3090

HIC1

ZBTB29|ZNF901|hic-1;hypermethylated in cancer 1;HIC1;hypermethylated in cancer 1

hypermethylated in cancer 1 protein|zinc finger and BTB domain-containing protein 29

17p13.3

protein-coding

HIC1 is a candidate tumor suppressor gene which is frequently hypermethylated in human tumors, and its location within the Miller-Dieker syndromes critical deletion region at chromosome 17p13.3 makes it a candidate gene for involvement in this gene deletion syndrome. To study the function of murine Hic1 in development, we have created Hic1 -deficient mice. These animals die perinatally and exhibit varying combinations of gross developmental defects throughout the second half of development, including acrania, exencephaly, cleft palate, limb abnormalities and omphalocele. These findings demonstrate a role for Hic1 in the development of structures affected in the Miller-Dieker syndrome, and provide functional evidence to strengthen its candidacy as a gene involved in this disorder.

Database searches identified on chromosome 22q11.2, a region subject to translocations, an homologue of the HIC1 (hypermethylated in cancer) candidate tumor suppressor gene located at 17p13.3. This gene was termed HRG22 for HIC1-related gene on chromosome 22. We have characterized a new HRG22 upstream coding exon and defined the complete coding sequence of the human and zebrafish HRG22 genes. Alignment of the HRG22 and HIC1 proteins from various species revealed high sequence homology in their N-terminal BTB/POZ and five C-terminal C(2)H(2) zinc finger domains and highlighted a conserved GLDLSKK/R peptide in their middle region. The full-length HRG22 and HIC1 proteins colocalize onto nuclear dots and share several functional properties since their BTB/POZ domains heterodimerize and are autonomous transcriptional repression domain insensitive to Trichostatin A, a histone deacetylase (HDAC) inhibitor. Thus, HIC1 and HRG22 define a subgroup of BTB/POZ domains unable to recruit repressing complexes containing an HDAC activity.

HIC1 (hypermethylated in cancer) and its close relative HRG22 (HIC1-related gene on chromosome 22) encode transcriptional repressors with five C(2)H(2) zinc fingers and an N-terminal BTB/POZ autonomous transcriptional repression domain that is unable to recruit histone deacetylases (HDACs). Alignment of the HIC1 and HRG22 proteins from various species highlighted a perfectly conserved GLDLSKK/R motif highly related to the consensus CtBP interaction motif (PXDLSXK/R), except for the replacement of the virtually invariant proline by a glycine. HIC1 strongly interacts with mCtBP1 both in vivo and in vitro through this conserved GLDLSKK motif, thus extending the CtBP consensus binding site. The BTB/POZ domain does not interact with mCtBP1, but the dimerization of HIC1 through this domain is required for the interaction with mCtBP1. When tethered to DNA by fusion with the Gal4 DNA-binding domain, the HIC1 central region represses transcription through interactions with CtBP in a trichostatin A-sensitive manner. In conclusion, our results demonstrate that HIC1 mediates transcriptional repression by both HDAC-independent and HDAC-dependent mechanisms and show that CtBP is a HIC1 corepressor that is recruited via a variant binding site.

The BTB/POZ transcriptional repressor HIC1 (Hypermethylated in cancer 1) is a tumor suppressor gene located at chromosome 17p13.3, a region frequently hypermethylated or deleted in human tumors and in a contiguous-gene syndrome, the Miller-Dieker syndrome. The human and murine HIC1 genes are composed of two alternative 5 exons, 1a and 1b fused to a large second coding exon 2. Exon 1a is a noncoding exon associated with a major G-C-rich promoter whereas exon 1b is a downstream coding exon associated with a minor TATA box promoter. By human-mouse genome comparison, we have identified a short upstream conserved sequence containing G-C boxes which were shown to be functional. Transcripts initiating from this new promoter were detected in various human and mouse tissues and contained a long 5-UTR sequence, called 1c which encompass the G-C-rich promoter associated with exon 1a and uses the same splice donor site. RT-PCR analyses of two primary breast epithelial cell lines identified two other 5-UTRs generated by alternative splicing within exon 1c. Our results thus highlight the existence of an unexpected complex transcriptional regulation of HIC1.

