miR-21 In Hepatocellular Carcinoma Research Articles

Regulation of hepatic glutamine metabolism by miR-122

ObjectiveIt is well established that the liver-specific miR-122, a bona fide tumor suppressor, plays a critical role in lipid homeostasis. However, its role, if any, in amino acid metabolism has not been explored. Since glutamine (Gln) is a critical energy and anaplerotic source for mammalian cells, we assessed Gln metabolism in control wild type (WT) mice and miR-122 knockout (KO) mice by stable isotope resolved metabolomics (SIRM) studies. MethodsSix-to eight-week-old WT and KO mice and 12- to 15-month-old liver tumor-bearing mice were injected with [U–13C5,15N2]-L-Gln, and polar metabolites from the liver tissues were analyzed by nuclear magnetic resonance (NMR) imaging and ion chromatography-mass spectrometry (IC-MS). Gln-metabolism was also assessed in a Gln-dependent hepatocellular carcinoma (HCC) cell line (EC4). Expressions of glutaminases (Gls and Gls2) were analyzed in mouse livers and human primary HCC samples. ResultsThe results showed that loss of miR-122 promoted glutaminolysis but suppressed gluconeogenesis in mouse livers as evident from the buildup of 13C- and/or 15N-Glu and decrease in glucose-6-phosphate (G6P) levels, respectively, in KO livers. Enhanced glutaminolysis is consistent with the upregulation of expressions of Gls (kidney-type glutaminase) and Slc1a5, a neutral amino acid transporter in KO livers. Both Gls and Slc1a5 were confirmed as direct miR-122 targets by the respective 3′-UTR-driven luciferase assays. Importantly, expressions of Gls and Slc1a5 as well as glutaminase activity were suppressed in a Gln-dependent HCC (EC4) cell line transfected with miR-122 mimic that resulted in decreased 13C-Gln, 13C-á-ketoglutarate, 13C-isocitrate, and 13C-citrate levels. In contrast, 13C-phosphoenolpyruvate and 13C-G6P levels were elevated in cells expressing ectopic miR-122, suggesting enhanced gluconeogenesis. Finally, The Cancer Genome Atlas—Liver Hepatocellular Carcinoma (TCGA-LIHC) database analysis showed that expression of GLS is negatively correlated with miR-122 in primary human HCCs, and the upregulation of GLS RNA is associated with higher tumor grade. More importantly, patients with higher expressions of GLS or SLC1A5 in tumors exhibited poor survival compared with those expressing lower levels of these proteins. ConclusionsCollectively, these results show that miR-122 modulates Gln metabolism both in vitro and in vivo, implicating the therapeutic potential of miR-122 in HCCs that exhibit relatively high GLS levels.

MiR-122 and hepatocellular carcinoma: from molecular biology to therapeutics.

miR-122 and hepatocellular carcinoma: from molecular biology to therapeutics.

Ligation-promoted hyperbranched rolling circle amplification enables ultrasensitive detection of microRNA in clinical specimens

MiRNA is reported as an important biomarker candidate and therapeutic target in a variety of diseases and cancers. However, ultrasensitive, straightforward, isothermal, low-cost and credible methods for the detection of miRNA from clinical specimens still remain challenges. Here, we establish an isothermal, highly sensitive and specific method for miRNA analysis based on a novel ligation-promoted hyperbranched rolling circle amplification (L-HRCA). This strategy exhibits 103-fold sensitivity enhancement compared to T4 ligase-assisted target-primer BRCA. The excellent specificity of L-HRCA allows for discriminating target miRNA from negative miRNAs. This method is applied to analyse the expression level of miR-21 in hepatocellular carcinoma. These results indicated that the L-HRCA strategy will become a promising tool to quantify miRNA in early clinical diagnostics.

LncRNA HOTAIR epigenetically suppresses miR-122 expression in hepatocellular carcinoma via DNA methylation.

