Proteomic identification of microRNA-122a target proteins in hepatocellular carcinoma

Micro RNAs in Regulation of Cellular Redox Homeostasis

In living cells Reactive Oxygen Species (ROS) participate in intra- and inter-cellular signaling and all cells contain specific systems that guard redox homeostasis. These systems contain both enzymes which may produce ROS such as NADPH-dependent and other oxidases or nitric oxide synthases, and ROS-neutralizing enzymes such as catalase, peroxiredoxins, thioredoxins, thioredoxin reductases, glutathione reductases, and many others. Most of the genes coding for these enzymes contain sequences targeted by micro RNAs (miRNAs), which are components of RNA-induced silencing complexes and play important roles in inhibiting translation of their targeted messenger RNAs (mRNAs). In this review we describe miRNAs that directly target and can influence enzymes responsible for scavenging of ROS and their possible role in cellular redox homeostasis. Regulation of antioxidant enzymes aims to adjust cells to survive in unstable oxidative environments; however, sometimes seemingly paradoxical phenomena appear where oxidative stress induces an increase in the levels of miRNAs which target genes which are supposed to neutralize ROS and therefore would be expected to decrease antioxidant levels. Here we show examples of such cellular behaviors and discuss the possible roles of miRNAs in redox regulatory circuits and further cell responses to stress.

PRDX2 plays an oncogenic role in esophageal squamous cell carcinoma via Wnt/β-catenin and AKT pathways

PURPOSE

To investigate the role of PRDX2 in esophageal carcinoma (ESCA).

METHODS

The expression of PRDX2 was detected in ESCA tissues. And PRDX2 expression in two ESCA cell lines was knocked down. Cell proliferation, metastasis and invasion were detected in these cells.

RESULTS

Here, we found that PRDX2 expression was significantly increased in ESCA tissues and was associated with a poor prognosis in ESCA patients. In addition, PRDX2 expression was significantly associated with pathological grading, infiltration degree and 5-year survival time in ESCA patients. Next, we knocked down PRDX2 expression by PRDX2-shRNA transfection in two ESCA cell lines, Eca-109 and TE-1. Proliferation analysis indicated that in vitro PRDX2 knockdown decreased growth and clone formation of ESCA cells. Scratch and transwell assays indicated that cell migration and invasion were significantly inhibited by PRDX2 knockdown. In addition, PRDX2 knockdown inhibited cell cycle of ESCA cells and down-regulated Cyclin D1-CDK4/6. Moreover, PRDX2 knockdown regulated proteins involved in mitochondrial-dependent apoptosis, including increased Bax and Caspase9/3 and decreased Bcl2. Mechanism investigation indicated that PRDX2 knockdown led to inactivation of Wnt/β-catenin and AKT pathways.

CONCLUSIONS

Our data suggest that PRDX2 may function as an oncogene in the development of ESCA via regulating Wnt/β-catenin and AKT pathways. Our study fills a gap in the understanding of the role of PRDX2 in ESCA and provides a potential target for ESCA treatment.

Peroxiredoxin2 downregulation enhances hepatocellular carcinoma proliferation and migration, and is associated with unfavorable prognosis in patients

It has been revealed by our previous proteomic study that the expression profile is different between well-differentiated and poorly differentiated hepatocellular carcinoma (HCC). Among those differently expressed proteins, peroxiredoxin2 (PRDX2) was our protein of interest. The present study aimed to further investigate the value of PRDX2 as a prognostic factor in HCC. Tissue microarrays were used to investigate the expression difference between HCC tissues and their adjacent normal liver tissues. The expression of PRDX2 at both mRNA and protein levels was examined by q-RT-PCR, western blotting and immunohistochemical assessment in HCC tissues and cell line HCCLM3. Silencing of PRDX2 in HCCLM3 was achieved usingpGMLV-SC1 lentiviral vectors. Cell Counting Kit-8 (CCK-8) and Transwell migration assays were used to assess cell proliferation and migration, respectively. Categorical variables were assessed using the Chi-square test, and ordinal variables were examined using the Mann-Whitney U test. The difference of continuous variables between groups were compared with t-tests. The Kaplan-Meier method was used to calculate the overall survival (OS) and disease-free survival (DFS) of patients, and the log-rank test was used to analyze the differences between groups. The results revealed that the expression of PRDX2 was decreased at both the mRNA and protein levels in an HCC cell line compared to that of a normal human liver cell line. PRDX2 protein expression levels were significantly downregulated in HCC tissues and were positively linked to overall survival (OS) and disease-free survival (DFS) of HCC patients. Patients with high PRDX2 expression levels had longer OS and DFS times than those with lower PRDX2 expression. Silencing of PRDX2 in the HCC cell line HCCLM3 promoted cancer cell proliferation and migration. Our findings indicated that PRDX2 may play an important role in HCC development; PRDX2 may serve as a useful prognostic factor and a therapeutic target.

Temporal and spatial changes of peroxiredoxin 2 levels in aortic media at very early stages of atherosclerotic lesion formation in apoE-knockout mice

The events that trigger early onset of atherosclerotic lesion formation are poorly understood. Initially, microscopic atherosclerotic lesions appear in the aortic root in 10-week-old apoE-knockout mice that are fed normal chow. Using proteome and immunohistochemical analyses, we investigated proteins in aortic media whose expression changes in athero-prone regions at the beginning of lesion formation. Protein profiles of the root/arch and thoracic/abdominal regions of aortas in 10-week-old apoE-knockout mice were analyzed using 2D-gel electrophoresis. Proteins in 81 spots with different abundance were identified. Among them, we focused on proteins related to oxidative stress and smooth muscle cells (SMCs). The level of peroxiredoxin 2 (Prx2), a major cellular antioxidant enzyme that reduces hydrogen peroxide, was lower in aortic root/arch compared with thoracic/abdominal aorta. Immunohistochemical staining demonstrated that Prx2 expression in SMCs in the aortic root was high at 4 weeks and decreased at 10 weeks in apoE-knockout mice, while Prx2 expression in the aorta was unchanged in wild-type mice. The level of Prx2 expression correlated positively with the SMC differentiation markers, α-smooth muscle actin and transgelin, suggesting that a decline in Prx2 expression accompanies SMC dedifferentiation. Accumulated acrolein-modified proteins and the infiltration of macrophages in aortic media were observed in areas with low Prx2 expression. These results showed that Prx2 expression declines in athero-prone aortic root before lesion formation, and this reduction in Prx2 expression correlates with lipid peroxidation, SMC dedifferentiation, and macrophage recruitment.