HIC1 (hypermethylated in cancer 1) is a tumor suppressor gene located at chromosome 17p13.3, a region frequently hypermethylated or deleted in human tumors and in a contiguous-gene syndrome, the Miller-Dieker syndrome. HIC1 is a transcriptional repressor containing five Kruppel-like C(2)H(2) zinc fingers and an N-terminal dimerization and autonomous repression domain called BTB/POZ. Although some of the HIC1 transcriptional repression mechanisms have been recently deciphered, target genes are still to be discovered. In this study, we determined the consensus binding sequence for HIC1 and investigated its DNA binding properties. Using a selection and amplification of binding sites technique, we identified the sequence 5-(C)/(G)NG(C)/(G)GGGCA(C)/(A) CC-3 as an optimal binding site. In silico and functional analyses fully validated this consensus and highlighted a GGCA core motif bound by zinc fingers 3 and 4. The BTB/POZ domain inhibits the binding of HIC1 to a single site but mediates cooperative binding to a probe containing five concatemerized binding sites, a property shared by other BTB/POZ proteins. Finally, full-length HIC1 proteins transiently expressed in RK13 cells and more importantly, endogenous HIC1 proteins from the DAOY medulloblastoma cell line, repress the transcription of a reporter gene through their direct binding to these sites, as confirmed by chromatin immunoprecipitation experiments. The definition of the HIC1-specific DNA binding sequence as well as the requirement for multiple sites for optimal binding of the full-length protein are mandatory prerequisites for the identification and analyses of bona fide HIC1 target genes.

tumor suppressor HIC1 (hypermethylated in cancer 1) is a gene that is essential for mammalian development, epigenetically silenced in many human tumors, and involved in a complex pathway regulating P53 tumor suppression activity. HIC1 encodes a sequence-specific transcriptional repressor containing five Kruppel-like C(2)H(2) zinc fingers and an N-terminal BTB/POZ repression domain. Here, we show that endogenous HIC1 is SUMOylated in vivo on a phylogenetically conserved lysine, K314, located in the central region which is a second repression domain. K314R mutation does not influence HIC1 subnuclear localization but significantly reduces its transcriptional repression potential, as does the mutation of the other conserved residue in the psiKXE consensus, E316A, or the overexpression of the deSUMOylase SSP3/SENP2. Furthermore, HIC1 is acetylated in vitro by P300/CBP. Strikingly, the K314R mutant is less acetylated than wild-type HIC1, suggesting that this lysine is a target for both SUMOylation and acetylation. We further show that HIC1 transcriptional repression activity is positively controlled by two types of deacetylases, SIRT1 and HDAC4, which increase the deacetylation and SUMOylation, respectively, of K314. Knockdown of endogenous SIRT1 by the transfection of short interfering RNA causes a significant loss of HIC1 SUMOylation. Thus, this dual-deacetylase complex induces either a phosphorylation-dependent acetylation-SUMOylation switch through a psiKXEXXSP motif, as previously shown for MEF2, or a phosphorylation-independent switch through a psiKXEP motif, as shown here for HIC1, since P317A mutation severely impairs HIC1 acetylation. Finally, our results demonstrate that HIC1 is a target of the class III deacetylase SIRT1 and identify a new posttranslational modification step in the P53-HIC1-SIRT1 regulatory loop.

Deletions in the short arm of chromosome 17 (17p) involving the tumor suppressor TP53 occur in up to 20% of diffuse large B-cell lymphomas (DLBCLs). Although inactivation of both alleles of a tumor suppressor gene is usually required for tumor development, the overlap between TP53 deletions and mutations is poorly understood in DLBCLs, suggesting the possible existence of additional tumor suppressor genes in 17p. Using a bacterial artificial chromosome (BAC) and Phage 1 artificial chromosome (PAC) contig, we here define a minimally deleted region in DLBCLs encompassing approximately 0.8 MB telomeric to the TP53 locus. This genomic region harbors the tumor suppressor Hypermethylated in cancer 1 (HIC1). Methylation-specific PCR demonstrated hypermethylation of HIC1 exon 1a in a substantial subset of DLBCLs, which is accompanied by simultaneous HIC1 deletion of the second allele in 90% of cases. In contrast, HIC1 inactivation by hypermethylation was rarely encountered in DLBCLs without concomitant loss of the second allele. DLBCL patients with complete inactivation of both HIC1 and TP53 may be characterized by an even inferior clinical course than patients with inactivation of TP53 alone, suggesting a functional cooperation between these two proteins. These findings strongly imply HIC1 as a novel tumor suppressor in a subset of DLBCLs.

