scholarly journals NR4A1 Regulates Tamoxifen Resistance by Suppressing ERK Signaling in ER-Positive Breast Cancer

Cells ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1633
Author(s):  
Yu Cheon Kim ◽  
Clara Yuri Kim ◽  
Ji Hoon Oh ◽  
Myoung Hee Kim
Keyword(s):  
Breast Cancer ◽  
Tamoxifen Resistance ◽  
Erk Signaling ◽  
Tamoxifen Treatment ◽  
Loss Of Function ◽  
Mcf7 Cells ◽  
Er Positive ◽  
Tamoxifen Resistant ◽  
Positive Breast Cancer

Endocrine therapy is used to treat estrogen receptor (ER)-positive breast cancer. Tamoxifen is effective against this cancer subtype. Nonetheless, approximately 30% of patients treated with tamoxifen acquire resistance, resulting in therapeutic challenges. NR4A1 plays key roles in processes associated with carcinogenesis, apoptosis, DNA repair, proliferation, and inflammation. However, the role of NR4A1 in tamoxifen-resistant ER-positive breast cancer has not yet been elucidated. Here, we propose that NR4A1 is a promising target to overcome tamoxifen resistance. NR4A1 gene expression was downregulated in tamoxifen-resistant MCF7 (TamR) cells compared to that in MCF7 cells. Kaplan-Meier plots were used to identify high NR4A1 expression correlated with increased survival rates in patients with ER-positive breast cancer following tamoxifen treatment. Gain and loss of function experiments showed that NR4A1 restores sensitivity to tamoxifen by regulating cell proliferation, migration, invasion, and apoptosis. NR4A1 localized to the cytoplasm enhanced the expression of apoptotic factors. In silico and in vitro analyses revealed that NR4A1 enhanced responsiveness to tamoxifen by suppressing ERK signaling in ER-positive breast cancer, suggesting that the NR4A1/ERK signaling axis modulates tamoxifen resistance. These results indicate that NR4A1 could be a potential therapeutic target to overcome tamoxifen resistance in ER-positive breast cancer.

scholarly journals TNFα Enhances Tamoxifen Sensitivity through Dissociation of ERα-p53-NCOR1 Complexes in ERα-Positive Breast Cancer

Cancers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 2601
Author(s):  
Hyunhee Kim ◽  
Seung-Ho Park ◽  
Jangho Lee ◽  
Gi-Jun Sung ◽  
Ji-Hye Song ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Tamoxifen Resistance ◽  
Estrogen Receptor Α ◽  
Tamoxifen Treatment ◽  
Mcf7 Cells ◽  
Cancer Cell Growth ◽  
Xenograft Mice ◽  
Positive Breast Cancer ◽  
Tamoxifen Sensitivity

Tamoxifen is widely used as a medication for estrogen receptor α (ERα)-positive breast cancer, despite the ~50% incidence of tamoxifen resistance. To overcome such resistance, combining tamoxifen with other agents is considered an effective approach. Here, through in vitro studies with ER-positive MCF7 cells and ER-negative MDA-MB-231 cells, validated by the use of xenograft mice, we investigated the potential of tumor necrosis factor α (TNFα) to enhance tamoxifen sensitivity and identified NCOR1 as a key downstream regulator. TNFα specifically degraded nuclear receptor corepressor 1 (NCOR1) in MCF7 cells. Moreover, knockdown of NCOR1, similar to TNFα treatment, suppressed cancer cell growth and promoted apoptosis only in MCF7 cells and MCF7 xenograft mice through the stabilization of p53, a tumor suppressor protein. Interestingly, NCOR1 knockdown with TNFα treatment increased the occupancy of p53 at the p21 promoter, while decreasing that of ERα. Notably, NCOR1 formed a complex with p53 and ERα, which was disrupted by TNFα. Finally, combinatorial treatment with tamoxifen, TNFα and short–hairpin (sh)-NCOR1 resulted in enhanced suppression of tumor growth in MCF7 xenograft mice compared to single tamoxifen treatment. In conclusion, TNFα promoted tamoxifen sensitivity through the dissociation of the ERα-p53-NCOR1 complex, pointing at NCOR1 as a putative therapeutic target for overcoming tamoxifen resistance in ERα-positive breast cancer.

