MicroRNA and cutaneous melanoma: from discovery to prognosis and therapy

In Vivo miRNA Decoy Screen Reveals miR-124a as a Suppressor of Melanoma Metastasis

Melanoma is a highly prevalent cancer with an increasing incidence worldwide and high metastatic potential. Brain metastasis is a major complication of the disease, as more than 50% of metastatic melanoma patients eventually develop intracranial disease. MicroRNAs (miRNAs) have been found to play an important role in the tumorigenicity of different cancers and have potential as markers of disease outcome. Identification of relevant miRNAs has generally stemmed from miRNA profiling studies of cells or tissues, but these approaches may have missed miRNAs with relevant functions that are expressed in subfractions of cancer cells. We performed an unbiased in vivo screen to identify miRNAs with potential functions as metastasis suppressors using a lentiviral library of miRNA decoys. Notably, we found that a significant fraction of melanomas that metastasized to the brain carried a decoy for miR-124a, a miRNA that is highly expressed in the brain/neurons. Additional loss- and gain-of-function in vivo validation studies confirmed miR-124a as a suppressor of melanoma metastasis and particularly of brain metastasis. miR-124a overexpression did not inhibit tumor growth in vivo, underscoring that miR-124a specifically controls processes required for melanoma metastatic growth, such as seeding and growth post-extravasation. Finally, we provide proof of principle of this miRNA as a promising therapeutic agent by showing its ability to impair metastatic growth of melanoma cells seeded in distal organs. Our efforts shed light on miR-124a as an antimetastatic agent, which could be leveraged therapeutically to impair metastatic growth and improve patient survival.

Non-coding RNAs in melanoma: Biological functions and potential clinical applications

Malignant melanoma (MM) is a malignant tumor that originates from melanocytes and has a high mortality rate. Therefore, early diagnosis and treatment are very important for survival. So far, the exact molecular mechanism leading to the occurrence of melanoma, especially the molecular metastatic mechanism, remains largely unknown. Non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNA (circRNAs), have been investigated and found to play vital roles in regulating tumor occurrence and development, including melanoma. In this review, we summarize the progress of recent research on the effects of ncRNAs on melanoma and attempt to elucidate the role of ncRNAs as molecular markers or potential targets that will provide promising application perspectives on melanoma.

Up-regulation of KISS1 as a novel target of Let-7i in melanoma serves as a potential suppressor of migration and proliferation in vitro

Melanoma is a kind of skin cancer that is begun by the alteration of melanocytes. miRNAs are small non-coding RNA molecules that regulate a variety of biological processes. KISS1, the metastasis-suppressor gene, encodes kisspeptins which inhibits migration and proliferation of cancers. This study was aimed to determine the role of Let-7i and KISS1 in melanoma cell migration and proliferation. At first, the expression of Let-7i and KISS1 was determined in patients with melanoma. In the in vitro part of the study, Let-7i mimics were transfected and the impact of its restoration on target gene expression, proliferation, migration and apoptosis of SK-MEL-3 melanoma cell line was assessed by real-time PCR and Western blotting, MTT assay, wound-healing assay and flow cytometry, respectively. Besides, KISS1 inhibitor siRNA alone and along with Let-7i was transfected to determine their probable correlation. The results revealed that either Let-7i or KISS1 were down-regulated in patients with melanoma. The results obtained from the in vitro part of the study revealed that restoration of Let-7i reduced the expression of metastasis- and proliferation-related target genes. Moreover, it was revealed that up-regulation of Let-7i attenuated migration and proliferation capability of SK-MEL-3 cells. Besides, it was demonstrated that Let-7i restoration induced apoptosis in melanoma cells. More importantly, the KISS1 inhibitor caused a prominent cell migration and proliferation, attenuated by Let-7i re-expression. To sum up, the present study revealed the impressive role of Let-7i restoration along with its correlation with KISS1 on melanoma carcinogenicity which may be applicable in future in vivo studies.

Slow transcription of the 99a/let-7c/125b-2 cluster results in differential miRNA expression and promotes melanoma phenotypic plasticity

Almost half of human miRNAs are encoded in clusters. Although transcribed as a single unit, the levels of individual mature miRNAs often differ. The mechanisms underlying differential biogenesis of clustered miRNAs and the resulting physiological implications are mostly unknown. Here, we report that the melanoma master transcription regulator MITF regulates the differential expression of the 99a/let-7c/125b-2 cluster by altering the distribution of RNA polymerase II (Pol-II) along the cluster. We discovered that MITF interacts with TRIM28, a known inhibitor of Pol-II transcription elongation, at the let-7c region resulting in Pol-II pausing and causing its elevated expression, whereas low levels of Pol-II occupation over miR-99a and miR-125b-2 regions decreases their biogenesis. Furthermore, we showed that this differential expression affects the phenotypic state of melanoma cells. RNA-seq analysis of proliferative melanoma cells that express miR-99a and miR-125b mimics revealed a transcriptomic shift toward an invasive phenotype. Conversely, expression of a let-7c mimic in invasive melanoma cells induced a shift to a more proliferative state. We confirmed direct target genes of these miRNAs: FGFR3, BAP1, Bcl2, TGFBR1, and CDKN1A. Our study demonstrates a MITF-governed biogenesis mechanism that results in differential expression of clustered 99a/let-7c/125b-2 miRNAs that control melanoma progression.

The Non-Coding Landscape of Cutaneous Malignant Melanoma: A Possible Route to Efficient Targeted Therapy

Considered to be highly lethal if not diagnosed in early stages, cutaneous malignant melanoma is among the most aggressive and treatment-resistant human cancers, and its incidence continues to rise, largely due to ultraviolet radiation exposure, which is the main carcinogenic factor. Over the years, researchers have started to unveil the molecular mechanisms by which malignant melanoma can be triggered and sustained, in order to establish specific, reliable biomarkers that could aid the prognosis and diagnosis of this fatal disease, and serve as targets for development of novel efficient therapies. The high mutational burden and heterogeneous nature of melanoma shifted the main focus from the genetic landscape to epigenetic and epitranscriptomic modifications, aiming at elucidating the role of non-coding RNA molecules in the fine tuning of melanoma progression. Here we review the contribution of microRNAs and lncRNAs to melanoma invasion, metastasis and acquired drug resistance, highlighting their potential for clinical applications as biomarkers and therapeutic targets.