The Hypermethylated in cancer 1 (HIC1) gene encodes a zinc finger transcriptional repressor that cooperates with p53 to suppress cancer development. We and others recently showed that HIC1 is a transcriptional target of p53. To identify additional transcriptional regulators of HIC1, we screened a set of transcription factors for regulation of a human HIC1 promoter reporter. We found that E2F1 strongly activates the full-length HIC1 promoter reporter. Promoter deletions and mutations identified two E2F responsive elements in the HIC1 core promoter region. Moreover, in vivo binding of E2F1 to the HIC1 promoter was shown by chromatin immunoprecipitation assays in human TIG3 fibroblasts expressing tamoxifen-activated E2F1. In agreement, activation of E2F1 in TIG3-E2F1 cells markedly increased HIC1 expression. Interestingly, expression of E2F1 in the p53(-/-) hepatocellular carcinoma cell line Hep3B led to an increase of endogenous HIC1 mRNA, although bisulfite genomic sequencing of the HIC1 promoter revealed that the region bearing the two E2F1 binding sites is hypermethylated. In addition, endogenous E2F1 induced by etoposide treatment bound to the HIC1 promoter. Moreover, inhibition of E2F1 strongly reduced the expression of etoposide-induced HIC1. In conclusion, we identified HIC1 as novel E2F1 transcriptional target in DNA damage responses.

The tumor suppressor gene HIC1 (Hypermethylated in cancer 1) that is epigenetically silenced in many human tumors and is essential for mammalian development encodes a sequence-specific transcriptional repressor. The few genes that have been reported to be directly regulated by HIC1 include ATOH1, FGFBP1, SIRT1, and E2F1. HIC1 is thus involved in the complex regulatory loops modulating p53-dependent and E2F1-dependent cell survival and stress responses. We performed genome-wide expression profiling analyses to identify new HIC1 target genes, using HIC1-deficient U2OS human osteosarcoma cells infected with adenoviruses expressing either HIC1 or GFP as a negative control. These studies identified several putative direct target genes, including CXCR7, a G-protein-coupled receptor recently identified as a scavenger receptor for the chemokine SDF-1/CXCL12. CXCR7 is highly expressed in human breast, lung, and prostate cancers. Using quantitative reverse transcription-PCR analyses, we demonstrated that CXCR7 was repressed in U2OS cells overexpressing HIC1. Inversely, inactivation of endogenous HIC1 by RNA interference in normal human WI38 fibroblasts results in up-regulation of CXCR7 and SIRT1. In silico analyses followed by deletion studies and luciferase reporter assays identified a functional and phylogenetically conserved HIC1-responsive element in the human CXCR7 promoter. Moreover, chromatin immunoprecipitation (ChIP) and ChIP upon ChIP experiments demonstrated that endogenous HIC1 proteins are bound together with the C-terminal binding protein corepressor to the CXCR7 and SIRT1 promoters in WI38 cells. Taken together, our results implicate the tumor suppressor HIC1 in the transcriptional regulation of the chemokine receptor CXCR7, a key player in the promotion of tumorigenesis in a wide variety of cell types.

An intractable problem impeding breast cancer treatment by the most frequently prescribed endocrine therapy tamoxifen is the inevitable development of resistance, and the molecular mechanisms underlying this loss of responsiveness by breast cancers have been under intense investigation but are not yet fully elucidated. Our recent reports demonstrated that the tumor suppressor heavily methylated in cancers 1 (HIC1) plays an essential role in growth suppression mediated by external stimuli. We report here that novel tumor suppressor HIC1 is required for growth suppression by estrogen antagonists in breast cancer cells. We also find that HIC1 expression is dramatically induced by exposure to estrogen antagonists in sensitive cells, via a c-Jun N-terminal kinase 1 (JNK1) and prohibitin-mediated signaling pathway. This induction is lost in spontaneously antagonist-resistant breast cancer cells. Furthermore, reintroducing HIC1 into resistant breast cancer cells restored their sensitivity to the estrogen antagonists, indicating the existence of a novel regulatory mechanism for growth control of breast cancer cells.

