Identification of miRNAs as biomarkers for acquired endocrine resistance in breast cancer

Novel Endocrine Therapeutic Opportunities for Estrogen Receptor-Positive Ovarian Cancer-What Can We Learn from Breast Cancer?

Low-grade serous ovarian cancer (LGSOC) is a rare ovarian malignancy primarily affecting younger women and is characterized by an indolent growth pattern. It exhibits indolent growth and high estrogen/progesterone receptor expression, suggesting potential responsiveness to endocrine therapy. However, treatment efficacy remains limited due to the development of endocrine resistance. The mechanisms of resistance, whether primary or acquired, are still largely unknown and present a significant hurdle in achieving favorable treatment outcomes with endocrine therapy in these patients. In estrogen receptor-positive breast cancer, mechanisms of endocrine resistance have been largely explored and novel treatment strategies to overcome resistance have emerged. Considering the shared estrogen receptor positivity in LGSOC and breast cancer, we wanted to explore whether there are any parallel mechanisms of resistance and whether we can extend endocrine breast cancer treatments to LGSOC. This review aims to highlight the underlying molecular mechanisms possibly driving endocrine resistance in ovarian cancer, while also exploring the available therapeutic opportunities to overcome this resistance. By unraveling the potential pathways involved and examining emerging strategies, this review explores valuable insights for advancing treatment options and improving patient outcomes in LGSOC, which has limited therapeutic options available.

Research progress of exosomes in drug resistance of breast cancer

Since breast cancer is a heterogeneous disease, there are currently a variety of treatment methods available, including chemotherapy, endocrine therapy, molecular targeted therapy, immunotherapy, radiation therapy, etc. Breast cancer recurrence and metastasis, despite many treatment modalities, constitute a considerable threat to patients' survival time and pose a clinical challenge that is difficult to tackle precisely. Exosomes have a very special and crucial role in the treatment of drug resistance in breast cancer as a carrier of intercellular communication in the tumor microenvironment. Exosomes and breast cancer treatment resistance have been linked in a growing number of clinical investigations in recent years. This paper covers the status of research on exosomes in the treatment of breast cancer drug resistance and offers theoretical guidance for investigating new strategies to treat breast cancer drug resistance.

The Emerging Roles of Exosomal miRNAs in Breast Cancer Progression and Potential Clinical Applications

Breast cancer remains the leading malignancy in terms of morbidity and mortality today. The tumor microenvironment of breast cancer includes multiple cell types, secreted proteins, and signaling components such as exosomes. Among these, exosomes have a lipid bilayer structure. Exosomes can reflect the biological traits of the parent cell and carry a variety of biologically active components, including proteins, lipids, small molecules, and non-coding RNAs, which include miRNA, lncRNA, and circRNA. MiRNAs are a group of non-coding RNAs of approximately 20-23 nucleotides in length encoded by the genome, triggering silencing and functional repression of target genes. MiRNAs have been shown to play a significant role in the development of cancer owing to their role in the prognosis, pathogenesis, diagnosis, and treatment of cancer. MiRNAs in exosomes can serve as effective mediators of information transfer from parental cells to recipient cells and trigger changes in biological traits such as proliferation, invasion, migration, and drug resistance. These changes can profoundly alter the progression of breast cancer. Therefore, here, we systematically summarize the association of exosomal miRNAs on breast cancer progression, diagnosis, and treatment in the hope of providing novel strategies and directions for subsequent breast cancer treatment.

The role of mir-151a-5p in tumorigenesis; A systematic review

BACKGROUND

Highly supported microRNAs (miRNAs) are key players in cancer development. Each of these miRNAs may act as an oncomir, a tumor-suppressor, or both in various cancers. Mir-151a-5p is believed to be one of these miRNAs with diverse roles. We have conducted this systematic review to clarify the role of mir-151a-5p in formation of various cancers.

METHODS AND MATERIALS

We searched for existing articles in PubMed, Web of Science, Cochrane, Scopus, and RNAcentral databases up to November 2022. A total of 23 articles were qualified and included in the present systematic review. This review is registered on JBI at https://jbi.global/systematic-review-register. Expression levels, diagnostic and prognostic values, biological processes, and targeted downstream genes are included.

