Biallelic expression of the H19 and IGF2 genes in hepatocellular carcinoma

Insulin-like growth factor 2 (IGF2) expression in adrenocortical disease due to PRKAR1A mutations compared to other benign adrenal tumors

PURPOSE

Insulin-like growth factor-II (IGF2), a key regulator of cell growth and development, is tightly regulated in its expression by epigenetic control that maintains its monoallelic expression in most tissues. Biallelic expression of IGF2 resulting from loss of imprinting (LOI) has been reported in adrenocortical tumors. In this study, we wanted to check whether adrenocortical lesions due to PRKAR1A mutations lead to increased IGF2 expression from LOI and compare these findings to those in other benign adrenal lesions.

METHODS

We compared the expression of IGF2 by RNA and protein studies in primary pigmented nodular adrenocortical disease (PPNAD) caused by PRKAR1A gene mutations to that in primary macronodular adrenocortical hyperplasia (PMAH) and cortisol-producing adenomas (CPA) that did not have any mutations in known genes. We also checked LOI in all lesions by DNA allelic studies and the expression of other components of IGF2 signaling at the RNA and protein level.

RESULTS

We identified cell clusters overexpressing IGF2 in PPNAD; although immunostaining was patchy, overall, by RNA and immunoblotting PPNAD expressed high IGF2 message and protein. However, this was not due to LOI, as there was no correlation between IGF2 expression and the presence of LOI.

CONCLUSIONS

Our data pointed to over-expression of IGF2 protein in PPNAD compared to other benign adrenocortical lesions, such as PMAH and CPA. However, there was no correlation of IGF2 mRNA levels with LOI of IGF2/H19. The discrepancy between mRNA and protein levels with regards to LOI points, perhaps, to different control of IGF2 gene expression in PPNAD.

RP11-81H3.2 Acts as an Oncogene via microRNA-490-3p Inhibition and Consequential Tankyrase 2 Up-Regulation in Hepatocellular Carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is a serious threat to human lives and is usually diagnosed at the late stages. Recently, there has been a rapid advancement in the treatment options for HCC, but novel therapeutic targets are still needed, especially for precision medicine.

AIMS

We aimed to investigate the involvement of non-coding RNA RP11-81H3.2 in HCC.

METHODS

The expression of RP11-81H3.2 was examined in the blood samples of HCC patients, and in the human HCC cell lines, including HepG2, Smmc-7721, and Huh7. Cell proliferation was determined using the CCK-8 and EdU assay, and cell invasion and migration were determined using the transwell/wound healing assay. The effects of RP11-81H3.2 knockdown on in vivo tumor growth were evaluated utilizing the nude mice HepG2 tumor xenograft model.

RESULTS

Here, we have identified a long non-coding RNA, RP11-81H3.2, which is enriched in HCC and can promote its proliferation, migration, and invasion both in vitro and in vivo. In addition, our results showed that RP11-81H3.2 binds to and regulate miR-490-3p expression in the HCC cells. Moreover, we found that RP11-81H3.2 regulates the expression of TNKS2 via miR-490-3p. Further, we found that RP11-81H3.2 and miR-490-3p form a regulatory loop; the release of RP11-81H3.2 leads to the suppression of miR-490-3p expression, thus, further enhancing the expression of RP11-81H3.2.

CONCLUSIONS

Our data have provided a novel target for the diagnosis and treatment of HCC, and sheds light on the lncRNA-miRNA regulatory nexus that can control the HCC related pathogenesis.

The AC006262.5-miR-7855-5p-BPY2C axis facilitates hepatocellular carcinoma proliferation and migration

Hepatocellular carcinoma (HCC) is typically fatal, and patients with hepatocellular carcinoma are usually diagnosed at the late stages. Although the treatments for HCC have been rapidly advancing, novel targets for HCC are still desperately needed, especially for targeted therapies. Here, we identified an enriched long non-coding RNA, AC006262.5, associated with HCC, that promoted the proliferation, migration, and invasiveness of HCC cells, both in vitro and in vivo. In addition, our results revealed that AC006262.5 bound to and regulated miR-7855-5p, a tumor-suppressive miRNA, in HCC. Moreover, our data show that AC006262.5 regulates the expression of BPY2C via miR-7855-5p. Finally, we found that AC006262.5 and miR-7855-5p formed a regulatory loop. Upregulation of AC006262.5 resulted in decreased expression of miR-7855-5p, and downregulation of miR-7855-5p further facilitated the expression of AC006262.5. Our work provides novel targets for HCC diagnosis and treatment, and sheds light on the lncRNA-miRNA regulatory nexus that controls the pathology of HCC.

Long non‑coding RNA‑based risk scoring system predicts prognosis of alcohol‑related hepatocellular carcinoma

Increasing evidence suggests that long non-coding RNAs (lncRNAs) serve a crucial role in predicting prognosis for hepatocellular carcinoma (HCC). However, prognostic performance may not be the same for alcohol‑related HCC. The aim of the present study was to screen prognosis‑associated lncRNAs and construct a risk scoring system for alcohol‑related HCC. The expression profiles of lncRNAs in 113 patients with alcohol‑related HCC and 224 with non‑alcohol‑related HCC were obtained from The Cancer Genome Atlas (TCGA) database and screened for differentially expressed lncRNAs. Cox regression analysis was performed to identify prognosis‑associated lncRNAs and select the optimal lncRNA model. A risk scoring system was established to calculate the risk score for each patient. The prognostic ability of this system was tested. Functional enrichment analysis was performed for genes that were highly associated with lncRNA expression. A total of 102 differentially expressed lncRNAs were identified between alcohol‑related and non‑alcohol‑related HCC. Four lncRNAs (AC012640.1, AC013451.2, AC062004.1 and LINC02334) were used to construct the risk assessment model to predict overall survival (OS), and five lncRNAs (ERVH48‑1, LINC02043, LINC01605, AC062004.1 and AL139385) were used to predict recurrence‑free survival (RFS). Patients were assigned to high‑ or low‑risk groups according to the risk score. OS in the high‑risk group was significantly shorter than that of the low‑risk group. The area under the receiver operating characteristic (ROC) curve of risk scoring systems was >0.7. The risk score was an independent prognostic factor for alcohol‑related HCC. Functional enrichment analysis demonstrated that lncRNA‑related genes found in this system were mainly involved in chemical carcinogenesis, drug metabolism, and the cell cycle. In conclusion, this study developed and validated a prognostic scoring system for alcohol‑related HCC based on lncRNAs.

The Good, the Bad, the Question-H19 in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC), the most common primary liver cancer, is challenging to treat due to its typical late diagnosis, mostly at an advanced stage. Therefore, there is a particular need for research in diagnostic and prognostic biomarkers and therapeutic targets for HCC. The use of long noncoding (lnc) RNAs can widen the list of novel molecular targets improving cancer therapy. In hepatocarcinogenesis, the role of the lncRNA H19, which has been known for more than 30 years now, is still controversially discussed. H19 was described to work either as a tumor suppressor in vitro and in vivo, or to have oncogenic features. This review attempts to survey the conflicting study results and tries to elucidate the potential reasons for the contrary findings, i.e., different methods, models, or readout parameters. This review encompasses in vitro and in vivo models as well as studies on human patient samples. Although the function of H19 in HCC remains elusive, a short outlook summarizes some ideas of using the H19 locus as a novel target for liver cancer therapy.

