Project description:Resistance to tamoxifen is a major challenge in the treatment of estrogen receptor positive breast cancer. Acquired resistance to drug involves multilayered genetic and epigenetic regulation . The oncogene EZH2 plays significant role in the development of resistance against tamoxifen, widely used in the treatment of breast cancer. Inhibition of EZH2 has proven to reverse the tamoxifen resistance breast cancer cells back to the sensitive state. The molecular mechanism through which EZH2 inhibition triggers its effects are not known.This study was conducted to understand the global change in proteome profile of tamoxifen resistant MCF-7 breast cancer cells as a result of effect of EZH2 knockdown. Label Free Quantitative proteomics revealed a large number of proteins altered in acquired tamoxifen resistant cells compared to the sensitive cells. A total of 286 proteins were identified with normalized RT for each m/z out of which 86 proteins were upregulated by more than 1.3 fold and 98 proteins were down regulated by more than 1.3 fold in MCF-7 tamoxifen resistant breast cancer cells in comparison to the sensitive breast cancer cells. Upon EZH2 knockdown in tamoxifen resistant cells, a total of 115 proteins were found to be altered with 20 proteins upregulated by more than 1.3 fold and 49 proteins down regulated by more than 1.3 fold. Among the top upregulated proteins were L-lactate dehydrogenase A chain, Alpha and Gamma-enolase, Calreticulin, heat shock protein HSP-90-beta, Alpha-actinin-4, Elongation factor 1-alpha, Vimentin, Protein S100A6, Putative protein FAM10A5, Heterogeneous nuclear ribonucleoprotein A1 and Keratin 1. In addition, 15 proteins were found to be down regulated in EZH2si transfected tamoxifen sensitive cells which otherwise were highlyup regulated in resistant cells in the presence of normal level of EZH2. This indicates a possible regulation of these molecules by EZH2 leading to loss of resistance. Our data unveils important molecular players downstream to EZH2 knockdown leading to regain of sensitivity to tamoxifen in acquired tamoxifen resistance.Thus, EZH2 seems to exert its effects through regulation of metabolism, epithelial to mesenchymal transition and protein synthesis & folding. Hence, targeting EZH2 or the molecules down the cascade might be helpful in reacquiring sensitivity to tamoxifen intamoxifen-resistant cells.

Project description:Purpose: Tamoxifen is the most commonly used antiestrogen drug for breast cancer treatment, however, acquired resistance is a considerable challenge in clinic. Complexity and redundancy in biological system implies tamoxifen resistance is associated with complex biological processes. The aim of this study is to attempt to reveal the mechanism of tamoxifen resistance using high-throughput sequencing technique. Methods: We applied digital gene expression (DGE), RNA-seq, Small RNA-seq, bisulifte-seq (reduced representation bisuflite sequencing (RRBS)) with Illumina sequencing platforms, and Array CGH to analyze two well-established tamoxifen resistant cell line models: one is the LCC cell line model that was derived from MCF-7 breast cancer cell line and developed tamoxifen resistance following a step-wise strategy. This cell line model includes LCC0 (estrogen-dependent and tamoxifen sensitive), LCC1 (estrogen-independent and tamoxifen sensitive), LCC2 (derived from LCC1 with increased small-dosage tamoxifen treatment, estrogen-independent, and tamoxifen-resistant), and LCC9 (derived from LCC1 with increased small-dosage fluvestrant treatment, estrogen-independent, and cross-resistance to both fluvestrant and tamoxifen). The other is the TAMR cell line model that was derived from MCF-7 breast cancer cell line and developed four tamoxifen-resistant sublines following the strategy of high-dosage of tamoxifen treatment. Each subline was developed from the survived single cell after the tamoxifen treatment. Results: The DGE and RNA-seq results showed characteristic expression features for the both cell line models, for instance, high expression of SOX2 and alterations of other SOX gene family members, decreased expression of PGR, PTEN, TP53, EZH2, SMAD3, TGF-β1, DNMT1, APOBEC3B, FOXO3 and FOXO4, and increased expression of CDH1, APOBEC3H, FOXA1, TET2, TET3, TDG, MBD4, DNMT3a and DNMT3b between the tamoxifen-resistant cell lines with their matched parental cell lines. Small RNA seq showed the decreased expressions of miR-1, miR-196-3p, miR-18a-5p, miR-125b-5p, and the increased expression of miR-23a-3p, miR-26b-5p, miR-320d, miR-141-3p, miR-23a-3p, miR-30a-5p, miR-9-5p, miR-200c, miR-129-5p, miR-125b-5p, miR-1285-3p and miR-30b-5p between the tamoxifen-resistant cell lines and their matched parental cell lines. Additionally, let-7a and let-7c have been found to present high expression levels in the tamoxifen resistant cells in the both cell line models, even it showed significantly decreased in some TAMR cells compared with their parental cell line. The RRBS showed similar DNA methylation levels between the LCC cell lines. Array CGH showed a small number of copy number variants between the LCC cell lines. Conclusion: Our present study suggests the development of tamoxifen resistance is associated with a dynamic process of cell fate changing. Therefore, new therapeutic method that targets whole cell system and cell fate dynamics, will be a promising strategy.

Dataset Information

Phosphoproteomic analysis of tamoxifen resistant breast cancer

Publications

Phosphoproteomic Analysis Identifies Focal Adhesion Kinase 2 (FAK2) as a Potential Therapeutic Target for Tamoxifen Resistance in Breast Cancer.

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