BackgroundMicroRNA-122 (miR-122), a pivotal liver-specific miRNA, is frequently repressed in hepatocellular carcinoma (HCC) and associated with poor prognosis. Long non-coding RNA (lncRNA) HOTAIR has been proved to function as an oncogene in multiple cancers including HCC. However, the relationship between HOTAIR and miR-122 in HCC remains largely unknown.MethodsWe investigated the function of HOTAIR and miR-122 in HCC cell models and a xenograft mouse model. The regulatory network between HOTAIR and miR-122 was further detected following overexpression or knockdown of HOTAIR. DNA methylation status of miR-122 promoter region, as well as expression levels of DNMTs, EZH2 and Cyclin G1 were analyzed.FindingsIn this study, we found that HOTAIR was highly expressed whereas miR-122 was suppressed in HCC, and HOTAIR negatively regulated miR-122 expression in HCC cells. Furthermore, knockdown of HOTAIR dramatically inhibited HCC cell proliferation and induced cell cycle arrest in vitro and suppressed tumorigenicity in vivo by upregulating miR-122 expression. Mechanistically, a CpG island was located in the miR-122 promoter region. HOTAIR epigenetically suppressed miR-122 expression via DNMTs-mediated DNA methylation. Moreover, HOTAIR upregulated DNMTs expression via EZH2. In addition, suppression of miR-122 induced by HOTAIR directly reactivated oncogene Cyclin G1 expression. Collectively, our results suggest that HOTAIR epigenetically suppresses miR-122 expression via DNA methylation, leading to activation of Cyclin G1 and promotion of tumorigenicity in HCC, which provide new insight into the mechanism of HOTAIR-mediated hepatocarcinogenesis via suppressing miR-122.

Expression Analysis of MicroRNA-21 and MicroRNA-122 in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a multistep process starting from chronic hepatitis (CH) that progress through cirrhosis to HCC. The expression level of microRNA (miRNA) was found to be deregulated in HCC. The study was designed to find out whether the expression level of miR-21 and miR-122 was deregulated in HCC compared to controls without HCC. Real-time quantitative polymerase chain reaction was performed to find out the miRNA expression level using Ct value followed by statistical analysis where P value≤0.05 was considered as significant. Overexpression of miR-21 and miR-122 in HCC was detected. All changes in the expression level of miR-21 and miR-122 were due to HCC compared with healthy control, CH, and liver cirrhosis. Hence miR-21 and miR-122 are suitable to differentiate HCC with an efficient diagnostic power of sensitivity, specificity, and expression level, but they might not have any role in patients' survival. miR-21 and miR-122 could be considered as potential markers of HCC screening molecule in addition to other approved markers. However the current study is limited to expression levels of miRNAs from serum; therefore, it needs further validated study in a large group of population to fulfill all the criteria of a biomarker.

Nuclear miR-122 directly regulates the biogenesis of cell survival oncomiR miR-21 at the posttranscriptional level.

Hepatic miR-122 can serve as a pro-apoptotic factor to suppress tumorigenesis. The underlying mechanism, however, remains incompletely understood. Here we present the first evidence that miR-122 promotes hepatocellular carcinoma cell apoptosis through directly silencing the biogenesis of cell survival oncomiR miR-21 at posttranscriptional level. We find that miR-122 is strongly expressed in primary liver cell nucleus but its nuclear localization is markedly decreased in transformed cells particularly in chemoresistant tumor cells. MiRNA profiling and RT-qPCR confirm an inverse correlation between miR-122 and miR-21 in hepatocellular carcinoma tissues/cells, and increasing or decreasing nuclear level of miR-122 respectively reduces or increases miR-21 expression. Mechanistically, nuclear miR-122 suppresses miR-21 maturation via binding to a 19-nt UG-containing recognition element in the basal region of pri-miR-21 and preventing the Drosha-DGCR8 microprocessor's conversion of pri-miR-21 into pre-miR-21. Furthermore, both in vitro and in vivo studies demonstrate that nuclear miR-122 participates in the regulation of HCC cell apoptosis through modulating the miR-21-targeted programmed cell death 4 (PDCD4) signal pathway.

Interest of variations in microRNA-152 and -122 in a series of hepatocellular carcinomas related to hepatitis C virus infection.