Hypoxic Melanoma Cells Deliver microRNAs to Dendritic Cells and Cytotoxic T Lymphocytes through Connexin-43 Channels

Alterations in microRNA (miRNA) profiles, induced by tumor microenvironment stressors, like hypoxia, allow cancer cells to acquire immune-resistance phenotypes. Indeed, hypoxia-induced miRNAs have been implicated in cancer progression through numerous cancer cell non-autonomous mechanisms, including the direct transfer of hypoxia-responsive miRNA from cancer to immune cells via extracellular vesicles. Connexin-43 (Cx43)-constituted gap junctions (GJs) have also been involved in miRNA intercellular mobilization, in other biological processes. In this report, we aimed to evaluate the involvement of Cx43-GJs in the shift of miRNAs induced by hypoxia, from hypoxic melanoma cells to dendritic cells and melanoma-specific cytotoxic T lymphocytes (CTLs). Using qRT-PCR arrays, we identified that miR-192-5p was strongly induced in hypoxic melanoma cells. Immune cells acquired this miRNA after co-culture with hypoxic melanoma cells. The transfer of miR-192-5p was inhibited when hypoxic melanoma cells expressed a dominant negative Cx43 mutant or when Cx43 expression was silenced using specific short-hairpin RNAs. Interestingly, miR-192-5p levels on CTLs after co-culture with hypoxic melanoma cells were inversely correlated with the cytotoxic activity of T cells and with ZEB2 mRNA expression, a validated immune-related target of miR-192-5p, which is also observed in vivo. Altogether, our data suggest that hypoxic melanoma cells may suppress CTLs cytotoxic activity by transferring hypoxia-induced miR-192-5p through a Cx43-GJs driven mechanism, constituting a resistance strategy for immunological tumor escape.

miR-140-3p Inhibits Cutaneous Melanoma Progression by Disrupting AKT/p70S6K and JNK Pathways through ABHD2

Because cutaneous melanoma (CM) is one of the most lethal human tumors, major treatment advances are vital. miR-140-3p has been suggested to act as a suppressor in a range of malignant tumors, implying its possible use as a biomarker for effective antineoplastic treatment. However, the potential role of miR-140-3p in CM and the underlying mechanism remain unclear. In the present study, we identified lower levels of miR-140-3p in both CM tissues and cell lines; this downregulation was strongly associated with worse CM survival. Additionally, overexpression of miR-140-3p significantly inhibited cell proliferation, migration, and invasion in CM cells with different cell line origins. Importantly, by means of both bioinformatics analysis and luciferase reporter assay, we revealed abhydrolase domain containing 2 (ABHD2) to be a target of miR-140-3p in CM cells. Upregulation of ABHD2 reversed the tumor-suppressive effects of miR-140-3p in CM cells. Furthermore, miR-140-3p-targeted ABHD2 played a role in both activation of JNK signaling and inhibition of the AKT/p70S6K pathway in CM cells. Finally, in vivo results strongly suggested the suppressive effects of miR-140-3p on CM growth and metastasis. Collectively, our findings highlight a novel antineoplastic function for miR-140-3p in CM through ABHD2.

Identification of miR-200a-5p targeting the peptide transporter TAP1 and its association with the clinical outcome of melanoma patients

Tumor escape is often associated with abnormalities in the surface expression of the human leukocyte antigen class I (HLA-I) antigens thereby limiting CD8+ cytotoxic T cell responses. This impaired HLA-I surface expression can be mediated by deficient expression of components of the antigen processing and presentation machinery (APM) due to epigenetic, transcriptional and/or post-transcriptional processes. Since a discordant mRNA and protein expression pattern of APM components including the peptide transporter associated with antigen processing 1 (TAP1) has been frequently described in tumors of distinct origin, a post-transcriptional control of APM components caused by microRNAs (miR) was suggested. Using an in silico approach, miR-200a-5p has been identified as a candidate miR binding to the 3' untranslated region (UTR) of TAP1. Luciferase reporter assays demonstrated a specific binding of miR-200a-5p to the TAP1 3'-UTR. Furthermore, the miR-200a-5p expression is inversely correlated with the TAP1 protein expression in HEK293T cells and in a panel of melanoma cell lines as well as in primary melanoma lesions. High levels of miR-200a-5p expression were associated with a shorter overall survival of melanoma patients. Overexpression of miR-200a-5p reduced TAP1 levels, which was accompanied by a decreased HLA-I surface expression and an enhanced NK cell sensitivity of melanoma cells. These data show for the first time a miR-mediated control of the peptide transporter subunit TAP1 in melanoma thereby leading to a reduced HLA-I surface expression accompanied by an altered immune recognition and reduced patients' survival.

Abbreviations

Ab: antibody; ACTB: β-actin; APM: antigen processing and presentation machinery; ATCC: American tissue culture collection; β2-m: β2-microglobulin; BSA: bovine serum albumin; CTL: cytotoxic T lymphocyte; FCS: fetal calf serum; FFL: firefly luciferase; FFPE: formalin-fixed paraffin-embedded; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; HC: heavy chain; HLA: human leukocyte antigen; HLA-I: HLA class I; HRP: horseradish peroxidase; IFN: interferon; im-miR: immune modulatory miRNA; LMP: low molecular weight protein; luc: luciferase; MFI: mean fluorescence intensity; MHC: major histocompatibility complex; miR: microRNA; NC: negative control; NK: natural killer; NSCLC: non-small cell lung carcinoma; OS: overall survival; PBMC: peripheral blood mononuclear cells; RBP: RNA-binding proteins; RL: Renilla; RLU: relative light units; TAP: transporter associated with antigen processing; tpn: tapasin; UTR: untranslated region.

How microRNAs affect the PD-L1 and its synthetic pathway in cancer

Programmed cell death-ligand 1 (PD-L1) is a glycoprotein that is expressed on the cell surface of both hematopoietic and nonhematopoietic cells. PD-L1 play a role in the immune tolerance and protect self-tissues from immune system attack. Dysfunction of this molecule has been highlighted in the pathogenesis of tumors, autoimmunity, and infectious disorders. MicroRNAs (miRNAs) are endogenous molecules that are classified as small non-coding RNA with approximately 20-22 nucleotides (nt) length. The function of miRNAs is based on complementary interactions with target mRNA via matching completely or incompletely. The result of this function is decay of the target mRNA or preventing mRNA translation. In the past decades, several miRNAs have been discovered which play an important role in the regulation of PD-L1 in various malignancies. In this review, we discuss the effect of miRNAs on PD-L1 expression and consider the effect of miRNAs on the synthetic pathway of PD-L1, especially during cancers.

A preliminary study of microRNA expression in different types of primary melanoma

MicroRNAs (miRNAs) have been proven to regulate the development and progression of cancer through various mechanisms. The aim of the present study was to compare miRNA expression between primary melanomas from different sites. We analyzed the expression of 84 miRNAs in 27 primary melanoma and 5 nevus formalin-fixed paraffin-embedded (FFPE) samples using the Human Cancer PathwayFinder miScript miRNA PCR Array. The FFPE samples were obtained from the archives of the Municipal Clinical Emergency Hospital of Timisoara and included 10 cutaneous melanomas, 10 uveal melanomas, 7 mucosal melanomas, and 5 cutaneous nevi. Out of 84 miRNAs, 11 miRNAs showed altered expression in all types of melanoma compared with the nevi. Among these, miR-155-5p, miR-9-5p, miR-142-5p, miR-19a-3p, miR-134-5p, and miR-301a-3p were upregulated, while miR-205-5p, miR-203a-3p, miR-27b-3p, miR-218-5p, and miR-23b-3p were downregulated. The highest similarity in miRNA expression pattern was found between uveal and mucosal melanoma groups, i.e., 15 miRNAs had altered expression in both groups. Overall, we identified several miRNAs with significantly altered expression in primary melanomas, including those reported for the first time in this type of cancer. Among them, mir-9-5p, mir-203a-3p, mir-19a-3p, mir-27b-3p, and mir-218-5p showed altered expression in all three melanoma types vs. nevi. Further research should explore the potential of these miRNAs in melanoma.