RESULTS

Assembled data indicate the expression levels of mir-151a-5p vary from down- to up-regulated based on the type of the cancer. Its functional role depends on the genetic profile of cancerous tissue. Results mostly point to the oncogenic role of this miRNA in Pituitary adenomas, Acute Myeloid Leukemia (AML), Endometrial, Lung, Barrett's carcinogenesis, Colorectal, Myelodysplastic syndromes, Hepatocellular carcinoma and Breast cancers, as its inhibited targets seem to be controlling several signaling pathways, cell adhesion, and cell cycle. At the same time, tumor-suppressing role has also been observed only in Malignant Pleural Mesothelioma, Central Nerve System (CNS) lymphoma, Chronic Myeloid and Acute Lymphocytic Leukemia. Two types of cancers, prostate and colon, show contradictory results as there are studies supporting both up- and down-regulation in these cancers. Pituitary adenomas, Barrett's carcinogenesis and CNS lymphomas are top cancers diagnosed with mir-151-5p. However, prognostic feature is only applicable to Lung adenocarcinoma.

DISCUSSION

Based on the present findings and further studies in the future, mir-151a-5p may be used as diagnostic and prognostic biomarkers or even a therapeutic target in cancer studies.

DATA AVAILABILITY STATEMENT

The articles used in this study can be found with the defined search phrase in mentioned databases. A list of selected articles will be available on reasonable requests.

Non-Coding RNAs Modulating Estrogen Signaling and Response to Endocrine Therapy in Breast Cancer

The largest part of human DNA is transcribed into RNA that does not code for proteins. These non-coding RNAs (ncRNAs) are key regulators of protein-coding gene expression and have been shown to play important roles in health, disease and therapy response. Today, endocrine therapy of ERα-positive breast cancer (BC) is a successful treatment approach, but resistance to this therapy is a major clinical problem. Therefore, a deeper understanding of resistance mechanisms is important to overcome this resistance. An increasing amount of evidence demonstrate that ncRNAs affect the response to endocrine therapy. Thus, ncRNAs are considered versatile biomarkers to predict or monitor therapy response. In this review article, we intend to give a summary and update on the effects of microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) on estrogen signaling in BC cells, this pathway being the target of endocrine therapy, and their role in therapy resistance. For this purpose, we reviewed articles on these topics listed in the PubMed database. Finally, we provide an assessment regarding the clinical use of these ncRNA types, particularly their circulating forms, as predictive BC biomarkers and their potential role as therapy targets to overcome endocrine resistance.

The history of small extracellular vesicles and their implication in cancer drug resistance

Small extracellular vesicles (EVs) in the last 20 years are demonstrated to possess promising properties as potential new drug delivery systems, biomarkers, and therapeutic targets. Moreover, EVs are described to be involved in the most important steps of tumor development and progression including drug resistance. The acquired or intrinsic capacity of cancer cells to resist chemotherapies is one of the greatest obstacles to overcome to improve the prognosis of many patients. EVs are involved in this mechanism by exporting the drugs outside the cells and transferring the drug efflux pumps and miRNAs in recipient cells, in turn inducing drug resistance. In this mini-review, the main mechanisms by which EVs are involved in drug resistance are described, giving a rapid and clear overview of the field to the readers.

Exploring the Mechanism of Baicalin Intervention in Breast Cancer Based on MicroRNA Microarrays and Bioinformatics Strategies

Objective

To explore the mechanism of baicalin intervention in breast cancer based on microRNA microarrays.

Methods

The inhibitory rate of baicalin intervention in MCF-7 breast cancer cells was determined by MTT. Then, the miRNA microarrays were used to validate the key microRNAs. After that, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to validate microRNA, hsa-miR-15a, hsa-miR-100, hsa-miR-16, and hsa-miR-7t. Finally, the potential targets of these key microRNAs are predicted by miRWalk, and DAVID was utilized for gene ontology (GO) enrichment analysis and pathway enrichment analysis.