The tumor suppressor gene hypermethylated in cancer 1 (HIC1), which encodes a transcriptional repressor, is epigenetically inactivated in various human cancers. In this study, we show that HIC1 is a direct transcriptional repressor of the gene encoding ephrin-A1, a cell surface ligand implicated in the pathogenesis of epithelial cancers. We also show that mouse embryos lacking both Hic1 alleles manifest developmental defects spatially associated with the misexpression of ephrin-A1, and that overexpression of ephrin-A1 is a feature of tumors arising in Hic1 heterozygous mice in which the remaining wild-type allele is epigenetically silenced. In breast cancer, we find that ephrin-A1 expression is common in vivo, but that in cell culture, expression of the EphA receptors is predominant. Restoration of HIC1 function in breast cancer cells leads to a reduction in tumor growth in vivo, an effect that can be partially rescued by co-overexpression of ephrin-A1. Interestingly, overexpression of ephrin-A1 in vitro triggers downregulation of EphA2 and EphA4 levels, resulting in an expression pattern similar to that seen in vivo. We conclude that Hic1 spatially restricts ephrin-A1 expression in development, and that upregulated expression of ephrin-A1 resulting from epigenetic silencing of HIC1 in cancer cells may be an important mechanism in epithelial malignancy.

Hypermethylation at the promoter region is an important epigenetic mechanism underlying the inactivation of tumor suppressor genes and frequently occurs as an early event in the development of different types of cancer including colorectal carcinoma (CRC). The aim of the present study is the detection of methylation status for some tumor suppressor genes including RASSF1A, MGMT, and HIC-1 in both cancerous and precancerous lesions of colorectal mucosa to evaluate the possibility of developing epigenetic biomarker for early detection of Egyptian CRC. Tissue biopsy was collected from 72 patients (36 CRC, 17 adenomatous polyps, and 19 ulcerative colitis), and in addition, adjacent normal-appearing tissues were collected as control. Promoter hypermethylation status for RSSAF1A, MGMT, and HIC-1 genes was detected after isolation of genomic DNA from the tissues samples using methylation-specific PCR technique. High frequency of methylation at MGMT, RASSFA, and HIC-1 was detected in CRC patients (25%, 47.2%, and 41.7% respectively). The highest methylation detected in adenomatous polyps patients was in MGMT gene (47.1%) followed by 35.3% for HIC-1 and only 5.9% for RASSF1A gene. HIC-1 gene exhibited highest frequency of methylation in ulcerative colitis patients (57.8%) whereas it was 26.3% for both RASSF1A and MGMT genes. A nonsignificant association was recorded between the methylation status in different genes examined with the clinicopathological factors except the association between methylation at RASSF1A gene with gender (p=0.005), and it was significant. In conclusion, aberrant hypermethylation at promoter region of RASSFA, MGMT, and HIC-1 genes is involved in Egyptian CRCs. Hypermethylation of MGMT and HIC-1 genes plays an important role in the initiation of disease especially ulcerative colitis-carcinoma pathway.

HIC1 (hypermethylated in cancer 1) is a tumor suppressor gene located on chromosome 17p13.3, a region frequently hypermethylated or deleted in human neoplasias. In mouse, Hic1 is essential for embryonic development and exerts an antitumor role in adult animals. Since Hic1-deficient mice die perinatally, we generated a conditional Hic1 null allele by flanking the Hic1-coding region by loxP sites. When crossed to animals expressing Cre recombinase in a cell-specific manner, the Hic1 conditional mice will provide new insights into the function of Hic1 in developing and mature tissues. Additionally, we used gene targeting to replace sequence-encoding amino acids 186-893 of Hic1 by citrine fluorescent protein cDNA. We demonstrate that the distribution of Hic1-citrine fusion polypeptide corresponds to the expression pattern of wild-type Hic1. Consequently, Hic1-citrine "reporter" mice can be used to monitor the activity of the Hic1 locus using citrine fluorescence.

Previously, we identified 3 overlapping regions showing loss of heterozygosity (LOH, R(1)-R(3) from 11 to 30 cM) on chromosome 17 in 45 primary gastric cancers (GCs). The data indicated the presence of tumor suppressor genes (TSGs) on chromosome 17 involved in GC. Among the putative TSGs in these regions, HIC1 (in SR(1)) and TOB1 (in SR(3)) remain to be examined in GC. By immunohistochemistry (IHC), methylation-specific PCR (MSP) and western blot, we evaluated the expression and regulation status for HIC1 and TOB1 protein in GC. We narrowed down the deletion intervals on chromosome 17 and defined five smaller LOH subregions, SR(1)-SR(5) (0.54 to 3.42 cM), in GC. We found that HIC1 had downregulated expression in 86% (91/106) and was methylated in 87% (26/30) of primary GCs. Of the primary GCs showing downregulation of HIC1 protein, 75% (18/24) had methylated HIC1 gene. TOB1 was either absent or expressed at reduced levels in 75% (73/97) of the GC samples. In addition, a general reduction was found in total and the ratio of unphosphorylated to phosphorylated TOB1 protein levels in the differentiated GC cell lines. Further analysis revealed significant simultaneous downregulation of both HIC1 and TOB1 protein in GC tissue microarray samples (67%, 52/78) and in primary GCs (65%, 11/17). These results indicate that silencing of HIC1 and TOB1 expression is a common occurrence in GC and may contribute to the development and progression of the disease.