MEG3-derived miR-493-5p overcomes the oncogenic feature of IGF2-miR-483 loss of imprinting in hepatic cancer cells

Numerous studies have described the critical role played by microRNAs (miRNAs) in cancer progression and the potential of these small non-coding RNAs for diagnostic or therapeutic applications. However, the mechanisms responsible for the altered expression of miRNAs in malignant cells remain poorly understood. Herein, via epigenetic unmasking, we identified a group of miRNAs located in the imprinted delta like non-canonical Notch ligand 1 (DLK1)-maternally expressed 3 (MEG3) locus that were repressed in hepatic tumor cells. Notably, miR-493-5p epigenetic silencing was correlated with hypermethylation of the MEG3 differentially regulated region (DMR) in liver cancer cell lines and tumor tissues from patients. Experimental rescue of miR-493-5p promoted an anti-cancer response by hindering hepatocellular carcinoma (HCC) cell growth in vitro and tumor progression in vivo. We found that miR-493-5p mediated part of its tumor-suppressor activity by abrogating overexpression of insulin-like growth factor 2 (IGF2) and the IGF2-derived intronic oncomir miR-483-3p in HCC cells characterized by IGF2 loss of imprinting (LOI). In summary, this study describes an unknown miRNA-dependent regulatory mechanism between two distinct imprinted loci and a possible therapeutic window for liver cancer patients exhibiting IGF2-miR-483 LOI and amplification.

Rs217727 polymorphism in H19 promotes cell apoptosis by regulating the expressions of H19 and the activation of its downstream signaling pathway

BACKGROUND

The objective of the current study was to explore the role of H19 rs217727 polymorphism in the control of hepatocellular carcinoma (HCC).

METHOD

The Student's t test, Cox regression, and Kaplan-Meier analyses were used to clarify whether the H19 rs217727 polymorphism played an important role in the development of HCC. Real-time polymerase chain reaction (PCR) and western-blot analysis were carried out to measure the levels of H19, microRNA (miR)-675, FAS-associated death domain (FADD), caspase-8, and caspase-3 among H19 CC, CT, and TT groups, as well as in cells transfected with H19/si-H19, or miR-675 mimic/inhibitor. The MTT assay, colony formation assay, and flow cytometry assay were performed to detect the effect of H19/miR-675 on cell viability, cell colony formation, and cell apoptosis.

RESULT

T allele of H19 rs217727 polymorphism apparently increased the survival rate of patients with HCC. Meanwhile, H19 enhanced miR-675 expression but reduced the mRNA and protein levels of FADD, caspase-3, and caspase-8. The T allele of H19 rs217727 polymorphism apparently increased the apoptotic rate of HCC cells. Furthermore, FADD was a virtual target gene of miR-675 with a potential "hit" located in the 3'-untranslated region (UTR) of FADD, whereas H19 inhibited FADD expression via increasing the expression of miR-675. Moreover, H19 upregulated the expression of miR-675 whereas reducing the expression of FADD, caspase-3, and caspase-8. Finally, H19 and miR-675 promoted cell proliferation and cell colony formation but repressed cell apoptosis.

CONCLUSION

In summary, the above findings demonstrated that the polymorphism of rs217727 in H19 was associated with HCC via the H19/miR-675/FADD/caspase-8/caspase-3/apoptosis signaling pathway.

Transgenic expression of the RNA binding protein IMP2 stabilizes miRNA targets in murine microsteatosis

Adult expression of IMP2 is often associated with several types of disease and cancer. The RNA binding protein IMP2 binds and stabilizes the IGF2 mRNA as well as hundreds of other transcripts during development. To gain insight into the molecular action of IMP2 and its contribution to disease in context of adult cellular metabolism, we analyze transgenic overexpression of IMP2 in mouse livers, which has been shown to induce a steatosis-like phenotype and enhanced risk to develop hepatocellular carcinoma (HCC). Our data show up-regulation of several HCC marker genes and miRNAs (miR438-3p and miR151-5p). To characterize the impact of miRNAs to their targets, integrative analysis of transcriptome-and miRNAome-dynamics in combination with IMP2 target prediction was carried out. Our analyses show that targets of expressed miRNAs become accumulated in the case that these transcripts have positive IMP2 binding prediction. Therefore, our data indicates that overexpression of IMP2 alters the regulatory capacity of many miRNAs and we conclude that IMP2 competes with miRNAs for binding sites on thousands of transcripts. As a result, our data implicates that overexpression of IMP2 has distinct effects to the regulatory capacity of miRNAs with yet unknown consequences for translational efficiency.

Analysis of long non-coding RNA (lncRNA) expression in hepatitis B patients

Long non-coding RNAs (lncRNAs) have been implicated in numerous biological processes, including epigenetic regulation, cell-cycle control, and transcriptional/translational regulation of gene expression. Differential expression of lncRNAs and disruption of the regulatory processes are recognized as critical steps in cancer development. The role of lncRNAs in hepatitis B virus (HBV) infection is not well understood. Here we analyzed the expression of 135 lncRNAs in plasma samples of 82 HBV patients (classified as chronic patients, inactive carriers, or resolved patients) at diagnosis and at 12 months of treatment in relation to control group (81 healthy volunteers). We also investigated the effect of small interfering RNA (siRNA)-mediated silencing of lincRNA-SFMBT2 on HBV-positive human liver cancer cell line. lncRNA expression was analyzed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Chemically synthesized siRNAs were transfected into the cell lines using Lipofectamine 2000 Reagent (Thermo Fisher Scientific). HBV DNA and HBsAg and HBeAg were detected in transfected cultures by real-time PCR and ELISA, respectively, using commercial kits. We observed changes in lncRNA expression in all three HBV groups, compared to control group. Most notably, the expression of anti-NOS2A, lincRNA-SFMBT2, and Zfhx2as was significantly increased and expression of Y5 lncRNA was decreased in chronic HBV patients. A decreased Y5 expression and increased lincRNA-SFMBT2 expression were observed in inactive HBsAg carriers. The expression of HOTTIP, MEG9, and PCAT-32 was increased in resolved HBV patients, and no significant change in the expression of Y5 was observed, compared to control group. siRNA-mediated inhibition of lincRNA-SFMBT2 decreased the level of HBV DNA in human liver cancer cells. Further research is needed to confirm the prognostic as well as therapeutic role of these lncRNAs in HBV patients.

The role of H19, a long non-coding RNA, in mouse liver postnatal maturation

H19 RNA is highly expressed at early postnatal ages and precipitously decreases at a specific time corresponding with increases in expression of genes important for mature liver function, such as drug metabolizing enzymes. H19’s role in the regulation of liver maturation is currently unknown. Using an H19 knockout mouse model to determine the role of H19 in liver development, we quantified gene expression for insulin growth factor signaling, Wnt signaling, key cytochrome P450 (P450) enzymes known to change as the liver develops, and fetal and adult plasma protein produced in liver. In mice lacking H19 expression, liver weights were significantly increased immediately after birth and significant increases were found in the number of actively proliferating cells. Increases in cell proliferation may be due to increases in β-catenin protein affecting Wnt signaling, increases in insulin-like growth factor 2 (IGF2) expression, and/or increases in insulin-like growth factor 1 receptor (IGF1R) expression at the protein level. Loss of targeted inhibition of IGF1R by microRNA 675 (miR-675) may be the cause of IGF1R increases, as miR-675 expression is also abrogated with loss of H19 expression in our model. P450 expression patterns were largely unchanged. No change in the production of plasma proteins was found, indicating H19 may not be important for liver maturation despite its role in controlling cell proliferation during liver growth. H19 may be important for normal liver development, and understanding how the liver matures will assist in predicting drug efficacy and toxicity in pediatric populations.

Long Noncoding RNAs as a Key Player in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a major malignancy in the liver and has emerged as one of the main cancers in the world with a high mortality rate. However, the molecular mechanisms of HCC are still poorly understood. Long noncoding RNAs (lncRNAs) have recently come to the forefront as functional non-protein-coding RNAs that are involved in a variety of cellular processes ranging from maintaining the structural integrity of chromosomes to gene expression regulation in a spatiotemporal manner. Many recent studies have reported the involvement of lncRNAs in HCC which has led to a better understanding of the underlying molecular mechanisms operating in HCC. Long noncoding RNAs have been shown to regulate development and progression of HCC, and thus, lncRNAs have both diagnostic and therapeutic potentials. In this review, we present an overview of the lncRNAs involved in different stages of HCC and their potential in clinical applications which have been studied so far.