Hepatocellular carcinoma (HCC) is a common outcome of chronic hepatitis C virus (HCV) infection and constitutes the main burden of this disease. The molecular mechanisms underlying the development of HCC are multiple and might involve certain microRNA (miR). As discordant results have been reported concerning the detection of expression of miR-152 and miR-122 in HCC, our aim was to measure the levels of both miRs in serum and liver samples. We analyzed miR-152 and miR-122 expression by reverse transcription-quantitative polymerase chain reaction in a serum cohort from 14 HCV-infected patients who developed HCC, 20 HCV+ patients without HCC, and 19 control patients. We also studied miR-152 and miR-122 in an independent tissue cohort from 11 normal livers, and from paired HCC and non-tumor adjacent livers of 11 HCV-infected patients and 12 non-infected patients. In serum samples, higher levels of miR-122 were found in non-HCC HCV+ compared to HCC HCV+ and control groups, whereas miR-152 was detectable in a lower range in HCC HCV+ compared to non-HCC HCV+ and control groups. We found higher signals for miR-122 and miR-152 in non-tumor liver and HCC tissues compared to control tissues. Hepatocellular carcinoma etiology had no detectable influence on miR-122 expression, whereas miR-152 was increased in HCV+ tissue samples. Detection of low values of circulating miR-152 is a potentially interesting marker of hepatocarcinogenesis in HCV+ patients, in contrast to miR-122, which varies according to hepatocyte damage.

Crosstalk between microRNA-122 and FOX family genes in HepG2 cells.

MicroRNA-122 (miR-122) is liver specific and plays an important role in physiology as well as diseases including hepatocellular carcinoma (HCC). Downregulation of miR-122 in HCC modulates apoptosis. Similarly, the putative targets of miR-122, the forkhead box (FOX) family genes also play an important role in the regulation of apoptosis. Hence, an interplay between miR-122 and FOX family genes has been explored in this study. Initially, an augmentation of apoptosis was noticed in HepG2 cells after transfection with miR-122. Further, the predicted miR-122 targets, the FOX family genes ( FOXM1b, FOXP1, and FOXO4) were selected via in silico analysis based on their role in apoptosis. We checked the expression of all these genes at transcript level after the transfection of miR-122 and found that the relative expression of FOXP1 and FOXM1b was significantly downregulated (p < 0.005) and that of FOXO4 was upregulated (p < 0.005). Thus, the finding indicates deregulation of these FOX genes as a result of miR-122 augmentation might be involved in the modulation of apoptosis.

Circulating microRNAs in Hepatocellular Carcinoma: Potential Diagnostic and Prognostic Biomarkers.

Hepatocellular carcinoma (HCC) is one of the most common types of malignancies worldwide. There is little information on the mechanisms involved in the pathogenesis of this disease. Diagnosis of HCC at early stages would be crucial for increasing the survival of patients. Circulating miRNAs have emerged as one of the most attractive tools for an early diagnosis of cancers. Various studies have shown that there is an aberrant expression of miRNAs such as miR-25, miR-375, miR-206, miR-223, miR- 92a, miR-222, miR-1, let- 7f and miR-21 in HCC. Circulating and tissue miRNAs have also key roles in the pathogenesis of HCC by affecting several biologically important pathways such as p53, p21, PTEN, PI3K-AKT, c-Myc and STAT3. In this review, we summarize the current knowledge on the role of miRNAs in diagnosis, prognosis, and treatment of HCC.

WNT1 Gene from WNT Signaling Pathway Is a Direct Target of miR-122 in Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is an invasive form of hepatic cancer arising from the accumulation of multiple genetic alterations. In this study, the causal role of disturbed canonical Wnt/β-catenin pathway was approved, and some of HCC-driven important gene candidates were determined. MicroRNAs (miRNAs), small non-coding RNAs, are the key regulators of important cancer genes, and their participation in tumorigenesis has been shown. By reviewing literature, WNT1 gene with functional significance was selected to approve miRNAs as new subjects for targeted therapy.For proper and fast miRNA detection and also confirmation of the role of bioinformatics in obtaining practical data, we benefited from different bioinformatics tools such as TargetScan, miRanda, and DIANA. In order to use an HCC model, we used HepG2 cell line. Luciferase assay was applied to assess the ability of the selected miRNAs in targeting WNT1 3'-UTR. To overexpress the selected miRNA in HepG2 cell line, viral construct was prepared. Quantitative real-time PCR was performed to evaluate selected miRNA and target gene expression levels. miR-122 was selected according to data concerning various bioinformatics tools.miR-122 was downregulated and WNT1 gene expression was upregulated in HepG2 cell line. After viral construct transduction, miR-122 expression was elevated and WNT1 expression was notably declined. Finally, we introduced WNT1 gene as one of the important genes in HCC, and also, we showed that miR-122 can regulate WNT1 gene expression.Moreover, our study determines the potential of bioinformatics analyses in providing accurate and reliable data for miRNA: messenger RNA (mRNA) prediction.