miRNAs in the Diagnosis and Prognosis of Skin Cancer

Skin cancer is, at present, the most common type of malignancy in the Caucasian population. Its incidence has increased rapidly in the last decade for both melanoma and non-melanoma skin cancer. Differential expression profiles of microRNAs (miRNAs) have been reported for a variety of different cancers, including skin cancers. Since miRNAs’ discovery as regulators of gene expression, their importance grew in the field of oncology. miRNAs can post-transcriptionally regulate gene expression, tumor initiation, development progression, and aggressiveness. Nowadays, these short regulatory RNAs are perceived as one of the epigenetic markers for the identification of new diagnostic and/or prognostic molecular markers. Moreover, as miRNAs can drive tumorigenesis, they might eventually represent new therapy targets. Some miRNAs are pleiotropic, such as miR-214, which was found deregulated in several other tumors besides skin cancers. Some others are specific for one or more skin cancer types, like miR-21 and miR-221 for cutaneous melanoma and cutaneous squamous carcinoma or miR-155 for melanoma and cutaneous lymphoma. The goal of this review was to summarize some of the main miRNA detection technologies that are used to evaluate miRNAs in tissues and body fluids. Furthermore, their quantification limits, conformity, and robustness are discussed. Aberrant miRNA expression is analyzed for cutaneous melanoma, cutaneous squamous cell carcinoma (CSCC), skin lymphomas, cutaneous lymphoma, and Merkel cell carcinoma (MCC). In this type of disease, miRNAs are described as potential biomarkers to diagnose early lesion and/or early metastatic disease. In the future, whether in tissue or circulating in body fluids, miRNAs will gain their place in skin cancer diagnosis, prognosis, and future therapeutic targets.

The miRNAs Role in Melanoma and in Its Resistance to Therapy

Melanoma is the less common but the most malignant skin cancer. Since the survival rate of melanoma metastasis is about 10–15%, many different studies have been carried out in order to find a more effective treatment. Although the development of target-based therapies and immunotherapeutic strategies has improved chances for patient survival, melanoma treatment still remains a big challenge for oncologists. Here, we collect recent data about the emerging role of melanoma-associated microRNAs (miRNAs) currently available treatments, and their involvement in drug resistance. We also reviewed miRNAs as prognostic factors, because of their chemical stability and resistance to RNase activity, in melanoma progression. Moreover, despite miRNAs being considered small conserved regulators with the limitation of target specificity, we outline the dual role of melanoma-associated miRNAs, as oncogenic and/or tumor suppressive factors, compared to other tumors.

Role of miRNAs in Melanoma Metastasis

Tumour metastasis is a multistep process. Melanoma is a highly aggressive cancer and metastasis accounts for the majority of patient deaths. microRNAs (miRNAs) are non-coding RNAs that affect the expression of their target genes. When aberrantly expressed they contribute to the development of melanoma. While miRNAs can act locally in the cell where they are synthesized, they can also influence the phenotype of neighboring melanoma cells or execute their function in the direct tumour microenvironment by modulating ECM (extracellular matrix) and the activity of fibroblasts, endothelial cells, and immune cells. miRNAs are involved in all stages of melanoma metastasis, including intravasation into the lumina of vessels, survival during circulation in cardiovascular or lymphatic systems, extravasation, and formation of the pre-metastatic niche in distant organs. miRNAs contribute to metabolic alterations that provide a selective advantage during melanoma progression. They play an important role in the development of drug resistance, including resistance to targeted therapies and immunotherapies. Distinct profiles of miRNA expression are detected at each step of melanoma development. Since miRNAs can be detected in liquid biopsies, they are considered biomarkers of early disease stages or response to treatment. This review summarizes recent findings regarding the role of miRNAs in melanoma metastasis.

MicroRNA-211 Loss Promotes Metabolic Vulnerability and BRAF Inhibitor Sensitivity in Melanoma

The clinical management of malignant melanoma remains a challenge because these tumors are intrinsically aggressive and prone to therapeutic resistance. MicroRNA (miR)-211 is an emerging melanoma oncogene. Melanoma metabolism adapts to promote survival, including in response to BRAFV600E inhibition, but how miR-211 participates in this process is unknown. Here, we generated miR-211 loss-of-function cell lines using CRISPR/Cas9 technology and show that miR-211 loss slowed growth and invasion in vitro, inhibited phosphoinositol-3-kinase signaling, and inhibited melanoma growth in vivo. miR-211 deficiency rendered melanoma cells metabolically vulnerable by attenuating mitochondrial respiration and tricarboxylic acid cycling. miR-211 was up-regulated by the BRAF inhibitor vemurafenib and in vemurafenib-resistant melanoma cells, with miR-211 loss rendering them more drug sensitive. miR-211 loss represents a "two-pronged" anticancer strategy by inhibiting both critical growth-promoting cell signaling pathways and rendering cells metabolically vulnerable, making it an extremely attractive and specific candidate combinatorial therapeutic target in melanoma.

Downregulation of intratumoral expression of miR-205, miR-200c and miR-125b in primary human cutaneous melanomas predicts shorter survival

While only 15–25 percent of melanoma patients develop distant metastasis and die, this disease is still responsible for the majority of skin cancer-related deaths. The availability of adjuvant therapies makes the selection of high-risk patients essential. We evaluated the intratumoral expression of ten miRNAs in primary melanomas in relation to its ability to predict melanoma survival. To this end, we correlated miRNA expression in 132 cryopreserved primary and metastatic tumors with clinicopathological factors and clinical outcome. We found sequential downregulation of intratumoral expression of miR-125b, miR-182, miR-200c and miR-205 over the full spectrum of melanoma progression. Moreover, downregulation of these miRNAs occurred in primary melanomas that further disseminated to distant sites. Furthermore, miR-125b, miR-200c and miR-205 correlated as independent factors with shorter survival. Our in vitro findings demonstrate that loss of miR-205 potentiates the invasive ability of melanoma cells. We conclude that the downregulation of miR-205 in primary melanomas is an intrinsic property that might contribute to distant metastasis. In particular, the interaction of melanoma cells with the extracellular matrix is one of the key mechanisms by which miR-205 influences melanoma metastasis. In conclusion, miR-125b, miR-200c and miR-205 are useful prognostic biomarkers at the time of diagnosis to select high-risk patients.

miR-23a acts as an oncogene in pancreatic carcinoma by targeting FOXP2

MicroRNAs have been reported to play an important role in tumor development and progression by targeting oncogenes and tumor suppressors. miR-23a has been described as significantly upregulated in multiple cancers and involved in tumorigenesis. The aim of this study was to evaluate the potential roles of miR-23a in pancreatic ductal adenocarcinoma (PDAC). We found that miR-23a level was significantly increased in tissues of PDAC compared with that in the control by real-time PCR. FOXP2 expression was downregulated and inversely correlated with miR-23a. miR-23a directly targeted the 3'-untranslated region of FOXP2 mRNA and repressed its expression. Mechanistically, enhancement of miR-23a by transfection with mimics in Aspc-1 cells significantly promoted cell proliferation and invasion, while miR-23a inhibitors transfection in SW1990 cells induced an inhibitory effect. Moreover, restoration of FOXP2 impaired the pro-proliferation and proinvasion effects of miR-23a, indicating FOXP2 is a direct mediator of miR-23a functions. In conclusion, our findings suggest a novel miR-23a/FOXP2 link contributing to PDAC development and invasion. It may be a potential diagnostic and therapeutic target for PDAC.

