The receptor tyrosine kinase EphA2 is a direct target gene of hypermethylated in cancer 1 (HIC1)

The transcription factor Hypermethylated in Cancer 1 (Hic1) regulates neural crest migration via interaction with Wnt signaling

The transcription factor Hypermethylated in Cancer 1 (HIC1) is associated with both tumorigenesis and the complex human developmental disorder Miller-Dieker Syndrome. While many studies have characterized HIC1 as a tumor suppressor, HIC1 function in development is less understood. Loss-of-function mouse alleles show embryonic lethality accompanied with developmental defects, including craniofacial abnormalities that are reminiscent of human Miller-Dieker Syndrome patients. However, the tissue origin of the defects has not been reported. In this study, we use the power of the Xenopus laevis model system to explore Hic1 function in early development. We show that hic1 mRNA is expressed throughout early Xenopus development and has a spatial distribution within the neural plate border and in migrating neural crest cells in branchial arches. Targeted manipulation of hic1 levels in the dorsal ectoderm that gives rise to neural and neural crest tissues reveals that both overexpression and knockdown of hic1 result in craniofacial defects with malformations of the craniofacial cartilages. Neural crest specification is not affected by altered hic1 levels, but migration of the cranial neural crest is impaired both in vivo and in tissue explants. Mechanistically, we find that Hic1 regulates cadherin expression profiles and canonical Wnt signaling. Taken together, these results identify Hic1 as a novel regulator of the canonical Wnt pathway during neural crest migration.

The prognostic value of ephrin type-A2 receptor and Ki-67 in renal cell carcinoma patients: An Immunohistochemical and Bioinformatical Approach; A STROBE - compliant article

Patients with renal cell carcinoma (RCC), the most common malignant renal epithelial tumor, usually present with advanced disease and unpredicted clinical behavior. The receptor tyrosine kinase, ephrin type-A receptor 2 (EphA2) was found to be overexpressed in several malignancies and its expression was found to be associated with poor prognostic features.Our study is an observational study with the aim of investigating the prognostic value of EphA2 in RCC patients and its association with clinicopathological parameters as well as Ki-67 expression, which is a well-known proliferative and prognostic marker in RCC.EphA2 and Ki-67 immunohistochemical staining was performed on whole sections representative of 50 patients diagnosed with primary RCC from 2013 to 2018. In addition, the association between EphA2 mRNA expression and clinicopathological parameters as well as the patients' outcome was also evaluated using two large publicly available databases.Our results showed a significant association between EphA2 immunohistochemical expression and tumor size, nuclear grade, tumor stage, patients' outcome and Ki-67 expression (P < .05 for all). The same trend was also observed with EphA2 mRNA expression using larger patients' cohorts in 2 publicly available databases. Notably, EphA2 protein expression showed higher levels of co-expression with the proliferative marker Ki-67.Our results suggested that higher expression of EphA2 and Ki-67 in tumor tissues predicts a locally aggressive behaviour and poor outcome of patients with RCC. Moreover, our results give a rationale for the potential benefits of using novel therapeutic strategies with the aim of targeting EphA2 receptor in RCC patients that might help in improving their outcome.

Downregulation of hypermethylated in cancer-1 by miR-4532 promotes adriamycin resistance in breast cancer cells

Background

MicroRNAs are small RNAs (~ 22 nt) that modulate the expression of thousands of genes in tumors and play important roles in the formation of multidrug resistance. In this study, we firstly investigated that miR-4532 involved in the multidrug resistance formation of breast cancer by targeting hypermethylated in cancer 1 (HIC-1), a tumor-suppressor gene.

Methods

To identify and characterize the possible miRNAs in regulating multidrug resistance, we employed the transcriptome sequencing approach to profile the changes in the expression of miRNAs and their target mRNAs were obtained by bioinformatics prediction. Then the molecular biology experiments were conducted to confirm miR-4532 involved in multidrug resistance formation of breast cancer.