Results

Baicalin may inhibit the proliferation of MCF-7 cells in a dose-dependent and time-dependent manner. The concentration of baicalin 150 μmol/L was determined for the subsequent miRNA chip research. A total of 92 upregulated microRNAs and 35 downregulated microRNAs were obtained. The upregulated miRNAs include hsa-miR-6799-5p, hsa-miR-6126, hsa-miR-4792, hsa-miR-6848-5p, hsa-miR-3197, hsa-miR-6779-5p, and hsa-miR -654-5p. The downregulated miRNAs include hsa-miR-3911, hsa-miR-504-5p, hsa-miR-30a-3p, hsa-miR-193b-3p, and hsa-miR-181b-5p. Then, differentially expressed miRNA was verified by qRT-PCR. The results showed that the expression of hsa-miR-15a, hsa-miR-100, hsa-miR-16, and hsa-let-7c was upregulated (P < 0.05), which was consistent with the results of the miRNA microarray. The enrichment analysis showed that baicalin might regulate the DNA-templated proliferation, DNA-templated transcription, p53 signaling pathway, etc., of MCF-7 breast cancer cells through miRNA.

Conclusion

Baicalin inhibits the proliferation of breast cancer cells. It may achieve antitumor effects through regulating microRNAs so as to affect the DNA replication (such as cellular response to DNA damage stimulus and DNA binding), RNA transcription (such as regulation of transcription, DNA-templated, transcription from RNA polymerase II promoter, and transcription factor binding), protein synthesis (such as mRNA binding, Golgi apparatus, and protein complex), endocytosis, pathways in cancer, p53 signaling pathway, and so on.

Identification and Roles of miR-29b-1-3p and miR29a-3p-Regulated and Non-Regulated lncRNAs in Endocrine-Sensitive and Resistant Breast Cancer Cells

Despite improvements in the treatment of endocrine-resistant metastatic disease using combination therapies in patients with estrogen receptor α (ERα) primary tumors, the mechanisms underlying endocrine resistance remain to be elucidated. Non-coding RNAs (ncRNAs), including microRNAs (miRNA) and long non-coding RNAs (lncRNA), are targets and regulators of cell signaling pathways and their exosomal transport may contribute to metastasis. Previous studies have shown that a low expression of miR-29a-3p and miR-29b-3p is associated with lower overall breast cancer survival before 150 mos. Transient, modest overexpression of miR-29b1-3p or miR-29a-3p inhibited MCF-7 tamoxifen-sensitive and LCC9 tamoxifen-resistant cell proliferation. Here, we identify miR-29b-1/a-regulated and non-regulated differentially expressed lncRNAs in MCF-7 and LCC9 cells using next-generation RNA seq. More lncRNAs were miR-29b-1/a-regulated in LCC9 cells than in MCF-7 cells, including DANCR, GAS5, DSCAM-AS1, SNHG5, and CRND. We examined the roles of miR-29-regulated and differentially expressed lncRNAs in endocrine-resistant breast cancer, including putative and proven targets and expression patterns in survival analysis using the KM Plotter and TCGA databases. This study provides new insights into lncRNAs in endocrine-resistant breast cancer.

Current research on circular RNAs and their potential clinical implications in breast cancer

Breast cancer (BC) is one of the most common cancers and the leading causes of death among women worldwide, and its morbidity rate is growing. Discovery of novel biomarkers is necessary for early BC detection, treatment, and prognostication. Circular RNAs (circRNAs), a novel type of endogenous non-coding RNAs with covalently closed continuous loops, have been found to have a crucial role in tumorigenesis. Studies have demonstrated that circRNAs are aberrantly expressed in the tumor tissues and plasma of patients with BC, and they modulate gene expression affecting the proliferation, metastasis, and chemoresistance of BC by specifically binding and regulating the expression of microRNAs (miRNAs). Therefore, circRNAs can be used as novel potential diagnostic and prognostic markers, and therapeutic targets for BC. This article summarizes the properties, functions, and regulatory mechanisms of circRNAs, particularly current research on their association with BC proliferation, metastasis, and chemoresistance.