HBx-induced miR-21 suppresses cell apoptosis in hepatocellular carcinoma by targeting interleukin-12.

Hepatitis B virus (HBV) Xprotein (HBx) plays a key role in the initiation and progression of HBV infection‑induced hepatocellular carcinoma (HCC). Oncogenic microRNA-21(miR-21) can be modulated by HBx protein in HCC. However, critical regulator genes in the pathway of HBx-induced miR-21 in HCC remain unclear. This study aimed to investigate the role of HBx-induced miR-21 in the apoptosis of HCC cells. In the study, interleukin-12(IL-12) was demonstrated as a direct target of miR-21 by dual‑luciferase report assay, and miR-21 was highly expressed in HCC cells (HepG2 and HepG22.2.15) compared to L02 cells, but IL-12 was weakly expressed as detected by real-time quantitative PCR (RT-qPCR). Furthermore, miR-21 mimics, inhibitor, HBx-targeted siRNA, and the HBx overexpression vector(pHBx) were used to observe the regulatory effects of HBx-induced miR-21 via IL-12, and cell apoptosis was assessed. The results showed that overexpression of HBx resulted in the inhibition of IL-12. A high level of miR-21 resulted in a significant increase in proliferation and a decrease in IL-12 expression. Inhibition of miR-21 resulted in a significant increase in apoptosis and increased IL-12 expression. The results suggest that HCC cell apoptosis was suppressed at least partially through HBx-induced miR-21 by targeting IL-12.

High-Mobility Group Box 1 Promotes Hepatocellular Carcinoma Progression through miR-21-Mediated Matrix Metalloproteinase Activity.

Liver inflammation plays a critical role in hepatocellular carcinoma (HCC) etiology. Damage-associated molecular patterns (DAMP), such as high-mobility group box 1 (HMGB1), and dysregulated miRNAs involved in inflammatory disease states, such as miR-21, may participate in the link between inflammation and cancer. We sought to determine the role of HMGB1 signaling in HCC tumor progression. We first document the concordant expression increase of HMGB1 and miR-21 in HCC cell lines and primary HCC tumor samples and subsequently show that HMGB1 stimulation results in overexpression of miR-21. These changes were found to be dependent on the IL6/STAT3 signaling axis. Invasion and migration of HCC cells in vitro were inhibited by both STAT3 and miR-21 antagonists, suggesting a role for this pathway in HCC tumor progression. We verified that HMGB1-induced expression of miR-21 in HCC provides a posttranscriptional repression of the matrix metalloproteinase (MMP) inhibitors RECK and TIMP3, which are known to impact HCC progression and metastases. Finally, we found that inhibition of miR-21 in murine HMGB1-overexpressing HCC xenografts led to reduced tumor MMP activity through released repression of the miR-21 targets RECK and TIMP3, which ultimately impeded tumor progression. The prototypical DAMP, HMGB1, is released during liver inflammation and provides a favorable environment for HCC growth. HMGB1 signaling increases miR-21 expression to mediate the enhanced activity of MMPs through RECK and TIMP3. These findings provide a novel mechanism for HMGB1-mediated HCC progression through the IL6/Stat3-miR-21 axis.

Decreased miR122 in hepatocellular carcinoma leads to chemoresistance with increased arginine.

Reduced expression of microRNA122 (miR122), a liver-specific microRNA, is frequent in hepatocellular carcinoma (HCC). However, its biological significances remain poorly understood. Because deregulated amino acid levels in cancers can affect their biological behavior, we determined the amino acid levels in miR122-silenced mouse liver tissues, in which intracellular arginine levels were significantly increased. The increased intracellular arginine levels were through upregulation of the solute carrier family 7 (SLC7A1), a transporter of arginine and a direct target of miR122. Arginine is the substrate for nitric oxide (NO) synthetase, and intracellular NO levels were increased in miR122-silenced HCC cells, with increased resistance to sorafenib, a multikinase inhibitor. Conversely, maintenance of the miR122-silenced HCC cells in arginine-depleted culture media, as well as overexpression of miR122 in miR122-low-expressing HCC cells, reversed these effects and rendered the cells more sensitive to sorafenib. Using a reporter knock-in construct, chemical compounds were screened, and Wee1 kinase inhibitor was identified as upregulators of miR122 transcription, which increased the sensitivity of the cells to sorafenib. These results provide an insight into sorafenib resistance in miR122-low HCC, and suggest that arginine depletion or a combination of sorafenib with the identified compound may provide promising approaches to managing this HCC subset.