Results

The luciferase reporter assay experiment was employed to confirm that HIC-1 was the target of miR-4532. Transfection with an miR-4532 mimic indicated miR-4532 mimic significantly increased breast cancer cell resistance to adriamycin. Cell proliferation and invasion assay experiments showed overexpression of HIC-1 inhibited the invasion and metastasis of breast cancer cells. Meanwhile, the interleukin (IL)-6/signal transducer and activator of transcription 3 (STAT3) signaling pathway was confirmed to be involving in multidrug resistance by western blotting experiments.

Conclusions

These results suggest that downregulation of hypermethylated in cancer-1 by miR-4532 could promote adriamycin resistance in breast cancer cells, in which the IL-6/STAT3 pathway was regulated by the HIC-1. This finding might contribute to new therapeutic target for reversal of tumor resistance.

Electronic supplementary material

The online version of this article (10.1186/s12935-018-0616-x) contains supplementary material, which is available to authorized users.

The tumor suppressor Hic1 maintains chromosomal stability independent of Tp53

Hypermethylated-in-Cancer 1 (Hic1) is a tumor suppressor gene frequently inactivated by epigenetic silencing and loss-of-heterozygosity in a broad range of cancers. Loss of HIC1, a sequence-specific zinc finger transcriptional repressor, results in deregulation of genes that promote a malignant phenotype in a lineage-specific manner. In particular, upregulation of the HIC1 target gene SIRT1, a histone deacetylase, can promote tumor growth by inactivating TP53. An alternate line of evidence suggests that HIC1 can promote the repair of DNA double strand breaks through an interaction with MTA1, a component of the nucleosome remodeling and deacetylase (NuRD) complex. Using a conditional knockout mouse model of tumor initiation, we now show that inactivation of Hic1 results in cell cycle arrest, premature senescence, chromosomal instability and spontaneous transformation in vitro. This phenocopies the effects of deleting Brca1, a component of the homologous recombination DNA repair pathway, in mouse embryonic fibroblasts. These effects did not appear to be mediated by deregulation of Hic1 target gene expression or loss of Tp53 function, and rather support a role for Hic1 in maintaining genome integrity during sustained replicative stress. Loss of Hic1 function also cooperated with activation of oncogenic KRas in the adult airway epithelium of mice, resulting in the formation of highly pleomorphic adenocarcinomas with a micropapillary phenotype in vivo. These results suggest that loss of Hic1 expression in the early stages of tumor formation may contribute to malignant transformation through the acquisition of chromosomal instability.

The role of WT1 isoforms in vasculogenic mimicry and metastatic potential of human triple negative breast cancer cells

Triple negative breast cancer (TNBC) is highly aggressive and has a few therapeutic treatments, so new targeted therapy and biomarkers are required to provide alternative choices for treating TNBC patients. Recent studies showed that vasculogenic mimicry (VM), the formation of blood channels by aggressive cancer cells that mimic endothelial cells, is a factor contributing to poor prognosis in TNBC. Wilms' tumor 1 (WT1) gene has been found to be highly expressed in TNBC, and has 4 major distinct isoforms; isoform A (-17AA/-KTS; -/-), isoform B (+17AA/-KTS; +/-), isoform C (-17AA/+KTS; -/+) and isoform D (+17AA/+KTS; +/+). The involvement of each WT1 isoform in TNBC progression remains largely unclear. In this study, WT1 isoform-overexpressing cell sublines were established from a TNBC cell line, MDA-MB-231, by stable transfection, and the aggressive behavior of the cell sublines were evaluated. Only the WT1 isoform B- and isoform C-overexpressing cell sublines showed the significant increase in VM forming capability compared to the parental cell line and other isoform cell sublines. qRT-PCR was used to explore the change in expression level of two VM-related genes, EphA2 and VE-cadherin. All WT1 isoform cell sublines showed up-regulation of EphA2 but the levels detected in the isoform B- and isoform C-cell sublines were higher than those observed in other cell sublines. In contrast, significant up-regulation of VE-cadherin was found only in isoform A- and isoform D-cell sublines. Isoform B- and isoform C-cell sublines showed higher rates of cell migration compared to those of other cell sublines, as determined by both wound healing and Transwell assays. Gelatin zymography revealed increased MMP-9 enzyme production in isoform D-cell subline compared to the parental cell line, but this change was not observed in other cell sublines. Western blot analysis showed significantly increased expression of β-catenin in isoform B- and isoform C-cell sublines, compared to parental cell line and other isoform cell sublines. In conclusion, our findings demonstrate that WT1 isoforms play different roles in modulating the VM-forming capacity and metastatic potential of TNBC cells.