Long non-coding RNAs as biomarkers and therapeutic targets: Recent insights into hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most prevalent primary liver cancer worldwide, and the survival rates of patients with HCC remains quite low after 5years. Long non-coding RNAs (LncRNAs) are a novel class of non-coding RNAs that are capable of regulating gene expression at various levels. Recent works have demonstrated that lncRNAs are often dysregulated in HCC, and the dysregulation of some of these lncRNAs are associated with the clinicopathological features of HCC. They regulate cell proliferation, apoptosis, autophagy, Epithelial-Mesenchymal Transition (EMT), invasion and metastasis of HCC by modulating gene expression and cancer-related signaling pathways, and thus contribute to the onset and progression of HCC. In this review, we provide a comprehensive survey of dysregulated lncRNAs in HCC, with particular focus on the functions and regulatory mechanisms of several essential and important lncRNAs, and discuss their potential clinical application as early diagnostic and/or prognostic biomarkers or therapeutic targets for HCC.

Downregulated long non-coding RNA TCONS_00068220 upregulates apoptosis in gastric cancer cells

Long non-coding RNAs (lncRNAs) are emerging as a fundamental class of biological effect or molecules that perform pivotal functions in the regulation of the genome. With advances in bioinformatics and genomics, extensive identification and characterization of lncRNAs is now possible. They regulate cellular growth, differentiation and apoptosis. Dysregulation of lncRNAs has been associated with numerous types of human cancer. In the present study, the expression profile of differentially expressed genes (DEGs) and lncRNAs in gastric cancer (GC) samples and normal tissue samples was evaluated with bioinformatics. The biological functions of the predicted lncRNA TCONS_00068220 were focused on; the DEGs co-expressed with TCONS_00068220 were enriched in cancer-associated pathways. TCONS_00068220 was demonstrated to be upregulated in GC tissues and cell lines compared with normal controls. In addition, an increased rate of apoptosis was observed in NCI-N87 cells following transfection with small interfering RNA against TCONS_00068220. These data suggest that TCONS_00068220 may be associated with the pathogenesis of GC, and it may serve as a potential therapeutic target.

The long non-coding RNA H19 suppresses carcinogenesis and chemoresistance in hepatocellular carcinoma

The long non-coding RNA (lncRNA) H19 represents a maternally expressed and epigenetically regulated imprinted gene product and is discussed to have either tumor-promoting or tumor-suppressive actions. Recently, H19 was shown to be regulated under inflammatory conditions. Therefore, aim of this study was to determine the function of H19 in hepatocellular carcinoma (HCC), an inflammation-associated type of tumor. In four different human HCC patient cohorts H19 was distinctly downregulated in tumor tissue compared to normal or non-tumorous adjacent tissue. We therefore determined the action of H19 in three different human hepatoma cell lines (HepG2, Plc/Prf5, and Huh7). Clonogenicity and proliferation assays showed that H19 overexpression could suppress tumor cell survival and proliferation after treatment with either sorafenib or doxorubicin, suggesting chemosensitizing actions of H19. Since HCC displays a highly chemoresistant tumor entity, cell lines resistant to doxorubicin or sorafenib were established. In all six chemoresistant cell lines H19 expression was significantly downregulated. The promoter methylation of the H19 gene was significantly different in chemoresistant cell lines compared to their sensitive counterparts. Chemoresistant cells were sensitized after H19 overexpression by either increasing the cytotoxic action of doxorubicin or decreasing cell proliferation upon sorafenib treatment. An H19 knockout mouse model (H19Δ3) showed increased tumor development and tumor cell proliferation after treatment with the carcinogen diethylnitrosamine (DEN) independent of the reciprocally imprinted insulin-like growth factor 2 (IGF2). In conclusion, H19 suppresses hepatocarcinogenesis, hepatoma cell growth, and HCC chemoresistance. Thus, mimicking H19 action might be a potential target to overcome chemoresistance in future HCC therapy.

Targeting H19, an Imprinted Long Non-Coding RNA, in Hepatic Functions and Liver Diseases

H19 is a long non-coding RNA regulated by genomic imprinting through methylation at the locus between H19 and IGF2. H19 is important in normal liver development, controlling proliferation and impacting genes involved in an important network controlling fetal development. H19 also plays a major role in disease progression, particularly in hepatocellular carcinoma. H19 participates in the epigenetic regulation of many processes impacting diseases, such as activating the miR-200 pathway by histone acetylation to inhibit the epithelial-mesenchymal transition to suppress tumor metastasis. Furthermore, H19's normal regulation is disturbed in diseases, such as hepatocellular carcinoma. In this disease, aberrant epigenetic maintenance results in biallelic expression of IGF2, leading to uncontrolled cellular proliferation. This review aims to further research utilizing H19 for drug discovery and the treatment of liver diseases by focusing on both the epigenetic regulation of H19 and how H19 regulates normal liver functions and diseases, particularly by epigenetic mechanisms.

IGF2 Is Up-regulated by Epigenetic Mechanisms in Hepatocellular Carcinomas and Is an Actionable Oncogene Product in Experimental Models

BACKGROUND & AIMS

Effective treatments are urgently needed for hepatocellular carcinoma (HCC), which is usually diagnosed at advanced stages. Signaling via the insulin-like growth factor (IGF) pathway is aberrantly activated in HCC by IGF2 overexpression. We aimed to elucidate the mechanism of IGF2 overexpression and its oncogenic activities and evaluate the anti-tumor effects of reducing IGF2 signaling.

METHODS

We obtained 228 HCC samples from patients who underwent liver resection, 168 paired non-tumor adjacent cirrhotic liver samples, and 10 non-tumor liver tissues from patients undergoing resection for hepatic hemangioma. We analyzed gene expression, microRNA, and DNA methylation profiles for all samples, focusing on genes in the IGF signaling pathway. IGF2 was expressed in SNU449 and PLC5 HCC cells and knocked down with small hairpin RNAs in Hep3B and Huh7 cell lines. We analyzed these cells for proliferation, apoptosis, migration, and colony formation. We performed studies in mice engineered to express Myc and Akt1 in liver, which develop liver tumors, with or without hepatic expression of Igf2. Mice with xenograft tumors grown from HCC cells were given a monoclonal antibody against IGF1 and IGF2 (xentuzumab), along with sorafenib; tumor growth was measured and tissues were analyzed by immunohistochemistry and immunoblots.

RESULTS

Levels of IGF2 messenger RNA and protein were increased >20-fold in 15% of human HCC tissues compared with non-tumor liver tissues. Methylation at the fetal promoters of IGF2 was reduced in the HCC samples and cell lines that overexpressed IGF2, compared with those that did not overexpress this gene, and non-tumor tissues. Tumors that overexpressed IGF2 had gene expression patterns significantly associated with hepatic progenitor cell features, stellate cell activation, NOTCH signaling, and an aggressive phenotype (P < .0001). In mice engineered to express Myc and Akt1 in liver, co-expression of Igf2 accelerated formation of liver tumors, compared to mice with livers expressing only Myc and Akt1, and shortened survival times (P = .02). The antibody xentuzumab blocked phosphorylation of IGF1 receptor in HCC cell lines and reduced their proliferation and colony formation. In mice with xenograft tumors, injection of xentuzumab, with or without sorafenib, slowed tumor growth and increased survival times compared to vehicle or sorafenib alone. Xentuzumab inhibited phosphorylation of IGF1 receptor and AKT and reduced decreased tumor vascularization compared with vehicle.

