Mitochondrial biogenesis in epithelial cancer cells promotes breast cancer tumor growth and confers autophagy resistance

Here, we set out to test the novel hypothesis that increased mitochondrial biogenesis in epithelial cancer cells would “fuel” enhanced tumor growth. For this purpose, we generated MDA-MB-231 cells (a triple-negative human breast cancer cell line) overexpressing PGC-1α and MitoNEET, which are established molecules that drive mitochondrial biogenesis and increased mitochondrial oxidative phosphorylation (OXPHOS). Interestingly, both PGC-1α and MitoNEET increased the abundance of OXPHOS protein complexes, conferred autophagy resistance under conditions of starvation and increased tumor growth by up to ~3-fold. However, this increase in tumor growth was independent of neo-angiogenesis, as assessed by immunostaining and quantitation of vessel density using CD31 antibodies. Quantitatively similar increases in tumor growth were also observed by overexpression of PGC-1β and POLRMT in MDA-MB-231 cells, which are also responsible for mediating increased mitochondrial biogenesis. Thus, we propose that increased mitochondrial “power” in epithelial cancer cells oncogenically promotes tumor growth by conferring autophagy resistance. As such, PGC-1α, PGC-1β, mitoNEET and POLRMT should all be considered as tumor promoters or “metabolic oncogenes.” Our results are consistent with numerous previous clinical studies showing that metformin (a weak mitochondrial “poison”) prevents the onset of nearly all types of human cancers in diabetic patients. Therefore, metformin (a complex I inhibitor) and other mitochondrial inhibitors should be developed as novel anticancer therapies, targeting mitochondrial metabolism in cancer cells.     

Mitochondrial biogenesis in epithelial cancer cells promotes breast cancer tumor growth and confers autophagy resistance

Here, we set out to test the novel hypothesis that increased mitochondrial biogenesis in epithelial cancer cells would “fuel” enhanced tumor growth. For this purpose, we generated MDA-MB-231 cells (a triple-negative human breast cancer cell line) overexpressing PGC-1α and MitoNEET, which are established molecules that drive mitochondrial biogenesis and increased mitochondrial oxidative phosphorylation (OXPHOS). Interestingly, both PGC-1α and MitoNEET increased the abundance of OXPHOS protein complexes, conferred autophagy resistance under conditions of starvation and increased tumor growth by up to ~3-fold. However, this increase in tumor growth was independent of neo-angiogenesis, as assessed by immunostaining and quantitation of vessel density using CD31 antibodies. Quantitatively similar increases in tumor growth were also observed by overexpression of PGC-1β and POLRMT in MDA-MB-231 cells, which are also responsible for mediating increased mitochondrial biogenesis. Thus, we propose that increased mitochondrial “power” in epithelial cancer cells oncogenically promotes tumor growth by conferring autophagy resistance. As such, PGC-1α, PGC-1β, mitoNEET and POLRMT should all be considered as tumor promoters or “metabolic oncogenes.” Our results are consistent with numerous previous clinical studies showing that metformin (a weak mitochondrial “poison”) prevents the onset of nearly all types of human cancers in diabetic patients. Therefore, metformin (a complex I inhibitor) and other mitochondrial inhibitors should be developed as novel anticancer therapies, targeting mitochondrial metabolism in cancer cells.     

MicroRNA-221/222 negatively regulates estrogen receptor alpha and is associated with tamoxifen resistance in breast cancer