scholarly journals YAP, CTGF, and Cyr61 are overexpressed in tamoxifen-resistant breast cancer and induce transcriptional repression of ERα

2021 ◽  
Author(s):  
Hyungjoo Kim ◽  
Seogho Son ◽  
Yunhyo Ko ◽  
Jeong Eon Lee ◽  
Sangmin Kim ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Transcriptional Repression ◽  
Estrogen Receptor Alpha ◽  
Tamoxifen Resistance ◽  
Tissue Growth ◽  
Tamoxifen Treatment ◽  
Transcriptional Level ◽  
Er Positive ◽  
Tamoxifen Resistant ◽  
Positive Breast Cancer

About 70% of breast cancer overexpresses estrogen receptor alpha (ERα). Tamoxifen, a competitive inhibitor of estrogen that binds to ER, has been widely used as a treatment for ER-positive breast cancer. However, 20-30% of breast cancer is resistant to tamoxifen treatment. The mechanisms underlying tamoxifen resistance remains elusive. We found that Yes-associated protein (YAP), connective tissue growth factor (CTGF), and cysteine-rich angiogenic inducer 61 (Cyr61) are overexpressed, while ERα is downregulated in tamoxifen-resistant breast cancer. Inhibition of YAP, CTGF, and Cyr61 restored ERα and increased sensitivity to tamoxifen. Overexpression of YAP, CTGF, and Cyr61 led to downregulation of ERα and conferred resistance to tamoxifen in ER-positive breast cancer cells. Mechanistically, CTGF and Cyr61 downregulated ERα expression at the transcriptional level by directly binding to the regulatory regions of ERα, leading to increased tamoxifen resistance. Also, CTGF induced Glut3 expression, leading to increased glycolysis, which enhanced cell proliferation and migration in tamoxifen-resistant cells. Together, these results demonstrate a novel role of YAP, CTGF, and Cyr61 in tamoxifen resistance and provide a molecular basis for their function in tamoxifen-resistant breast cancer.

scholarly journals SET Overexpression is Associated with Worse Recurrence-Free Survival in Patients with Primary Breast Cancer Receiving Adjuvant Tamoxifen Treatment

2018 ◽  
Vol 7 (9) ◽  
pp. 245 ◽  
Author(s):  
Yu-Hsiang Huang ◽  
Pei-Yi Chu ◽  
Ji-Lin Chen ◽  
Chun-Teng Huang ◽  
Chia-Han Lee ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Protein Phosphatase ◽  
Tamoxifen Treatment ◽  
Adjuvant Tamoxifen ◽  
Recurrence Free Survival ◽  
Free Survival ◽  
Er Positive ◽  
Phosphatase 2A ◽  
Positive Breast Cancer

Adjuvant tamoxifen reduces the recurrence rate of estrogen receptor (ER)-positive breast cancer. Previous in vitro studies have suggested that tamoxifen can affect the cancerous inhibitor of protein phosphatase 2A (CIP2A)/protein phosphatase 2A (PP2A)/phosphorylation Akt (pAkt) signaling in ER-negative breast cancer cells. In addition to CIP2A, SET nuclear proto-oncogene (SET) oncoprotein is another intrinsic inhibitor of PP2A, participating in cancer progression. In the current study, we explored the clinical significance of SET, CIP2A, PP2A, and Akt in patients with ER-positive breast cancer receiving adjuvant tamoxifen. A total of 218 primary breast cancer patients receiving adjuvant tamoxifen with a median follow-up of 106 months were analyzed, of which 17 (7.8%) experienced recurrence or metastasis. In an immunohistochemical (IHC) stain, SET overexpression was independently associated with worse recurrence-free survival (RFS) (hazard ratio = 3.72, 95% confidence interval 1.26–10.94, p = 0.017). In silico analysis revealed mRNA expressions of SET, PPP2CA, and AKT1 significantly correlated with worse RFS. In vitro, SET overexpression reduced tamoxifen-induced antitumor effects and drove luciferase activity in an Estrogen receptor element (ERE)-dependent manner. In conclusion, SET is a prognostic biomarker in patients with primary ER-positive breast cancer receiving adjuvant tamoxifen and may contribute to the failure of the tamoxifen treatment by modulating the ER signaling. Our study warrants further investigation into the potential role of SET in ER-positive breast cancer.