MicroRNA-122 negatively associates with peroxiredoxin-II expression in human gefitinib-resistant lung cancer stem cells

Previously, we demonstrated that Prx II is important for survival of the gefitinib-resistant A549 (A549/GR) cell line, an NSCLC cell line derived by repeated exposure to gefitinib. Therefore, in this study, we used A549/GR cells to investigate the role of Prx II in GR NSCLC stemness. Initially, to explore the stemness characteristics and investigate the association of Prx II with those stemness characteristics, we successfully isolated a stem cell-like population from A549/GR cells. A549/GR CD133⁺ cells possessed important cancer stemness characteristics, including the abilities to undergo metastasis, angiogenesis, self-renewal, and to express stemness genes and epithelial–mesenchymal transition (EMT) markers. However, those characteristics were abolished by knocking down Prx II expression. MicroRNA 122 (miR-122) targets Prx II in A549/GR cancer stem cells (CSCs), thereby inhibiting the stemness characteristics in vitro and in vivo. Next, we investigate whether miR-122 overexpression was associated with Prx II expression and Prx-II-induced stemness characteristics, we transfected miR-122 into A549/GR CSCs. MiR-122 inhibited A549/GR stemness by downregulating the Hedgehog, Notch, and Wnt/β-catenin pathways. Taken together, our data suggest that Prx II promotes A549/GR stemness, and that targeting Prx II and miR-122 is a potentially viable strategy for anti-cancer-stem cell therapy in GR NSCLCs.

VDAC2 interacts with PFKP to regulate glucose metabolism and phenotypic reprogramming of glioma stem cells

Plastic phenotype convention between glioma stem cells (GSCs) and non-stem tumor cells (NSTCs) significantly fuels glioblastoma heterogeneity that causes therapeutic failure. Recent progressions indicate that glucose metabolic reprogramming could drive cell fates. However, the metabolic pattern of GSCs and NSTCs and its association with tumor cell phenotypes remain largely unknown. Here we found that GSCs were more glycolytic than NSTCs, and voltage-dependent anion channel 2 (VDAC2), a mitochondrial membrane protein, was critical for metabolic switching between GSCs and NSTCs to affect their phenotypes. VDAC2 was highly expressed in NSTCs relative to GSCs and coupled a glycolytic rate-limiting enzyme platelet-type of phosphofructokinase (PFKP) on mitochondrion to inhibit PFKP-mediated glycolysis required for GSC maintenance. Disruption of VDAC2 induced dedifferentiation of NSTCs to acquire GSC features, including the enhanced self-renewal, preferential expression of GSC markers, and increased tumorigenicity. Inversely, enforced expression ofVDAC2 impaired the self-renewal and highly tumorigenic properties of GSCs. PFK inhibitor clotrimazole compromised the effect of VDAC2 disruption on glycolytic reprogramming and GSC phenotypic transition. Clinically, VDAC2 expression inversely correlated with glioma grades (Immunohistochemical staining scores of VDAC2 were 4.7 ± 2.8, 3.2 ± 1.9, and 1.9 ± 1.9 for grade II, grade III, and IV, respectively, p < 0.05 for all) and the patients with high expression of VDAC2 had longer overall survival than those with low expression of VDAC2 (p = 0.0008). In conclusion, we demonstrate that VDAC2 is a new glycolytic regulator controlling the phenotype transition between glioma stem cells and non-stem cells and may serves as a new prognostic indicator and a potential therapeutic target for glioma patients.

Identification of an Anti-Inflammation Protein, Annexin A1, in Tendon Derived Stem Cells (TDSCs) of Cystic Fibrosis Mice: A Comparative Proteomic Analysis

PURPOSE

A previous study reported an elevated inflammation during tendon injury in mice with cystic fibrosis (CF), indicating the inadequate management of inflammation due to dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR). The objective of this study is to identify the targets of CFTR that contribute to the abnormal inflammation during tendon injury.

EXPERIMENTAL DESIGN

A 2D gel electrophoresis and mass-spectrometry-based comparative proteomics is performed to find the molecular targets of CFTR. And the targeted protein is further confirmed at both mRNA and protein levels.

RESULTS

It is identified that 14 proteins are differentially expressed, with annexin A1 being one of the most significantly downregulated protein. Further confirmation shows that annexin A1 is significantly decreased in TDSCs isolated from DF508 mice. As an essential anti-inflammation mediator, it is also downregulated in the injured tendon tissue of DF508 mice when compared with WT mice.

CONCLUSIONS AND CLINICAL RELEVANCE

Decreased annexin A1 expression can contribute to the elevated inflammation in DF508 mice during tendon injury. Therefore, annexin A1 can be considered as a new potential biomarker or drug target for a possible therapeutic approach in clinical practice.

Neuroprotection afforded by circadian regulation of intracellular glutathione levels: A key role for miRNAs

Circadian rhythms are approximately 24-h oscillations of physiological and behavioral processes that allow us to adapt to daily environmental cycles. Like many other biological functions, cellular redox status and antioxidative defense systems display circadian rhythmicity. In the central nervous system (CNS), glutathione (GSH) is a critical antioxidant because the CNS is extremely vulnerable to oxidative stress; oxidative stress, in turn, causes several fatal diseases, including neurodegenerative diseases. It has long been known that GSH level shows circadian rhythm, although the mechanism underlying GSH rhythm production has not been well-studied. Several lines of recent evidence indicate that the expression of antioxidant genes involved in GSH homeostasis as well as circadian clock genes are regulated by post-transcriptional regulator microRNA (miRNA), indicating that miRNA plays a key role in generating GSH rhythm. Interestingly, several reports have shown that alterations of miRNA expression as well as circadian rhythm have been known to link with various diseases related to oxidative stress. A growing body of evidence implicates a strong correlation between antioxidative defense, circadian rhythm and miRNA function, therefore, their dysfunctions could cause numerous diseases. It is hoped that continued elucidation of the antioxidative defense systems controlled by novel miRNA regulation under circadian control will advance the development of therapeutics for the diseases caused by oxidative stress.