Functional non-coding polymorphism in an EPHA2 promoter PAX2 binding site modifies expression and alters the MAPK and AKT pathways

To identify possible genetic variants influencing expression of EPHA2 (Ephrin-receptor Type-A2), a tyrosine kinase receptor that has been shown to be important for lens development and to contribute to both congenital and age related cataract when mutated, the extended promoter region of EPHA2 was screened for variants. SNP rs6603883 lies in a PAX2 binding site in the EPHA2 promoter region. The C (minor) allele decreased EPHA2 transcriptional activity relative to the T allele by reducing the binding affinity of PAX2. Knockdown of PAX2 in human lens epithelial (HLE) cells decreased endogenous expression of EPHA2. Whole RNA sequencing showed that extracellular matrix (ECM), MAPK-AKT signaling pathways and cytoskeleton related genes were dysregulated in EPHA2 knockdown HLE cells. Taken together, these results indicate a functional non-coding SNP in EPHA2 promoter affects PAX2 binding and reduces EPHA2 expression. They further suggest that decreasing EPHA2 levels alters MAPK, AKT signaling pathways and ECM and cytoskeletal genes in lens cells that could contribute to cataract. These results demonstrate a direct role for PAX2 in EPHA2 expression and help delineate the role of EPHA2 in development and homeostasis required for lens transparency.

Hypermethylation of the HIC1 promoter and aberrant expression of HIC1/SIRT1 contribute to the development of thyroid papillary carcinoma

Hypermethylation leading to the loss of hypermethylated in cancer-1 (HIC1) gene expression occurs in many different types of human cancer. HIC1 is a transcriptional repressor that directly binds to the promoter region of NAD-dependent deacetylase sirtuin-1 (SIRT1). SIRT1 functions in cell growth, is anti-apoptotic, protect neurons, functions in senescence, and regulates energy restriction. Epigenetic modification and dysregulation affecting the HIC1/SIRT1 axis is potentially important for the development of malignancies. However, the importance of HIC1 expression in the development of papillary thyroid carcinoma, especially in Chinese patients, is uncertain. Therefore, we assessed the level of methylation in the HIC1 promoter and the mRNA and protein expression levels of HIC1 and SIRT1 in human thyroid papillary carcinoma and tumor adjacent control tissues. The demethylation reagent 5-aza-2'-deoxyctidine (5-aza-dc) and an HIC1 overexpression plasmid were used to manipulate the HIC1/SIRT1 pathway, and the effects on cell senescence, apoptosis, and cell cycle progression were assessed. Compared to normal thyroid tissue, thyroid tumors had lower expression of HIC1 and higher SIRT1 expression. The level of HIC1 methylation was also higher in thyroid carcinoma tissues than adjacent tissues. HIC1 expression was closely correlated with patient age and tumor progression. Restoration of HIC1 expression through an overexpression plasmid or 5-aza-dC treatment reduced SIRT1 expression and cell proliferation, and led to senescence, cell cycle arrest, and apoptosis. Aberrant expression of HIC1/SIRT1 and hypermethylation of the HIC1 promoter may be critical for the development and progression of papillary thyroid cancer.

HIC1 epigenetically represses CIITA transcription in B lymphocytes

Differentiation of B lymphocytes into isotope-specific plasma cells represents a hallmark event in adaptive immunity. During B cell maturation, expression of the class II transactivator (CIITA) gene is down-regulated although the underlying epigenetic mechanism is not completely defined. Here we report that hypermethylated in cancer 1 (HIC1) was up-regulated in differentiating B lymphocytes paralleling CIITA repression. Over-expression of HIC1 directly repressed endogenous CIITA transcription in B cells. Reporter assay and chromatin immunoprecipitation (ChIP) assay confirmed that HIC1 bound to the proximal CIITA type III promoter (-545/-113); mutation of a conserved HIC1 site within this region abrogated CIITA trans-repression. More important, depletion of HIC1 with small interfering RNA (siRNA) restored CIITA expression in differentiating B cells. Mechanistically, HIC1 preferentially interacted with and recruited DNMT1 and DNMT3b to the CIITA promoter to synergistically repress CIITA transcription. On the contrary, silencing of DNMT1/DNMT3b or inhibition of DNMT activity with 5-aza-dC attenuated CIITA trans-repression. Therefore, our data identify HIC1 as a novel factor involved in B cell differentiation acting as an epigenetic repressor of CIITA transcription.