A search for regulators of estrogen receptor alpha (ERalpha) expression has yielded a set of microRNAs (miRNAs) for which expression is specifically elevated in ERalpha-negative breast cancer. Here we show distinct expression of a panel of miRNAs between ERalpha-positive and ERalpha-negative breast cancer cell lines and primary tumors. Of the elevated miRNAs in ERalpha-negative cells, miR-221 and miR-222 directly interact with the 3'-untranslated region of ERalpha. Ectopic expression of miR-221 and miR-222 in MCF-7 and T47D cells resulted in a decrease in expression of ERalpha protein but not mRNA, whereas knockdown of miR-221 and miR-222 partially restored ERalpha in ERalpha protein-negative/mRNA-positive cells. Notably, miR-221- and/or miR-222-transfected MCF-7 and T47D cells became resistant to tamoxifen compared with vector-treated cells. Furthermore, knockdown of miR-221 and/or miR-222 sensitized MDA-MB-468 cells to tamoxifen-induced cell growth arrest and apoptosis. These findings indicate that miR-221 and miR-222 play a significant role in the regulation of ERalpha expression at the protein level and could be potential targets for restoring ERalpha expression and responding to antiestrogen therapy in a subset of breast cancers.     

Snail and Slug mediate tamoxifen resistance in breast cancer cells through activation of EGFR-ERK independent of epithelial-mesenchymal transition

Breast cancer is the second most common type of cancer and the leading cause of cancer death in women worldwide. Adjuvant tamoxifen therapy significantly slows down estrogen receptor （ER）-positive breast cancer progression, prolongs diseasefree survival, and contributes to the decrease in breast cancer mortality （Musgrove and Sutherland, 2009）. However, majority of the death from breast cancer is due to metastasis that is resistant to therapy （Musgrove and Sutherland, 2009）.     

Proteomics profiling identify CAPS as a potential predictive marker of tamoxifen resistance in estrogen receptor positive breast cancer

Background

Despite the success of tamoxifen since its introduction, about one-third of patients with estrogen (ER) and/or progesterone receptor (PgR) - positive breast cancer (BC) do not benefit from therapy. Here, we aim to identify molecular mechanisms and protein biomarkers involved in tamoxifen resistance.

Results

Using iTRAQ and Immobilized pH gradient-isoelectric focusing (IPG-IEF) mass spectrometry based proteomics we compared tumors from 12 patients with early relapses (<2 years) and 12 responsive to therapy (relapse-free > 7 years). A panel of 13 proteins (TCEAL4, AZGP1, S100A10, ALDH6A1, AHNAK, FBP1, S100A4, HSP90AB1, PDXK, GFPT1, RAB21, MX1, CAPS) from the 3101 identified proteins, potentially separate relapse from non-relapse BC patients. The proteins in the panel are involved in processes such as calcium (Ca²⁺) signaling, metabolism, epithelial mesenchymal transition (EMT), metastasis and invasion. Validation of the highest expressed proteins in the relapse group identify high tumor levels of CAPS as predictive of tamoxifen response in a patient cohort receiving tamoxifen as only adjuvant therapy.

Conclusions

This data implicate CAPS in tamoxifen resistance and as a potential predictive marker.

Electronic supplementary material

The online version of this article (doi:10.1186/s12014-015-9080-y) contains supplementary material, which is available to authorized users.     