RKIP and peroxiredoxin 2 expression predicts the proliferative potential of gastric cancer stem cells

Gastric cancer is associated with a high mortality rate, with the development of gastric cancer stem cells underlying this. Gastric cancer stem cells are responsible for tumor initiation, progression and recurrence. However, the link between gastric cancer and gastric cancer stem cells remains to be fully understood. Murine models mimic a human microenvironment more accurately than in vitro studies and are useful models for understanding the behavior of different markers. The present study compared the expression of cluster of differentiation 44 (CD44), a stem cell marker, with the expression of other cancer-associated markers, including Raf kinase inhibitor protein (RKIP) and peroxiredoxin 2, in different pathological conditions of gastric cancer development using histological, immunohistological and western blot analyses. Initially, the murine model of gastric cancer was established using N-methyl-N-nitrosourea, a chemical carcinogen. Following initiation of cancer, immunohistochemistry was used to compare the expression of CD44, RKIP and peroxiredoxin 2 at different stages of cancer development. The results suggested CD44 and peroxiredoxin 2 expression was upregulated as the tumor progressed. However, expression of RKIP, a metastasis suppressor, was elevated in the initial stage of gastric cancer and suppressed during the aggressive stages. In agreement with previous data suggesting higher expressions of RKIP in the initial stages of cancer and its downregulation in the advanced stage, the results of the present study revealed that RKIP exhibited a negative effect on initial tumor development, and that the downregulation of RKIP in the advanced stages of cancer facilitated CD44 and peroxiredoxin 2 overexpression.

MKRMDA: multiple kernel learning-based Kronecker regularized least squares for MiRNA-disease association prediction

Background

Recently, as the research of microRNA (miRNA) continues, there are plenty of experimental evidences indicating that miRNA could be associated with various human complex diseases development and progression. Hence, it is necessary and urgent to pay more attentions to the relevant study of predicting diseases associated miRNAs, which may be helpful for effective prevention, diagnosis and treatment of human diseases. Especially, constructing computational methods to predict potential miRNA–disease associations is worthy of more studies because of the feasibility and effectivity.

Methods

In this work, we developed a novel computational model of multiple kernels learning-based Kronecker regularized least squares for MiRNA–disease association prediction (MKRMDA), which could reveal potential miRNA–disease associations by automatically optimizing the combination of multiple kernels for disease and miRNA.

Results

MKRMDA obtained AUCs of 0.9040 and 0.8446 in global and local leave-one-out cross validation, respectively. Meanwhile, MKRMDA achieved average AUCs of 0.8894 ± 0.0015 in fivefold cross validation. Furthermore, we conducted three different kinds of case studies on some important human cancers for further performance evaluation. In the case studies of colonic cancer, esophageal cancer and lymphoma based on known miRNA–disease associations in HMDDv2.0 database, 76, 94 and 88% of the corresponding top 50 predicted miRNAs were confirmed by experimental reports, respectively. In another two kinds of case studies for new diseases without any known associated miRNAs and diseases only with known associations in HMDDv1.0 database, the verified ratios of two different cancers were 88 and 94%, respectively.

Conclusions

All the results mentioned above adequately showed the reliable prediction ability of MKRMDA. We anticipated that MKRMDA could serve to facilitate further developments in the field and the follow-up investigations by biomedical researchers.

Electronic supplementary material

The online version of this article (10.1186/s12967-017-1340-3) contains supplementary material, which is available to authorized users.

Ubiquitin specific peptidase 5 mediates Histidine-rich protein Hpn induced cell apoptosis in hepatocellular carcinoma through P14-P53 signaling

Hpn is a small histidine-rich cytoplasmic protein from Helicobacter pylori and has been recognized as a high-risk factor for several cancers including gastric cancer, colorectal cancer, and MALT lymphoma. However, the relationship between Hpn and cancers remains elusive. In this study, we discovered that Hpn protein effectively suppressed cell growth and induced apoptosis in hepatocellular carcinoma (HCC). A two-dimensional gel electrophoresis and mass spectrometry-based comparative proteomics was performed to find the molecular targets of Hpn in HCC cells. It was identified that twelve proteins were differentially expressed, with USP5 being one of the most significantly downregulated protein. The P14^ARF -P53 signaling was activated by USP5 knockdown in HCC cells. Furthermore, USP5 overexpression significantly rescued the suppressive effect of Hpn on the viability of HCC cells. In conclusion, our study suggests that Hpn plays apoptosis-inducing roles through suppressing USP5 expression and activating the P14^ARF -P53 signaling. Therefore, Hpn may be a potential candidate for developing novel anti-HCC drugs.

Proteomic identification of proteins differentially expressed following overexpression of hTERT (human telomerase reverse transcriptase) in cancer cells

Reverse transcriptase activity of telomerase adds telomeric repeat sequences at extreme ends of the newly replicated chromosome in actively dividing cells. Telomerase expression is not detected in terminally differentiated cells but is noticeable in 90% of the cancer cells. hTERT (human telomerase reverse transcriptase) expression seems to promote invasiveness of cancer cells. We here present proteomic profiles of cells overexpressing or knocked down for hTERT. This study also attempts to find out the potential interacting partners of hTERT in cancer cell lines. Two-dimensional gel electrophoresis (2-DE) of two different cell lines U2OS (a naturally hTERT negative cell line) and HeLa revealed differential expression of proteins in hTERT over-expressing cells. In U2OS cell line 28 spots were picked among which 23 spots represented upregulated and 5 represented down regulated proteins. In HeLa cells 21 were upregulated and 2 were down regulated out of 23 selected spots under otherwise identical experimental conditions. Some heat shock proteins viz. Hsp60 and Hsp70 and GAPDH, which is a housekeeping gene, were found similarly upregulated in both the cell lines. The upregulation of these proteins were further confirmed at RNA and protein level by real-time PCR and western blotting respectively.

The potential value of microRNA-4463 in the prognosis evaluation in hepatocellular carcinoma

The purpose of this study is to measure the expression of microRNA-4463 and microRNA-6087 between normal persons and patients with hepatocellular carcinoma (HCC), and to clarify the meaning of them in the prognosis evaluation in HCC. Forty-five samples from healthy people and patients, who had been diagnosed with hepatocellular carcinoma before any treatment, were collected to study respectively. Real-time PCR was used to detect the expression of miRNA-4463 and miRNA-6087 in the serum of control group and hepatocellular carcinoma patients. The expression of miR-4463 in the serum of HCC patients was significantly higher than that in control group (P < 0.05), and the expression level was independent of gender, tumor size, cell types, stages, alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL) and HBsAg status (P > 0.05). But there was a significant difference of different level of AFP in HCC (P < 0.05), and the difference between the group of AFP lower than 400 ug/l and the control group is statistically significant (P < 0.05). Besides, the survival time had showed a significant difference at the high and low expression levels (P < 0.05). But the expression level of miRNA-6087 was no difference in HCC and control group. The disorder of miRNA-4463 occurred in HCC, even the AFP level doesn't rises. What's more, patients who get the high level of miRNA-4463 seem to have a shorter survival time. And it contributes great to the prognostic evaluation. This is the first study to illustrate the potential significance of miRNA-4463 in the prognosis in HCC.