Here, we demonstrate that protein-coding RNA transcripts can crosstalk by competing for common microRNAs, with microRNA response elements as the foundation of this interaction. We have termed such RNA transcripts as competing endogenous RNAs (ceRNAs). We tested this hypothesis in the context of PTEN, a key tumor suppressor whose abundance determines critical outcomes in tumorigenesis. By a combined computational and experimental approach, we identified and validated endogenous protein-coding transcripts that regulate PTEN, antagonize PI3K/AKT signaling, and possess growth- and tumor-suppressive properties. Notably, we also show that these genes display concordant expression patterns with PTEN and copy number loss in cancers. Our study presents a road map for the prediction and validation of ceRNA activity and networks and thus imparts a trans-regulatory function to protein-coding mRNAs.

Hypermethylated genomic DNA is a common feature in tumoral tissues, although the prevalence of this modification remains poorly understood. We aimed to determine the frequency of five tumor suppressor (TS) genes in prostate cancer and the correlation between promoter hypermethylation of these genes and low and high grade of prostate carcinomas. A total of 30 prostate tumor specimens were investigated for promoter methylation status of TS hypermethylated in cancer 1 (HIC1), death-associated protein kinase 1 (DAPK1), secreted frizzled-related protein 2 (SFRP2), cyclin-dependent kinase inhibitor 2A (p16), and O-6-methylguanine-DNA methyltransferase (MGMT) genes by using bisulfite modifying method. A high frequency of promoter hypermethylation was found in HIC1 (70.9%), SFRP2 (58.3%), and DAPK1 (33.3%) genes in tumor samples that were examined. The current data show high frequency of hypermethylation changes in HIC1, SFRP2, and DAPK1 genes in prostate carcinomas of high Gleason Score (GS).

HIC-1 (hypermethylated in cancer) is a candidate tumor suppressor gene which is located at 17p13.3, a region which frequently undergoes allelic loss in breast and other human cancers. HIC-1 is proposed to be commonly inactivated in human cancers by hypermethylation of a normally unmethylated dense CpG island which encompasses the entire gene. To study whether HIC-1 inactivation may be important to the development of breast cancer, we first measured methylation of the HIC-1 gene in normal breast ductal tissues from microdissected frozen breast tissues and from epithelial cells purified from mammoplasty specimens. Surprisingly, in all normal breast ductal tissues we found approximately equal amounts of densely methylated HIC-1 and completely unmethylated HIC-1. This is in contrast to most normal tissues, in which all copies of HIC-1 are completely unmethylated. We then evaluated 39 primary breast cancer tissues and found virtually complete methylation of the HIC-1 gene in 26 (67%) of the cases. We also found loss of heterozygosity at the telomeric portion of chromosomal arm 17p in 22 of the 26 cases with strongly methylated HIC-1, suggesting that loss of an unmethylated HIC-1 allele may contribute to the inactivation of HIC-1 in cells with a pre-existing methylated allele. Finally, by RNase protection analysis, HIC-1 was found to be expressed in microdissected normal breast ductal tissues and unmethylated tumors but not in tumors with hypermethylation of the HIC-1 gene. These results indicate that hypermethylation of HIC-1 and associated loss of HIC-1 expression is common in primary breast cancer. Furthermore, the HIC-1 gene is densely methylated in approximately one-half of the alleles in normal breast epithelium, which may predispose this tissue to inactivation of this gene by loss of heterozygosity.

HIC-1 (hypermethylated in cancer), a new candidate tumor suppressor gene located in 17p13.3, encodes a protein with five Kruppel-like C2H2 zinc finger motifs and a N-terminal protein-protein interaction domain called BTB/POZ. These two domains appeared as the only conserved regions found between human HIC-1 and its avian homologue, gammaFBP-B, isolated as a transcriptional repressor of the gammaF-Crystallin gene. We have recloned the HIC-1 gene and found four nucleotide differences within the 3 part of its published coding sequence. The corrected HIC-1 C-terminal end exhibits now significant homology (70%) to the chicken gammaFBP-B C-terminal end and appears thus as a third phylogenetically conserved domain that may serve an important, yet unknown function in HIC-1.