A novel nk-2-related transcription factor associated with human fetal liver and hepatocellular carcinoma

Differential use of the Nkx2.2 NK2 domain in developing pancreatic islets and neurons

The homeodomain transcription factor (TF) Nkx2.2 governs crucial cell fate decisions in several developing organs, including the central nervous system (CNS), pancreas, and intestine. How Nkx2.2 regulates unique targets in these different systems to impact their individual transcriptional programs remains unclear. In this issue of Genes & Development Abarinov and colleagues (pp. 490-504) generated and analyzed mice in which the Nkx2.2 SD is mutated and found that the SD is required for normal pancreatic islet differentiation but dispensable for most aspects of neuronal differentiation.

Nkx2.8 promotes chemosensitivity in bladder urothelial carcinoma via transcriptional repression of MDR1

Multidrug resistance gene 1 (MDR1), a key factor contributing to drug insensitivity, has been associated with treatment failure and poor prognoses in various cancers, including bladder urothelial carcinoma (UC). Here we show that positive Nkx2.8 expression was associated with better prognosis of UC patients received chemotherapy. Patients with positive Nkx2.8 expression had promising prognosis from adjuvant chemotherapy. Enforced expression of Nkx2.8 promotes drug sensitivity of UC cells. Mechanistic investigations showed that Nkx2.8 negatively regulated expression of MDR1 by binds directly to the MDR1 promoter and transcriptionally represses MDR1 expression. P-gp inhibitor reversed chemosensitivity inhibition by Nkx2.8 scilencing. In clinical UC specimens, expression of Nkx2.8 inversely correlated with P-gp expression, and UC patients with Nkx2.8 positivity and low P-gp expression displayed the best prognosis. Our findings uncovered a new mechanism of chemosensitivity in UC cells and proposing Nkx2.8-MDR1 axis as a novel candidate target for therapeutic intervention of UC.

Nkx2.9 Contributes to Mid-Hindbrain Patterning by Regulation of mdDA Neuronal Cell-Fate and Repression of a Hindbrain-Specific Cell-Fate

Nkx2.9 is a member of the NK homeobox family and resembles Nkx2.2 both in homology and expression pattern. However, while Nkx2.2 is required for development of serotonergic neurons, the role of Nkx2.9 in the mid-hindbrain region is still ill-defined. We have previously shown that Nkx2.9 expression is downregulated upon loss of En1 during development. Here, we determined whether mdDA neurons require Nkx2.9 during their development. We show that Nkx2.9 is strongly expressed in the IsO and in the VZ and SVZ of the embryonic midbrain, and the majority of mdDA neurons expressed Nkx2.9 during their development. Although the expression of Dat and Cck are slightly affected during development, the overall development and cytoarchitecture of TH-expressing neurons is not affected in the adult Nkx2.9-depleted midbrain. Transcriptome analysis at E14.5 indicated that genes involved in mid- and hindbrain development are affected by Nkx2.9-ablation, such as Wnt8b and Tph2. Although the expression of Tph2 extends more rostral into the isthmic area in the Nkx2.9 mutants, the establishment of the IsO is not affected. Taken together, these data point to a minor role for Nkx2.9 in mid-hindbrain patterning by repressing a hindbrain-specific cell-fate in the IsO and by subtle regulation of mdDA neuronal subset specification.

Conditions of embryo culture from days 5 to 7 of development alter the DNA methylome of the bovine fetus at day 86 of gestation

PURPOSE

We tested whether in vitro production (IVP) causes changes in DNA methylation in fetal liver and skeletal muscle and if exposure of cultured embryos to colony-stimulating factor 2 (CSF2) alters DNA methylation.

METHODS

Female fetuses were produced by artificial insemination or transfer of an IVP embryo. Embryos were treated from days 5 to 7 after fertilization with CSF2 or vehicle. DNA methylation in fetal liver and skeletal muscle was determined by post-bisulfite adaptor tagging-based sequencing. The degree of DNA methylation for CpG sites in 50-bp windows of the promoter region 500 bp upstream of the transcriptional start site was compared between treatments.

RESULTS

For liver, there were 12 genes (6% of those analyzed) in which DNA methylation was affected by treatment, with one 50-bp window per gene affected by treatment. For muscle, the degree of DNA methylation was affected by treatment for 32 windows (19% of the total windows analyzed) representing 28 distinct genes (23% of analyzed genes). For 19 of the 28 genes in muscle, the greatest deviation in DNA methylation was for the CSF2 group.