Redox Regulating Enzymes and Connected MicroRNA Regulators Have Prognostic Value in Classical Hodgkin Lymphomas

There are no previous studies assessing the microRNAs that regulate antioxidant enzymes in Hodgkin lymphomas (HLs). We determined the mRNA levels of redox regulating enzymes peroxiredoxins (PRDXs) I–III, manganese superoxide dismutase (MnSOD), nuclear factor erythroid-derived 2-like 2 (Nrf2), and Kelch-like ECH-associated protein 1 (Keap1) from a carefully collected set of 41 classical HL patients before receiving any treatments. The levels of redoxmiRs, miRNAs known to regulate the above-mentioned enzymes, were also assessed, along with CD3, CD20, and CD30 protein expression. RNAs were isolated from freshly frozen lymph node samples and the expression levels were analyzed by qPCR. mir23b correlated inversely with CD3 and CD20 expressions (p = 0.00076; r = −0.523 and p = 0.0012; r = −0.507) and miR144 with CD3, CD20, and CD30 (p = 0.030; r = −0.352, p = 0.041; r = −0.333 and p = 0.0032; r = −0.47, resp.). High MnSOD mRNA levels associated with poor HL-specific outcome in the patients with advanced disease (p = 0.045) and high miR-122 levels associated with worse HL-specific survival in the whole patient population (p = 0.015). When standardized according to the CD30 expression, high miR212 and miR510 predicted worse relapse-free survival (p = 0.049 and p = 0.0058, resp.). In conclusion, several redoxmiRs and redox regulating enzyme mRNA levels associate with aggressive disease outcome and may also produce prognostic information in classical HL.

Estimating survival time of patients with glioblastoma multiforme and characterization of the identified microRNA signatures

BACKGROUND

Though glioblastoma multiforme (GBM) is the most frequently occurring brain malignancy in adults, clinical treatment still faces challenges due to poor prognoses and tumor relapses. Recently, microRNAs (miRNAs) have been extensively used with the aim of developing accurate molecular therapies, because of their emerging role in the regulation of cancer-related genes. This work aims to identify the miRNA signatures related to survival of GBM patients for developing molecular therapies.

RESULTS

This work proposes a support vector regression (SVR)-based estimator, called SVR-GBM, to estimate the survival time in patients with GBM using their miRNA expression profiles. SVR-GBM identified 24 out of 470 miRNAs that were significantly associated with survival of GBM patients. SVR-GBM had a mean absolute error of 0.63 years and a correlation coefficient of 0.76 between the real and predicted survival time. The 10 top-ranked miRNAs according to prediction contribution are as follows: hsa-miR-222, hsa-miR-345, hsa-miR-587, hsa-miR-526a, hsa-miR-335, hsa-miR-122, hsa-miR-24, hsa-miR-433, hsa-miR-574 and hsa-miR-320. Biological analysis using the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway on the identified miRNAs revealed their influence in GBM cancer.

CONCLUSION

The proposed SVR-GBM using an optimal feature selection algorithm and an optimized SVR to identify the 24 miRNA signatures associated with survival of GBM patients. These miRNA signatures are helpful to uncover the individual role of miRNAs in GBM prognosis and develop miRNA-based therapies.

Long noncoding RNA Hotair mediated angiogenesis in nasopharyngeal carcinoma by direct and indirect signaling pathways

Nasopharyngeal carcinoma (NPC), as a unique head and neck cancer type, is particularly prevalent in certain geographic areas such as eastern Asia. Until now, the therapeutic options have been restricted mainly to radiotherapy or chemotherapy. However, the clinical treatment effect remains unsatisfactory even if the combined radio-chemotherapies. Therefore, it is urgently needed to develop effective novel therapies against NPC. In this study, we discovered that lncRNA Hotair was extremely abundant in NPC cells and clinical NPC samples. Further studies showed that Hotair knockdown significantly attenuated both in vitro and in vivo tumor cell growth and angiogenesis. Our study also demonstrated that Hotair promoted angiogenesis through directly activating the transcription of angiogenic factor VEGFA as well as through GRP78-mediated upregulation of VEGFA and Ang2 expression. Therefore, Hotair may serve as a promising diagnostic marker and therapeutic target for NPC patients.

Epigenetic regulation of peroxiredoxins: Implications in the pathogenesis of cancer

Peroxiredoxin I to VI (PRX I-VI), a family of highly conserved antioxidants, has been implicated in numerous diseases. There have been reports that PRXs are expressed aberrantly in a variety of tumors, implying that they could play an important role in carcinogenesis. Epigenetic mechanisms such as DNA methylation, histone modifications, and microRNAs have been reported to modulate expression of PRXs. In addition, the use of epigenetic regulators, such as histone deacetylases, has been demonstrated to restore PRX to normal levels, indicating that the reversible nature of epigenetics can be exploited for future treatments.

PRDX2 protects hepatocellular carcinoma SMMC-7721 cells from oxidative stress

Peroxiredoxin2 (PRDX2) is a member of the peroxiredoxin family of antioxidant enzymes. A number of previous studies have indicated that PRDX2 may serve a cell type-dependent role in tumorigenesis. Recently, PRDX2 has been identified to be the new target of miR-122a, which has been demonstrated to be frequently downregulated in hepatocellular carcinoma (HCC). Thus, PRDX2 may have a pro-tumorigenic role in HCC. Because the role of PRDX2 in HCC has not yet been reported, it is of interest to explore how PRDX2 may affect reactive oxygen species (ROS)-mediated cell death in HCC cells. The present study analyzed the effects of PRDX2 knockdown or overexpression on hydrogen peroxide (H₂O₂)-induced cell death in HCC SMMC-7721 cells. Tumor necrosis factor-α (TNF-α)-induced cell death upon PRDX2 knockdown or overexpression was also examined in SMMC-7721 cells. It was found that PRDX2 knockdown augmented H₂O₂-induced cell death in SMMC-7721 cells, whereas PRDX2 overexpression exhibited opposite effects. By contrast, PRDX2 knockdown enhanced TNF-α-induced apoptosis, whereas PRDX2 overexpression reduced it, even though both treatments showed little effects on TNF-α-induced necrosis in SMMC-7721 cells. Further exploration confirmed PRDX2 knockdown led to enhanced ROS generation in response to H₂O₂. Taken together, the present study supports that PRDX2 serves a pro-tumorigenic role in HCC through, at least partially, limiting ROS-mediated apoptosis under oxidative stress.

