Primary tumors facilitate metastasis by directing bone marrowderived cells (BMDCs) to colonize the lungs before the arrival of cancer cells. Here, we demonstrate that hypoxia-inducible factor 1 ...(HIF-1) is a critical regulator of breast cancer metastatic niche formation through induction of multiple members of the lysyl oxidase (LOX) family, including LOX, LOX-like 2, and LOX-like 4, which catalyze collagen cross-linking in the lungs before BMDC recruitment. Only a subset of LOX family members was expressed in any individual breast cancer, but HIF-1 was required for expression in each case. Knockdown of HIF-1 or hypoxia-induced LOX family members reduced collagen cross-linking, CD11b⁺ BMDC recruitment and metastasis formation in the lungs of mice after orthotopic transplantation of human breast cancer cells. Metastatic niche formation is an HIF-1-dependent event during breast cancer progression.
Eukaryotic translation initiation factor 4E (eIF4E) selectively promotes translation of mRNAs with atypically long and structured 5'-UTRs and has been implicated in drug resistance. Through ...genome-wide transcriptome and translatome analysis we revealed eIF4E overexpression could promote cellular activities mediated by ERα and FOXM1 signalling pathways. Whilst eIF4E overexpression could enhance the translation of both ERα and FOXM1, it also led to enhanced transcription of FOXM1. Polysome fractionation experiments confirmed eIF4E could modulate the translation of ERα and FOXM1 mRNA. The enhancement of FOXM1 transcription was contingent upon the presence of ERα, and it was the high levels of FOXM1 that conferred Tamoxifen resistance. Furthermore, tamoxifen resistance was conferred by phosphorylation independent eIF4E overexpression. Immunohistochemistry on 134 estrogen receptor (ER
) primary breast cancer samples confirmed that high eIF4E expression was significantly associated with increased ERα and FOXM1, and significantly associated with tamoxifen resistance. Our study uncovers a novel mechanism whereby phosphorylation independent eIF4E translational reprogramming in governing the protein synthesis of ERα and FOXM1 contributes to anti-estrogen insensitivity in ER
breast cancer. In eIF4E overexpressing breast cancer, the increased ERα protein expression in turn enhances FOXM1 transcription, which together with its increased translation regulated by eIF4E, contributes to tamoxifen resistance. Coupled with eIF4E translational regulation, our study highlights an important mechanism conferring tamoxifen resistance via both ERα dependent and independent pathways.
The androgen receptor (AR) is a steroid hormone receptor widely detected in breast cancer. Evidence suggests that the AR might be a tumor suppressor in estrogen receptor alpha-positive (ERα+ve) ...breast cancer but a tumor promoter in estrogen receptor alpha-negative (ERα-ve) breast cancer. Modulating AR activity could be a potential strategy for treating breast cancer. For ERα+ve breast cancer, activation of the AR had been demonstrated to suppress the disease. In contrast, for ERα-ve breast cancer, blocking the AR could confer better prognosis to patients. These studies support the feasibility of utilizing AR modulators as anti-cancer drugs for different subtypes of breast cancer patients. Nevertheless, several issues still need to be addressed, such as the lack of standardization in the determination of AR positivity and the presence of AR splice variants. In future, the inclusion of the AR status in the breast cancer report at the time of diagnosis might help improve disease classification and treatment decision, thereby providing additional treatment strategies for breast cancer.