Reversal of tamoxifen resistant breast cancer by low dose estrogen therapy

Currently, the standard of care for estrogen receptor (ER)-positive breast cancer is 5 years of tamoxifen (TAM) or an aromatase inhibitor (AI) such as anastrozole. New studies indicate that extending antiestrogen therapy beyond 5 years with sequential regimens will improve disease-free survival. Based on the emerging concept that longer therapies are better, we have developed sequential models of tamoxifen-resistant breast cancer in vivo to mimic the clinical scenario of long-term antiestrogen therapy. The goal of the current study was to investigate the consequences of long-term treatment with tamoxifen on the growth of breast tumors in athymic mice. The results demonstrate that there are distinct phases of resistance to tamoxifen that correlate with time of treatment and expression of HER2/neu mRNA. In the treatment phase, 17β-estradiol (E₂) stimulated growth, while TAM inhibited growth of MCF-7 tumors (MCF-7E₂). The withdrawal of treatment, mimicking the use of an AI, completely prevented growth. In Phase I resistance, the tumors (MCF-7TAMST) were growth-stimulated by either E₂ or TAM, but inhibited by no treatment, fulvestrant, or E₂ + fulvestrant. Phase II-resistant tumors (MCF-7TAMLT) were treated for more than 5 years and growth-stimulated by TAM. However, no treatment, fulvestrant, or E₂ completely inhibited growth. Interestingly, the few tumors (MCF-7TAMLT) that survived in response to E₂ were robustly re-stimulated by E₂ after transplantation into new generations of athymic mice. These E₂-stimulated tumors (MCF-7TAME) were inhibited by TAM in a dose-dependent similar to their parental tumors (MCF-7E₂). In addition, the MCF-7TAME tumors were inhibited by either no treatment or fulvestrant. HER2/neu and HER3 mRNAs were over-expressed in TAM-stimulated MCF-7TAMLT tumors and remained high in E₂-stimulated MCF-7TAME tumors. The data indicate that complete reversal of resistance to TAM can be achieved with the use of low dose E₂ therapy. Also, these data suggest that over-expression of HER2/neu alone is insufficient to predict resistance to TAM. Based on the results, we suggest using an alternating treatment regimen, cycling antiestrogen with estrogen therapy to avoid drug-resistance.     

Lactate dehydrogenase A regulates autophagy and tamoxifen resistance in breast cancer

Estrogen receptor (ER) antagonist, tamoxifen has been universally used for the treatment of the ER-positive breast cancer; however, the inevitable emergence of resistance to tamoxifen obstructs the successful treatment of this cancer. So, there is an immediate requirement for the search of a novel therapeutic target for treatment of this cancer. Acquired tamoxifen-resistant breast cancer cell lines MCF-7 (MCF-7/TAM-R) and T47D (T47D/TAM-R) showed higher apoptotic resistance accompanied by induction of pro-survival autophagy compared to their parental cells. Besides, tamoxifen resistance was associated with reduced production of ATP and with overexpression of glycolytic pathways, leading to induced autophagy to meet the energy demand. Further, our study revealed that LDHA; one of the key molecules of glycolysis in association with Beclin-1 induced pro-survival autophagy in tamoxifen-resistant breast cancer. Mechanistically, pharmacological and genetic inhibition of LDHA reduced the pro-survival autophagy, with the restoration of apoptosis and reverting back the EMT like phenomena noticed in tamoxifen-resistant breast cancer. In total, targeting LDHA opened a novel strategy to interrupt autophagy and tamoxifen resistance in breast cancer.     

A mechanism of drug resistance to tamoxifen in breast cancer

Drug resistance to tamoxifen (Tam) is a significant clinical problem but the mechanism through which this occurs remains elusive. We have developed a number of xenograft models of Tam-stimulated growth that model breast cancer progression using estrogen receptor positive MCF-7 or T47D breast cancer cells. When estrogen-stimulated T47D:E2 tumors are treated long term with Tam, Tam-stimulated tumors develop (T47D:Tam) that are stimulated by both estrogen and Tam. When HER-2/neu status is determined, it is clear that the T47D:Tam tumors express significantly higher levels of HER-2/neu protein by immunohistochemistry and mRNA as measured by real-time RT-PCR. The T47D:Tam tumors also express higher levels of estrogen receptor and progesterone receptor protein than their estrogen-stimulated T47D:E2 counterparts. We compared out results to the MCF-7 model of Tam-stimulated growth. The MCF-7:Tam ST (estrogen- and Tam-stimulated) and MCF-7:Tam LT (estrogen-inhibited, Tam-stimulated) were bilaterally transplanted to account for any mouse to mouse variation and characteristic growth patterns were observed. TUNEL staining was performed on MCF-7:Tam LT treated with either estrogen or Tam and it was concluded that estrogen-inhibited tumor growth was a result of increased apoptosis. Three phases of tumor progression are described that involve increases in HER-2/neu expression, de-regulation of estrogen receptor expression and increases in apoptosis which in concert determine the phenotype of drug resistance to Tam.     