CONCLUSIONS

A large proportion of HCC samples were found to overexpress IGF2, via demethylation of its fetal promoter. Overexpression of IGF2 accelerates formation of liver tumors in mice with hepatic expression of MYC and AKT1, via activation of IGF1 receptor signaling. An antibody against IGF1 and IGF2 slows growth of xenograft tumors and increases survival of these mice.

Integrated Multiple "-omics" Data Reveal Subtypes of Hepatocellular Carcinoma

Hepatocellular carcinoma is one of the most heterogeneous cancers, as reflected by its multiple grades and difficulty to subtype. In this study, we integrated copy number variation, DNA methylation, mRNA, and miRNA data with the developed “cluster of cluster” method and classified 256 HCC samples from TCGA (The Cancer Genome Atlas) into five major subgroups (S1-S5). We observed that this classification was associated with specific mutations and protein expression, and we detected that each subgroup had distinct molecular signatures. The subclasses were associated not only with survival but also with clinical observations. S1 was characterized by bulk amplification on 8q24, TP53 mutation, low lipid metabolism, highly expressed onco-proteins, attenuated tumor suppressor proteins and a worse survival rate. S2 and S3 were characterized by telomere hypomethylation and a low expression of TERT and DNMT1/3B. Compared to S2, S3 was associated with less copy number variation and some good prognosis biomarkers, including CRP and CYP2E1. In contrast, the mutation rate of CTNNB1 was higher in S3. S4 was associated with bulk amplification and various molecular characteristics at different biological levels. In summary, we classified the HCC samples into five subgroups using multiple “-omics” data. Each subgroup had a distinct survival rate and molecular signature, which may provide information about the pathogenesis of subtypes in HCC.

Prohibitin 1 Regulates the H19-Igf2 Axis and Proliferation in Hepatocytes

Prohibitin 1 (PHB1) is a mitochondrial chaperone that regulates cell growth. Phb1 knock-out mice exhibit liver injury and hepatocellular carcinoma (HCC). Phb1 knock-out livers show induction of tumor growth-associated genes, H19 and insulin-like growth factor 2 (Igf2). These genes are controlled by the imprinting control region (ICR) containing CCCTC-binding transcription factor (CTCF)-binding sites. Because Phb1 knock-out mice exhibited induction of H19 and Igf2, we hypothesized that PHB1-mediated regulation of the H19-Igf2 axis might control cell proliferation in normal hepatocytes. H19 and Igf2 were induced (8-20-fold) in 3-week-old Phb1 knock-out livers, in Phb1 siRNA-treated AML12 hepatocytes (2-fold), and HCC cell lines when compared with control. Phb1 knockdown lowered CTCF protein in AML12 by ∼30% when compared with control. CTCF overexpression lowered basal H19 and Igf2 expression by 30% and suppressed Phb1 knockdown-mediated induction of these genes. CTCF and PHB1 co-immunoprecipitated and co-localized on the ICR element, and Phb1 knockdown lowered CTCF ICR binding activity. The results suggest that PHB1 and CTCF cooperation may control the H19-Igf2 axis. Human HCC tissues with high levels of H19 and IGF2 exhibited a 40-50% reduction in PHB1 and CTCF expression and their ICR binding activity. Silencing Phb1 or overexpressing H19 in the mouse HCC cell line, SAMe-D, induced cell growth. Blocking H19 induction prevented Phb1 knockdown-mediated growth, whereas H19 overexpression had the reverse effect. Interestingly H19 silencing induced PHB1 expression. Taken together, our results demonstrate that the H19-Igf2 axis is negatively regulated by CTCF-PHB1 cooperation and that H19 is involved in modulating the growth-suppressive effect of PHB1 in the liver.

Role of Long Noncoding RNAs in Neoplasia: Special Emphasis on Prostate Cancer

Recent advances in sequencing technology have dramatically improved the ability of investigators to study nucleic acid biology. Bolstered by these new and powerful techniques, the field of noncoding RNA (ncRNA) research, in particular, has witnessed a period of significant progress, wherein multiple new and unique species of ncRNA elements have been discovered and characterized. The current categories of ncRNAs include tRNA, rRNA, snoRNA, snRNA, piRNA, miRNA, and lncRNA, among others. The largest of these RNAs are the long noncoding RNAs (lncRNAs) that perform a diverse set of functions within the cell. Importantly, lncRNAs have recently been implicated in the pathogenesis of multiple types of cancer, including breast, lung, gastric, liver, and prostate. This reviews the major lncRNAs currently believed to play a role in human malignancies with a special emphasis on lncRNAs germane to cancer of the prostate gland. Continued investigation of lncRNA will likely prove to be exceedingly valuable, as they may provide novel therapeutic targets for the treatment of cancer. In addition, lncRNAs offer the potential to serve as diagnostic and prognostic biomarkers for cancer. The present state of lncRNA-based strategies for use in the management of cancer will also be highlighted.

Extracellular vesicle long noncoding RNA as potential biomarkers of liver cancer

Analysis of extracellular vesicles (EV) and their contents may be useful as disease biomarkers if they reflect the contents of cells of origin, differ between normal and diseased tissue and can be reliably detected. An increasing number of long noncoding RNA (lncRNA) are being reported to be aberrantly expressed in human cancers. These tumor-associated lncRNA may have potential as new biomarkers of disease. In this review, we highlight lncRNAs that are commonly associated with hepatocellular cancer, and summarize their potential biological roles and underlying molecular mechanisms. While lncRNA can be detected in the circulation, their low expression within circulating vesicles will require the use of highly sensitive detection technologies such as digital polymerase chain reaction or next-generation sequencing. While the integrity and functional role of tumor-specific lncRNAs within EV have yet to be established, their presence or enrichment within tumor cell-derived EV offers promise for their potential as disease biomarkers.

Aberrant DNA methylation of imprinted loci in hepatocellular carcinoma and after in vitro exposure to common risk factors

BACKGROUND

Hepatocellular carcinoma (HCC) is among the most frequent human malignancies and a major cause of cancer-related death worldwide. It is characterized by late detection and fast progression, and it is believed that epigenetic disruption may be one of the molecular mechanisms leading to hepatocarcinogenesis. Previous studies from our group revealed that HCC tumors exhibit specific DNA methylation signatures associated with major risk factors and tumor progression. Imprinted genes are mono-allelically expressed in a parent-of-origin-dependent manner and have been suggested to be more susceptible to deregulation in cancer. To test this notion, we performed a targeted analysis of DNA methylation in known imprinted genes, using HCC samples and in vitro models of carcinogenic exposure.

RESULTS

Analysis of HCC DNA methylation in two independent datasets showed that differentially methylated loci are significantly enriched in imprinted genes. Most of the promoters of imprinted genes were found hypomethylated in HCC tumors compared to surrounding tissues, contrasting with the frequent promoter hypermethylation observed in tumors. We next investigated the status of methylation of the imprinting control region (ICR) of different imprinted clusters and found that the 15q11-13 ICR was significantly hypomethylated in tumors relative to their surrounding tissues. In addition, expression of imprinted genes within this cluster was frequently deregulated in a gene-specific manner, suggesting distinct mechanisms of regulation in this region. Finally, primary human hepatocytes and hepatocyte-like HepaRG cells displayed higher methylation variability in certain imprinted loci after natural hepatitis B virus (HBV) infection and after lipid accumulation, respectively.

CONCLUSION

The methylation status of a large panel of imprinted genes was found deregulated in HCC, suggesting a major role of this mechanism during hepatocarcinogenesis. In vitro models support the hypothesis of imprinted gene methylation as a potential marker of environmental exposures.