Hypoxia-regulated gene expression explains differences between melanoma cell line-derived xenografts and patient-derived xenografts

Cell line-derived xenografts (CDXs) are an integral part of drug efficacy testing during development of new pharmaceuticals against cancer but their accuracy in predicting clinical responses in patients have been debated. Patient-derived xenografts (PDXs) are thought to be more useful for predictive biomarker identification for targeted therapies, including in metastatic melanoma, due to their similarities to human disease. Here, tumor biopsies from fifteen patients and ten widely-used melanoma cell lines were transplanted into immunocompromised mice to generate PDXs and CDXs, respectively. Gene expression profiles generated from the tumors of these PDXs and CDXs clustered into distinct groups, despite similar mutational signatures. Hypoxia-induced gene signatures and overexpression of the hypoxia-regulated miRNA hsa-miR-210 characterized CDXs. Inhibition of hsa-miR-210 with decoys had little phenotypic effect in vitro but reduced sensitivity to MEK1/2 inhibition in vivo, suggesting down-regulation of this miRNA could result in development of resistance to MEK inhibitors.

High intensity focused ultrasound inhibits melanoma cell migration and metastasis through attenuating microRNA-21-mediated PTEN suppression

High intensity focused ultrasound (HIFU) technology is becoming a potential noninvasive treatment for solid tumor. To explore whether HIFU can be applied to treat melanoma and its metastasis, we investigated the effect of HIFU on murine melanoma model. While there was little influence on cell survival, viability or apoptosis, HIFU exposure suppressed melanoma cell migration in vitro and metastasis in vivo. The expression of microRNA-21(miR-21) was down-regulated and PTEN expression was up-regulated in response to HIFU exposure, which was in concomitant with the reduction of AKT activity. Furthermore, ectopic miR-21 expression suppressed this effect of HIFU. These results demonstrate that HIFU exposure can inhibit AKT-mediated melanoma metastasis via miR-21 inhibition to restore PTEN expression. Therefore, targeting the miR-21/PTEN/AKT pathway might be a novel strategy of HIFU in treatment of melanoma.

MicroRNA-Directed Cancer Therapies: Implications in Melanoma Intervention

Acquired tumor resistance to cancer therapies poses major challenges in the treatment of cancers including melanoma. Among several signaling pathways or factors that affect neocarcinogenesis, cancer progression, and therapies, altered microRNAs (miRNAs) expression has been identified as a crucial player in modulating the key pathways governing these events. While studies in the miRNA field have grown exponentially in the last decade, much remains to be discovered, particularly with respect to their roles in cancer therapies. Since immune and nonimmune signaling cascades prevail in cancers, identification and evaluation of miRNAs, their molecular mechanisms and cellular targets involved in the underlying development of cancers, and acquired therapeutic resistance would help in devising new strategies for the prognosis, treatment, and an early detection of recurrence. Importantly, in-depth validation of miRNA-targeted molecular events could lead to the development of accurate progression-risk biomarkers, improved effectiveness, and improved patient responses to standard therapies. The current review focuses on the roles of miRNAs with recent updates on regulated cell cycle and proliferation, immune responses, oncogenic/epigenetic signaling pathways, invasion, metastasis, and apoptosis, with broader attention paid to melanomagenesis and melanoma therapies.

Recent advances in melanoma research via "omics" platforms

Melanoma has a high mortality rate and metastatic melanoma is highly resistant to conventional therapies. "Omics" fields such as proteomics and microRNA and exosome studies have provided new knowledge to complement the information generated by genomic studies. This work aimed to review the current status of biomarker discovery for melanoma through multi-"omics" platforms. A few sets of novel microRNAs and proteins are described, some of them with important implications in suppressing melanoma at different stages. Upregulation of genes involved in angiogenesis, immunosuppressive factors, modification of stroma, capture of melanoma cells in lymph nodes and factors responsible for tumour cell recruitment have been identified in exosomes, among molecules with other functions. A remarkable series of proteins involved in epithelial-mesenchymal/mesenchymal-epithelial transitions, inflammation, motility, proliferation and progression processes, centrosome amplification, aneuploidy, inhibition of CD8+ effector T-cells, and metastasis in general were identified. Genomic and protein-protein interactions or metabolome levels were not analysed. Proteomics tools such as Orbitrap shotgun mass spectrometry or deep mining proteomic analysis utilizing high-resolution reversed phase nanoseparation in combination with mass spectrometry are also discussed. The application of these tools together with bioinformatics approaches applied to the clinical setting will enable the implementation of personalized medicine in the near future.

Genetic 3'UTR variation is associated with human pigmentation characteristics and sensitivity to sunlight

Sunlight exposure induces signalling pathways leading to the activation of melanin synthesis and tanning response. MicroRNAs (miRNAs) can regulate the expression of genes involved in pigmentation pathways by binding to the complementary sequence in their 3'untranslated regions (3'UTRs). Therefore, 3'UTR SNPs are predicted to modify the ability of miRNAs to target genes, resulting in differential gene expression. In this study, we investigated the role in pigmentation and sun-sensitivity traits, as well as in melanoma susceptibility, of 38 different 3'UTR SNPs from 38 pigmentation-related genes. A total of 869 individuals of Spanish origin (526 melanoma cases and 343 controls) were analysed. The association of genotypic data with pigmentation traits was analysed via logistic regression. Web-based tools for predicting the effect of genetic variants in microRNA-binding sites in 3'UTR gene regions were also used. Seven 3'UTR SNPs showed a potential implication in melanoma risk phenotypes. This association is especially noticeable for two of them, rs2325813 in the MLPH gene and rs752107 in the WNT3A gene. These two SNPs were predicted to disrupt a miRNA-binding site and to impact on miRNA-mRNA interaction. To our knowledge, this is the first time that these two 3'UTR SNPs have been associated with sun-sensitivity traits. We state the potential implication of these SNPs in human pigmentation and sensitivity to sunlight, possibly as a result of changes in the level of gene expression through the disruption of putative miRNA-binding sites.

miR-204-5p acts as a tumor suppressor by targeting matrix metalloproteinases-9 and B-cell lymphoma-2 in malignant melanoma

An increasing number of microRNAs have been found to be involved in tumorigenesis, including melanoma tumorigenesis. miR-204-5p is down-regulated and functions as a tumor suppressor in many human malignant tumors. miR-204-5p expression is also decreased in melanoma tissues, but its biological roles and molecular mechanisms in malignant melanoma remain unclear. In this study, the aberrant down-regulation of miR-204-5p was detected in melanoma, especially in metastatic melanoma. miR-204-5p also served as a protective factor for the prognosis of melanoma patients. We determined that miR-204-5p suppresses cell proliferation, migration and invasion, and promotes cell apoptosis in melanoma. Matrix metalloproteinases-9 and B-cell lymphoma-2 are the functional targets of miR-204-5p, through which it plays an important biological role in malignant melanoma. The effect of miR-204-5p on malignant melanoma is verified using a xenograft model. We also determined that miR-204-5p increases 5-fluorouracil and cisplatin (DDP) chemosensitivity in malignant melanoma cells. This finding elucidates new functions and mechanisms for miR-204-5p in melanoma development, and provides potential therapeutic targets for the treatment of melanoma.