Breast cancer is the most common female cancer. About 70% of breast cancer patients are estrogen receptor α (ERα) positive (ER+) with tamoxifen being the most commonly used anti-endocrine therapy. ...However, up to 50% of patients who receive tamoxifen suffer recurrence. We previously identified BQ323636.1 (BQ), a novel splice variant of NCOR2, can robustly predict tamoxifen resistance in ER+ primary breast cancer. Here we show that BQ can enhance IL-6/STAT3 signalling. We demonstrated that through interfering with NCOR2 suppressive activity, BQ favours the binding of ER to IL-6 promoter and the binding of NF-ĸB to IL-6 receptor (IL-6R) promoter, leading to the up-regulation of both IL-6 and IL-6R and thus the activation of STAT3. Knockdown of IL-6R could compromise tamoxifen resistance mediated by BQ. Furthermore, Tocilizumab (TCZ), an antibody that binds to IL-6R, could effectively reverse tamoxifen resistance both in vitro and in vivo. Analysis of clinical breast cancer samples confirmed that IL-6R expression was significantly associated with BQ expression and tamoxifen resistance in primary breast cancer, with high IL-6R expression correlating with poorer survival. Multivariate Cox-regression analysis confirmed that high IL-6R expression remained significantly associated with poor overall as well as disease-specific survival in ER+ breast cancer.
Biomarkers can be used for diagnosis, prognosis, and prediction in targeted therapy. The estrogen receptor α (ERα) and human epidermal growth factor receptor 2 (HER2) are standard biomarkers used in ...breast cancer for guiding disease treatment. The androgen receptor (AR), a nuclear hormone receptor, contributes to the development and progression of prostate tumors and other cancers. With increasing evidence to support that AR plays an essential role in breast cancer, AR has been considered a useful biomarker in breast cancer, depending on the context of breast cancer sub-types. The existing survival analyses suggest that AR acts as a tumor suppressor in ER + ve breast cancers, serving as a favorable prognostic marker. However, AR functions as a tumor promoter in ER-ve breast cancers, including HER2 + ve and triple-negative (TNBC) breast cancers, serving as a poor prognostic factor. AR has also been shown to be predictive of the potential of response to adjuvant hormonal therapy in ER + ve breast cancers and to neoadjuvant chemotherapy in TNBC. However, conflicting results do exist due to intrinsic molecular differences between tumors and the scoring method for AR positivity. Applying AR expression status to guide treatment in different breast cancer sub-types has been suggested. In the future, AR will be a feasible biomarker for breast cancer. Clinical trials using AR antagonists in breast cancer are active. Targeting AR alone or other therapeutic agents provides alternatives to existing therapy for breast cancer. Therefore, AR expression will be necessary if AR-targeted treatment is to be used.
Breast cancer is a heterogeneous disease. Tamoxifen is frequently used to treat ER-positive breast cancer. Our team has identified a novel splice variant of NCOR2, BQ323636.1 (BQ), that mediates ...tamoxifen resistance. However, the upstream factors that modulate BQ expression are not apparent. This study reveals that tamoxifen treatment causes induction of DNA damage which can enhance BQ expression. We show that DNA damage can activate the ATM/CHK2 and ATR/CHK1 signalling cascades and confirm that ATM/CHK2 signalling is responsible for enhancing the protein stability of BQ. siRNA or a small inhibitor targeting CHK2 resulted in the reduction in BQ expression through reduced phosphorylation and enhanced poly-ubiquitination of BQ. Inhibition of CHK2 by CCT241533 could reverse tamoxifen resistance in vitro and in vivo. Using clinical samples in the tissue microarray, we confirmed that high p-CHK2 expression was significantly associated with high nuclear BQ expression, tamoxifen resistance and poorer overall and disease-specific survival. In conclusion, tamoxifen treatment can enhance BQ expression in ER-positive breast cancer by activating the ATM/CHK2 axis. Targeting CHK2 is a promising approach to overcoming tamoxifen resistance in ER-positive breast cancer.