Bioinformatic analysis of microRNA networks following the activation of the constitutive androstane receptor (CAR) in mouse liver

The constitutive androstane receptor (CAR; NR1I3) is a member of the nuclear receptor superfamily that functions as a xenosensor, serving to regulate xenobiotic detoxification, lipid homeostasis and energy metabolism. CAR activation is also a key contributor to the development of chemical hepatocarcinogenesis in mice. The underlying pathways affected by CAR in these processes are complex and not fully elucidated. MicroRNAs (miRNAs) have emerged as critical modulators of gene expression and appear to impact many cellular pathways, including those involved in chemical detoxification and liver tumor development. In this study, we used deep sequencing approaches with an Illumina HiSeq platform to differentially profile microRNA expression patterns in livers from wild type C57BL/6J mice following CAR activation with the mouse CAR-specific ligand activator, 1,4-bis-[2-(3,5,-dichloropyridyloxy)] benzene (TCPOBOP). Bioinformatic analyses and pathway evaluations were performed leading to the identification of 51 miRNAs whose expression levels were significantly altered by TCPOBOP treatment, including mmu-miR-802-5p and miR-485-3p. Ingenuity Pathway Analysis of the differentially expressed microRNAs revealed altered effector pathways, including those involved in liver cell growth and proliferation. A functional network among CAR targeted genes and the affected microRNAs was constructed to illustrate how CAR modulation of microRNA expression may potentially mediate its biological role in mouse hepatocyte proliferation. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

Quantitative Proteomics Analysis of the Hepatitis C Virus Replicon High-Permissive and Low-Permissive Cell Lines

Chronic hepatitis C virus (HCV) infection is one of the leading causes of severe hepatitis. The molecular mechanisms underlying HCV replication and pathogenesis remain unclear. The development of the subgenome replicon model system significantly enhanced study of HCV. However, the permissiveness of the HCV subgenome replicon greatly differs among different hepatoma cell lines. Proteomic analysis of different permissive cell lines might provide new clues in understanding HCV replication. In this study, to detect potential candidates that might account for the differences in HCV replication. Label-free and iTRAQ labeling were used to analyze the differentially expressed protein profiles between Huh7.5.1 wt and HepG2 cells. A total of 4919 proteins were quantified in which 114 proteins were commonly identified as differentially expressed by both quantitative methods. A total of 37 differential proteins were validated by qRT-PCR. The differential expression of Glutathione S-transferase P (GSTP1), Ubiquitin carboxyl-terminal hydrolase isozyme L1 (UCHL1), carboxylesterase 1 (CES1), vimentin, Proteasome activator complex subunit1 (PSME1), and Cathepsin B (CTSB) were verified by western blot. And over-expression of CTSB or knock-down of vimentin induced significant changes to HCV RNA levels. Additionally, we demonstrated that CTSB was able to inhibit HCV replication and viral protein translation. These results highlight the potential role of CTSB and vimentin in virus replication.

Peroxiredoxin II promotes hepatic tumorigenesis through cooperation with Ras/Forkhead box M1 signaling pathway

The current study was carried out to define the involvement of Peroxiredoxin (Prx) II in progression of hepatocellular carcinoma (HCC) and the underlying molecular mechanism(s). Expression and function of Prx II in HCC was determined using H-ras(G12V)-transformed HCC cells (H-ras(G12V)-HCC cells) and the tumor livers from H-ras(G12V)-transgenic (Tg) mice and HCC patients. Prx II was upregulated in H-ras(G12V)-HCC cells and H-ras(G12V)-Tg mouse tumor livers, the expression pattern of which highly similar to that of forkhead Box M1 (FoxM1). Moreover, either knockdown of FoxM1 or site-directed mutagenesis of FoxM1-binding site of Prx II promoter significantly reduced Prx II levels in H-ras(G12V)-HCC cells, indicating FoxM1 as a direct transcription factor of Prx II in HCC. Interestingly, the null mutation of Prx II markedly decreased the number and size of tumors in H-ras(G12V)-Tg livers. Consistent with this, knockdown of Prx II in H-ras(G12V)-HCC cells reduced the expression of cyclin D1, cell proliferation, anchorage-independent growth and tumor formation in athymic nude mice, whereas overexpression of Prx II increased or aggravated the tumor phenotypes. Importantly, the expression of Prx II was correlated with that of FoxM1 in HCC patients. The activation of extracellular signal-related kinase (ERK) pathway and the expression of FoxM1 and cyclin D1 were highly dependent on Prx II in H-ras(G12V)-HCC cells and H-ras(G12V)-Tg livers. Prx II is FoxM1-dependently-expressed antioxidant in HCC and function as an enhancer of Ras(G12V) oncogenic potential in hepatic tumorigenesis through activation of ERK/FoxM1/cyclin D1 cascade.

MiR-218-targeting-Bmi-1 mediates the suppressive effect of 1,6,7-trihydroxyxanthone on liver cancer cells

Traditional Chinese medicine is recently emerged as anti-cancer therapy or adjuvant with reduced side-effects and improved quality of life. In the present study, an active ingredient, 1,6,7-trihydroxyxanthone (THA), derived from Goodyera oblongifolia was found to strongly suppress cell growth and induce apoptosis in liver cancer cells. MicroRNAs are a group of small non-coding RNAs that regulate gene expression at post-transcriptional levels. Our results demonstrated that miR-218 was up-regulated and oncogene Bmi-1 was down-regulated by THA treatment. Further investigation showed that THA-induced-miR-218 up-regulation could lead to activation of tumor suppressor P16(Ink4a) and P14(ARF), the main down-stream targets of Bmi-1. In conclusion, THA might be a potential anti-cancer drug candidate, at least in part, through the activation of miR-218 and suppression of Bmi-1 expression.

MicroRNAs dysregulation in hepatocellular carcinoma: Insights in genomic medicine

Hepatocellular carcinoma (HCC) is the leading primary liver cancer and its clinical outcome is still poor. MicroRNAs (miRNAs) have demonstrated an interesting potential to regulate gene expression at post-transcriptional level. Current findings suggest that miRNAs deregulation in cancer is caused by genetic and/or epigenetic, transcriptional and post-transcriptional modifications resulting in abnormal expression and hallmarks of malignant transformation: aberrant cell growth, cell death, differentiation, angiogenesis, invasion and metástasis. The important role of miRNAs in the development and progression of HCC has increased the efforts to understand and develop mechanisms of control overt this single-stranded RNAs. Several studies have analyzed tumoral response to the regulation and control of deregulated miRNAs with good results in vitro and in vivo, proving that targeting aberrant expression of miRNAs is a powerful anticancer therapeutic. Identification of up and/or down regulated miRNAs related to HCC has led to the discovery of new potential application for detection of their presence in the affected organism. MiRNAs represent a relevant new target for diagnosis, prognosis and treatment in a wide variety of pathologic entities, including HCC. This manuscript intends to summarize current knowledge regarding miRNAs and their role in HCC development.