Prognostic significance of autophagy related genes in estrogen receptor positive tamoxifen treated breast cancer

Resistance to Tamoxifen constitutes a major therapeutic challenge in treating hormone sensitive breast cancer. The induction of autophagy has been shown to be involved as one of the mechanism responsible for Tamoxifen resistance. Autophagy related gene (ATG) members are the regulators and effectors of Macroautophagy process in the cellular systems. In this study, we evaluated the prognostic significance of ATGs in Tamoxifen treated breast cancer. The "Kaplan- Meier plotter" database was utilized to analyze the relevance and significance of ATGs mRNA expression to Relapse Free Survival in breast cancer patients. We used the data of patients who are Estrogen receptor positive and are treated with Tamoxifen. Hazard ratio and log-rank p-value were calculated using KM survival plots for various ATGs. Overexpressed ATG3, ATG 5, ATG 8B and PIK3R4 resulted in a poor prognosis. A gene signature of these ATGs predicts deteriorated RFS (p-value=8.3e-05 and HR=1.84 (1.35-2.51) and Distant Metastasis Free Survival (p value = 0.0027 and HR=2.03 (1.27-3.26). We report the distinct prognostic values of ATGs in patients of breast cancer treated with Tamoxifen. Thus, better understandings of the induction of autophagy pathway may potentially form the basis for use of autophagy inhibitors in the Tamoxifen treated breast cancer.     

PRPF19 promotes tongue cancer growth and chemoradiotherapy resistance

Pre-mRNA processing factor 19 (PRPF19) is a multifaceted protein and participates in DNA damage response and pre-mRNA processing.The role of PRPF19 in cancer is...     

Induction of tamoxifen resistance in breast cancer cells by ELF electromagnetic fields

The incidence of breast cancer in western societies has been rising ever since the Second World War. Besides the exposure to a multitude of new chemical compounds, electromagnetic field exposure has been linked to breast cancer through a radiation-mediated anti-melatonin pathway. We investigated, whether low-frequency electromagnetic field exposure interferes with the anti-estrogenic activity of tamoxifen. Two different clones of the breast cancer cell line MCF-7 were exposed to highly homogeneous 50Hz electromagnetic fields and IC(50) values were calculated from dose-response curves of tamoxifen at various field intensities. An intensity-dependent shift of tamoxifen dose-response curves to higher concentrations with a maximal response at 1.2muT was observed. Hypothetically, electromagnetic field exposure could contribute to tamoxifen resistance observed in breast cancer after long-term treatment.     

AIB1 is required for the acquisition of epithelial growth factor receptor-mediated tamoxifen resistance in breast cancer cells

Acquired resistance to tamoxifen has become a serious obstacle in breast cancer treatment. The underlying mechanism responsible for this condition has not been completely elucidated. In this study, a tamoxifen-resistant (Tam-R) MCF-7 breast cancer cell line was developed to mimic the occurrence of acquired tamoxifen resistance as seen in clinical practice. Increased expression levels of HER1, HER2 and the estrogen receptor (ER)-AIB1 complex were found in tamoxifen-resistant cells. EGF stimulation and gefitinib inhibition experiments further demonstrated that HER1/HER2 signaling and AIB1 were involved in the proliferation of cells that had acquired Tam resistance. However, when AIB1 was silenced with AIB1-siRNA in Tam-R cells, the cell growth stimulated by the HER1/HER2 signaling pathway was significantly reduced, and the cells were again found to be inhibited by tamoxifen. These results suggest that the AIB1 protein could be a limiting factor in the HER1/HER2-mediated hormone-independent growth of Tam-R cells. Thus, AIB1 may be a new therapeutic target, and the removal of AIB1 may decrease the crosstalk between ER and the HER1/HER2 pathway, resulting in the restoration of tamoxifen sensitivity in tamoxifen-resistant cells.     