scholarly journals LAMP3 is involved in tamoxifen resistance in breast cancer cells through the modulation of autophagy

2014 ◽  
Vol 21 (1) ◽  
pp. 101-112 ◽  
Author(s):  
Anika Nagelkerke ◽  
Anieta M Sieuwerts ◽  
Johan Bussink ◽  
Fred C G J Sweep ◽  
Maxime P Look ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Mrna Expression ◽  
Cancer Cells ◽  
Breast Cancer Cells ◽  
Tamoxifen Resistance ◽  
Tamoxifen Treatment ◽  
Breast Cancer Patients ◽  
Mcf7 Cells ◽  
First Line ◽  
Tamoxifen Resistant

Lysosome-associated membrane protein 3 (LAMP3) is a member of the LAMP-family of proteins, which are involved in the process of autophagy. Autophagy is induced by tamoxifen in breast cancer cells and may contribute to tamoxifen resistance. In this study, the significance of LAMP3 for tamoxifen resistance in breast cancer was examined. The methods employed included use of clonogenic assays to assess the survival of MCF7 breast cancer cells with LAMP3 knockdown after tamoxifen treatment and of quantitative real-time PCR of LAMP3 to evaluate its predictive value for first-line tamoxifen treatment in patients with advanced breast cancer. Results show that tamoxifen treatment of MCF7 cells induced LAMP3 mRNA expression. LAMP3 knockdown in these cells increased tamoxifen sensitivity. Evaluation of expression of the autophagy markers, LC3B and p62, after LAMP3 knockdown showed increased expression levels, indicating that cells with LAMP3 knockdown have a suppressed ability to complete the autophagic process. In addition, knockdown of autophagy-associated genes resulted in sensitization to tamoxifen. Next, tamoxifen-resistant MCF7 cells were cultured. These cells had a sevenfold higher LAMP3 mRNA expression, showed elevated basal autophagy levels, and could be significantly resensitized to tamoxifen by LAMP3 knockdown. In patients treated with first-line tamoxifen for advanced disease (n=304), high LAMP3 mRNA expression was associated with shorter progression-free survival (P=0.003) and shorter post-relapse overall survival (P=0.040), also in multivariate analysis. Together, these results indicate that LAMP3 contributes to tamoxifen resistance in breast cancer. Tamoxifen-resistant cells are resensitized to tamoxifen by the knockdown of LAMP3. Therefore, LAMP3 may be clinically relevant to countering tamoxifen resistance in breast cancer patients.

scholarly journals Tamoxifen resistance alters sensitivity to 5-fluorouracil in a subset of estrogen receptor-positive breast cancer

PLoS ONE ◽  
2021 ◽  
Vol 16 (6) ◽  
pp. e0252822
Author(s):  
Takayuki Watanabe ◽  
Takaaki Oba ◽  
Keiji Tanimoto ◽  
Tomohiro Shibata ◽  
Shinobu Kamijo ◽  
...  
Keyword(s):  
Breast Cancer ◽  
T Cells ◽  
Estrogen Receptor ◽  
Endocrine Therapy ◽  
Chemotherapeutic Agents ◽  
Breast Cancers ◽  
Mcf7 Cells ◽  
Er Positive ◽  
Tamoxifen Resistant ◽  
Positive Breast Cancer