The emergence of long non-coding RNAs in the tumorigenesis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third cause of cancer-related death worldwide. However, the treatments for HCC are limited, and most of them are only available to the early stage. In the later stages, traditional chemotherapy has only marginal effects and may include toxicity. Thus, the identification of new predictive markers is urgently needed. New targets for non-conventional treatments will help to accelerate research on the molecular pathogenesis of HCC. A new class of transcripts, long non-coding RNAs (lncRNAs), has recently been found to be pervasively transcribed in the human genome. Aberrant expression of several lncRNAs was found to be involved in the tumorigenesis of HCC. In this review, we describe the possible molecular mechanisms that underlie lncRNA expression changes in HCC, as well as potential future applications of lncRNA research in the diagnosis and treatment of HCC.

Long non-coding RNAs: critical players in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a complex disease with multiple underlying pathogenic mechanisms caused by a variety of etiologic factors. Emerging evidence showed that long non-coding RNAs (lncRNAs), with size larger than 200 nucleotides (nt), play important roles in various types of cancer development and progression. In recent years, some dysregulated lncRNAs in HCC have been revealed and roles for several of them in HCC have been characterized. All these findings point to the potential of lncRNAs as prospective novel therapeutic targets in HCC. In this review, we summarize known dysregulated lncRNAs in HCC, and review potential biological roles and underlying molecular mechanisms of lncRNAs in HCC. Additionally, we discussed prospects of lncRNAs as potential biomarker and therapeutic target for HCC. In conclusion, this paper will help us gain better understanding of molecular mechanisms by which lncRNAs perform their function in HCC and also provide general strategies and directions for future research.

Long noncoding RNAs in liver cancer: what we know in 2014

INTRODUCTION

Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer with an estimated over half a million new cases diagnosed annually. Due to the difficulty in early diagnosis and lack of effective treatment options, HCC is currently ranked as the second highest neoplastic-related mortality in the world, with an extremely low 5-year survival rate of between 6 and 11%. Long noncoding RNAs (lncRNAs), are genes lacking protein coding ability, have recently emerged as pivotal participants in biological processes, often dysregulated in a range of cancers, including HCC.

AREAS COVERED

In this review, we highlight the recent findings of lncRNAs in HCC pathogenesis, with particular attention on epigenetic events. In silico analysis was utilized to emphasize intrinsic linkages within the ncRNA families associated with hepatocarcinogenesis.

EXPERT OPINION

While our understanding of lncRNAs in the onset and progression of HCC is still in its infancy, there is no doubt that understanding the activities of ncRNAs will certainly secure strong biomarkers and improve treatment options for HCC patients.

Deregulation of RB1 expression by loss of imprinting in human hepatocellular carcinoma

The tumour suppressor gene RB1 is frequently silenced in many different types of human cancer, including hepatocellular carcinoma (HCC). However, mutations of the RB1 gene are relatively rare in HCC. A systematic screen for the identification of imprinted genes deregulated in human HCC revealed that RB1 shows imprint abnormalities in a high proportion of primary patient samples. Altogether, 40% of the HCC specimens (16/40) showed hyper- or hypomethylation at the CpG island in intron 2 of the RB1 gene. Re-analysis of publicly available genome-wide DNA methylation data confirmed these findings in two independent HCC cohorts. Loss of correct DNA methylation patterns at the RB1 locus leads to the aberrant expression of an alternative RB1-E2B transcript, as measured by quantitative real-time PCR. Demethylation at the intron 2 CpG island by DNMT1 knock-down or aza-deoxycytidine (DAC) treatment stimulated expression of the RB1-E2B transcript, accompanied by diminished RB1 main transcript expression. No aberrant DNA methylation was found at the RB1 locus in hepatocellular adenoma (HCA, n = 10), focal nodular hyperplasia (FNH, n = 5) and their corresponding adjacent liver tissue specimens. Deregulated RB1 expression due to hyper- or hypomethylation in intron 2 of the RB1 gene is found in tumours without loss of heterozygosity and is associated with a decrease in overall survival (p = 0.032) if caused by hypermethylation of CpG85. This unequivocally demonstrates that loss of imprinting represents an important additional mechanism for RB1 pathway inactivation in human HCC, complementing well-described molecular defects.

Long Noncoding RNAs in Interaction With RNA Binding Proteins in Hepatocellular Carcinoma

BACKGROUND

Gene expression microarrays' analyses provide a description of long noncoding RNAs (lncRNAs) with lack of coding protein function that is often important in human cancer.

OBJECTIVES

A number of lncRNAs that have been well characterized in hepatocellular carcinoma (HCC) have been scheduled in this study to discuss for protein-lncRNA interaction.

MATERIALS AND METHODS

The identified lncRNAs were analyzed by bioinformatics tools, starBase and lncRNA db, to anticipate the RNA-binding proteins (RBPs) that tend to interact to HCC-related lncRNAs. The most important predicted RBPs in interaction with well-known lncRNAs in HCC were briefly discussed.

RESULTS

The lncRNAs HOTTIP, H19, HOTAIR, MALAT1, antisense Igf2r (AIR), HOXA13, GTL2 (also called MEG3) and uc002mb have been reported in association with HCC. Besides, this study predicted that eIF4AIII, PTB and FUS were the most involved RBPs in interaction with HCC-related lncRNAs.

CONCLUSIONS

This information provides an explanation for the previously valuable literature on the functions of lncRNAs and suggest for the novel therapeutic targeting.

Long noncoding RNAs: Novel insights into hepatocelluar carcinoma

Recent advances in non-protein coding part of human genome analysis have discovered extensive transcription of large RNA transcripts that lack of coding protein function, termed long noncoding RNAs (lncRNAs). It is becoming evident that lncRNAs may be an important class of pervasive genes involved in carcinogenesis and metastasis. However, the biological and molecular mechanisms of lncRNAs in diverse diseases are not yet fully understood. Thus, it is anticipated that more efforts should be made to clarify the lncRNAs world. Moreover, accumulating studies have demonstrated that a class of lncRNAs are dysregulated in hepatocellular carcinoma(HCC) and closely related with tumorigenesis, metastasis, prognosis or diagnosis. In this review, we will briefly discuss the regulation and functional role of lncRNAs in HCC, therefore evaluating the potential of lncRNAs as prospective novel therapeutic targets in HCC.

Loss of imprinting and allelic switching at the DLK1-MEG3 locus in human hepatocellular carcinoma

Deregulation of imprinted genes is an important molecular mechanism contributing to the development of cancer in humans. However, knowledge about imprinting defects in human hepatocellular carcinoma (HCC), the third leading cause of cancer mortality worldwide, is still limited. Therefore, a systematic meta-analysis of the expression of 223 imprinted loci in human HCC was initiated. This screen revealed that the DLK1-MEG3 locus is frequently deregulated in HCC. Deregulation of DLK1 and MEG3 expression accompanied by extensive aberrations in DNA methylation could be confirmed experimentally in an independent series of human HCC (n = 40) in more than 80% of cases. Loss of methylation at the DLK1-MEG3 locus correlates linearly with global loss of DNA methylation in HCC (r(2) = 0.63, p<0.0001). Inhibition of DNMT1 in HCC cells using siRNA led to a reduction in MEG3-DMR methylation and concomitant increase in MEG3 RNA expression. Allele-specific expression analysis identified loss of imprinting in 10 out of 31 informative samples (32%), rendering it one of the most frequent molecular defects in human HCC. In 2 cases unequivocal gain of bi-allelic expression accompanied by substantial loss of methylation at the IG-DMR could be demonstrated. In 8 cases the tumour cells displayed allelic switching by mono-allelic expression of the normally imprinted allele. Allelic switching was accompanied by gains or losses of DNA methylation primarily at IG-DMR1. Analysis of 10 hepatocellular adenomas (HCA) and 5 cases of focal nodular hyperplasia (FNH) confirmed that this epigenetic instability is specifically associated with the process of malignant transformation and not linked to increased proliferation per se. This widespread imprint instability in human HCC has to be considered in order to minimize unwanted side-effects of therapeutic approaches targeting the DNA methylation machinery. It might also serve in the future as predictive biomarker and for monitoring response to epigenetic therapy.