Regulation of breast cancer metastasis signaling by miRNAs

Despite the decline in death rate from breast cancer and recent advances in targeted therapies and combinations for the treatment of metastatic disease, metastatic breast cancer remains the second leading cause of cancer-associated death in U.S. women. The invasion-metastasis cascade involves a number of steps and multitudes of proteins and signaling molecules. The pathways include invasion, intravasation, circulation, extravasation, infiltration into a distant site to form a metastatic niche, and micrometastasis formation in a new environment. Each of these processes is regulated by changes in gene expression. Noncoding RNAs including microRNAs (miRNAs) are involved in breast cancer tumorigenesis, progression, and metastasis by post-transcriptional regulation of target gene expression. miRNAs can stimulate oncogenesis (oncomiRs), inhibit tumor growth (tumor suppressors or miRsupps), and regulate gene targets in metastasis (metastamiRs). The goal of this review is to summarize some of the key miRNAs that regulate genes and pathways involved in metastatic breast cancer with an emphasis on estrogen receptor α (ERα+) breast cancer. We reviewed the identity, regulation, human breast tumor expression, and reported prognostic significance of miRNAs that have been documented to directly target key genes in pathways, including epithelial-to-mesenchymal transition (EMT) contributing to the metastatic cascade. We critically evaluated the evidence for metastamiRs and their targets and miRNA regulation of metastasis suppressor genes in breast cancer progression and metastasis. It is clear that our understanding of miRNA regulation of targets in metastasis is incomplete.

Exosomes and breast cancer drug resistance

Drug resistance is a daunting challenge in the treatment of breast cancer (BC). Exosomes, as intercellular communicative vectors in the tumor microenvironment, play an important role in BC progression. With the in-depth understanding of tumor heterogeneity, an emerging role of exosomes in drug resistance has attracted extensive attention. The functional proteins or non-coding RNAs contained in exosomes secreted from tumor and stromal cells mediate drug resistance by regulating drug efflux and metabolism, pro-survival signaling, epithelial–mesenchymal transition, stem-like property, and tumor microenvironmental remodeling. In this review, we summarize the underlying associations between exosomes and drug resistance of BC and discuss the unique biogenesis of exosomes, the change of exosome cargo, and the pattern of release by BC cells in response to drug treatment. Moreover, we propose exosome as a candidate biomarker in predicting and monitoring the therapeutic drug response of BC and as a potential target or carrier to reverse the drug resistance of BC.

Resistance and Overcoming Resistance in Breast Cancer

The incidence and mortality of breast cancer (BC) have increased in recent years, and BC is the main cause of cancer-related death in women worldwide. One of the most significant clinical problems in the treatment of patients with BC is the development of therapeutic resistance. Therefore, elucidating the molecular mechanisms involved in drug resistance is critical. The therapeutic decision for the management of patients with BC is based not only on the assessment of prognostic factors but also on the evaluation of clinical and pathological parameters. Although this has been a successful approach, some patients relapse and/or eventually develop resistance to treatment. This review is focused on recent studies on the possible biological and molecular mechanisms involved in both response and resistance to treatment in BC. Additionally, emerging treatments that seek to overcome resistance and reduce side effects are also described. A greater understanding of the mechanisms of action of treatments used in BC might contribute not only to the enhancement of our understanding of the mechanisms involved in the development of resistance but also to the optimization of the existing treatment regimens.

Evaluation of LDL receptor and Scavenger Receptor, Class B, Type 1 in the malignant and benign breast tumors: The correlation with the expression of miR-199a-5p, miR-199b-5p and miR-455-5p

AIMS

The purpose of present study was to examine the correlations of LDL (LDLR) and HDL (SR-B1) receptors with lipoproteins, miR-199a-5p, miR-199b-5p, miR-455-5p in the malignant and benign breast tumors.

METHODS

Total cholesterol-rich-lipoproteins and the receptors were determined using enzymatic-homogeneous and ELISA methods. The expression levels of miRNAs were detected by qRT-PCR.

RESULTS

Receptor expressions and lipoproteins concentration were significantly higher in the malignant tumors (p < 0.05). Positive correlation was found for LDLR with Ki67% and Her2+. HDL-C content of TNBC tumors was higher than those of Non-TNBC (p < 0.05). The expression level of miR-199a-5p was found to be downregulated significantly in the malignant tumors of <2 cm, TNBC, HER2- or stage3. The expression of miR-199b-5p was downregulated in the malignant tumors and was negatively associated with TNBC, stage and Her2+. The expression of miR-455-5p was significantly correlated with Her2- (p < 0.05). A positive correlation was observed for SR-B1 or LDLR with HDL-C or LDL-C and also for SR-B1 with LDLR, although a reverse association was detected for the expression of miR-199b-5p with LDLR in the malignant tumors (p < 0.05). No significant correlations were found for miR-199a-5p or miR-455-5p with LDLR or SR-B1 expressions and also for LDL-C and SR-B1 with clinicopathological features (p ≥ 0.05).