Epigenetic silencing of HIC1 promotes epithelial-mesenchymal transition and drives progression in esophageal squamous cell carcinoma

Downregulation of the novel tumor suppressor gene HIC1 (hypermethylated in cancer 1) occurs frequently in various tumors where it causes tumor progression and metastasis. In this study, we investigated a role of HIC1 in esophageal squamous cell carcinoma (ESCC) and the underlying mechanisms. Downregulation of HIC1 occurred in approximately 70% of primary ESCCs at both mRNA and protein level where it was associated significantly with vascular invasion, advanced clinical stage, lymph node metastasis, and poor disease free survival (DFS). The promoter methylation analyses suggested that loss of HIC1 expression was mediated by epigenetic mechanisms. Functional studies established that ectopic re-expression of HIC1 in ESCC cells inhibited cell proliferation, clonogenicity, cell motility, tumor formation and epithelial-mesenchymal transition (EMT). Our results decipher the mechanism through which HIC1 deficiency induce ESCC cells to undergo EMT and promote tumor progression and metastasis through activation of EphA2 signaling pathway. Together, loss of the regulation of EphA2 pathway through HIC1 epigenetic silencing could be an important mechanism in the ESCC progression. We identify a novel pathway that linking HIC1 downregulation to EphA2-inducing EMT in ESCC cells and may shed light on the development of novel anti-tumor therapeutics.

HIC1 Expression Distinguishes Intestinal Carcinomas Sensitive to Chemotherapy

Neoplastic growth is frequently associated with genomic DNA methylation that causes transcriptional silencing of tumor suppressor genes. We used a collection of colorectal polyps and carcinomas in combination with bioinformatics analysis of large datasets to study the expression and methylation of Hypermethylated in cancer 1 (HIC1), a tumor suppressor gene inactivated in many neoplasms. In premalignant stages, HIC1 expression was decreased, and the decrease was linked to methylation of a specific region in the HIC1 locus. However, in carcinomas, the HIC1 expression was variable and, in some specimens, comparable to healthy tissue. Importantly, high HIC1 production distinguished a specific type of chemotherapy-responsive tumors.

EphB1 Suppression in Acute Myelogenous Leukemia: Regulating the DNA Damage Control System

Loss of ephrin receptor (EphB1) expression may associate with aggressive cancer phenotypes; however, the mechanism of action remains unclear. To gain detailed insight into EphB1 function in acute myelogenous leukemia (AML), comprehensive analysis of EphB1 transcriptional regulation was conducted. In AML cells, EphB1 transcript was inversely correlated with EphB1 promoter methylation. The presence of EphB1 allowed EfnB1 ligand-mediated p53 DNA binding, leading to restoration of the DNA damage response (DDR) cascade by the activation of ATR, Chk1, p53, p21, p38, CDK1(tyr15), and Bax, and downregulation of HSP27 and Bcl2. Comparatively, reintroduction of EphB1 expression in EphB1-methylated AML cells enhanced the same cascade of ATR, Chk1, p21, and CDK1(tyr15), which consequently enforced programmed cell death. Interestingly, in pediatric AML samples, EphB1 peptide phosphorylation and mRNA expression were actively suppressed as compared with normal bone marrow, and a significant percentage of the primary AML specimens had EphB1 promoter hypermethylation. Finally, EphB1 repression associated with a poor overall survival in pediatric AML. Combined, the contribution of EphB1 to the DDR system reveals a tumor-suppressor function for EphB1 in pediatric AML.

IMPLICATIONS

The tumor-suppressor function of EphB1 is clinically relevant across many malignancies, suggesting that EphB1 is an important regulator of common cancer cell transforming pathways.