MicroRNA-21 promotes cell proliferation in human hepatocellular carcinoma partly by targeting HEPN1.

It has been reported that miR-21 is upregulated in hepatocellular carcinoma (HCC), and overexpressed miR-21 plays a key role in promoting cell cycle progression, reducing cell death and favoring angiogenesis and invasion. Overexpression of hepatocellular carcinoma, downregulated 1 (HEPN1) exhibits an antiproliferative effect on HepG2 cells, suggesting that silencing of HEPN1 may contribute to carcinogenesis of hepatocytes. In silico analysis revealed that HEPN1 may be a potential target of miR-21. Using quantitative reverse transcription PCR and Western blot, we found that HEPN1 was strikingly downregulated in both mRNA (fold change was 33.5, P < 0.0001) and protein levels in human HCC tumor tissues, in comparison with the adjacent non-tumor tissues. More importantly, the expression level of HEPN1 was inversely correlated with the expression of miR-21 in HCC (R (2) = 0.442, P < 0.0001). The combination between the 3' untranslated region (UTR) of HEPN1 with miR-21 was experimentally verified by a miRNA luciferase reporter approach. The suppressed cell proliferation upon stimulation of miR-21 inhibitor could be partially abolished by knocking down HEPN1, so inhibition of miR-21 expression in HCC cells profoundly suppressed cell proliferation partially by upregulating HEPN1 expression. Taken together, the current study suggested an underlying mechanism that miR-21 directly target HEPN1 and inhibit its expression during the carcinogenesis of HCC. HEPN1 may thus be a candidate as a therapeutic target for patients with HCC.

High serum microRNA-122 level is independently associated with higher overall survival rate in hepatocellular carcinoma patients.

Previous studies have shown that some microRNAs (miRs) are intensively involved in the development of hepatocellular carcinoma. We analyzed the prognostic role of serum microRNA (miR-122) levels in hepatocellular carcinoma patients using a retrospective design. MiR-122 levels in 122 hepatocellular carcinoma patients were measured, and Cox regression analysis was performed to analyze the prognostic role of miR-122 in hepatocellular carcinoma, and the hazard ratio (HR) with 95 % confidence interval (95 %CI) was used to evaluate its prognostic role. Patients with large tumor size had lower levels of serum miR-122 (P = 0.04). However, there was no significant association of serum miR-122 levels with other clinical characteristics. Kaplan-Meier method showed that there was higher overall survival rate in hepatocellular carcinoma patients with high serum miR-122 levels compared with those with low miR-122 level (P < 0.01). When using Cox regression analysis, high serum miR-122 level was independently associated with better overall survival in hepatocellular carcinoma patients (HR = 0.26; 95 %CI 0.14-0.47, P < 0.01). Subgroup analysis by gender showed that high serum miR-122 level was independently associated with better overall survival in male patients (HR = 0.08; 95 %CI 0.03-0.22, P < 0.01), but not in female patients (HR = 0.48; 95 %CI 0.18-1.32, P = 0.16). Thus, the outcomes in the analysis suggest that high serum miR-122 level is independently associated with higher overall survival rate in hepatocellular carcinoma patients, and it is a good biomarker of better prognosis in patients with hepatocellular carcinoma.