CONCLUSION

Results are consistent with alterations in the methylome being one of the mechanisms by which IVP can result in altered fetal development and postnatal function in the resultant offspring. In addition, results indicate that maternally derived cell-signaling molecules can regulate the pattern of DNA methylation.

Computational modeling suggests impaired interactions between NKX2.5 and GATA4 in individuals carrying a novel pathogenic D16N NKX2.5 mutation

NKX2.5, a homeobox containing gene, plays an important role in embryonic heart development and associated mutations are linked with various cardiac abnormalities. We sequenced the NKX2.5 gene in 100 congenital heart disease (CHD) patients and 200 controls. Our analysis revealed a total of 7 mutations, 3 in intronic region, 3 in coding region and 1 in 3’ UTR. Of the above mutations, one mutation was found to be associated with tetralogy of fallot (TOF) and two (rs2277923 and a novel mutation, D16N) were strongly associated with VSD. A novel missense mutation, D16N (p-value =0.009744), located in the tinman (TN) region and associated with ventricular septal defect (VSD), is the most significant findings of this study. Computational analysis revealed that D16N mutation is pathogenic in nature. Through the molecular modeling, docking and molecular dynamics simulation studies, we have identified the location of mutant D16N in NKX2.5 and its interaction map with other partners at the atomic level. We found NKX2.5-GATA4 complex is stable, however, in case of mutant we observed significant conformational changes and loss of key polar interactions, which might be a cause of the pathogenic behavior. This study underscores the structural basis of D16N pathogenic mutation in the regulation of NKX2.5 and how this mutation renders the structural-functional divergence that possibly leading towards the diseased state.

Nkx2.8 Inhibits Epithelial-Mesenchymal Transition in Bladder Urothelial Carcinoma via Transcriptional Repression of Twist1

Epithelial-to-mesenchymal transition (EMT) promotes metastasis, which is the main cause of bladder urothelial carcinoma-related death. Loss of the candidate tumor-suppressor gene Nkx2.8 has been associated with urothelial carcinoma lymph node metastasis. Here, we show that enforced expression of Nkx2.8 is sufficient to inhibit EMT, reduce motility, and blunt invasiveness of urothelial carcinoma cells. Mechanistic investigations showed that Nkx2.8 negatively regulated expression of the EMT inducer Twist1 in urothelial carcinoma cells, at both the level of mRNA and protein accumulation. Nkx2.8 bound directly to the promoter region of this gene and transcriptionally repressed its expression. Twist1 upregulation reversed EMT inhibition by Nkx2.8, restoring the invasive phenotype of urothelial carcinoma cells. In clinical urothelial carcinoma specimens, expression of Nkx2.8 inversely correlated with Twist1 expression, and urothelial carcinoma patients with Nkx2.8 positivity and low Twist1 expression displayed the best prognosis. Our findings highlight the Nkx2.8-Twist1 axis as candidate target for therapeutic intervention in advanced urothelial carcinoma.Significance: These findings highlight a novel EMT signaling axis as a candidate target for therapeutic intervention in advanced urothelial carcinomas. Cancer Res; 78(5); 1241-52. ©2018 AACR.

Alpha-Fetoprotein: From a Diagnostic Biomarker to a Key Role in Female Fertility

Alpha-fetoprotein (AFP) is a well-known diagnostic biomarker used in medicine to detect fetal developmental anomalies such as neural tube defects or Down's syndrome, or to follow up the development of tumors such as hepatocellular carcinomas. However, and despite the fact that the protein was discovered almost half a century ago, little was known about its physiological function. The study of Afp knock-out mice uncovered a surprising function of AFP: it is essential for female fertility and for expression of normal female behaviors, and this action is mediated through its estrogen binding capacity. AFP sequestrates estrogens and by so doing protects the female developing brain from deleterious (defeminizing/masculinizing) effects of these hormones.