Subcellular localization of MTA proteins in normal and cancer cells

The subcellular localization of a protein is closely linked to and indicates its function. The metastatic tumor antigen (MTA) family has been under continuous investigation since its identification two decades ago. MTA1, MTA2, and MTA3 are the main members of the MTA family. MTA1, as the representative member of this family, has been shown to be widely expressed in both embryonic and adult tissues, as well as in normal and cancerous conditions, indicating that MTA1 has functions both in physiological and pathological contexts. MTA1 is expressed at a higher level in most cancers than in their normal tissue counterparts. Even in normal cells, MTA1 levels vary a great deal from tissue to tissue. Importantly, MTA1 shows a multiple localization pattern in the cell, as do MTA2 and MTA3. Different MTA components in different subcellular compartments may exert different molecular functions in the cell. Previous studies revealed that MTA1 and MTA2 are predominately localized to the nucleus, while MTA3 is observed in both the nucleus and cytoplasm. Recent studies have reported that MTA1 is located in the nucleus, cytoplasm, and the nuclear envelope. In the nucleus, MTA1 dynamically interacts with chromatin in a MTA1-K532 methylation-dependent manner, whereas cytoplasmic MTA1 binds to the microtubule skeleton. MTA1 also shows a dynamic distribution during the cell cycle. Further investigations are needed to identify the exact subcellular localizations of MTA proteins. We review the sub-cellular localization patterns of the MTA family members and give a comprehensive overview of their respective molecular activities in multiple contexts.

Metabolic inflexibility impairs insulin secretion and results in MODY-like diabetes in triple FoxO-deficient mice

Pancreatic β cell failure in type 2 diabetes is associated with functional abnormalities of insulin secretion and deficits of β cell mass. It's unclear how one begets the other. We have shown that loss of β cell mass can be ascribed to impaired FoxO1 function in different models of diabetes. Here we show that ablation of the three FoxO genes (1, 3a, and 4) in mature β cells results in early-onset, maturity-onset diabetes of the young (MODY)-like diabetes, with abnormalities of the MODY networks Hnf4α, Hnf1α, and Pdx1. FoxO-deficient β cells are metabolically inflexible, i.e., they preferentially utilize lipids rather than carbohydrates as an energy source. This results in impaired ATP generation and reduced Ca(2+)-dependent insulin secretion. The present findings demonstrate a secretory defect caused by impaired FoxO activity that antedates dedifferentiation. We propose that defects in both pancreatic β cell function and mass arise through FoxO-dependent mechanisms during diabetes progression.

Transcriptional regulation of the human thromboxane A2 receptor gene by Wilms' tumor (WT)1 and hypermethylated in cancer (HIC) 1 in prostate and breast cancers

The prostanoid thromboxane (TX) A(2) plays a central role in hemostasis and is increasingly implicated in neoplastic disease, including prostate and breast cancers. In humans, TXA(2) signals through the TPα and TPβ isoforms of the T prostanoid receptor, two structurally related receptors transcriptionally regulated by distinct promoters, Prm1 and Prm3, respectively, within the TP gene. Focusing on TPα, the current study investigated its expression and transcriptional regulation through Prm1 in prostate and breast cancers. Expression of TPα correlated with increasing prostate and breast tissue tumor grade while the TXA(2) mimetic U46619 promoted both proliferation and migration of the respective prostate (PC3) and breast (MCF-7 and MDA-MD-231) derived-carcinoma cell lines. Through 5' deletional and genetic reporter analyses, several functional upstream repressor regions (URRs) were identified within Prm1 in PC3, MCF-7 and MDA-MB-231 cells while site-directed mutagenesis identified the tumor suppressors Wilms' tumor (WT)1 and hypermethylated in cancer (HIC) 1 as the trans-acting factors regulating those repressor regions. Chromatin immunoprecipitation (ChIP) studies confirmed that WT1 binds in vivo to multiple GC-enriched WT1 cis-elements within the URRs of Prm1 in PC3, MCF-7 and MDA-MB-231 cells. Furthermore, ChIP analyses established that HIC1 binds in vivo to the HIC1((b))cis-element within Prm1 in PC3 and MCF-7 cells but not in the MDA-MB-231 carcinoma line. Collectively, these data establish that WT1 and HIC1, both tumor suppressors implicated in prostate and breast cancers, transcriptionally repress TPα expression and thereby provide a strong genetic basis for understanding the role of TXA2 in the progression of certain human cancers.