Upregulation of MicroRNA-1246 Is Associated with BRAF Inhibitor Resistance in Melanoma Cells with Mutant BRAF

Purpose

Intrinsic and acquired resistance limit the therapeutic benefits of inhibitors of oncogenic BRAF in melanoma. To identify microRNAs (miRNAs) associated with resistance to a BRAF inhibitor, we compared miRNA expression levels in three cell lines with different BRAF inhibitor sensitivity.

Materials and Methods

miRNA microarray analysis was conducted to compare miRNA expression levels. Real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) was performed to confirm the expression of differentially expressed miRNAs. The cellular effects of miR-1246 were further examined by MTT assay, immunoblotting analysis, cell cycle analysis, flow cytometric assay of apoptosis, and autophagy assay.

Results

The miRNA microarray analysis and qRT-PCR identified five miRNAs (miR-3617, miR-92a-1, miR-1246, miR-193b-3p, and miR-17-3p) with expression that was consistently altered in two BRAF inhibitor-resistant cell lines. Among the five miRNAs, a miR-1246 mimic significantly reduced the antiproliferative effects of the BRAF inhibitor PLX4720 in BRAF inhibitor–resistant A375P (A375P/Mdr) cells, suggesting that miR-1246 upregulation confers acquired resistance to BRAF inhibition. In particular, apoptosis was identified as a major type of cell death in miR-1246–transfected cells; however, necrosis predominated in mimic-control-transfected cells, indicating that the resistance to PLX4720 in miR-1246 mimic-transfected cells is predominantly due to a reduction in necrosis. Furthermore, we found that miR-1246 promoted G₂/M arrest through autophagy as a way to escape cell death by necrosis and apoptosis in response to PLX4720. The promotion of BRAF inhibitor resistance by miR-1246 was associated with lowered levels of p-ERK.

Conclusion

These results suggest that miR-1246 may be a potential therapeutic target in melanoma with acquired resistance to BRAF inhibitors.

MicroRNAs role as potential biomarkers and key regulators in melanoma

Malignant melanoma (MM) is a highly aggressive skin cancer with high incidence worldwide. It originates from melanocytes and is characterized by invasion, early metastasis and despite the use of new drugs it is still characterized by high mortality. Since an early diagnosis determines a better prognosis, it is important to explore novel prognostic markers in the management of patients with MM. microRNAs (miRNAs) are small (∼22 nucleotides) single-stranded non-coding RNAs that negatively regulate the expression of more than 60% of human genes.miRNAs alterations are involved in several cancers, including MM, where a differential expression for some of them has been reported between healthy controls and MM patients. Moreover, since miRNAs are stable and easily detectable in body fluids, they might be considered as robust candidate biomarkers useful to identify risk of MM, to diagnose an early lesion and/or an early metastatic disease. This review highlights the importance of miRNAs as risk factors, prognostic factors and their role as molecular regulator in the development and progression of MM. © 2016 Wiley Periodicals, Inc.

miR-579-3p controls melanoma progression and resistance to target therapy

Therapy of melanoma patients harboring activating mutations in the BRAF (V-raf murine sarcoma viral oncogene homolog B1) oncogene with a combination of BRAF and MEK inhibitors is plagued by the development of drug resistance. Mutational events, as well as adaptive mechanisms, contribute to the development of drug resistance. In this context we uncover here the role of a miRNA, miR-579-3p. We first show that low expression of miR-579-3p is a negative prognostic factor correlating with poor survival. Expression levels of miR-579-3p decrease from nevi to stage III/IV melanoma samples and even further in cell lines resistant to BRAF/MEK inhibitors. Mechanistically, we demonstrate that miR-579-3p acts as an oncosuppressor by targeting the 3'UTR of two oncoproteins: BRAF and an E3 ubiquitin protein ligase, MDM2. Moreover miR-579-3p ectopic expression impairs the establishment of drug resistance in human melanoma cells. Finally, miR-579-3p is strongly down-regulated in matched tumor samples from patients before and after the development of resistance to targeted therapies.

Identification, Review, and Systematic Cross-Validation of microRNA Prognostic Signatures in Metastatic Melanoma

In metastatic melanoma, it is vital to identify and validate biomarkers of prognosis. Previous studies have systematically evaluated protein biomarkers or mRNA-based expression signatures. No such analyses have been applied to microRNA (miRNA)-based prognostic signatures. As a first step, we identified two prognostic miRNA signatures from publicly available data sets (Gene Expression Omnibus/The Cancer Genome Atlas) of global miRNA expression profiling information. A 12-miRNA signature predicted longer survival after surgery for resection of American Joint Committee on Cancer stage III disease (>4 years, no sign of relapse) and outperformed American Joint Committee on Cancer standard-of-care prognostic markers in leave-one-out cross-validation analysis (error rates 34% and 38%, respectively). A similar 15-miRNA biomarker derived from The Cancer Genome Atlas miRNA-seq data performed slightly worse (39%) than these current biomarkers. Both signatures were then assessed for replication in two independent data sets and subjected to systematic cross-validation together with the three other miRNA-based prognostic signatures proposed in the literature to date. Five miRNAs (miR-142-5p, miR-150-5p, miR-342-3p, miR-155-5p, and miR-146b-5p) were reproducibly associated with patient outcome and have the greatest potential for application in the clinic. Our extensive validation approach highlighted among multiple independent cohorts the translational potential and limitations of miRNA signatures, and pointed to future directions in the analysis of this emerging class of markers.

The Response of microRNAs to Solar UVR in Skin-Resident Melanocytes Differs between Melanoma Patients and Healthy Persons

The conversion of melanocytes into cutaneous melanoma is largely dictated by the effects of solar ultraviolet radiation (UVR). Yet to be described, however, is exactly how these cells are affected by intense solar UVR while residing in their natural microenvironment, and whether their response differs in persons with a history of melanoma when compared to that of healthy individuals. By using laser capture microdissection (LCM) to isolate a pure population of melanocytes from a small area of skin that had been intermittingly exposed or un-exposed to physiological doses of solar UVR, we can now report for the first time that the majority of UV-responsive microRNAs (miRNAs) in the melanocytes of a group of women with a history of melanoma are down-regulated when compared to those in the melanocytes of healthy controls. Among the miRNAs that were commonly and significantly down-regulated in each of these women were miR-193b (P<0.003), miR-342-3p (P<0.003), miR186 (P<0.007), miR-130a (P<0.007), and miR-146a (P<0.007). To identify genes potentially released from inhibition by these repressed UV-miRNAs, we analyzed databases (e.g., DIANA-TarBase) containing experimentally validated microRNA-gene interactions. In the end, this enabled us to construct UV-miRNA-gene regulatory networks consisting of individual genes with a probable gain-of-function being intersected not by one, but by several down-regulated UV-miRNAs. Most striking, however, was that these networks typified well-known regulatory modules involved in controlling the epithelial-to-mesenchymal transition and processes associated with the regulation of immune-evasion. We speculate that these pathways become activated by UVR resulting in miRNA down regulation only in melanocytes susceptible to melanoma, and that these changes could be partially responsible for empowering these cells toward tumor progression.