Abstract 4787: Targeting miR-21 in hepatocellular carcinoma

Abstract Hepatocellular carcinoma (HCC) remains a significant unmet medical need with few therapeutic options available. Micro RNA 21 (miR-21) has been shown to be upregulated in HCC, however, contribution of this onco-miR to the maintenance of tumorigenic phenotype in liver cancer remains poorly understood. We have developed potent and specific single-stranded oligonucleotide inhibitors of miR-21 (anti-miR-21) and used them to interrogate dependency on miR-21 in a panel of 20 commercially available HCC cell lines in vitro. Upon lipid-mediated transfection, anti-miR-21, but not its mismatched (MM) control, caused significant de-repression of known direct targets of miR-21 (ANKRD46, DDAH1, RECK1) and inhibited survival of a large subset of HCC cell lines. Treatment of these sensitive HCC cell lines with anti-miR-21 resulted in dose- and time-dependent induction of caspase 3/7 activity. In contrast, non-responder HCC cell lines failed to significantly upregulate caspase activity and maintained viability in the presence of anti-miR compound. Further analysis of responder cell lines revealed robust induction of cell death, inhibition of cell migration and suppression of clonogenic growth upon treatment with miR-21 inhibitor. To better understand the consequences of miR-21 suppression in HCC, we carried out global gene expression profiling of anti-miR-21 treated sensitive liver cancer cells. Striking enrichment in miR-21 targets was noted among upregulated transcripts. Gene ontology analysis identified key cellular processes affected by miR-21 inhibition, including deregulation of metabolic pathways. In addition to the induction of direct miR-21 targets, cyclin H was found to be significantly downregulated upon miR-21 inhibition in the majority of responder cell lines. We hypothesize that inhibition of cyclin H expression, while an indirect effect of miR-21 suppression, could contribute to the activity of anti-miR-21 compounds. In summary, our data suggest that inhibition of miR-21 merits further investigation in the treatment of hepatocellular carcinoma. Citation Format: Sonya Zabludoff, Timothy Wagenaar, Francisco Adrian, Charles Allerson, Heike Arlt, Raffaele Baffa, Bal Bhat, Hui Cao, Scott Davis, Carlos Garcia-Echeverria, Kathrin Heermeier, Shih-Min Huang, Lan Jiang, Eric Marcusson, Christiane Metz-Weidmann, Adam Pavlicek, Jack Pollard, Jennifer Rocnik, Sabine Scheidler, Chaomei Shi, Fangxian Sun, Tatiana Tolstykh, Qunyan Yu, Gang Zheng, Dmitri Wiederschain. Targeting miR-21 in hepatocellular carcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4787. doi:10.1158/1538-7445.AM2014-4787

Antitumor function of microRNA-122 against hepatocellular carcinoma

MicroRNA-122 (miR-122), a highly abundant and liver-specific miRNA, acts as a tumor suppressor against hepatocellular carcinoma (HCC). Decreased expression of miR-122 in HCC is frequently observed and is associated with poor differentiation, larger tumor size, metastasis and invasion, and poor prognosis. Mutant mice with knockout (KO) of the miR-122 locus developed steatohepatitis due to increased triglyceride (TG) synthesis and decreased TG secretion from hepatocytes, and eventually developed HCC. Exogenic miR-122 introduction into miR-122 KO mice inhibited the development of HCC. Target genes of miR-122, including cyclin G1, a disintegrin and metalloprotease (ADAM)10, serum response factor, insulin-like growth factor-1 receptor, ADAM17, transcription factor CUTL1, the embryonic isoform of pyruvate kinase (Pkm2), Wnt1, pituitary tumor-transforming gene 1 binding factor, Cut-like homeobox 1, and c-myc, are involved in hepatocarcinogenesis, epithelial mesenchymal transition, and angiogenesis. MiR-122 expression is regulated by liver-enriched transcription factors such as hepatocyte nuclear factor (HNF)1α, HNF3β, HNF4α, HNF6, and CCAAT/enhancer-binding protein (C/EBP)α. A positive feedback loop exists between C/EBPα and miR-122 and between HNF6 and miR-122, whereas a negative feedback loop exists between c-myc and miR-122. Since cotreatment of 5-Aza-Cd and histone deacetylase inhibitor restored miR-122 expression in HCC cells, epigenetic modulation of miR-122 expression is involved in the suppression of miR-122 in HCC. Several experiments suggest that increasing miR-122 levels in HCC with or without antitumor agents may be a promising strategy for HCC treatment.