HIC1 interacts with and modulates the activity of STAT3

HIC1 (hypermethylated in cancer 1) is a tumor suppressor gene, expression of which is frequently suppressed in human cancers. Very little is known about the molecular basis of HIC1 in antagonizing oncogenic pathways. Here, we report that HIC1 forms complexes with the signal transducers and activators of transcription 3 (STAT3) and attenuates STAT3-mediated transcription. STAT3 was identified as a HIC1-interacting protein by affinity capture and followed by mass spectrometry analysis. Overexpression or depletion of HIC1 resulted in decreased or increased levels of interleukin-6 (IL-6)/oncostatin M (OSM)-induced STAT3-mediated reporter activity and expression of target genes such as VEGF and c-Myc, respectively. Furthermore, HIC1 suppressing the VEGF and c-Myc promoter activity and the colony formation of MDA-MB 231 cells were STAT3-dependent. Further studies showed that HIC1 interacts with the DNA binding domain of STAT3 and suppresses the binding of STAT3 to its target gene promoters. Domain mapping study revealed that HIC1 C-terminal domain binds to STAT3. HIC1 mutant defective in STAT3 interaction reduced its repressive effect on STAT3 DNA binding activity, the reporter activity and gene expression of the VEGF and c-Myc genes, and cell growth in MDA-MB 231 cells. Altogether, our findings not only provide a novel role of HIC1 in antagonizing STAT3-mediated activation of VEGF and c-Myc gene expression and cell growth, but also elucidate a molecular basis underlying the inhibitory effect of HIC1 on STAT3 transcriptional potential.

Eph receptors and ephrins as targets for cancer therapy

Eph receptor tyrosine kinases and their ephrin ligands are involved in various signalling pathways and mediate critical steps of a wide variety of physiological and pathological processes. Increasing experimental evidence demonstrates that both Eph receptor and ephrin ligands are overexpressed in a number of human tumours, and are associated with tumour growth, invasiveness and metastasis. In this regard, the Eph/ephrin system provides the foundation for potentially exciting new targets for anticancer therapies for Eph-expressing tumours. The purpose of this review is to outline current advances in the role of Eph receptors and ephrin ligands in cancer, and to discuss novel therapeutic approaches of anticancer therapies.

Small activating RNA restores the activity of the tumor suppressor HIC-1 on breast cancer

HIC-1 is a gene that is hypermethylated in cancer, and commonly downregulated in human breast cancer. However, the precise mechanisms and molecular pathways regulated by HIC-1 remain unclear. We assessed HIC-1 expression on a tissue microarray containing 80 cases of breast cancer. We also analyzed its biological function by restoring HIC-1 expression using 5-aza-2′ deoxycytidine (5-CdR) and small-activating RNAs for the reversal of HIC-1 tumor suppressive effects on MCF-7 and MDA-MB-231 cell lines. An Agilent Q44h global expressing microarray was probed after restoring the expression of HIC-1. Data demonstrated that HIC-1 expression was reduced significantly in breast cancer tissues. HIC-1 immunohistochemistry resulted in mean staining scores in cancer tissue and normal ductal epithelia of 3.54 and 8.2, respectively (p<0.01). 5-CdR partially reversed HIC-1 expression, and modulated cell growth and apoptosis. dsHIC1-2998, an saRNA, showed activating efficacy in breast cancer cells. A group of differentially expressed genes were characterized by cDNA microarray. Upon saRNA treatment, genes upregulated included those involved in immune activation, cell cycle interference, the induction of apoptosis, anti-metastasis, and cell differentiation. Downregulated genes included oncogenes and those that play roles in cell invasion, cell growth, and cell division. Our findings may provide valuable resources not only for gene functional studies, but also for potential clinical applications to develop novel drug targets.