A set of imprinted genes required for normal body growth also promotes growth of rhabdomyosarcoma cells

INTRODUCTION

In many normal tissues, proliferation rates decline postnatally, causing somatic growth to slow. Previous evidence suggests that this decline is due, in part, to decline in the expression of growth-promoting imprinted genes including Mest, Plagl1, Peg3, Dlk1, and Igf2. Embryonal cancers are composed of cells that maintain embryonic characteristics and proliferate rapidly in childhood. We hypothesized that the abnormal persistent rapid proliferation in embryonal cancers occurs in part because of abnormal persistent high expression of growth-promoting imprinted genes.

RESULTS

Analysis of microarray data showed elevated expression of MEST, PLAGL1, PEG3, DLK1, and IGF2 in various embryonal cancers, especially rhabdomyosarcoma, as compared to nonembryonal cancers and normal tissues. Similarly, mRNA expression, assessed by real-time PCR, of MEST, PEG3, and IGF2 in rhabdomyosarcoma cell lines was increased as compared to nonembryonal cancer cell lines. Furthermore, siRNA-mediated knockdown of MEST, PLAGL1, PEG3, and IGF2 expression inhibited proliferation in Rh30 rhabdomyosarcoma cells.

DISCUSSION

These findings suggest that the normal postnatal downregulation of growth-promoting imprinted genes fails to occur in some embryonal cancers, particularly rhabdomyosarcoma, and contributes to the persistent rapid proliferation of rhabdomyosarcoma cells and, more generally, that failure of the mechanisms responsible for normal somatic growth deceleration can promote tumorigenesis.

Epithelial-mesenchymal transition predicts sensitivity to the dual IGF-1R/IR inhibitor OSI-906 in hepatocellular carcinoma cell lines

A growing body of data indicates that inhibiting the type 1 insulin-like growth factor receptor (IGF-1R) might be an effective treatment strategy for hepatocellular carcinoma (HCC). OSI-906 is a dual IGF-1R/IR kinase inhibitor currently in phase II clinical development for HCC. However, biomarkers are lacking to help identify patients with HCC who are more likely to benefit from OSI-906 treatment. We sought to determine the effect of OSI-906 on proliferation against a panel of 21 HCC cell lines and to investigate molecular determinants of responsiveness to OSI-906. We identified a subset of HCC cell lines that was sensitive to OSI-906, and sensitivity is associated with elevated phosphorylation levels of IGF-1R and IR and greater inhibition of AKT signaling. Dual targeting of both receptors seems to be important for maximal inhibition as treatment with a selective IGF-1R-neutralizing antibody was associated with increased IR signaling, whereas OSI-906 fully inhibited both phosphorylated IR and IGF-1R and resulted in greater inhibition of the IRS/AKT pathway. Epithelial-mesenchymal transition (EMT) seems to predict HCC cell sensitivity to OSI-906, as the epithelial phenotype is strongly associated with expression of IGF-2 and IR, activation of IGF-1R and IR, and sensitivity to OSI-906, alone or in combination with erlotinib. Induction of EMT upon treatment with TGFβ reduced sensitivity to OSI-906. Collectively, these data support the concept for dual IGF-1R/IR targeting in HCC, where EMT status and expressions of IGF-2 and IR may be used to identify those patients who are most likely to benefit from treatment with an IGF-1R/IR dual inhibitor.

Somatically acquired hypomethylation of IGF2 in breast and colorectal cancer

The imprinted insulin-like growth factor 2 (IGF2) gene is expressed predominantly from the paternal allele. Loss of imprinting (LOI) associated with hypomethylation at the promoter proximal sequence (DMR0) of the IGF2 gene was proposed as a predisposing constitutive risk biomarker for colorectal cancer. We used pyrosequencing to assess whether IGF2 DMR0 methylation is either present constitutively prior to cancer or whether it is acquired tissue-specifically after the onset of cancer. DNA samples from tumour tissues and matched non-tumour tissues from 22 breast and 42 colorectal cancer patients as well as peripheral blood samples obtained from colorectal cancer patients [SEARCH (n=case 192, controls 96)], breast cancer patients [ABC (n=case 364, controls 96)] and the European Prospective Investigation of Cancer [EPIC-Norfolk (n=breast 228, colorectal 225, controls 895)] were analysed. The EPIC samples were collected 2–5 years prior to diagnosis of breast or colorectal cancer. IGF2 DMR0 methylation levels in tumours were lower than matched non-tumour tissue. Hypomethylation of DMR0 was detected in breast (33%) and colorectal (80%) tumour tissues with a higher frequency than LOI indicating that methylation levels are a better indicator of cancer than LOI. In the EPIC population, the prevalence of IGF2 DMR0 hypomethylation was 9.5% and this correlated with increased age not cancer risk. Thus, IGF2 DMR0 hypomethylation occurs as an acquired tissue-specific somatic event rather than a constitutive innate epimutation. These results indicate that IGF2 DMR0 hypomethylation has diagnostic potential for colon cancer rather than value as a surrogate biomarker for constitutive LOI.

The H19 non-coding RNA is essential for human tumor growth

Background

Mutations and epigenetic aberrant signaling of growth factors pathways contribute to carcinogenesis. Recent studies reveal that non-coding RNAs are controllers of gene expression. H19 is an imprinted gene that demonstrates maternal monoallelic expression without a protein product; although its expression is shut off in most tissues postnatally, it is re-activated during adult tissue regeneration and tumorigenesis. Moreover, H19 is highly expressed in liver metastasis derived from a range of carcinomas. The objective of this study is to explore the role of H19 in carcinogenesis, and to determine its identification as an anti-tumor target.

Methodology/ Principle Findings

By controlling oxygen pressure during tumor cell growth and H19 expression levels, we investigated the role of H19 expression in vitro and in vivo in hepatocellular (HCC) and bladder carcinoma. Hypoxia upregulates the level of H19 RNA. Ablations of tumorigenicity of HCC and bladder carcinomas in vivo are seen by H19 knockdown which also significantly abrogates anchorage-independent growth after hypoxia recovery, while ectopic H19 expression enhances tumorigenic potential of carcinoma cells in vivo. Knocking-down H19 message in hypoxic stress severely diminishes p57^kip2 induction. We identified a number of potential downstream targets of H19 RNA, including angiogenin and FGF18.

Conclusions

H19 RNA harbors pro-tumorigenic properties, thus the H19 gene behaves as an oncogene and may serve as a potential new target for anti-tumor therapy.

Clinicopathologic significance of hypoxia-inducible factor 1alpha overexpression in gastric carcinomas

BACKGROUND

Hypoxia-inducible factor 1alpha (HIF-1alpha) plays a key role in responses to hypoxia and expression of HIF-1alpha downstream genes leads to both an adapted metabolism and increased oxygen supply. We investigated the clinical significance of HIF-1alpha expression in gastric carcinoma.

METHODS

We examined HIF-1alpha, vascular endothelial growth factor (VEGF), and insulin-like growth factor-2 (IGF-2) expression patterns immunohistochemically in 126 specimens of gastric carcinoma. CD34 antigen levels were also examined by immunohistochemistry to determine microvessel density (MVD) within tumors and correlations between HIF-1alpha expression, clinicopathological features, and survival were examined.

RESULTS

HIF-1alpha expression correlated with tumor size (P<0.005), depth of invasion (P=0.018), VEGF expression (P=0.03), and intra-tumor MVD (P<0.005). IGF-2 expression was more prevalent in HIF-1alpha positive than in HIF-1alpha negative tumors and the 5-year survival rate was 58.4% for HIF-1alpha positive patients and 81.5% for HIF-1alpha negative patients (P=0.009). HIF-1alpha expression is an independent prognostic factor in gastric carcinoma (P=0.032).