miR-339-3p Is a Tumor Suppressor in Melanoma

Determinants of invasion and metastasis in cancer remain of great interest to define. Here, we report the definition of miR-339-3p as a novel tumor suppressive microRNA that blocks melanoma cell invasion without affecting cell survival. miR-339-3p was identified by a comprehensive functional screen of a human miRNA mimetic library in a cell-based assay for invasion by the melanoma cell line A375. miR-339-3p was determined as a strong inhibitor of invasion differentially expressed in melanoma cells and healthy melanocytes. MCL1 was defined as a target for downregulation by miR-339-3p, functioning through direct interaction with the 3' untranslated region of MCL1 mRNA. Blocking miR-339-3p by an antagomiR was sufficient to increase melanoma cell invasion, an effect that could be phenocopied by RNAi-mediated silencing of MCL1. In vivo studies established that miR-339-3p overexpression was sufficient to decrease lung colonization by A375 melanoma cells in NSG mice, relative to control cells. Overall, our results defined miR-339-3p as a melanoma tumor suppressor, the levels of which contributes to invasive aggressiveness. Cancer Res; 76(12); 3562-71. ©2016 AACR.

miR-33a functions as a tumor suppressor in melanoma by targeting HIF-1α

BACKGROUND

Our previous findings showed that miR-33 expressed abnormally in clinical specimens of melanoma, but the exact molecular mechanism has not been elucidated.

OBJECT

To determine miR-33's roles in melanoma and confirm whether HIF-1α is a direct target gene of miR-33a.

METHODS

First miR-33a/b expression levels were detected in HM, WM35, WM451, A375 and SK-MEL-1. Then lentiviral vectors were constructed to intervene miR-33a expression in melanoma cells. Cell proliferation, invasion and metastasis were detected. A375 cells mice model was performed to test the tumorigenesis of melanoma in vivo. Finally the dual reporter gene assay was carried out to confirm whether HIF-1α is a direct target gene of miR-33a.

RESULTS

MiR-33a/b exhibited a lower expression in WM35, WM451, A375 and SK-MEL-1 of the metastatic skin melanoma cell lines than that in HM. Then inhibition of miR-33a expression in WM35 and WM451 cell lines could promote cell proliferation, invasion and metastasis. Conversely, increased expression of miR-33a in A375 cells could inhibit cellproliferation, invasion and metastasis. In vivo tests also confirmed that overexpression of miR-33a in A375 cells significantly inhibited melanoma tumorigenesis. Finally, we confirmed that HIF-1α is a direct target gene of miR-33a.

CONCLUSION

The newly identified miR-33a/HIF-1α axis might provide a new strategy for the treatment of melanoma.

Prognostic and predictive biomarkers in melanoma: an update

Malignant melanoma is one of the most aggressive cancers. Several new therapeutic strategies that focus on immuno- and/or targeted therapy have been developed, which have entered clinical trials or already been approved. This review provides an update on prognostic and predictive biomarkers in melanoma that may be used to improve the clinical management of patients. Prognostic markers include conventional histopathological characteristics, chromosomal aberrations, gene expression patterns and miRNA profiles. There is a trend towards multi-marker assays and whole-genome molecular screening methods to determine the prognosis of individual patients. Predictive biomarkers, including targeted components of signal transduction, developmental or transcriptional pathways, can be used to determine patient response towards a particular treatment or combination thereof. The rapid evolution of sequencing technologies and multi-marker screening will change the spectrum of patients who become candidates for therapeutic agents, and in addition create new ethical and regulatory challenges.

MicroRNAs as potential diagnostic and prognostic biomarkers in melanoma

Melanoma is a life-threatening malignancy with poor prognosis and a relatively high burden of mortality in advanced stages. The efficacy of current available therapeutic strategies is limited, with a survival rate of less than 10%. Despite rapid advances in biomarker-guided drug development in different tumour types, including melanoma, only a very small number of biomarkers have been identified. Recently, microRNAs (miRNAs) have emerged as a molecular regulator in the development and progression of melanoma. Aberrant activation of some known miRNAs, e.g. let-7a and b, miR-148, miR-155, miR-182, miR-200c, miR-211, miR-214, miR-221 and 222, has been recognised to be linked with melanoma-associated genes such as NRAS, microphthalmia-associated transcription factor, receptor tyrosine kinase c-KIT, AP-2 transcription factor, etc. There is accumulating evidence suggesting the potential impact of circulating miRNAs as diagnostic and therapeutic markers in diseases. In addition, miRNAs have turned out to play important roles in drug-resistance mechanisms; suggesting their modulation as a potential approach to overcome chemoresistance. This review highlights recent preclinical and clinical studies on circulating miRNAs and their potential role as diagnosis, and therapeutic targets in melanoma.

miRNAs in melanoma: a defined role in tumor progression and metastasis

The crosstalk of melanoma cells with components of the microenvironment promotes malignant cell proliferation and spread to distant tissues. Although the major pathogenetic events have already been elucidated, the mechanisms that drive the metastatic behavior of tumor cells are still undefined. MicroRNAs (miRNAs) are small non-coding RNAs that control post-transcriptional gene expression through interconnected kinases upstream of functional genes involved in tumor progression. Here, we review the biological relevance of melanoma-related miRNAs and focus on their potential role in propagating signals that may cause tumor microenvironment rearrangements, as well as disablement of the immune system and melanoma cell proliferation.

Extremely Low-Frequency Electromagnetic Fields Affect the miRNA-Mediated Regulation of Signaling Pathways in the GC-2 Cell Line

Extremely low-frequency electromagnetic fields (ELF-EMFs) can affect male reproductive function, but the underlying mechanism of this effect remains unknown. miRNA-mediated regulation has been implicated as an important epigenetic mechanism for regulatory pathways. Herein, we profiled miRNA expression in response to ELF-EMFs in vitro. Mouse spermatocyte-derived GC–2 cells were intermittently exposed to a 50 Hz ELF-EMF for 72 h (5 min on/10 min off) at magnetic field intensities of 1 mT, 2 mT and 3 mT. Cell viability was assessed using the CCK–8 assay. Apoptosis and the cell cycle were analyzed with flow cytometry. miRNA expression was profiled using Affymetrix Mouse Genechip miRNA 3.0 arrays. Our data showed that the growth, apoptosis or cell cycle arrest of GC–2 cells exposed to the 50 Hz ELF-EMF did not significantly change. However, we identified a total of 55 miRNAs whose expression significantly changed compared with the sham group, including 19 differentially expressed miRNAs (7 miRNAs were upregulated, and 12 were downregulated) in the 1 mT exposure group and 36 (9 miRNAs were upregulated, and 27 were downregulated) in the 3 mT exposure group. The changes in the expression of 15 selected miRNAs measured by real-time PCR were consistent with the microarray results. A network analysis was used to predict core miRNAs and target genes, including miR-30e-5p, miR-210-5p, miR-196b-5p, miR-504-3p, miR-669c-5p and miR-455-3p. We found that these miRNAs were differentially expressed in response to different magnetic field intensities of ELF-EMFs. GO term and KEGG pathway annotation based on the miRNA expression profiling results showed that miRNAs may regulate circadian rhythms, cytokine-cytokine receptor interactions and the p53 signaling pathway. These results suggested that miRNAs could serve as potential biomarkers, and the miRNA-mediated regulation of signaling pathways might play significant roles in the biological effects of ELF-EMFs.