An important role for peroxiredoxin II in survival of A549 lung cancer cells resistant to gefitinib

Redox adaptation is an important concept that explains the mechanisms by which cancer cells survive under persistent endogenous oxidative stress and become resistant to certain anticancer agents. To investigate this concept, we determined the expression levels of peroxiredoxins (Prxs), antioxidant enzymes in drug-resistant non-small cell lung carcinoma cells. Prx II was remarkably increased only in A549/GR (gefitinib-resistant) cells compared with A549 cells, consistent with methylation/demethylation. Prx II was highly methylated in the A549 cells but was demethylated in the A549/GR cells. The elevated expression of Prx II resulted in the downregulation of reactive oxygen species (ROS) and cell death and upregulation of cell cycle progression in the A549/GR cells. When Prx II mRNA in the A549/GR cells was knocked down, the levels of ROS and apoptosis were significantly recovered to the levels of the controls. In addition, signaling molecules involved in apoptosis were increased in the A549/GR-shPrx II cells. There was no difference in the expression of MAPK/ERK between the A549/GR cells and A549/GR-shPrx II cells, but the phosphorylation of JNK was increased in the A549/GR cells and was markedly decreased in the A549/GR-shPrx II cells. Colony number and tumor growth were significantly decreased in the A549/GR-shPrx II cells compared with the A549/GR cells. Our findings suggest that Prx II has an important role in cancer cell survival via the modulation of signaling molecules involved in apoptosis and the phosphorylation of JNK by the downregulation of ROS levels in A549/GR cells.

Long noncoding RNA SPRY4-IT1 predicts poor patient prognosis and promotes tumorigenesis in gastric cancer

Gastric cancer (GC) is the second common cause of cancer-related death worldwide. Long noncoding RNAs (lncRNAs) are emerging as novel regulators in the cancer paradigm. However, investigation of lncRNAs on GC is still in its infancy. In this study, we focused on lncRNA SPRY4 intronic transcript 1 (SPRY4-IT1) and investigated its expression pattern, clinical significance, biological function, and molecular mechanism in GC. SPRY4-IT1 expression was examined, and its correlation with clinicopathological characteristics and patient prognosis was analyzed. A series of assays were performed to understand the role of SPRY4-IT1 in GC. SPRY4-IT1 expression was elevated in GC tissues and cell lines, and SPRY4-IT1 levels were highly positively correlated with tumor size, invasion depth, distant metastasis, TNM stage, and reduced overall survival (OS) and disease-free survival (DFS). A multivariate analysis showed that SPRY4-IT1 expression is an independent prognostic factor of OS and DFS in patients with GC. Additionally, the results of in vitro assays showed that the suppression of SPRY4-IT1 expression in GC cell line MKN-45 significantly reduced cell proliferation, colony formation, and cell migration/invasion. Moreover, the tumorigenic effects of SPRY4-IT1 were partially mediated by the regulation of certain cyclins and matrix metalloproteinases (MMPs)-related genes. Our data suggest that SPRY4-IT1 plays a critical role in GC tumorigenesis and may represent a novel prognostic marker and potential therapeutic target in patients with GC.

Identification of 14-3-3β gene as a novel miR-152 target using a proteome-based approach

Recent studies demonstrated that miR-152 overexpression down-regulates the nonclassical human leukocyte antigen (HLA) class I molecule HLA-G in human tumors thereby contributing to their immune surveillance. Using two-dimensional gel electrophoresis followed by MALDI-TOF mass spectrometry, the protein expression profile of HLA-G(+), miR-152(low) cells, and their miR-152-overexpressing (miR(high)) counterparts was compared leading to the identification of 24 differentially expressed proteins. These were categorized according to their function and localization demonstrating for most of them an important role in the initiation and progression of tumors. The novel miR-152 target 14-3-3 protein β/α/YWHAB (14-3-3β) is down-regulated upon miR-152 overexpression, although its overexpression was often found in tumors of distinct origin. The miR-152-mediated reduction of the 14-3-3β expression was accompanied by an up-regulation of BAX protein expression resulting in a pro-apoptotic phenotype. In contrast, the reconstitution of 14-3-3β expression in miR-152(high) cells increased the expression of the anti-apoptotic BCL2 gene, enhances the proliferative activity in the presence of the cytostatic drug paclitaxel, and causes resistance to apoptosis induced by this drug. By correlating clinical microarray data with the patients' outcome, a link between 14-3-3β and HLA-G expression was found, which could be associated with poor prognosis and overall survival of patients with tumors. Because miR-152 controls both the expression of 14-3-3β and HLA-G, it exerts a dual role in tumor cells by both altering the immunogenicity and the tumorigenicity.

microRNA expression in peripheral blood cells following acute ischemic stroke and their predicted gene targets

Background

microRNA (miRNA) are important regulators of gene expression. In patients with ischemic stroke we have previously shown that differences in immune cell gene expression are present. In this study we sought to determine the miRNA that are differentially expressed in peripheral blood cells of patients with acute ischemic stroke and thus may regulate immune cell gene expression.

Methods

miRNA from peripheral blood cells of forty-eight patients with ischemic stroke and vascular risk factor controls were compared. Differentially expressed miRNA in patients with ischemic stroke were determined by microarray with qRT-PCR confirmation. The gene targets and pathways associated with ischemic stroke that may be regulated by the identified miRNA were characterized.

Results

In patients with acute ischemic stroke, miR-122, miR-148a, let-7i, miR-19a, miR-320d, miR-4429 were decreased and miR-363, miR-487b were increased compared to vascular risk factor controls. These miRNA are predicted to regulate several genes in pathways previously identified by gene expression analyses, including toll-like receptor signaling, NF-κβ signaling, leukocyte extravasation signaling, and the prothrombin activation pathway.

Conclusions

Several miRNA are differentially expressed in blood cells of patients with acute ischemic stroke. These miRNA may regulate leukocyte gene expression in ischemic stroke including pathways involved in immune activation, leukocyte extravasation and thrombosis.

Synergistic effect of MiR-146a mimic and cetuximab on hepatocellular carcinoma cells

Previously, we found that the expression of microRNA-146a (miR-146a) was downregulated in hepatocellular carcinoma (HCC) formalin-fixed paraffin-embedded (FFPE) tissues compared to the adjacent noncancerous hepatic tissues. In the current study, we have explored the in vitro effect of miR-146a on the malignant phenotypes of HCC cells. MiR-146a mimic could suppress cell growth and increase cellular apoptosis in HCC cell lines HepG2, HepB3, and SNU449, as assessed by spectrophotometry, fluorimetry, and fluorescence microscopy, respectively. Furthermore, western blot showed that miR-146a mimic downregulated EGFR, ERK1/2, and stat5 signalings. These effects were less potent compared to that of a siRNA targeting EGFR, a known target gene of miR-146a. Moreover, miR-146a mimic could enhance the cell growth inhibition and apoptosis induction impact of various EGFR targeting agents. The most potent combination was miR-146a mimic with cetuximab, presenting a synergistic effect. In conclusion, miR-146a plays a vital role in the cell growth and apoptosis of HCC cells and inducing miR-146a level might be a critical targeted molecular therapy strategy for HCC.