Effects of low-dose tamoxifen on breast cancer biomarkers Ki-67, estrogen and progesterone receptors

Breast carcinoma is the most common malignancy among women and it has a major impact on mortality. Studies of primary chemoprevention with tamoxifen have generated high expectations and considerable success rates. The efficacy of lower doses of tamoxifen is similar to that seen with a standard dose of the drug, and there has been a reduction in healthcare costs and side effects.The immune reaction to monoclonal antibody Ki-67 (MIB-1) and the expression of estrogen receptors (1D5) and progesterone receptors (PgR 636) in breast carcinoma were studied in patients treated with 10 mg of tamoxifen for a period of 14 days.A prospective randomized clinical trial was conducted with 38 patients divided into two groups: Group A: N = 20 (control group-without medication) and Group B: N = 18 (tamoxifen/10 mg/day for 14 days). All patients signed an informed consent term previously approved by both institutions. Patients underwent incisional biopsy before treatment and 14 days later a tumor tissue sample was obtained during surgical treatment. Positivity was quantitatively assessed, counting at least 1.000 cells per slide. For statistical data analysis, a Wilcoxon non-parametric test was used, and α was set at 5%.Both groups (A and B) were considered homogeneous regarding control variables. In Group A (control), there was no statistically significant reduction in Ki-67 (MIB-1) (p = 0.627), estrogen receptor (1D5) (p = 0.296) and progesterone receptor positivity (PgR 636) (p = 0.381).In Group B (tamoxifen 10 mg/day), the mean percentage of nuclei stained by Ki-67 (MIB-1) was 24.69% before and 10.43% after tamoxifen treatment. Mean percentage of nuclei stained by estrogen receptor (1D5) was 59.53% before and 25.99% after tamoxifen treatment. Mean percentage of nuclei stained by progesterone receptor (PgR 636), was 59.34 before and 29.59% after tamoxifen treatment. A statistically significant reduction was found with the three markers (p < 0.001).Tamoxifen significantly reduced monoclonal antibody Ki-67 (MIB-1), estrogen receptor (1D5) and progesterone receptor positivity (PgR 636) in the breast epithelium of carcinoma patients treated with a 10 mg dose of tamoxifen for 14 days.     

Functional screen for genes responsible for tamoxifen resistance in human breast cancer cells

Antiestrogens, such as tamoxifen, are widely used for endocrine treatment of estrogen receptor-positive breast cancer. However, as breast cancer progresses, development of tamoxifen resistance is inevitable. The mechanisms underlying this resistance are not well understood. To identify genes involved in tamoxifen resistance, we have developed a rapid screening method. To alter the tamoxifen-sensitive phenotype of human ZR-75-1 breast cancer cells into a tamoxifen-resistant phenotype, the cells were infected with retroviral cDNA libraries derived from human placenta, human brain, and mouse embryo. Subsequently, the cells were selected for proliferation in the presence of 4-hydroxy-tamoxifen (OH-TAM) and integrated cDNAs were identified by sequence similarity searches. From 155 OH-TAM-resistant cell colonies, a total of 25 candidate genes were isolated. Seven of these genes were identified in multiple cell colonies and thus cause antiestrogen resistance. The epidermal growth factor receptor, platelet-derived growth factor receptor-alpha, platelet-derived growth factor receptor-beta, colony-stimulating factor 1 receptor, neuregulin1, and fibroblast growth factor 17 that we have identified have been described as key regulators in the mitogen-activated protein kinase pathway. Therefore, this pathway could be a valuable target in the treatment of patients with breast cancer resistant to endocrine treatment. In addition, the putative gene LOC400500, predicted by in silico analysis, was identified. We showed that ectopic expression of this gene, designated as breast cancer antiestrogen resistance 4 (BCAR4), caused OH-TAM resistance and anchorage-independent cell growth in ZR-75-1 cells and that the intact open reading frame was required for its function. We conclude that retroviral transfer of cDNA libraries into human breast cancer cells is an efficient method for identifying genes involved in tamoxifen resistance.