Metabolic reprogramming of metastatic breast cancer and melanoma by let-7a microRNA

Let‑7a suppresses cell proliferation via the TGF‑β/SMAD signaling pathway in cervical cancer

Cervical cancer is the second most commonly diagnosed type of cancer among women after breast cancer. Recent research has addressed the role of microRNAs in cervical cancer. In the present study, we aimed to determine the effect of let‑7a on the regulation of the cell proliferation of cervical cancer and the related signaling pathway. Real‑time RT‑PCR was used to detect the expression of let‑7a in the blood of cervical cancer patients and normal controls. The expression of let‑7a was also assessed in cervical cancer cell lines: HeLa, SiHa and normal human immortalized keratinocyes HaCaT. Cell proliferation was tested by MTT assay, and cell apoptosis and cell cycle were examined by flow cytometric analysis in HeLa cells. Moreover, bioinformatic analysis, dual‑luciferase reporter assay and western blotting were used to confirm the target gene for let‑7a. In addition, the expression of TGF‑β1, SMAD4 and p53 were assessed by western blotting and real‑time PCR. Our studies showed that the expression of let‑7a in cervical cancer was significantly reduced in cervical cancer patients compared with the expression in the normal control group. Cell proliferation of HeLa cells was inhibited by overexpression of let‑7a. The cell cycle analysis showed that an increased population was arrested in the G2 phase in the let‑7a mimic group when compared with that in the mimic control and untreated groups. In addition, the cell cycle‑related factor p53 was increased in the let‑7a overexpression group compared with that in the control and untreated groups. Furthermore, TGFBR1 was confirmed to be a target of let‑7a. Moreover, the expression of TGF‑β1 and SMAD4 proteins was elevated in cervical squamous carcinoma and cervical adenocarcinoma tissues. However, the expression of TGF‑β1 and SMAD4 was decreased in the let‑7a‑overexpressing cervical cancer cell lines (HeLa, SiHa and CaSki). Our data suggest that let‑7a may play a role in the cell proliferation of cervical cancer by regulating the TGF‑β/SMAD pathway, and may participate in the regulation of the occurrence and development of cervical cancer.

Hepatitis B virus mRNAs functionally sequester let-7a and enhance hepatocellular carcinoma

Hepatitis B virus (HBV) infection induces hepatocarcinogenesis and malignant progression, yet global effects of the redundant viral mRNAs produced during infection are unexplored. Here, microRNA (miRNA) target prediction and whole genome expression analysis revealed that HBV pre-C/C mRNA leads to upregulation of multiple let-7a targeted genes. A let-7a complementary region from nt 86 to 108 in the HBV genome was then identified in HBV pre-C/C, pre-S, and S mRNAs. The let-7a sequestration effect by HBV mRNAs was observed under transfection and virus infection, which is dependent on the let-7a response sequence. Moreover, we found reduced AGO2 binding, as well as functional mRNA and protein de-repression of let-7a targets (e.g., c-myc, K-RAS, and CCR7), upon viral mRNA expression. Let-7a levels in the liver were significantly decreased in hepatocellular carcinoma (HCC) patients with HBV infection and were negatively correlated with intrahepatic pre-S2 mRNA levels. Finally, both in vitro and in vivo studies demonstrated that let-7a inhibition by HBV mRNAs resulted in enhanced HCC cell colony formation and tumor growth, providing evidence of the oncogenic potential of HBV mRNAs.

MicroRNAs serve as a bridge between oxidative stress and gastric cancer (Review)

Gastric cancer (GC) remains one of the most prevalent tumors worldwide and affects human health due to its high morbidity and mortality. Mechanisms underlying occurrence and development of GC have been widely studied. Studies have revealed reactive oxygen species (ROS) generated by cells under oxidative stress (OS) are involved in gastric tumorigenesis, and modulate expression of microRNAs (miRs). As such, miRs have been shown to be associated with OS-related GC. Given the association of OS and miRs in development of GC, this review aims to summarize the relationship between miRs and OS and their role in GC development. Serving as a link between OS and GC, miRs may offer new approaches for gaining a more in-depth understanding of mechanisms of GC and may lead to the identification of new therapeutic approaches against GC.