CONCLUSIONS

Overexpression of HIF-1alpha in gastric carcinomas may upregulate its downstream gene products leading to VEGF-mediated angiogenesis, and resulting in a poor prognosis for patients.

Gain of allelic gene expression for IGF-II occurs frequently in Barrett's esophagus

The IGF-II gene normally exhibits genomic imprinting, a DNA modification that allows the expression of only one of the two inherited alleles. With loss of imprinting, there is a gain of allelic gene expression (GOAGE) due to IGF-II being expressed by both alleles. GOAGE for IGF-II has been demonstrated in a number of malignancies and in normal epithelia surrounding malignancies, but not in epithelia without associated neoplasia. We hypothesized that nonneoplastic Barrett's epithelium might have GOAGE for IGF-II that could facilitate its progression to neoplasia. Endoscopic biopsies were obtained from metaplastic esophageal, normal gastric, and normal duodenal epithelia from 43 patients with Barrett's esophagus. Genomic DNA were analyzed using PCR followed by ApaI restriction enzyme digestion or allele-specific PCR to identify an ApaI polymorphism of IGF-II. cDNA from patients with the ApaI polymorphism were analyzed for IGF-II GOAGE using exon connection PCR, followed by a secondary nested PCR and ApaI restriction enzyme digestion. We found that 13 (30%) of 43 samples of Barrett's metaplasia contained the ApaI polymorphism and were thus informative for IGF-II, and sufficient material was available for GOAGE analysis in 9 of those 13 cases. GOAGE for IGF-II was demonstrated in five (56%) of those nine cases. All patients with GOAGE in Barrett's metaplasia also demonstrated GOAGE in the gastric and duodenal epithelia. In contrast, patients without GOAGE in Barrett's metaplasia also had no GOAGE in their gastric and duodenal epithelia. We conclude that in patients with Barrett's esophagus, GOAGE for IGF-II is found frequently in the metaplastic esophageal epithelium as well as in normal gastric and duodenal epithelia.

Loss of parental-specific methylation at the IGF2 locus in human hepatocellular carcinoma

Significant production of the growth factor IGF2 has been reported in human hepatocellular carcinomas (HCCs). Disturbances associated with changes in methylation at this locus or affecting the 11p15.5 imprinting domain as a whole can be postulated in HCCs. In the present study, the methylation status of differentially methylated regions of the imprinted genes TSSC5, LIT1, and IGF2, which span the 11p15 domain, was analysed in 71 liver tissues from virus-associated and non-virus-associated HCCs compared with six normal liver tissues. Altered methylation of TSSC5 and LIT1 was observed in only 6% and 8% of HCCs, respectively, compared with 89% at the IGF2 locus, suggesting that these loci were not concomitantly dysregulated. These observations suggest that loss of parental-specific methylation at the IGF2 locus may be specifically associated with HCC, whether virus-associated or non-virus-associated, and arising in cirrhotic or non-cirrhotic livers.

Alterations in specific gene expression and focal neoplastic growth during spontaneous hepatocarcinogenesis in albumin-SV40 T antigen transgenic rats

Transgenic rats containing the mouse albumin promoter and enhancer directing the expression of simian virus (SV40) T antigen (T Ag) exhibited a 100% incidence of hepatic neoplasms by 24-36 wk of age. These transgenic rats exhibited expression of large T Ag and c-myc protein within focal basophilic lesions and nodules, but not in surrounding hepatocytes. At 24 wk of age, female TG+ rats exhibited a significantly greater number of lesions and a much greater percentage of the liver occupied by TG+ focal hepatic lesions than did their male TG+ littermates. Previous studies on these animals [Sargent et al., Cancer Res 1997;57:3451-3456] demonstrate that at 12 wk of age approximately one-third of metaphases in hepatocytes exhibit a duplication of the 1q3.7-1q4.1 region of rat chromosome 1, with the smallest common region of duplication being that of 1q4.1. Duplication of the 1q3.7-1q4.3 region is also noted in many primary hepatic neoplasms resulting from the multistage model of Initiation-Promotion-Progression (IPP) [Sargent et al., Cancer Res 1996;56:2985-2991]. This region is syntenic with human 11p15.5 and mouse 7ter, which have been implicated in the development of specific neoplasms. Within the syntenic region was a cluster of imprinted genes whose expression we investigated in livers and neoplasms of TG+ rats. H19 was expressed in almost all of the neoplasms, but not in normal adult liver cells. Igf2 expression was detected in the majority of hepatic neoplasms of female TG+ rats, but in a relatively smaller number of neoplasms of TG+ males. The expression of p57Kip2 (Kip2), a cyclin-dependent kinase inhibitor that was also in the imprinted region, exhibited some variable increased expression predominantly in hepatic neoplasms from livers of female TG+ rats. Other imprinted genes within the imprinted gene cluster-insulin II (Ins2), Mash2 (which codes for a basic helix-loop-helix transcription factor), and Kvlqt1 (coding for a component of a potassium transport channel)-showed no consistently different expression from that seen in normal hepatocytes. Another gene, also located on the long arm of chromosome 1, that showed changes was the ribonucleotide reductase M1 subunit (Rrm1), in which an increase in its expression was found. This was seen in hepatic neoplasms of TG+ rats of both sexes compared with surrounding normal-appearing liver. Because hepatic neoplasms developing in livers of rats treated with chemical carcinogens commonly exhibit an increased expression of c-myc mRNA, expression of this gene was investigated in focal lesions and livers of TG+ rats, although c-myc was not located on chromosome 1. c-myc mRNA was increased in focal lesions, nodules, and neoplasms in both male and female TG+ rats compared with adult and surrounding liver. Immunostaining for c-myc protein demonstrated detectable levels in isolated single cells as well as focal lesions and neoplasms. Thus, the enhanced c-myc expression, common to all hepatic neoplasms in this system, coupled with enhanced expression of Igf2 in female TG+ rats, may be responsible for the increase in growth rate in hepatic neoplasms of female TG+ rats compared with that in livers of male TG+ rats and may contribute to neoplastic progression in the liver of this transgenic model.

Loss of Igf2 imprinting in monoclonal mouse hepatic tumor cells is not associated with abnormal methylation patterns for the H19, Igf2, and Kvlqt1 differentially methylated regions

IGFII, the peptide encoded by the Igf2 gene, is a broad spectrum mitogen with important roles in prenatal growth as well as cancer progression. Igf2 is transcribed from the paternally inherited allele, whereas the linked H19 is transcribed from the maternal allele. Igf2 imprinting is thought to be maintained by differentially methylated regions (DMRs) located at multiple sites such as upstream of H19 and Igf2 and within Kvlqt1 loci. Biallelic expression (loss of imprinting (LOI)) of Igf2 is frequently observed in cancers, and a subset of Wilms' and intestinal tumors have been shown to exhibit abnormal methylation at H19DMR associated with loss of maternal H19 expression, but it is not known whether such changes are common in other neoplasms. Because cancers consist of diverse cell populations with and without Igf2 LOI, we established four independent monoclonal cell lines with Igf2 LOI from mouse hepatic tumors. We here demonstrate retention of normal differential methylation at H19, Igf2, or Kvlqt1 DMR by all of the cell lines. Furthermore, H19 was found to be expressed exclusively from the maternal allele, and levels of CTCF, a multifunctional nuclear factor that has an important role in the Igf2 imprinting, were comparable with those in normal hepatic tissues with no mutational changes detected. These data indicate that Igf2 LOI in tumor cells is not necessarily linked to abnormal methylation at H19, Igf2, or Kvlqt1 loci.