CONCLUSIONS

Mechanisms potentially involved in the present findings may be due to the lipid internalization and lipoprotein consumption through LDLR and SR-B1 over expression. It is noteworthy that the expression of miR-199b-5p is negatively correlated with LDLR which may suggest it as a suppressor for LDLR expression in the breast cancer.

Prognostic role of microRNAs in breast cancer: A systematic review

MicroRNAs (miRNAs) have been found to play an important role in breast cancer, functioning either as potential oncogenes or tumor suppressor genes, but their role in the prognosis of patients remains unclear. The aim of the present review study is to highlight recent preclinical and clinical studies performed on both circulating and tissue-specific miRNAs and their potential role as prognostic markers in breast cancer. We systematically searched the PubMed database to explore the prognostic value of miRNAs in breast cancer. After performing the literature search and review, 117 eligible studies were identified. We found that 110 aberrantly expressed miRNAs have been associated with prognosis in breast cancer. In conclusion, the collective data presented in this review indicate that miRNAs could serve as novel prognostic tools in breast cancer, while the clinical application of these findings has yet to be verified.

MiR-32 Inhibits Proliferation and Metastasis by Targeting EZH2 in Glioma

Purpose:

Glioma is identified as a broad category of brain and spinal cord tumors. MiR-32 is important in regulating the genesis of different cancers; however, the underlying mechanisms of miR-32 in glioma still largely unknown. This study aimed to elucidate pathobiological functions of miR-32 in glioma and verify its effect on the regulation of enhancer of zeste homolog 2.

Methods:

The expression of miR-32 and enhancer of zeste homolog 2 was detected by quantitative real-time polymerase chain reaction and Western blot in glioma tissues and cells. Cell Counting Kit-8 (CCK-8) assay was used to examine the effects of miR-32 on human glioma cells proliferation. Transwell assay was used to examine cell metastasis, respectively. Two bioinformatics analysis software and luciferase reporter assay were chosen to confirm targeting association between miR-32 and enhancer of zeste homolog 2.

Results:

MiR-32 was downregulated in glioma tissues and cells. Furthermore, enhancer of zeste homolog 2 expression was upregulated and negatively correlated with miR-32 in clinical tissues. Ectopic expression of miR-32 inhibited glioma cell proliferation, migration, and invasion. Enhancer of zeste homolog 2 was identified as direct target gene of miR-32 in glioma. Overexpression of enhancer of zeste homolog 2 ablated the inhibitory effects of miR-32.

Conclusion:

In summary, our finding suggests that miR-32 acts an important role in inhibiting glioma cell proliferation and metastasis and suppresses the expression of ABCC4 by directly targeting its 3′-untranslated region. The miR-32/enhancer of zeste homolog 2 axis may provide new insights to the treatment for glioma.

Predictive and Prognostic Value of Selected MicroRNAs in Luminal Breast Cancer

Breast cancer (BrC) is the most frequent malignancy and the leading cause of cancer death among women worldwide. Approximately 70% of BrC are classified as luminal-like subtype, expressing the estrogen receptor. One of the most common and effective adjuvant therapies for this BrC subtype is endocrine therapy. However, its effectiveness is limited, with relapse occurring in up to 40% of patients. Because microRNAs have been associated with several mechanisms underlying endocrine resistance and sensitivity, they may serve as predictive and/or prognostic biomarkers in this setting. Hence, the main goal of this study was to investigate whether miRNAs deregulated in endocrine-resistant BrC may be clinically relevant as prognostic and predictive biomarkers in patients treated with adjuvant endocrine therapy. A global expression assay allowed for the identification of microRNAs differentially expressed between luminal BrC patients with or without recurrence after endocrine adjuvant therapy. Then, six microRNAs were chosen for validation using quantitative reverse transcription polymerase chain reaction in a larger set of tissue samples. Thus, miR-30c-5p, miR-30b-5p, miR-182-5p, and miR-200b-3p were found to be independent predictors of clinical benefit from endocrine therapy. Moreover, miR-182-5p and miR-200b-3p displayed independent prognostic value for disease recurrence in luminal BrC patients after endocrine therapy. Our results indicate that selected miRNAs’ panels may constitute clinically useful ancillary tools for management of luminal BrC patients. Nevertheless, additional validation, ideally in a multicentric setting, is required to confirm our findings.