A miRNA-Based Signature Detected in Primary Melanoma Tissue Predicts Development of Brain Metastasis

PURPOSE

Brain metastasis is the major cause of mortality among patients with melanoma. A molecular prognostic test that can reliably stratify patients at initial melanoma diagnosis by risk of developing brain metastasis may inform the clinical management of these patients.

EXPERIMENTAL DESIGN

We performed a retrospective, cohort-based study analyzing genome-wide and targeted microRNA expression profiling of primary melanoma tumors of three patient cohorts (n = 92, 119, and 45) with extensive clinical follow-up. We used Cox regression analysis to establish a microRNA-based signature that improves the ability of the current clinicopathologic staging system to predict the development of brain metastasis.

RESULTS

Our analyses identified a 4-microRNA (miR-150-5p, miR-15b-5p, miR-16-5p, and miR-374b-3p) prognostic signature that, in combination with stage, distinguished primary melanomas that metastasized to the brain from nonrecurrent and non-brain metastatic primary tumors (training cohort: C-index = 81.4%, validation cohort: C-index = 67.4%, independent cohort: C-index = 76.9%). Corresponding Kaplan-Meier curves of high- versus low-risk patients displayed a clear separation in brain metastasis-free and overall survival (training: P < 0.001; P < 0.001, validation: P = 0.033; P = 0.007, independent: P = 0.021; P = 0.022, respectively). Finally, of the microRNA in the prognostic model, we found that the expression of a key lymphocyte miRNA, miR-150-5p, which is less abundant in primary melanomas metastatic to brain, correlated with presence of CD45(+) tumor-infiltrating lymphocytes.

CONCLUSIONS

A prognostic assay based on the described miRNA expression signature combined with the currently used staging criteria may improve accuracy of primary melanoma patient prognoses and aid clinical management of patients, including selection for adjuvant treatment or clinical trials of adjuvant therapies.

MicroRNA and mRNA expression profiling in metastatic melanoma reveal associations with BRAF mutation and patient prognosis

The role of microRNAs (miRNAs) in melanoma is unclear. We examined global miRNA expression profiles in fresh-frozen metastatic melanomas in relation to clinical outcome and BRAF mutation, with validation in independent cohorts of tumours and sera. We integrated miRNA and mRNA information from the same samples and elucidated networks associated with outcome and mutation. Associations with prognosis were replicated for miR-150-5p, miR-142-3p and miR-142-5p. Co-analysis of miRNA and mRNA uncovered a network associated with poor prognosis (PP) that paradoxically favoured expression of miRNAs opposing tumorigenesis. These miRNAs are likely part of an autoregulatory response to oncogenic drivers, rather than drivers themselves. Robust association of miR-150-5p and the miR-142 duplex with good prognosis and earlier stage metastatic melanoma supports their potential as biomarkers. miRNAs overexpressed in association with PP in an autoregulatory fashion will not be suitable therapeutic targets.

Expression heterogeneity research of ITGB3 and BCL-2 in lung adenocarcinoma tissue and adenocarcinoma cell line

OBJECTIVE

To analyze expression heterogeneity of Integrin beta 3 (ITGB3) and B-cell lymphoma 2 (BCL-2) in lung adenocarcinoma tissue and adenocarcinoma cell line and further provide theoretical direction for molecular biological research of lung adenocarcinoma.

METHODS

Tissue microarray was used to observe relation among expression, heterogeneitpy and clinical characteristics of ITGB3 and BCL-2 in lung cancer.

RESULTS

ITGB3 and BCL-2 increased significantly in A549 cells in CAFs group withβ-actin as control; the expression level of BCL-2 also increased in ITGB3 transfected cells with GFP plasmid transfected A549 cells as control; immunohistochemistry staining showed that positive rates of ITGB3, ITGB1 and BCL-2 in normal lung tissues were 0, the positive rates in lung adenocarcinoma were 7.04%, 84.51% and 4.23%, respectively; in the results of immunohistochemistry staining, the expression of Girdin protein in lung adenocarcinoma was homogeneous, however protein expression of ITGB3, ITGB1 and BCL-2 showed different patterns in the same location with significant heterogeneity; majority of ITGB3, ITGB1 or BCL-2 positive tissue showed heterogeneity that expression in trailing edge was higher than that of trailing edge in lung adenocarcinoma tissue, the patients with BCL-2 heterogeneity showed higher lymph node metastasis ratio and lower clinical stage (P<0.05); and the expression of ITGB3 and the clinical characteristics of patients were not significant related (P>0.05).

CONCLUSIONS

Expression of ITGB3 and BCL-2 in lung adenocarcinoma and adenocarcinoma cell line showed heterogeneity that expression in trailing edge was higher than that of trailing edge, which may play an important role in promoting tumor lymph node metastasis and vascular invasion, and provides a new research direction for exploration of lung adenocarcinoma metastasis mechanism.

Decreased serum microRNA-206 level predicts unfavorable prognosis in patients with melanoma

BACKGROUND AND PURPOSE

MicroRNA-206 (miR-206) acts as a tumor suppressor in melanoma cell lines. However, its clinical significance remains unclear. The aim of this study was to detect the serum level of miR-206 in patients with melanoma and to determine the feasibility of using it as a noninvasive prognostic biomarker.

METHODS

Expression levels of miR-206 in serum samples from 60 patients with melanoma and 30 healthy controls were detected by real-time quantitative polymerase chain reaction (q-PCR).

RESULTS

Expression levels of miR-206 in serum samples from patients with melanoma were significantly lower than those in healthy controls (P<0.001). In addition, low serum miR-206 level was more frequently observed in patients with two or more metastatic sites (P=0.02). Its serum level was also significantly associated with the response to treatment (P=0.01). Moreover, melanoma patients with low serum miR-206 levels had higher clinical stage than those with high serum miR-206 levels (P<0.001). Furthermore, melanoma patients with low serum miR-206 level had a dramatically shorter 5-year overall and disease-free survival than those with high serum miR-206 level (both P=0.001). Multivariate analysis also identified the serum miR-206 level as an independent marker for both 5-year overall and disease-free survivals (both P=0.01) in patients with melanoma.

CONCLUSIONS

Our results offer the convincing evidence that miR-206 may be implicated in aggressive progression of melanoma. More importantly, the serum level of miR-206 may be a noninvasive prognostic biomarker for the patients with melanoma.

Cholesterol-conjugated let-7a mimics: antitumor efficacy on hepatocellular carcinoma in vitro and in a preclinical orthotopic xenograft model of systemic therapy

Background

A major challenge to the clinical utility of let-7 for hepatocellular carcinoma (HCC) therapy is the lack of an effective carrier to target tumours. We confirmed the high transfection efficiency of cholesterol-conjugated let-7a miRNA mimics (Chol-let-7a) in human HCC cells, as well as their high affinity for liver tissue in nude mice. However, their antitumor efficacy via systemic delivery remains unknown.