The Reelin receptors ApoER2 and VLDLR are direct target genes of HIC1 (Hypermethylated In Cancer 1)

The tumor suppressor gene HIC1 (Hypermethylated In Cancer 1) is located in 17p13.3 a region frequently hypermethylated or deleted in tumors and in a contiguous-gene syndrome, the Miller-Dieker syndrome which includes classical lissencephaly (smooth brain) and severe developmental defects. HIC1 encodes a transcriptional repressor involved in the regulation of growth control, DNA damage response and cell migration properties. We previously demonstrated that the membrane-associated G-protein-coupled receptors CXCR7, ADRB2 and the tyrosine kinase receptor EphA2 are direct target genes of HIC1. Here we show that ectopic expression of HIC1 in U2OS and MDA-MB-231 cell lines decreases expression of the ApoER2 and VLDLR genes, encoding two canonical tyrosine kinase receptors for Reelin. Conversely, knock-down of endogenous HIC1 in BJ-Tert normal human fibroblasts through RNA interference results in the up-regulation of these two Reelin receptors. Finally, through chromatin immunoprecipitation (ChIP) in BJ-Tert fibroblasts, we demonstrate that HIC1 is a direct transcriptional repressor of ApoER2 and VLDLR. These data provide evidence that HIC1 is a new regulator of the Reelin pathway which is essential for the proper migration of neuronal precursors during the normal development of the cerebral cortex, of Purkinje cells in the cerebellum and of mammary epithelial cells. Deregulation of this pathway through HIC1 inactivation or deletion may contribute to its role in tumor promotion. Moreover, HIC1, through the direct transcriptional repression of ATOH1 and the Reelin receptors ApoER2 and VLDLR, could play an essential role in normal cerebellar development.

DNA double-strand breaks lead to activation of hypermethylated in cancer 1 (HIC1) by SUMOylation to regulate DNA repair

HIC1 (hypermethylated in cancer 1) is a tumor suppressor gene frequently epigenetically silenced in human cancers. HIC1 encodes a transcriptional repressor involved in the regulation of growth control and DNA damage response. We previously demonstrated that HIC1 can be either acetylated or SUMOylated on lysine 314. This deacetylation/SUMOylation switch is governed by an unusual complex made up of SIRT1 and HDAC4 which deacetylates and thereby favors SUMOylation of HIC1 by a mechanism not yet fully deciphered. This switch regulates the interaction of HIC1 with MTA1, a component of the NuRD complex and potentiates the repressor activity of HIC1. Here, we show that HIC1 silencing in human fibroblasts impacts the repair of DNA double-strand breaks whereas ectopic expression of wild-type HIC1, but not of nonsumoylatable mutants, leads to a reduced number of γH2AX foci induced by etoposide treatment. In this way, we demonstrate that DNA damage leads to (i) an enhanced HDAC4/Ubc9 interaction, (ii) the activation of SIRT1 by SUMOylation (Lys-734), and (iii) the SUMO-dependent recruitment of HDAC4 by SIRT1 which permits the deacetylation/SUMOylation switch of HIC1. Finally, we show that this increase of HIC1 SUMOylation favors the HIC1/MTA1 interaction, thus demonstrating that HIC1 regulates DNA repair in a SUMO-dependent way. Therefore, epigenetic HIC1 inactivation, which is an early step in tumorigenesis, could contribute to the accumulation of DNA mutations through impaired DNA repair and thus favor tumorigenesis.

Deciphering HIC1 control pathways to reveal new avenues in cancer therapeutics

INTRODUCTION

The tumor suppressor gene HIC1 (Hypermethylated in Cancer 1), which encodes a transcriptional repressor with multiple partners and multiple targets, is epigenetically silenced but not mutated in tumors. HIC1 has broad biological roles during normal development and is implicated in many canonical processes of cancer such as control of cell growth, cell survival upon genotoxic stress, cell migration, and motility.

AREAS COVERED

The HIC1 literature herein discussed includes its discovery as a candidate tumor suppressor gene hypermethylated or deleted in many human tumors, animal models establishing it as tumor suppressor gene, its role as a sequence-specific transcriptional repressor recruiting several chromatin regulatory complexes, its cognate target genes, and its functional roles in normal tissues. Finally, this review discusses how its loss of function contributes to the early steps in tumorigenesis.