Overcoming Tamoxifen Resistance by Regulation of Del-1 in Breast Cancer

BACKGROUND

Hormone receptor-positive breast cancer accounts for nearly two-thirds of breast cancer cases; it ultimately acquires resistance during endocrine treatment and becomes more aggressive. This study evaluated the role of developmental endothelial locus (Del)-1 in tamoxifen-resistant (TAM-R) breast cancer.

METHODS

Del-1 expression in recurrent TAM-R breast cancer tissue was evaluated and compared to that in the original tumor tissue from the same patients. Del-1 expression was also evaluated in TAM-R cells by quantitative real-time PCR, western blotting, and enzyme-linked immunosorbent assay. The effects of Del-1 knockdown on the proliferation, migration, and invasion of TAM-R cells was assessed with wound-healing and Matrigel transwell assays.

RESULTS

Del-1 was more highly expressed in recurrent breast cancer as compared to the original tumor tissues before initiation of endocrine treatment. Del-1 mRNA was upregulated in TAM-R and small interfering RNA-mediated knockdown of Del-1 suppressed the migration and proliferation of TAM-R cells while partly restoring TAM sensitivity. And the TAM resistance was recovered by knockdown of Del-1.

CONCLUSIONS

TAM-R breast cancer is characterized by Del-1 overexpression and tumor progression can be inhibited by Del-1 depletion, which restores TAM sensitivity. Thus, therapeutic strategies that target Del-1 may be effective for the treatment of hormone-resistant breast cancer.

Non-Coding RNAs in Breast Cancer: Intracellular and Intercellular Communication

Non-coding RNAs (ncRNAs) are regulators of intracellular and intercellular signaling in breast cancer. ncRNAs modulate intracellular signaling to control diverse cellular processes, including levels and activity of estrogen receptor α (ERα), proliferation, invasion, migration, apoptosis, and stemness. In addition, ncRNAs can be packaged into exosomes to provide intercellular communication by the transmission of microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) to cells locally or systemically. This review provides an overview of the biogenesis and roles of ncRNAs: small nucleolar RNA (snRNA), circular RNAs (circRNAs), PIWI-interacting RNAs (piRNAs), miRNAs, and lncRNAs in breast cancer. Since more is known about the miRNAs and lncRNAs that are expressed in breast tumors, their established targets as oncogenic drivers and tumor suppressors will be reviewed. The focus is on miRNAs and lncRNAs identified in breast tumors, since a number of ncRNAs identified in breast cancer cells are not dysregulated in breast tumors. The identity and putative function of selected lncRNAs increased: nuclear paraspeckle assembly transcript 1 (NEAT1), metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), steroid receptor RNA activator 1 (SRA1), colon cancer associated transcript 2 (CCAT2), colorectal neoplasia differentially expressed (CRNDE), myocardial infarction associated transcript (MIAT), and long intergenic non-protein coding RNA, Regulator of Reprogramming (LINC-ROR); and decreased levels of maternally-expressed 3 (MEG3) in breast tumors have been observed as well. miRNAs and lncRNAs are considered targets of therapeutic intervention in breast cancer, but further work is needed to bring the promise of regulating their activities to clinical use.