Sequential treatment with endocrine or chemotherapy is generally used in the treatment of estrogen receptor (ER)-positive recurrent breast cancer. To date, few studies have investigated the effect of long-term endocrine therapy on the response to subsequent chemotherapy in ER-positive breast cancer. We examined whether a preceding endocrine therapy affects the sensitivity to subsequent chemotherapy in ER-positive breast cancer cells. Three ER-positive breast cancer cell lines (T47D, MCF7, BT474) and tamoxifen-resistant sublines (T47D/T, MCF7/T, BT474/T) were analyzed for sensitivity to 5-fluorouracil, paclitaxel, and doxorubicin. The mRNA levels of factors related to drug sensitivity were analyzed by RT-PCR. MCF7/T cells became more sensitive to 5-fluorouracil than wild-type (wt)-MCF7 cells. In addition, the apoptosis induced by 5-fluorouracil was significantly increased in MCF7/T cells. However, no difference in sensitivity to chemotherapeutic agents was observed in T47D/T and BT474/T cells compared with their wt cells. Dihydropyrimidine dehydrogenase (DPYD) mRNA expression was significantly decreased in MCF7/T cells compared with wt-MCF7 cells. The expression of DPYD mRNA was restored with 5-azacytidine treatment in MCF7/T cells. In addition, DPYD 3′-UTR luciferase activity was significantly reduced in MCF7/T cells. These data indicated that the expression of DPYD mRNA was repressed by methylation of the DPYD promoter region and post-transcriptional regulation by miRNA in MCF7/T cells. In the mouse xenograft model, capecitabine significantly reduced the tumor volume in MCF7/T compared with MCF7. The results of this study indicate that endocrine therapy could alter the sensitivity to chemotherapeutic agents in a subset of breast cancers, and 5-fluorouracil may be effective in tamoxifen-resistant breast cancers.

scholarly journals The Utility of SOX2 and AGR2 Biomarkers as Early Predictors of Tamoxifen Resistance in ER-Positive Breast Cancer Patients

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Yomna Zamzam ◽  
Yosra Abdelmonem Zamzam ◽  
Marwa Aboalsoud ◽  
Heba Harras
Keyword(s):  
Breast Cancer ◽  
Cancer Patients ◽  
Tamoxifen Resistance ◽  
Tamoxifen Treatment ◽  
Time To Failure ◽  
Breast Cancer Patients ◽  
Early Predictors ◽  
Er Positive ◽  
Group 1 ◽  
Positive Breast Cancer

Background. Despite the undeniable benefit of tamoxifen therapy for ER-positive breast cancer patients, approximately one-third of those patients either do not respond to tamoxifen or develop resistance. Thus, it is a crucial step to identify novel, reliable, and easily detectable biomarkers indicating resistance to this drug. Objective. The aim of this work is to explore SOX2 and AGR2 biomarker expression in the tumor tissue of ER-positive breast cancer patients in combination with the evaluation of serum AGR2 level of these patients in order to validate these biomarkers as early predictors of tamoxifen resistance. Methods. This study was conducted on 224 ER-positive breast cancer patients. All patients were primarily subjected to serum AGR2 levelling by ELISA and their breast cancer tissue immunostained for SOX2 and AGR2. After 5 years of follow-up, the patients were divided into 3 groups: group 1 was tamoxifen sensitive and groups 2 and 3 were tamoxifen resistant. Time to failure of tamoxifen treatment was considered the time from the beginning of tamoxifen therapy to the time of discovery of breast cancer recurrence or metastases (in months). Results. SOX2 and AGR2 biomarkers expression and serum AGR2 level were significantly higher in groups 2 and 3 in comparison to group 1, while the relationship between Her2 neu expression and Ki67 index in the 3 different groups was statistically nonsignificant. Lower SOX2 and AGR2 expression and low AGR2 serum levels in the studied patients of groups 2 and 3 were significantly associated with longer time-to-failure of tamoxifen treatment. According to the ROC curve, the combined use of studied markers validity was with a sensitivity of 100%, specificity of 96%, PPV 96%, and NPV 100% ( p < 0.001 ; AUC: 0.984). Conclusions. Integrated use of SOX2 and AGR2 biomarkers with serum AGR2 assay holds a promising hope for their future use as predictive markers for early detection of tamoxifen resistance in ER-positive breast cancer patients.

scholarly journals Association of tamoxifen resistance and lipid reprogramming in breast cancer

2018 ◽  
Author(s):  
Susanne Hultsch ◽  
Matti Kankainen ◽  
Lassi Paavolainen ◽  
Ruusu-Maaria Kovanen ◽  
Elina Ikonen ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Gene Expression ◽  
Cell Lines ◽  
Expression Patterns ◽  
Tamoxifen Resistance ◽  
Tamoxifen Treatment ◽  
Common Mechanism ◽  
Gene Expression Patterns ◽  
Er Positive ◽  
Tamoxifen Resistant

