF‑7 cells unravels novel targets for regaining sensitivity towards tamoxifen Kanchan Kumari 1  · Sudarshan Kumar 2  · Dillip K. Parida 3  · Sandip K. Mishra 1 Received: 14 June 2020 / Accepted: 16 September 2020 © The Japanese Breast Cancer Society 2020 Abstract Background Acquired resistance to drug involves multilayered genetic and epigenetic regulation. Inhibition of EZH2 has proven to reverse the tamoxifen resistance back to the sensitive state in breast cancer. However, the molecular players involved in EZH2-mediated efects on tamoxifen-resistant MCF-7 cells are unknown. This study was conducted to understand the global change in proteome profle of tamoxifen-resistant MCF-7 breast cancer cells upon EZH2 knockdown. Methods Tamoxifen resistance MCF-7 breast cancer cells were established using increasing concentrations of 4-hydroxy tamoxifen. Using label free proteomics approach, we studied the alteration in total proteome in resistant cells as well as cells transfected with siEZH2 in comparison to sensitive and cells transfected with non-targeting siRNA. Results Here, we report list of proteins that were previously not recognized for their role in tamoxifen resistance and hold a close association with breast cancer patient survival. Proteins Annexin A2, CD44, nucleosome assembly protein 1, and lamin A/C were among the most upregulated protein in tamoxifen-resistant cells that were found to be abrogated upon EZH2 knockdown. The study suggests the involvement for various proteins in acquiring resistance towards tamoxifen and anticipates further research for investigating their therapeutic potentials. Conclusion Overall, we propose that targeting EZH2 or the molecules down the cascade might be helpful in reacquiring sensitivity to tamoxifen in breast cancer. Keywords EZH2 · Tamoxifen · Breast cancer Introduction Resistance to tamoxifen is a major challenge in the treat- ment of estrogen receptor (ER) positive breast cancer. More than 70% of breast tumors express ER and respond to tamoxifen; however, a gradual resistance is developed towards tamoxifen during the treatment that poses a serious concern for the continuation of the therapy [1]. Apart from genetic infuence, contribution of epigenetic modifcation in the development of drug resistance is widely accepted [2–5]. Reversing the drug resistance has been investigated using epigenetic strategies [6]. Histone methylation by poly- comb group protein Enhancer of Zeste Homolog 2 (EZH2) regulates the expression of several tumor suppressor genes, thereby contributing considerably to cancer progression. Previous studies on tamoxifen resistance development have found high levels of EZH2 which is strongly correlated with the progression of cancer even in the presence of the drug [7–9]. Association of EZH2 with estrogen receptor alpha anticipated its role in tamoxifen resistance [8, 10, 11]. Recent study showed that upon EZH2 inhibition, tamox- ifen-resistant cells regains the sensitivity towards tamoxifen [7]. In another recent study, tamoxifen resistance was found to be regulated by EZH2–ERalpha–GREB1 transcriptional axis [9]. Although a defnite association has been found between EZH2 and acquired tamoxifen resistance, there are many missing links to correctly interpret the mechanism of Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12282-020-01166-0) contains supplementary material, which is available to authorized users. * Sandip K. Mishra sandipkmishra@hotmail.com 1 Cancer Biology Laboratory, Institute of Life Sciences, Department of Biotechnology (Govt. of India), Bhubaneswar, Odisha, India 2 Animal Biotechnology Center, National Dairy Research Institute, Karnal, Haryana, India 3 Department of Radiation Oncology, All India Institute of Medical Sciences, Bhubaneswar 751019, India