MicroRNA-206 suppresses proliferation and predicts poor prognosis of HR-HPV-positive cervical cancer cells by targeting G6PD

Cervical cancer (CC) is one of the most frequent gynecological malignancies in females worldwide. Aberrant expression of microRNA (miR)-206 was reported to play an important role in tumor progression. The aim of the present study was to evaluate the potential role of miR-206 and verify its influence on the function of glucose-6-phosphate dehydrogenase (G6PD) in CC. Western blot analysis and RT-PCR were employed to measure miR-206 and G6PD expression. Luciferase assays were performed to validate G6PD as miR-206 targets. CCK-8 assay was performed to examine the regulation of miR-206 and G6PD on CC proliferation. The result showed that miR-206 was downregulated, while G6PD was upregulated in high risk human papillomavirus (HR-HPV)(+) CC. miR-206 directly targeted the 3'-UTR of G6PD. miR-206 overexpressed or G6PD low-expressed suppressed cell proliferation. miR-206 low expressed or G6PD overexpressed predicted poor prognosis. In conclusion, miR-206 reduced cancer growth and suppresses the G6PD expression in CC. This newly identified miR-206 may provide further insight into tumor progression and offers a promising target for the CC therapy.

Exosome-Mediated Transfer of Cancer Cell Resistance to Antiestrogen Drugs

Exosomes are small vesicles which are produced by the cells and released into the surrounding space. They can transfer biomolecules into recipient cells. The main goal of the work was to study the exosome involvement in the cell transfer of hormonal resistance. The experiments were performed on in vitro cultured estrogen-dependent MCF-7 breast cancer cells and MCF-7 sublines resistant to SERM tamoxifen and/or biguanide metformin, which exerts its anti-proliferative effect, at least in a part, via the suppression of estrogen machinery. The exosomes were purified by differential ultracentrifugation, cell response to tamoxifen was determined by MTT test, and the level and activity of signaling proteins were determined by Western blot and reporter analysis. We found that the treatment of the parent MCF-7 cells with exosomes from the resistant cells within 14 days lead to the partial resistance of the MCF-7 cells to antiestrogen drugs. The primary resistant cells and the cells with the exosome-induced resistance were characterized with these common features: decrease in ERα activity and parallel activation of Akt and AP-1, NF-κB, and SNAIL1 transcriptional factors. In general, we evaluate the established results as the evidence of the possible exosome involvement in the transferring of the hormone/metformin resistance in breast cancer cells.

High N-Acetyltransferase 1 Expression Is Associated with Estrogen Receptor Expression in Breast Tumors, but Is not Under Direct Regulation by Estradiol, 5α-androstane-3β,17β-Diol, or Dihydrotestosterone in Breast Cancer Cells

N-acetyltransferase 1 (NAT1) is an enzyme that metabolizes carcinogens, which suggests a potential role in breast carcinogenesis. High NAT1 expression in breast tumors is associated with estrogen receptor α (ERα+) and the luminal subtype. We report that NAT1 mRNA transcript, protein, and enzyme activity were higher in human breast tumors with high expression of ERα/ESR1 compared with normal breast tissue. There was a strong correlation between NATb promoter and NAT1 protein expression/enzyme activity. High NAT1 expression in tumors was not the result of adipocytes, as evidenced by low perilipin (PLIN) expression. ESR1, NAT1, and XBP1 expression were associated in tumor biopsies. Direct regulation of NAT1 transcription by estradiol (E₂) was investigated in ERα (+) MCF-7 and T47D breast cancer cells. E₂ did not increase NAT1 transcript expression but increased progesterone receptor expression in a dose-dependent manner. Likewise, NAT1 transcript levels were not increased by dihydrotestosterone (DHT) or 5α-androstane-3β, (3β-adiol) 17β-diol. Dithiothreitol increased levels of the activated, spliced XBP1 in ERα (+) MCF-7 and T47D breast cancer cells but did not affect NAT1 or ESR1 expression. We conclude that NAT1 expression is not directly regulated by E₂, DHT, 3β-adiol, or dithiothreitol despite high NAT1 and ESR1 expression in luminal A breast cancer cells, suggesting that ESR1, XBP1, and NAT1 expression may share a common transcriptional network arising from the luminal epithelium associated with better survival in breast cancer. Clusters of high-expression genes, including NAT1, in breast tumors might serve as potential targets for novel therapeutic drug development.