Insights into the Regulatory Role of Non-coding RNAs in Cancer Metabolism

Cancer represents a complex disease originated from alterations in several genes leading to disturbances in important signaling pathways in tumor biology, favoring heterogeneity that promotes adaptability and pharmacological resistance of tumor cells. Metabolic reprogramming has emerged as an important hallmark of cancer characterized by the presence of aerobic glycolysis, increased glutaminolysis and fatty acid biosynthesis, as well as an altered mitochondrial energy production. The metabolic switches that support energetic requirements of cancer cells are closely related to either activation of oncogenes or down-modulation of tumor-suppressor genes, finally leading to dysregulation of cell proliferation, metastasis and drug resistance signals. Non-coding RNAs (ncRNAs) have emerged as one important kind of molecules that can regulate altered genes contributing, to the establishment of metabolic reprogramming. Moreover, diverse metabolic signals can regulate ncRNA expression and activity at genetic, transcriptional, or epigenetic levels. The regulatory landscape of ncRNAs may provide a new approach for understanding and treatment of different types of malignancies. In this review we discuss the regulatory role exerted by ncRNAs on metabolic enzymes and pathways involved in glucose, lipid, and amino acid metabolism. We also review how metabolic stress conditions and tumoral microenvironment influence ncRNA expression and activity. Furthermore, we comment on the therapeutic potential of metabolism-related ncRNAs in cancer.

Identification of Specific miRNA Signature in Paired Sera and Tissue Samples of Indian Women with Triple Negative Breast Cancer

Of several subtypes of breast cancer, triple negative breast cancer (TNBC) is a highly aggressive tumor that lacks expression of hormone receptors for estrogen, progesterone and human epidermal growth factor receptor 2 and shows a worst prognosis. The small noncoding RNAs (miRNAs) considered as master regulator of gene expression play a key role in cancer initiation, progression and drug resistance and have emerged as attractive molecular biomarkers for diagnosis, prognosis and treatment targets in cancer. We have done expression profiling of selected miRNAs in paired serum and tissue samples of TNBC patients and corresponding cell lines and compared with that of other subtypes, in order to identify novel serum miRNA biomarkers for early detection and progression of TNBC. A total of 85 paired tumor tissues and sera with an equal number of adjacent normal tissue margins and normal sera from age matched healthy women including tissue and sera samples from 15 benign fibroadenomas were employed for the study. We report for the first time an extremely high prevalence (73.9%) of TNBC in premenopausal women below 35 years of age and a significant altered expression of a panel of three specific oncogenic miRNAs- miR-21, miR-221, miR-210, and three tumor suppressor miRNAs- miR-195, miR-145 and Let-7a in both tissues and corresponding sera of TNBC patients when compared with triple positive breast cancer (TPBC) patients. While miR-21, miR-221 and miR-210 showed significant over-expression, miR-195 and miR-145 were downregulated and well correlated with various clinicopathological and demographic risk factors, tumor grade, clinical stage and hormone receptor status. Interestingly, despite being a known tumor suppressor, Let-7a showed a significant overexpression in TNBCs. It is suggested that this panel of six miRNA signature may serve as a minimally invasive biomarker for an early detection of TNBC patients.

Integrated analysis of mRNA, microRNA and protein in systemic lupus erythematosus-specific induced pluripotent stem cells from urine

Background

In clinical practice, it is difficult to monitor the repeating relapse in patients who have been suffering from systemic lupus erythematosus (SLE). The underlying etiology remains largely unknown.

Methods

Aiming to understand the pathogenesis of SLE, a detailed study was conducted. Renal tubular cells–derived iPSCs were successfully obtained from the urine of SLE patients and healthy controls. With the purpose to identify simultaneous expression profiling of microRNA, mRNA and protein, Illumina HiSeq™ 2000 System and iTRAQ-coupled 2D LC-MS/MS analysis were utilized in systemic lupus erythematosus-specific induced pluripotent stem cells (SLE-iPSCs) and normal control-iPSCs (NC-iPSCs). The integration of multiple profiling datasets was realized since it could facilitate the identification of non-seed miRNA targets, as well as differentially expressed mRNAs and proteins.

Results

For this study, profiling datasets of 1099 differentially expressed mRNAs, 223 differentially expressed microRNAs and 94 differentially expressed proteins were integrated. In order to investigate the influence of miRNA on the processes of regulating mRNAs and proteins’ levels, potential targets of differentially expressed mRNAs and proteins were predicted using miRanda, TargetScan and Pictar. Multiple profiling datasets were integrated to facilitate the identification of miRNA targets, as well as differentially expressed mRNAs and proteins. Through gene ontology (GO) analysis of differentially expressed mRNAs and proteins, biological processes that drive proliferation were identified, such as mRNA processing and translation. Western blot and Q-PCR confirmed AK4 protein and mRNA up-regulation. The findings also showed that TAGLN’s protein and mRNA level were down-regulated in SLE-iPSCs, both miR-371a-5p and let-7a-5p in SLE-iPSC were down-regulated and verified using Q-PCR. The up-regulation of AK4 involved in nucleotide biosynthesis suggested a general acceleration of anabolic metabolism induced by down-regulated miR-371a-5p, which might contribute to SLE.