Cross-talk between mesenchyme and epithelium increases H19 gene expression during scattering and morphogenesis of epithelial cells

The H19 gene is an imprinted gene expressed from the maternal allele. It is known to function as an RNA molecule. We previously reported that in breast adenocarcinoma, H19 is often overexpressed in stromal cells and preferentially located at the epithelium/stroma boundary, suggesting that epithelial/mesenchymal interactions can control H19 RNA expression. In some cases of breast adenocarcinoma with poor prognosis, H19 is overexpressed in epithelial cells. Therefore we examined whether mesenchymal factors can induce H19 expression in epithelial cells. Using quantitative RT-PCR and in situ hybridization, we found that when mammary epithelial cells were cultured in collagen gels, H19 expression was strongly up-regulated compared to when cells were cultured on plastic. Collagen gels allow three-dimensional growth of epithelial cells and morphogenetic responses to soluble factors. A conditioned medium from MRC-5 fibroblasts caused branching morphogenesis of HBL-100 cells and invasive growth of MDA-MB-231 cells, whereas MCF-7 cells were unresponsive. Induction of H19 expression correlated with morphological changes in HBL-100 and in MDA-MB-231 cells, whereas H19 expression was not induced in MCF-7 cells. Using a blocking antibody, HGF/SF was identified as the fibroblast-derived growth factor capable of inducing H19 expression and cell morphogenesis. We further demonstrated that H19 promoter activity was stimulated by various growth factors using transient transfection in MDCK epithelial cells. HGF/SF was more efficient than EGF or FGF-2 in transactivating the H19 promoter, whereas IGF-2, TGFbeta-1, and TNF-alpha were ineffective. This activation by HGF/SF was prevented by pharmacological inhibition of MAP kinase or of phospholipase C. We conclude that H19 is a target gene for HGF/SF, a known regulator of epithelial/mesenchymal interactions, and suggest that the up-regulation of H19 may be implicated in morphogenesis and/or migration of epithelial cells.

Expression profile of nine novel genes differentially expressed in hepatitis B virus-associated hepatocellular carcinomas

Chronic hepatitis B virus (HBV) infection is known to be one of the major causes in the development of hepatocellular carcinoma (HCC), although the biomolecular mechanism(s) involved remain unclear. To identify the cellular gene(s) involved in HBV-associated hepatocarcinogenesis, we used the mRNA differential display method and examined three paired tumor and nontumor tissues, all of which had chromosomally integrated HBV-DNA through chronic infection. Using 240 different combinations of three one-base anchored oligo-dT primers and 80 arbitrary 13-mers, genes decreased or increased in expression more than twofold between each tumor tissue and its paired nontumor tissue were identified. Twenty-nine known genes and four novel genes were differentially over-expressed in the HCC tumor tissues. In contrast, 27 known genes and five novel genes were under-expressed in those tumor tissues. The nucleotide sequences of the nine novel gene fragments were determined and their expression patterns were examined in 40 HCC samples. HA61T2, PT18, HG63T1, and HG57T1 were preferentially over-expressed in 32 cases (80%, P<0.001), 24 cases (60%), 23 cases (57.5%) and 22 cases (55%) of the 40 tumor tissues, respectively. There was an increased frequency of HG57T1 over-expression in HCC patients with HBV-positive serology and low serum alpha-feto protein (AFP) levels (P<0.05). DNT10, PT8, PT19, ENT25 and HA6T4 were under-expressed in 26 cases (65%), 23 cases (57.5%), 21 cases (53%), 20 cases (50%) and 18 cases (45%) of the 40 tumor samples, respectively. There was a strong correlation of DNT10 under-expression with high serum AFP level in HCC patients, irrespective of HBV serology (P<0.01). HA6T4 was preferentially under-expressed in HCC tumors in patients with HBV-positive serology and high serum AFP levels (P<0.05). Thus, the functional analyses of the known and novel genes identified in this study should prove valuable to further understand the mechanism(s) of hepatocarcinogenesis.

Genomic imprinting and cancer; new paradigms in the genetics of neoplasia

The role of epigenetic modification of gene expression is becoming increasingly important in how we understand the loss of tumour suppressor gene function in a variety of tumours and tumour predisposing syndromes. This review explores the importance of epimutation in Beckwith-Wiedemann syndrome and Wilms' tumour and focuses on genomic methylation in both imprinted and non-imprinted genes as a key mechanism in the development of cancer.

Relaxation of IGF2 imprinting in Wilms tumours associated with specific changes in IGF2 methylation

Relaxation of IGF2 imprinting occurs in Wilms tumours and many other cancers, but the mechanism of loss of imprinting (LOI) remains unknown. To investigate the role of altered DNA methylation in LOI, we examined the pattern of methylation of the human insulin-IGF2 region in Wilms tumours and the normal kidney. The analysis included regions homologous to three 'differentially methylated regions' of the mouse Igf2 gene (dmrs 0, 1 and 2). In tumours displaying normal IGF2 imprinting, and in the normal kidney, maternal allele-specific DNA methylation was identified spanning exons 2 and 3. This region is homologous to dmr 0, a site of maternal-specific differential methylation in the mouse. In Wilms tumours with relaxed imprinting or 11p15.5 LOH this region was unmethylated. No other differential methylation was identified. In particular, two sites of paternal methylation in the mouse (dmrs 1 and 2), and all three imprinted IGF2 promoters were not methylated in the kidney or in Wilms tumours. We postulate that LOI in Wilms tumours is associated with loss of maternal allele-specific methylation from a region located upstream of the imprinted IGF2 promoters. This region may contain cis acting sequences that coordinately influence imprinting.

Genomic imprinting and chromatin insulation in Beckwith-Wiedemann syndrome

Genes are recognized as undergoing genomic imprinting when they are capable of being expressed only from the paternal or only from the maternal chromosome. The process can occur coordinately within large physical domains in mammalian chromosomes. One interesting facet of the study of genomic imprinting is that it offers insight into the regulation of large chromosomal regions. Understanding this regulation involves elucidating the cis-acting regulators of gene expression and defining the elements that maintain chromatin insulation, both required for understanding more practically applicable areas of biological research, such as efficient transgene production. This review is focused on the regulation of the imprinted domain of human chromosome 11p15.5, responsible for Beckwith-Wiedemann syndrome (BWS). Recent findings indicate that the maintenance of imprinting within this domain is critically dependent on the stable maintenance of chromatin insulation.

Genomic imprinting: implications for human disease

Genomic imprinting refers to an epigenetic marking of genes that results in monoallelic expression. This parent-of-origin dependent phenomenon is a notable exception to the laws of Mendelian genetics. Imprinted genes are intricately involved in fetal and behavioral development. Consequently, abnormal expression of these genes results in numerous human genetic disorders including carcinogenesis. This paper reviews genomic imprinting and its role in human disease. Additional information about imprinted genes can be found on the Genomic Imprinting Website at http://www.geneimprint.com.

Genomic imprinting and cancer

Genomic imprinting is the phenomenon by which individual alleles of certain genes are expressed differentially according to their parent of origin. The alleles appear to be differentially marked during gametogenesis or during the early part of development. This mark is heritable but reversible from generation to generation, implying a stable epigenetic modification. Approximately 25 imprinted genes have been identified to date, and dysregulation of a number of these has been implicated in tumour development. The normal physiological role of many imprinted genes is in the control of cell proliferation and fetal growth, indicating potential mechanisms of action in tumour formation. Both dominant and recessive modes of action have been postulated for the role of imprinted genes in neoplasia, as a result of effective gene dosage alterations by epigenetic modification of the normal pattern of allele specific transcription. The aim of this review is to assess the importance of imprinted genes in generating tumours and to discuss the implications for novel mechanisms of transforming mutation.