Breast cancer is a heterogeneous disease. Around 70% of breast cancers are estrogen receptor-positive (ER+ve), with tamoxifen being most commonly used as an adjuvant treatment to prevent recurrence ...and metastasis. However, half of the patients will eventually develop tamoxifen resistance. The overexpression of c-MYC can drive the development of ER+ve breast cancer and confer tamoxifen resistance through multiple pathways. One key mechanism is to enhance ribosome biogenesis, synthesising mature ribosomes. The over-production of ribosomes sustains the demand for proteins necessary to maintain a high cell proliferation rate and combat apoptosis induced by therapeutic agents. c-MYC overexpression can induce the expression of eIF4E that favours the translation of structured mRNA to produce oncogenic factors that promote cell proliferation and confer tamoxifen resistance. Either non-phosphorylated or phosphorylated eIF4E can mediate such an effect. Since ribosomes play an essential role in c-MYC-mediated cancer development, suppressing ribosome biogenesis may help reduce aggressiveness and reverse tamoxifen resistance in breast cancer. CX-5461, CX-3543 and haemanthamine have been shown to repress ribosome biogenesis. Using these chemicals might help reverse tamoxifen resistance in ER+ve breast cancer, provided that c-MYC-mediated ribosome biogenesis is the crucial factor for tamoxifen resistance. To employ these ribosome biogenesis inhibitors to combat tamoxifen resistance in the future, identification of predictive markers will be necessary.
Loading of p53-binding protein 1 (53BP1) and receptor-associated protein 80 (RAP80) at DNA double-strand breaks (DSBs) drives cell cycle checkpoint activation but is counterproductive to ...high-fidelity DNA repair. ring finger protein 169 (RNF169) maintains the balance by limiting the deposition of DNA damage mediator proteins at the damaged chromatin. We report here that this attribute is accomplished, in part, by a predicted nuclear localization signal (NLS) that not only shuttles RNF169 into the nucleus but also promotes its stability by mediating a direct interaction with the ubiquitin-specific protease USP7. Guided by the crystal structure of USP7 in complex with the RNF169 NLS, we uncoupled USP7 binding fromits nuclear import function and showed that perturbing the USP7–RNF169 complex destabilized RNF169, compromised high-fidelity DSB repair, and hypersensitized cells to poly (ADP-ribose) polymerase inhibition. Finally, expression of USP7 and RNF169 positively correlated in breast cancer specimens. Collectively, our findings uncover an NLS-mediated bipartite mechanism that supports the nuclear function of a DSB response protein.
In this study, we report the identification of a novel role of SIRT6 in both epirubicin and paclitaxel resistance in breast cancer. We found that SIRT6 protein levels are elevated in paclitaxel- and ...epirubicin-resistant MCF-7 cells compared with the parental sensitive cells. SIRT6 knockout and depletion sensitized cells to both paclitaxel and epirubicin treatment, whereas SIRT6 ectopic overexpression led to increased resistance to paclitaxel and epirubicin. Moreover, our data suggest that SIRT6 could be mediating epirubicin resistance through enhancing the DNA repair response to epirubicin-induced DNA damage. Clonogenic assays also revealed that mouse embryonic fibroblasts (MEFs) lacking SIRT6 have decreased long-term viability in response to epirubicin. The tumour suppressor FOXO3a increases its levels of acetylation in MEFs depleted of SIRT6, whereas its induction by epirubicin is attenuated in breast cancer cells overexpressing SIRT6. Further cell viability studies demonstrate that deletion of FOXO1/3/4 in MEFs can confer sensitivity to both paclitaxel and epirubicin, suggesting that SIRT6 reduces paclitaxel and epirubicin sensitivity, at least in part, through modulating FOXO acetylation and expression. Consistently, immunohistochemical analysis of 118 breast cancer patient samples revealed that high SIRT6 nuclear staining is significantly associated with poorer overall survival (P = 0.018; Kaplan-Meier analysis). Multivariate Cox analysis demonstrated that nuclear SIRT6 staining remained associated with death after correcting for tumour stage and lymph-node involvement (P = 0.033). Collectively, our data suggest that SIRT6 has a role in paclitaxel and epirubicin sensitivity via targeting FOXO proteins and that SIRT6 could be a useful biomarker and therapeutic target for paclitaxel- and epirubicin-resistant cancer.
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