AbstractBackgroundTamoxifen treatment of estrogen receptor (ER)-positive breast cancer reduces mortality by 31%. However, over half of advanced ER-positive breast cancers are intrinsically resistant to tamoxifen and about 40% will acquire the resistance during the treatment.MethodsIn order to explore mechanisms underlying endocrine therapy resistance in breast cancer and to identify new therapeutic opportunities, we created tamoxifen-resistant breast cancer cell lines that represent the luminal A or the luminal B. Gene expression patterns revealed by RNA-sequencing in seven tamoxifen-resistant variants were compared with their isogenic parental cells. We further examined those transcriptomic alterations in a publicly available patient cohort.ResultsWe show that tamoxifen resistance cannot simply be explained by altered expression of individual genes, common mechanism across all resistant variants, or the appearance of new fusion genes. Instead, the resistant cell lines shared altered gene expression patterns associated with cell cycle, protein modification and metabolism, especially with the cholesterol pathway. In the tamoxifen-resistant T-47D cell variants we observed a striking increase of neutral lipids in lipid droplets as well as an accumulation of free cholesterol in the lysosomes. Tamoxifen-resistant cells were also less prone to lysosomal membrane permeabilization (LMP) and not vulnerable to compounds targeting the lipid metabolism. However, the cells were sensitive to disulfiram, LCS-1, and dasatinib.ConclusionAltogether, our findings highlight a major role of LMP prevention in tamoxifen resistance, and suggest novel drug vulnerabilities associated with this phenotype.

scholarly journals miR-449a Suppresses Tamoxifen Resistance in Human Breast Cancer Cells by Targeting ADAM22

2018 ◽  
Vol 50 (1) ◽  
pp. 136-149 ◽  
Author(s):  
Jun Li ◽  
Mingjie Lu ◽  
Jiao Jin ◽  
Xiyi Lu ◽  
Tongpeng Xu ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Cancer Cells ◽  
Breast Cancer Cells ◽  
Tamoxifen Resistance ◽  
Luciferase Assay ◽  
Protein Protein Interaction ◽  
Er Positive ◽  
Tamoxifen Resistant ◽  
Mcf 7 ◽  
Positive Breast Cancer

Background/Aims: Most of estrogen receptor positive breast cancer patients respond well initially to endocrine therapies, but often develop resistance during treatment with selective estrogen receptor modulators (SERMs) such as tamoxifen. Altered expression and functions of microRNAs (miRNAs) have been reportedly associated with tamoxifen resistance. Thus, it is necessary to further elucidate the function and mechanism of miRNAs in tamoxifen resistance. Methods: Tamoxifen sensitivity was validated by using Cell Counting Kit-8 in tamoxifen-sensitive breast cancer cells (MCF-7, T47D) and tamoxifen-resistant cells (MCF-7/TAM, T47D/ TAM). Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect the expression level of miR-449a in tamoxifen-sensitive/-resistant cells and patient serums. Dual-luciferase assay was used to identify the binding of miR-449a and predicted gene ADAM22. The expression level of ADAM22 was determined by qRT-PCR and western blotting in miR-449a +/- breast cancer cells. Subsequently, rescue experiments were carried out to identify the function of ADAM22 in miR-449a-reduced tamoxifen resistance. Finally, Gene ontology (GO) and Protein-protein interaction analyses were performed to evaluate the potential mechanisms of ADAM22 in regulating tamoxifen resistance. Results: MiR-449a levels were downregulated significantly in tamoxifen-resistant breast cancer cells when compared with their parental cells, as well as in clinical breast cancer serum samples. Overexpression of miR-449a re-sensitized the tamoxifen-resistant breast cancer cells, while inhibition of miR-449a conferred tamoxifen resistance in parental cells. Luciferase assay identified ADAM22 as a direct target gene of miR-449a. Additionally, silencing of ADAM22 could reverse tamoxifen resistance induced by miR-449a inhibition in ER-positive breast cancer cells. GO analysis results showed ADAM22 was mainly enriched in the biological processes of cell adhesion, cell differentiation, gliogenesis and so on. Protein-protein interaction analyses appeared that ADAM22 might regulate tamoxifen resistance through PPARG, LGI1, KRAS and LYN. Conclusion: Decreased miR-449a causes the upregulation of ADAM22, which induces tamoxifen resistance of breast cancer cells. These results suggest that miR-449a, functioning by targeting ADAM22, contributes to the mechanisms underlying breast cancer endocrine resistance, which may provide a potential therapeutic strategy in ER-positive breast cancers.