MicroRNA-21 promotes hepatocellular carcinoma HepG2 cell proliferation through repression of mitogen-activated protein kinase-kinase 3

BackgroundmicroRNA 21 (miR-21) has been demonstrated to be significantly elevated in many types of cancers, including the hepatocellular carcinoma (HCC). In the present study, we investigated the role of miR-21 in HCC by identifying its novel targets, as well as its underlying molecular mechanism.MethodsThe expression of mitogen-activated protein kinase-kinase 3 (MAP2K3) in human HCC tumor tissues and adjacent non-tumor tissues was determined by immunohistochemistry staining (IHC) analysis. The 3’-untranslated region (3’-UTR) of MAP2K3 combined with miR-21 was experimentally verified by a miRNA luciferase reporter approach. Moreover, the role of miR-21 in regulating HCC cell proliferation was analyzed by an MTT assay infected with miR-21mimics/sponge inhibitor Adenoviral viral vectors.ResultsBy immunohistochemistry staining analysis, we found that mitogen-activated protein kinase-kinase 3 (MAP2K3) was strikingly repressed in the human HCC tumor tissues, in comparison with the adjacent non-tumor tissues in clinical settings. More importantly, the repression of MAP2K3 was inversely correlated with the expression of miR-21 in HCC. Further study demonstrated that the MAP2K3 was a novel direct target of miR-21, which was experimentally validated by a miRNA luciferase reporter approach. In HepG2 cells, inhibition of miR-21 expression with an adenoviral miR-21 sponge vector profoundly suppressed cell proliferation by up-regulating MAP2K3 expression at both mRNA and protein levels.ConclusionsThese results provide a clinical evidence that MAP2K3 may be a tumor repressor gene, and it is a direct target of miR-21 in HCC, indicating an underlying mechanism by which miR-21 is able to directly target MAP2K3 and inhibit its expression during the carcinogenesis of HCC, at both transcriptional and post-translational levels. This study also suggests that targeting miR-21-MAP2K3 pathway may be a promising strategy in the prevention and treatment of HCC.

Abstract 141: Epigenetic silencing of miR-122 in hepatocellular carcinoma

Abstract It has been reported that miRNAs potently influence cellular function through the regulation of extensive gene expression networks and most tumors are characterized by globally diminished miRNA expression. However, the potential mechanism of microRNA expression change in tumorigenesis remains to be further investigated. In this study, we focus on the epigenetic regulation of miRNA expression in hepatocellular carcinoma. We first performed miRNA microarray analysis in HepG2 cells, which reveals significant changes in miRNA expression profiling with 23 upregulated miRNAs and 15 downregulated miRNAs induced by the treatment with 5′aza-2′deoxycytidine (5′-aza, DNA methylation inhibitor) and 4-phenylbutyric acid (PBA, histone deaceltylation inhibitor). Interestingly, miR-122, the most abundant miRNA in the liver, is upregulated by 5′-aza and PBA, which is validated by qRT-PCR analysis in both HepG2 and Huh7 cells. In addition, miR-122 expression is increased by the overexpression of PPARγ or the treatment of PPARγ agonist (15-keto PGE2 or 15d-PGJ2).We then demonstrate that peroxisome proliferator-activated receptor gamma (PPARγ) and retinoid X receptor alpha (RXRα) bind to conserved DR-1 and DR-2 (peroxisome proliferator-activated response element) in the miR-122 promoter region and these bindings are significantly increased by 5′-aza and PBA with the biotinylated oligonicleotides precipitation assay. However, 5′-aza and PBA inhibit the binding of N-CoR (nuclear receptor corepressor) or SMRT (silencing mediator for retinoid and thyroid hormone receptor) to DR-1 or DR-2. And we found that 5′-aza and PBA inhibit PPARγ/N-CoR/SMRT protein complex formation in HepG2 cells with the immunoprecipitation assay. Furthermore, we observe that SUV39H1(H3K9 methyl transferase) protein is decreased by the co-treatment of 5′aza and PBA; and the suppression of endogenous SUV39H1 expression with SUV39H1siRNA increases miR-122 expression. Taken together, our results suggest that histone acethylation and demethylation lead to the release of PPAR-gamma from PPAR-gamma/N-CoR/SMRT protein complex to activate miR-122 transcription and to the inhibition SUV39H1 protein expression for the elimination of histone methylation to further facilitate miR-122 transcription. In conclusion, Epigenetic silencing is one of the most important mechanisms for diminished miR122 expression in hepatic carcinogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 141. doi:1538-7445.AM2012-141