Methods

We explored the effects of Chol-let-7a on HCC in vitro and in vivo. Cell viability and mobility, let-7a abundance and the target ras genes was measured. Live-cell image and cell ultrastructure was observed. Antitumor efficacy in vivo was analyzed by ultrasonography, hispatholgogy and transmission electronic microscopy in a preclinical model of HCC orthotopic xenografts with systemic therapy.

Results

Chol-let-7a inhibited the viability and mobility of HCC cells. Chol-let-7a was primarily observed in the cytoplasm and induced organelle changes, including autophagy. Mild changes were observed in the cells treated with negative control miRNA. Chol-let-7a reached HCC orthotopic tumours, significantly inhibited tumour growth, and prevented local invasion and metastasis. Compared to control tumours, Chol-let-7a-treated tumours showed more necrosis. Tumour cells showed no significant atypia, and mitoses were very rare after systemic Chol-let-7a therapy. Furthermore, let-7a abundance in orthotopic xenografts was coincident with a reduction in the expression of 3 human ras mRNAs and RAS proteins.

Conclusions

Chol-let-7a exerted significant antitumor effects by down-regulating all human ras genes at the transcriptional and translational levels. Chol-let-7a inhibited cell proliferation, growth, and metastasis, and mainly functioned in the cytoplasm. Chol-let-7a represents a potential useful modified molecule for systemic HCC therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-889) contains supplementary material, which is available to authorized users.

miR-524-5p suppresses the growth of oncogenic BRAF melanoma by targeting BRAF and ERK2

It has been well documented that miRNAs can modulate the effectiveness of cancer-associated signaling pathways. Mitogen-activated protein kinase (MAPK/ERK) signaling plays an essential role in the progression of many cancers, including melanoma and colon cancers. However, no single miRNA is reported to directly target multiple components of the MAPK/ERK pathway. We performed a miRNA PCR array screening with various MAPK/ERK signaling activities. The miRNA array data revealed that the expression of miR-524-5p was decreased in cells with an active MAPK/ERK pathway and confirmed that the expression of miR-524-5p is inversely associated with the activity of the MAPK/ERK pathway. We demonstrated that miR-524-5p directly binds to the 3'-untranslated regions of both BRAFandERK2 and suppresses the expression of these proteins. Because BRAF and ERK2 are the main components of MAPK signaling, the overexpression of miR-524-5p effectively inhibits MAPK/ERK signaling, tumor proliferation, and melanoma cell migration. Moreover, tumors overexpressing miR-524-5p were significantly smaller than those of the negative control mice. Our findings provide new insight into the role of miR-524-5p as an important miRNA that negatively regulates the MAPK/ERK signaling pathway, suggesting that miR-524-5p could be a potent therapeutic candidate for melanoma treatment.

MicroRNA-mediated regulation of melanoma

Melanoma is one of the most aggressive and deadly skin cancers, and, in its advanced stages, accounts for > 80% mortality. The incidence of melanoma is increasing worldwide; however, beyond surgical removal of the tumour, there is currently no curative therapy available, especially for its advanced stages. This may, in part, be owing to incomplete understanding of the molecular mechanisms that regulate the initiation and/or progression of melanoma to metastasis. The molecular mechanisms leading to the development and progression of melanoma are the focus of intense investigation, and many genetic/epigenetic alterations affecting melanoma progression and development have been identified. microRNAs (miRNAs) are emerging as important causal modulators in the development and progression of melanoma. The understanding of miRNA-mediated regulation of tumours has grown immensely over the last few years, as it has been understood to regulate most biological processes. Here, we review the currently available data on miRNAs associated with melanoma, highlighting those deregulated miRNAs that target important genes and pathways involved in the progression of melanocytes to primary and metastatic melanoma. We also review their potential clinical utility as biomarkers and potential use in targeted therapy.

MicroRNA-143 targets Syndecan-1 to repress cell growth in melanoma

Melanoma is the most aggressive type of skin cancer with a rapid progression and a limited efficiency of therapeutics. Recently, studies have identified some microRNAs playing important roles in the development of melanoma. Syndecan-1 (Syn-1), dysregulated in many cancers, plays important roles in tumor progression by controlling cell proliferation. In this study, we investigated whether microRNA-143 (miR-143) is involved in the regulation of Syn-1 and thus plays a functional role in melanoma. We found that miR-143 expression was significantly lower in melanoma tissues than in normal tissues and its low expression was closely related to clinical stages of melanoma. Further experiments showed that consistent with the inhibitory effects induced by knockdown of Syn-1, overexpression of miR-143 suppressed cell proliferation, promoted G1 phase arrest and induced apoptosis in melanoma. Downregulation of miR-143 apparently produced opposite effects. Combined treatment of miR-143 overexpression and Syn-1 knockdown induced remarkable synergistic effects, while reconstitution of miR-143-resistant Syn-1 reversed the inhibitory activity of miR-143. Moreover, miR-143 level was inversely correlated with Syn-1 expression in melanoma cells. miR-143 directly targeted the 3′-untranslated regions of Syn-1 mRNA and they were in the same Argonaute2 complex. Taken together, this study revealed a link between miRNA-143 and Syn-1 in the pathogenesis of melanoma. MiR-143 plays an important role in the regulation of cell growth in melanoma. Restoration of miR-143 expression may represent a promising and efficient therapeutic approach for targeting malignant melanoma.

MicroRNAs in skin response to UV radiation

Solar ultraviolet (UV) radiation, an ubiquitous environmental carcinogen, is classified depending on the wavelength, into three regions; short-wave UVC (200-280 nm), mid-wave UVB (280-320 nm), and long-wave UVA (320- 400 nm). The human skin, constantly exposed to UV radiation, particularly the UVB and UVA components, is vulnerable to its various deleterious effects such as erythema, photoaging, immunosuppression and cancer. To counteract these and for the maintenance of genomic integrity, cells have developed several protective mechanisms including DNA repair, cell cycle arrest and apoptosis. The network of damage sensors, signal transducers, mediators, and various effector proteins is regulated through changes in gene expression. MicroRNAs (miRNAs), a group of small non-coding RNAs, act as posttranscriptional regulators through binding to complementary sequences in the 3´-untranslated region of their target genes, resulting in either translational repression or target degradation. Recent studies show that miRNAs add an additional layer of complexity to the intricately controlled cellular responses to UV radiation. This review summarizes our current knowledge of the role of miRNAs in the regulation of the human skin response upon exposure to UV radiation.

MiRNA in melanoma-derived exosomes

Proteins, RNAs and viruses can be spread through exosomes, therefore transport utilizing these nanovesicles is of the great interest. MiRNAs are common exosomal constituents capable of influencing expression of a variety of target genes. MiRNA signatures of exosomes are unique in cancer patients and differ from those in normal controls. The knowledge about miRNA profiles of tumor-derived exosomes may contribute to better diagnosis, determination of tumor progression and response to treatment, as well as to the development of targeted therapies. We summarize the current knowledge with regard to miRNAs that are found in exosomes derived from tumors, particularly from melanoma.