MiR-302b Suppresses Osteosarcoma Cell Migration and Invasion by Targeting Runx2

Osteosarcoma patients with lung metastasis and local invasion remain challenging to treat despite the significant contribution of the combination of surgery and neo-adjuvant chemotherapy. Our previous microarray study demonstrated that miR-302b had significantly lower expression in osteosarcoma cell lines than in osteoblast cell lines. In the present study, we further elucidated the role of miR-302b in regulating the migration and invasiveness of osteosarcoma. MiR-302b expression was markedly down-regulated in osteosarcoma cell lines and clinical tumour tissues. Lower levels of miR-302b expression were significantly associated with metastasis and high pathological grades. A functional study demonstrated that over-expression of miR-302b suppressed tumour cell proliferation, invasion and migration in vitro and in vivo. Runx2 was identified as a direct target gene for miR-302b by bioinformatics analysis and dual-luciferase reporter gene assay. Moreover, over-expression of miR-302b induced down-regulation of Runx2, OPN, MMP-2, MMP-9, MMP-12, MMP-14, and VEGF in 143B cells. Exogenous expression of Runx2 partially rescued the inhibitory effect of miR-302b on the invasion and migration activity of 143B osteosarcoma cells. Taken together, our results indicate that miR-302b functions as a tumour repressor in the invasion and migration of osteosarcoma by directly downregulating Runx2 expression and may be a potential therapeutic target for osteosarcoma.

Tamoxifen sensitivity-related microRNA-342 is a useful biomarker for breast cancer survival

MicroRNAs (miRNAs) have emerged as one of the crucial regulators of cancer progression. Some miRNAs are reported to be related to the response of breast cancer to tamoxifen (TAM). In this study, we investigated whether the levels of TAM response-related miRNAs translate to patient survival. The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) datasets were used and Gene Set Enrichment Analysis (GSEA) was performed. Four TAM response-related miRNAs, miR-221, miR-222, miR-342, and miR-451, were identified by literature search. Patients with high expression of miR-342, related to TAM sensitivity, were associated with better survival in TCGA cohort (Overall Survival (OS), p=0.02; Disease Free Survival (DFS), p=0.03, respectively), and in two other independent GEO cohorts (OS, p=0.02 and p=0.0007, respectively). High expression of miR-342 was associated with significantly better survival in ER-positive patients (p=0.04), but not in ER-negative or triple-negative patients. Surprisingly, high expression of miR-451, reported to increase the sensitivity to TAM, was associated with worse survival (p=0.002). MiR-221 and miR-222 did not show any significance in survival. Lastly, GSEA demonstrated that lower miR-342 expression was significantly associated with the enrichment of TAM resistance-related gene expression, and higher miR-342 expression with TAM sensitivity-related gene expression, but miR-221, miR-222 and miR-451 were not. For the first time, we used “big data” from TCGA and GEO cohorts to analyze multiple miRNAs with respect to survival impact and TAM sensitivities. We demonstrated that TAM sensitivity-related miR-342 could be a promising biomarker, especially in luminal type breast cancer patients.

The miR-29 transcriptome in endocrine-sensitive and resistant breast cancer cells

Aberrant microRNA expression contributes to breast cancer progression and endocrine resistance. We reported that although tamoxifen stimulated miR-29b-1/a transcription in tamoxifen (TAM)-resistant breast cancer cells, ectopic expression of miR-29b-1/a did not drive TAM-resistance in MCF-7 breast cancer cells. However, miR-29b-1/a overexpression significantly repressed TAM-resistant LCC9 cell proliferation, suggesting that miR-29b-1/a is not mediating TAM resistance but acts as a tumor suppressor in TAM-resistant cells. The target genes mediating this tumor suppressor activity were unknown. Here, we identify miR-29b-1 and miR-29a target transcripts in both MCF-7 and LCC9 cells. We find that miR-29b-1 and miR-29a regulate common and unique transcripts in each cell line. The cell-specific and common downregulated genes were characterized using the MetaCore Gene Ontology (GO) enrichment analysis algorithm. LCC9-sepecific miR-29b-1/a-regulated GO processes include oxidative phosphorylation, ATP metabolism, and apoptosis. Extracellular flux analysis of cells transfected with anti- or pre- miR-29a confirmed that miR-29a inhibits mitochondrial bioenergetics in LCC9 cells. qPCR,luciferase reporter assays, and western blot also verified the ATP synthase subunit genes ATP5G1 and ATPIF1 as bone fide miR29b-1/a targets. Our results suggest that miR-29 repression of TAM-resistant breast cancer cell proliferation is mediated in part through repression of genes important in mitochondrial bioenergetics.