scholarly journals Network-based Approach to Identify Prognosis-related Genes in Tamoxifen-treated Patients With Estrogen Receptor-positive Breast Cancer

2020 ◽  
Author(s):  
Yanyan Wang ◽  
Xiaonan Gong ◽  
Yujie Zhang
Keyword(s):  
Breast Cancer ◽  
Estrogen Receptor ◽  
Protein Targeting ◽  
Quantitative Polymerase Chain Reaction ◽  
Tamoxifen Resistance ◽  
The Cancer Genome Atlas ◽  
Tamoxifen Treatment ◽  
Hub Genes ◽  
Er Positive ◽  
Positive Breast Cancer

Abstract Background: The estrogen receptor (ER) antagonist tamoxifen is the most commonly used endocrine therapy for ER-positive breast cancer. However, tamoxifen resistance remains a major cause of cancer recurrence and progression. Here, we aimed to identify hub genes involved in the progression and prognosis of ER-positive breast cancer following tamoxifen treatment.Results: Microarray data (GSE9838) for 155 tamoxifen-treated primary ER-positive breast cancer samples were obtained from the Gene Expression Omnibus database. In total, 1706 differentially expressed genes (DEGs) associated with tamoxifen resistance, including 859 upregulated genes and 847 downregulated genes, were identified. These DEGs were mainly enriched in functions such as protein targeting to the ER and pathways such as ribosome and oxidative phosphorylation.Weighted correlation network analysis (WGCNA) clustered genes into 13 modules, among which the tan and blue modules were the most significantly related to prognosis. From these two modules, we further identified three prognosis-related hub genes (GRSF1, MAPT, and REC8) via survival analysis. High expression ofGRSF1 predicted poor prognosis, whereas MAPT andREC8indicated favorable survival outcomes in all patients with breast cancer and in patients with ER-positive breast cancer based on The Cancer Genome Atlas database. These hub genes were further verified by reverse transcription quantitative polymerase chain reaction.Conclusion: Our findings established novel prognostic biomarkers to predict tamoxifen sensitivity, which may facilitate individualized management of breast cancer.

MLL3 Induced by Luteolin Causes Apoptosis in Tamoxifen-Resistant Breast Cancer Cells through H3K4 Monomethylation and Suppression of the PI3K/AKT/mTOR Pathway

2020 ◽  
Vol 48 (05) ◽  
pp. 1221-1241 ◽  
Author(s):  
Han-Tsang Wu ◽  
Yi-En Liu ◽  
Kai-Wen Hsu ◽  
Yu-Fen Wang ◽  
Ya-Chi Chan ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Cancer Cells ◽  
Breast Cancer Cells ◽  
Tamoxifen Resistance ◽  
Mtor Inhibitors ◽  
Ras Gene ◽  
Ras Genes ◽  
Er Positive ◽  
Tamoxifen Resistant ◽  
Positive Breast Cancer

Tamoxifen is one of the most common hormone therapy drug for estrogen receptor (ER)-positive breast cancer. Tumor cells with drug resistance often cause recurrence and metastasis in cancer patients. Luteolin is a natural compound found from various types of vegetables and exhibit anticancer activity in different cancers. This study demonstrated that luteolin inhibits the proliferation and induces apoptosis of tamoxifen-resistant ER-positive breast cancer cells. Luteolin also causes cell cycle arrest at the G2/M phase and decreases mitochondrial membrane potential. Besides, luteolin reduces the levels of activated PI3K/AKT/mTOR signaling pathway. The combination treatment of luteolin and PI3K, AKT, or mTOR inhibitors synergistically increases apoptosis in tamoxifen-resistant ER-positive breast cancer cells. Ras gene family (K-Ras, H-Ras, and N-Ras), an activator of PI3K, was transcriptionally repressed by luteolin via induction of tumor suppressor mixed-lineage leukemia 3 (MLL3) expression. MLL3 increases the level of monomethylation of Histone 3 Lysine 4 on the enhancer and promoter region of Ras genes, thus causes repression of Ras expressions. Our finding implies that luteolin was a promising natural agent against tamoxifen resistance of breast cancer.

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