Conclusion

Based on high throughput analysis, integrated miRNA, mRNA, and protein expression data were generated. Differentially expressed dates were also adopted in conjunction with in-silico tools to identify potential candidates for SLE-iPSCs. Representative miRNA, mRNA and proteins were verified. It was also expected that the knowledge gained from this study can be applied to assess the usefulness of pathogenesis and novel biomarker candidates of SLE, which may develop a new way for SLE diagnosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2809-9) contains supplementary material, which is available to authorized users.

MicroRNA 211 Functions as a Metabolic Switch in Human Melanoma Cells

MicroRNA 211 (miR-211) negatively regulates genes that drive invasion of metastatic melanoma. Compared to normal human melanocytes, miR-211 expression is significantly reduced or absent in nonpigmented melanoma cells and lost during human melanoma progression. To investigate the molecular mechanism of its tumor suppressor function, miR-211 was ectopically expressed in nonpigmented melanoma cells. Ectopic expression of miR-211 reduced hypoxia-inducible factor 1α (HIF-1α) protein levels and decreased cell growth during hypoxia. HIF-1α protein loss was correlated with the downregulation of a miR-211 target gene, pyruvate dehydrogenase kinase 4 (PDK4). We present evidence that resumption of miR-211-mediated downregulation of PDK4 in melanoma cells causes inhibition of invasion by nonpigmented melanomas via HIF-1α protein destabilization. Thus, the tumor suppressor miR-211 acts as a metabolic switch, and its loss is expected to promote cancer hallmarks in human melanomas. Melanoma, one of the deadliest forms of skin cancer, kills nearly 10,000 people in the United States per year. We had previously shown that a small noncoding RNA, termed miR-211, suppresses invasion and the growth of aggressive melanoma cells. The results presented here support the hypothesis that miR-211 loss in melanoma cells causes abnormal regulation of energy metabolism, which in turn allows cancer cells to survive under low oxygen concentrations-a condition that generally kills normal cells. These findings highlight a novel mechanism of melanoma formation: miR-211 is a molecular switch that is turned off in melanoma cells, raising the hope that in the future we might be able to turn the switch back on, thus providing a better treatment option for melanoma.

Whom to blame for metastasis, the epithelial-mesenchymal transition or the tumor microenvironment?

Changes in the tumor microenvironment (TME) can trigger the activation of otherwise non-malignant cells to become highly aggressive and motile. This is evident during initial tumor growth when the poor vascularization in tumors generates hypoxic regions that trigger the latent embryonic program, epithelial-to-mesenchymal transition (EMT), in epithelial carcinoma cells (e-cars) leading to highly motile mesenchymal-like carcinoma cells (m-cars), which also acquire cancer stem cell properties. After that, specific bidirectional interactions take place between m-cars and the cellular components of TME at different stages of metastasis. These interactions include several vicious positive feedback loops in which m-cars trigger a phenotypic switch, causing normal stromal cells to become pro-tumorigenic, which then further promote the survival, motility, and proliferation of m-cars. Accordingly, there is not a single culprit accounting for metastasis. Instead both m-cars and the TME dynamically interact, evolve and promote metastasis. In this review, we discuss the current status of the known interactions between m-cars and the TME during different stages of metastasis and how these interactions promote the metastatic activity of highly malignant m-cars by promoting their invasive mesenchymal phenotype and CSC properties.

The Role of MicroRNAs in the Chemoresistance of Breast Cancer

Preclinical Research Breast cancer is the most prevalent malignancy in women with more than 1.3 million new cases every year worldwide. Chemotherapy is a critical therapeutic strategy for breast cancer, while chemoresistance remains a major obstacle to treatment success. In the past two decades, significant progress has been achieved in understanding drug resistance in breast cancer, involving drug efflux, alterations in DNA repair pathways, suppression of apoptosis as well as epithelial-mesenchymal transition, and cancer stem cells. However, more effective therapeutic targets and novel biomarkers are still urgently needed to improve the overall survival and refine the therapeutic strategy for breast cancer patients. MicroRNAs (miRNAs) play crucial roles in cellular processes, such as cell differentiation, proliferation, and apoptosis. The recent discovery of miRNAs in malignancy has provided new directions for research on mechanisms underlying response to chemotherapy. Furthermore, several studies have documented that selected miRNAs, such as miR-200c and miR-34a, may influence response to chemotherapy in several tumor types, including breast cancer. The use of miRNAs as therapeutic targets to overcome chemoresistance is currently under investigation. In this review, we summarize the roles of miRNAs in chemoresistance through multiple molecular mechanisms, and highlight the potential diagnostic and therapeutic applications of miRNAs in overcoming breast cancer chemoresistance.