Expression and clinicopathological significance of miR-146a in hepatocellular carcinoma tissues

BACKGROUND

Aberrant expression of microRNA-146a (miR-146a) has been found in several classes of cancers. However, its expression and clinicopathological contribution in hepatocellular carcinoma (HCC) has not been fully elucidated.

OBJECTIVE

To explore the clinicopathological significance of the miR-146a level in HCC formalin-fixed paraffin-embedded (FFPE) tissue.

METHODS

Eighty-five HCC samples and their para-cancerous normal liver tissues were collected. Total mRNA including miRNA was extracted, and miR-146a expression was determined using real-time RT-PCR. Furthermore, the correlation between the miR-146a expression and clinicopathological parameters was investigated.

RESULTS

MicroRNA-146a expression in HCC tissues was lower compared with that in adjacent non-cancerous hepatic tissues. MicroRNA-146a expression was also related to clinical TNM stage, metastasis, portal vein tumor embolus, and number of tumor nodes.

CONCLUSIONS

Down-regulation of miR-146a is related to HCC carcinogenesis and deterioration of HCC. MicroRNA-146a may act as a suppressor miRNA of HCC, and it is therefore a potential prognostic biomarker for HCC patients.

1,3,5-Trihydroxy-13,13-dimethyl-2H-pyran [7,6-b] xanthone directly targets heat shock protein 27 in hepatocellular carcinoma

We previously showed that the small molecule 1,3,5-trihydroxy-13,13-dimethyl-2H-pyran [7,6-b] xanthone (TDP) induces apoptosis in hepatocellular carcinoma (HCC) by suppressing Hsp27 expression, although the mechanism is not fully understood. To investigate the functional association between TDP and Hsp27 protein in HCC, recombinant Hsp27 protein was incubated with TDP at room temperature, and assayed by mass spectrum (MS) and natural electrophoresis. TDP effectively stimulated Hsp27 to form aggregates ex vitro, leading to suppression of its chaperone activity. The aggregates were degraded by the ubiquitin-proteasome (UPS) pathway. TDP directly interacted with Asp17 and Phe55 in chain C of Hsp27 on the basis of bioinformatic prediction. In conclusion, Hsp27 is a direct target of TDP in its anti-cancer activity, which provides strong support for a clinical application.

Proteomic identification of target proteins following Drosha knockdown in cervical cancer

The nuclear microRNA (miRNA) processing enzyme Drosha is upregulated in cervical cancer, and its overexpression is related to an invasive tumour phenotype. However, the mechanisms that underlie this effect remain poorly understood. The aim of this study was to identify the potential targets of Drosha in cervical cancer. Here, we demonstrated that Drosha knockdown (Drosha-KD) inhibited proliferation, colony formation and the migration of cervical cancer cells in vitro. A global upregulation of proteins in Drosha-KD cells was revealed by two-dimensional gel electrophoresis (2-DE). Eighteen proteins were identified by liquid chromatography and tandem mass spectrometry technology (LC-MS/MS) from 21 selected protein spots that exhibited significant alterations in Drosha-KD cells. The majority of the identified proteins have been previously associated with tumour formation. The downregulation of tubulin 5β in Drosha-KD cervical cancer cells was further confirmed by western blotting. Our results suggest that Drosha affects the biological activity of cervical cancer cells by regulating the expression of numerous tumour-associated proteins.

Quantitative proteomic strategies for the identification of microRNA targets

MicroRNAs (miRNAs) are small noncoding RNAs, approximately 22 nucleotides in length, found in diverse organisms. They have emerged in recent years as key regulators of a broad spectrum of cellular functions. miRNAs regulate biological processes by inducing translational inhibition and degradation of their target mRNAs through base pairing to partially or fully complementary sites. In the field of miRNA research, the identification of the targets of individual miRNAs is of utmost importance. Our understanding of the molecular mechanisms by which individual miRNAs modulate cellular functions will remain incomplete until a full set of miRNA targets is identified and validated. Since a miRNA may regulate many of its targets at the translational level without affecting mRNA abundance, proteomic methods are best suited for revealing the full spectrum of miRNA targets. Quantitative proteomics is emerging as a powerful toolbox for identifying miRNA targets and for quantifying the contribution of translational repression by miRNAs. In this review, the authors summarize the quantitative proteomic approaches that have been employed for identification of miRNA targets and discuss current challenges as well as possible ways of overcoming them.

Increased miR-221 expression in hepatocellular carcinoma tissues and its role in enhancing cell growth and inhibiting apoptosis in vitro

Background

MiR-221 is over-expressed in human hepatocellular carcinoma (HCC), but its clinical significance and function in HCC remains uncertain. The aim of the study was to investigate the relationship between miR-221 overexpression and clinicopathological parameters in HCC formalin-fixed paraffin-embedded (FFPE) tissues, and the effect of miR-221 inhibitor and mimic on different HCC cell lines in vitro.

Methods

MiR-221 expression was detected using real time RT-qPCR in FFPE HCC and the adjacent noncancerous liver tissues. The relationship between miR-221 level and clinicopathological features was also analyzed. Furthermore, miR-221 inhibitor and mimic were transfected into HCC cell lines HepB3, HepG2 and SNU449. The effects of miR-221 on cell growth, cell cycle, caspase activity and apoptosis were also investigated by spectrophotometry, fluorimetry, fluorescence microscopy and flow cytometry, respectively.

Results

The relative expression of miR-221 in clinical TNM stages III and IV was significantly higher than that in the stages I and II. The miR-221 level was also upregulated in the metastatic group compared to the nonmetastatic group. Furthermore, miR-221 over-expression was related to the status of tumor capsular infiltration in HCC clinical samples. Functionally, cell growth was inhibited, cell cycle was arrested in G1/S-phase and apoptosis was increased by miR-221 inhibitor in vitro. Likewise, miR-221 mimic accelerated the cell growth.

Conclusions

Expression of miR-221 in FFPE tissues could provide predictive significance for prognosis of HCC patients. Moreover, miR-221 inhibitor could be useful to suppress proliferation and induce apoptosis in HCC cells. Thus miR-221 might be a critical targeted therapy strategy for HCC.