EXPERT OPINION

Given HIC1's ability to direct repressive complexes to sequence-specific binding sites associated with its target genes, its loss results in specific changes in the transcriptional program of the cell. An understanding of this program through identification of HIC1's target genes and their involvement in feedback loops and cell process regulation will yield the ability to leverage this knowledge for therapeutic translation.

Signification of Hypermethylated in Cancer 1 (HIC1) as Tumor Suppressor Gene in Tumor Progression

Hypermethylated in cancer 1(HIC1) was identified as a strong suppressor gene in chromosome region 17p13.3 telomeric to TP53. This gene encodes a transcriptional repressor and is ubiquitously expressed in normal tissues but downexpressed in different tumor tissues where it is hypermethylated. The hypermethylation of this chromosomal region leads to epigenetic inactivation of HIC1, which would prompt cancer cells to alter survival and signaling pathways or specific transcription factors during the period of tumorigenesis. In vitro, HIC1 function is mainly a sequence-specific transcriptional repressor interacting with a still growing range of histone deacetylase(HDAC)-dependent and HDAC-independent corepressor complexes. Furthermore, a role for HIC1 in tumor development is firmly supported by Hic1 deficient mouse model and two double heterozygote models cooperate with p53 and Ptch1. Notably, our findings suggest that potential factors derived from tumor microenviroment may play a role in modulating HIC1 expression in tumor cells by epigenetic modification, which is responsible for tumor progression. In this review, we will describe genomic and proteinic structure of HIC1, and summary the potential role of HIC1 in human various solid tumors and leukemia, and explore the influence of tumor microenviroment on inducing HIC1 expression in tumor cells.

Hypermethylated in cancer 1 (HIC1) recruits polycomb repressive complex 2 (PRC2) to a subset of its target genes through interaction with human polycomb-like (hPCL) proteins

HIC1 (hypermethylated in cancer 1) is a tumor suppressor gene epigenetically silenced or deleted in many human cancers. HIC1 is involved in regulatory loops modulating p53- and E2F1-dependent cell survival, growth control, and stress responses. HIC1 is also essential for normal development because Hic1-deficient mice die perinatally and exhibit gross developmental defects throughout the second half of development. HIC1 encodes a transcriptional repressor with five C(2)H(2) zinc fingers mediating sequence-specific DNA binding and two repression domains: an N-terminal BTB/POZ domain and a central region recruiting CtBP and NuRD complexes. By yeast two-hybrid screening, we identified the Polycomb-like protein hPCL3 as a novel co-repressor for HIC1. Using multiple biochemical strategies, we demonstrated that HIC1 interacts with hPCL3 and its paralog PHF1 to form a stable complex with the PRC2 members EZH2, EED, and Suz12. Confirming the implication of HIC1 in Polycomb recruitment, we showed that HIC1 shares some of its target genes with PRC2, including ATOH1. Depletion of HIC1 by siRNA interference leads to a partial displacement of EZH2 from the ATOH1 promoter. Furthermore, in vivo, ATOH1 repression by HIC1 is associated with Polycomb activity during mouse cerebellar development. Thus, our results identify HIC1 as the first transcription factor in mammals able to recruit PRC2 to some target promoters through its interaction with Polycomb-like proteins.

Loss of Hypermethylated in Cancer 1 (HIC1) in breast cancer cells contributes to stress-induced migration and invasion through β-2 adrenergic receptor (ADRB2) misregulation

The transcriptional repressor HIC1 (Hypermethylated in Cancer 1) is a tumor suppressor gene inactivated in many human cancers including breast carcinomas. In this study, we show that HIC1 is a direct transcriptional repressor of β-2 adrenergic receptor (ADRB2). Through promoter luciferase activity, chromatin immunoprecipitation (ChIP) and sequential ChIP experiments, we demonstrate that ADRB2 is a direct target gene of HIC1, endogenously in WI-38 cells and following HIC1 re-expression in breast cancer cells. Agonist-mediated stimulation of ADRB2 increases the migration and invasion of highly malignant MDA-MB-231 breast cancer cells but these effects are abolished following HIC1 re-expression or specific down-regulation of ADRB2 by siRNA treatment. Our results suggest that early inactivation of HIC1 in breast carcinomas could predispose to stress-induced metastasis through up-regulation of the β-2 adrenergic receptor.