Metformin and cancer: Between the bioenergetic disturbances and the antifolate activity

For decades, metformin has been the first-line drug for the treatment of type II diabetes mellitus, and it thus is the most widely prescribed antihyperglycemic drug. Retrospective studies associate the use of metformin with a reduction in cancer incidence and cancer-related death. However, despite extensive research about the molecular effects of metformin in cancer cells, its mode of action remains controversial. In this review, we summarize the current molecular evidence in an effort to elucidate metformin's mode of action against cancer cells. Some authors describe that metformin acts directly on mitochondria, inhibiting complex I and restricting the cell's ability to cope with energetic stress. Furthermore, as the drug interrupts the tricarboxylic acid cycle, metformin-induced alteration of mitochondrial function leads to a compensatory increase in lactate and glycolytic ATP. It has also been reported that cell cycle arrest, autophagy, apoptosis and cell death induction is mediated by the activation of AMPK and Redd1 proteins, thus inhibiting the mTOR pathway. Additionally, unbiased metabolomics studies have provided strong evidence to support that metformin alters the methionine and folate cycles, with a concomitant decrease in nucleotide synthesis. Indeed, purines such as thymidine or hypoxanthine restore the proliferation of tumor cells treated with metformin in vitro. Consequently, some authors prefer to refer to metformin as an "antimetabolite drug" rather than a "mitochondrial toxin". Finally, we also review the current controversy concerning the relationship between the experimental conditions of in vitro-reported effects and the plasma concentrations achieved by chronic treatment with metformin.

Reduced Let-7a Is Associated with Chemoresistance in Primary Breast Cancer

Chemotherapy resistance remains an important problem in the breast cancer clinic. The ability to predict the patients who would respond to a distinct therapy would help to optimize tailored treatment options. miRNAs can mediate a number of genes in response to drug-induced acute cellular stress. Several studies suggest that let-7 miRNA may be involved in the chemosensitivity of cancer cell lines in vitro. However, it is not known whether this phenomenon occurs in clinical breast tumors. The present study showed that lower let-7a expression was associated with epirubicin resistance in primary breast tumors. Moreover, upregulation of let-7a expression sensitized resistant breast tumor cell lines to epirubicin by enhancing cellular apoptosis in vitro. Collectively, these findings indicate that lower expression of let-7a miRNA can induce chemoresistance in breast cancer by enhancing cellular apoptosis and suggest that let-7a may be used as a therapeutic target to modulate epirubicin-based chemotherapy resistance.

The role of Myc and let-7a in glioblastoma, glucose metabolism and response to therapy

Glioblastoma multiforme (GBM) is thought to result from an imbalance between glucose metabolism and tumor growth. The Myc oncogene and lethal-7a microRNA (let-7a miRNA) have been suggested to cooperatively regulate multiple downstream targets leading to changes in chromosome stability, gene mutations, and/or modulation of tumor growth. Here, we review the roles of Myc and let-7a in glucose metabolism and tumor growth and addresses their future potential as prognostic markers and therapeutic tools in GBM. We focus on the functions of Myc and let-7a in glucose uptake, tumor survival, proliferation, and mobility of glioma cells. In addition, we discuss how regulation of different pathways by Myc or let-7a may be useful for future GBM therapies. A large body of evidence suggests that targeting Myc and let-7a may provide a selective mechanism for the deregulation of glucose metabolic pathways in glioma cells. Indeed, Myc and let-7a are aberrantly expressed in GBM and have been linked to the regulation of cell growth and glucose metabolism in GBM. This article is part of a Special Issue entitled "Targeting alternative glucose metabolism and regulate pathways in GBM cells for future glioblastoma therapies".

Power in nursing: a collaborative approach

Breast cancers are very heterogeneous tissues with several cell types and metabolic pathways together sustaining the initiation and progression of disease and contributing to evasion from cancer therapies. Furthermore, breast cancer cells have an impressive metabolic plasticity that is regulated by the heterogeneous tumour microenvironment through bidirectional interactions. The structure and accessibility of nutrients within this unstable microenvironment influence the metabolism of cancer cells that shift between glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) to produce adenosine triphosphate (ATP). In this scenario, the mitochondrial energetic pathways of cancer cells can be reprogrammed to modulate breast cancer’s progression and aggressiveness. Moreover, mitochondrial alterations can lead to crosstalk between the mitochondria and the nucleus, and subsequently affect cancer tissue properties. This article reviewed the metabolic plasticity of breast cancer cells, focussing mainly on breast cancer mitochondrial metabolic reprogramming and the mitochondrial alterations influencing nuclear pathways. Finally, the therapeutic strategies targeting molecules and pathways regulating cancer mitochondrial alterations are highlighted.