Proteomics for understanding miRNA biology

MicroRNAs (miRNAs) are small noncoding RNAs that play important roles in posttranscriptional regulation of gene expression. Mature miRNAs associate with the RNA interference silencing complex to repress mRNA translation and/or degrade mRNA transcripts. Mass spectrometry-based proteomics has enabled identification of several core components of the canonical miRNA processing pathway and their posttranslational modifications which are pivotal in miRNA regulatory mechanisms. The use of quantitative proteomic strategies has also emerged as a key technique for experimental identification of miRNA targets by allowing direct determination of proteins whose levels are altered because of translational suppression. This review focuses on the role of proteomics and labeling strategies to understand miRNA biology.

Apoptosis induced by 1,3,6,7-tetrahydroxyxanthone in Hepatocellular carcinoma and proteomic analysis

Gamboge is a traditional Chinese medicine and our previous study showed that gambogic acid and gambogenic acid suppress the proliferation of HCC cells. In the present study, another active component, 1,3,6,7-tetrahydroxyxanthone (TTA), was identified to effectively suppress HCC cell growth. In addition, our Hoechst-PI staining and flow cytometry analyses indicated that TTA induced apoptosis in HCC cells. In order to identify the targets of TTA in HCC cells, a two-dimensional gel electrophoresis was performed, and proteins in different expressions were identified by MALDA-TOF MS and MS/MS analyses. In summary, eighteen proteins with different expressions were identified in which twelve were up-regulated and six were down-regulated. Among them, the four most distinctively expressed proteins were further studied and validated by western blotting. The β-tubulin and translationally controlled tumor protein were decreased while the 14-3-3σ and P16 protein expressions were up-regulated. In addition, TTA suppressed tumorigenesis partially through P16-pRb signaling. 14-3-3σ silence reversed the suppressive effect of cell growth and apoptosis induced by introducing TTA. In conclusion, TTA effectively suppressed cell growth through, at least partially, up-regulation of P16 and 14-3-3σ.

Primate-specific microRNA-637 inhibits tumorigenesis in hepatocellular carcinoma by disrupting signal transducer and activator of transcription 3 signaling

MiR-637 (microRNA-637) is a primate-specific miRNA belonging to the small noncoding RNA family, which represses gene regulation at the post-transcriptional expression level. Although it was discovered approximately 5 years ago, its biomedical significance and regulatory mechanism remain obscure. Our preliminary data showed that miR-637 was significantly suppressed in four HCC cell lines and, also, in most of the hepatocellular carcinoma (HCC) specimens, thereby suggesting that miR-637 would be a tumor suppressor in HCC. Simultaneously, the enforced overexpression of miR-637 dramatically inhibited cell growth and induced the apoptosis of HCC cells. The transcription factor, signal transducer and activator of transcription 3 (Stat3), is constitutively activated in multiple tumors, and aberrant Stat3 activation is linked to the promotion of growth and desensitization of apoptosis. Our study showed that Stat3 tyrosine 705 phosphorylation and several Stat3-regulated antiapoptotic genes were down-regulated in miR-637 mimics-transfected and Lv-miR637-infected HCC cells. In addition, miR-637 overexpression negatively regulated Stat3 phosphorylation by suppressing autocrine leukemia inhibitory factor (LIF) expression and exogenous LIF-triggered Stat3 activation and rescued cell growth in these cells. A nude mice model also demonstrated the above-described results, which were obtained from the cell model. Furthermore, we found that LIF was highly expressed in a large proportion of HCC specimens, and its expression was inversely associated with miR-637 expression.

CONCLUSION

Our data indicate that miR-637 acted as a tumor suppressor in HCC, and the suppressive effect was mediated, at least in part, by the disruption of Stat3 activation.

MiR-637 maintains the balance between adipocytes and osteoblasts by directly targeting Osterix

Bone development is dynamically regulated by homeostasis, in which a balance between adipocytes and osteoblasts is maintained. Disruption of this differentiation balance leads to various bone-related metabolic diseases, including osteoporosis. In the present study, a primate-specific microRNA (miR-637) was found to be involved in the differentiation of human mesenchymal stem cells (hMSCs). Our preliminary data indicated that miR-637 suppressed the growth of hMSCs and induced S-phase arrest. Expression of miR-637 was increased during adipocyte differentiation (AD), whereas it was decreased during osteoblast differentiation (OS), which suggests miR-637 could act as a mediator of adipoosteogenic differentiation. Osterix (Osx), a significant transcription factor of osteoblasts, was shown to be a direct target of miR-637, which significantly enhanced AD and suppressed OS in hMSCs through direct suppression of Osx expression. Furthermore, miR-637 also significantly enhanced de novo adipogenesis in nude mice. In conclusion, our data indicated that the expression of miR-637 was indispensable for maintaining the balance of adipocytes and osteoblasts. Disruption of miR-637 expression patterns leads to irreversible damage to the balance of differentiation in bone marrow.

MYC protein inhibits transcription of the microRNA cluster MC-let-7a-1~let-7d via noncanonical E-box

The human microRNA cluster MC-let-7a-1∼let-7d, with three members let-7a-1, let-7f-1, and let-7d, is an important cluster of the let-7 family. These microRNAs play critical roles in regulating development and carcinogenesis. Therefore, precise control of MC-let-7a-1∼let-7d level is critical for cellular functions. In this study, we first showed that the expression of these three members was significantly reduced in human hepatocellular carcinoma HepG2 cells as compared with the immortalized human liver L02 cells. We demonstrated that the MC-let-7a-1∼let-7d cluster was encoded by a single polycistronic transcript driven by a 10-kb upstream promoter, with two MYC-binding sites. Importantly, MYC inhibited MC-let-7a-1∼let-7d promoter activity via binding to the noncanonical E-box 3 downstream of the transcription start sites, whereas it enhanced promoter activity by binding to the canonical E-box 2 upstream of the transcription start sites. We found that although the binding affinity of MYC to E-box 2 was stronger than E-box 3, the binding quantum of MYC to E-box 3 was significantly higher in cancerous HepG2 cells as compared with the noncancerous L02 cells. In addition, forced expression of let-7 could reverse the MYC-mediated cell proliferation. These findings suggested that in L02 cells with a low level of MYC, MYC binds mainly to E-box 2 to enhance MC-let-7a-1∼let-7d expression. However, in HepG2 cells with an elevated MYC, the extra MYC could bind to E-box 3 to suppress the transcription of MC-let-7a-1∼let-7d and thus enable HepG2 cells to maintain a high level of MYC and a low level of let-7 microRNAs simultaneously.