Understanding the molecular mechanisms of human microtia via a pig model of HOXA1 syndrome

Microtia is a congenital malformation of the outer ears. Although both genetic and environmental components have been implicated in microtia, the genetic causes of this innate disorder are poorly understood. Pigs have naturally occurring diseases comparable to those in humans, providing exceptional opportunity to dissect the molecular mechanism of human inherited diseases. Here we first demonstrated that a truncating mutation in HOXA1 causes a monogenic disorder of microtia in pigs. We further performed RNA sequencing (RNA-Seq) analysis on affected and healthy pig embryos (day 14.25). We identified a list of 337 differentially expressed genes (DEGs) between the normal and mutant samples, shedding light on the transcriptional network involving HOXA1. The DEGs are enriched in biological processes related to cardiovascular system and embryonic development, and neurological, renal and urological diseases. Aberrant expressions of many DEGs have been implicated in human innate deformities corresponding to microtia-associated syndromes. After applying three prioritizing algorithms, we highlighted appealing candidate genes for human microtia from the 337 DEGs. We searched for coding variants of functional significance within six candidate genes in 147 microtia-affected individuals. Of note, we identified one EVC2 non-synonymous mutation (p.Asp1174Asn) as a potential disease-implicating variant for a human microtia-associated syndrome. The findings advance our understanding of the molecular mechanisms underlying human microtia, and provide an interesting example of the characterization of human disease-predisposing variants using pig models.

Summary: A pig model of HOXA1 syndrome provides novel insight into the molecular mechanisms of human microtia.

Telomerase inhibition decreases alpha-fetoprotein expression and secretion by hepatocellular carcinoma cell lines: in vitro and in vivo study

Alpha-fetoprotein (AFP) is a diagnostic marker for hepatocellular carcinoma (HCC). A direct relationship between poor prognosis and the concentration of serum AFP has been observed. Telomerase, an enzyme that stabilizes the telomere length, is expressed by 90% of HCC. The aim of this study was to investigate the effect of telomerase inhibition on AFP secretion and the involvement of the PI3K/Akt/mTOR signaling pathway. Proliferation and viability tests were performed using tetrazolium salt. Apoptosis was determined through the Annexin V assay using flow cytometry. The concentrations of AFP were measured using ELISA kits. The AFP mRNA expression was evaluated using RT-PCR, and cell migration was evaluated using a Boyden chamber assay. The in vivo effect of costunolide on AFP production was tested in NSG mice. Telomerase inhibition by costunolide and BIBR 1532 at 5 and 10 μM decreased AFP mRNA expression and protein secretion by HepG2/C3A cells. The same pattern was obtained with cells treated with hTERT siRNA. This treatment exhibited no apoptotic effect. The AFP mRNA expression and protein secretion by PLC/PRF/5 was decreased after treatment with BIBR1532 at 10 μM. In contrast, no effect was obtained for PLC/PRF/5 cells treated with costunolide at 5 or 10 μM. Inhibition of the PI3K/Akt/mTOR signaling pathway decreased the AFP concentration. In contrast, the MAPK/ERK pathway appeared to not be involved in HepG2/C3A cells, whereas ERK inhibition decreased the AFP concentration in PLC/PRF/5 cells. Modulation of the AFP concentration was also obtained after the inhibition or activation of PKC. Costunolide (30 mg/kg) significantly decreased the AFP serum concentration of NSG mice bearing HepG2/C3A cells. Both the inhibition of telomerase and the inhibition of the PI3K/Akt/mTOR signaling pathway decreased the AFP production of HepG2/C3A and PLC/PRF/5 cells, suggesting a relationship between telomerase and AFP expression through the PI3K/Akt/mTOR pathway.

Decreased expression of the Nkx2.8 gene correlates with tumor progression and a poor prognosis in HCC cancer

Background

Nkx2.8 (Nk2 homeobox 8) is a novel NK-2 gene family member that has been implicated in the progression of human cancer. Its role in the progression of HCC remains unknown. In this study, we investigated the expression levels and prognostic value of Nkx2.8 in hepatocellular carcinoma.

Methods

The expression of Nkx2.8 was determined by real-time quantitative RT-PCR (qRT-PCR) and immunochemistry in paired cancerous and non-cancerous tissues of 48 patients with HCC. The relationships between the Nkx2.8 expression levels, the clinicopathological characteristics and patient survival were analyzed. The effects of Nkx2.8 overexpression on cellular proliferation ability, including MTT and colony formation assays, were investigated.

Results

Nkx2.8 expression was significantly downregulated in HCC cancer tissues compared with adjacent non-cancerous tissues. Further immunohistochemical analysis showed low expression of Nkx2.8 in HCC cancer tissues, and the clinicopathological analysis showed that the Nkx2.8 mRNA and protein expression levels were significantly correlated with the TNM stage (p = 0.032; p = 0.026, respectively). Kaplan–Meier survival curves revealed that lower Nkx2.8 expression was associated with a poor overall survival in HCC patients (P = 0.00172). The overexpression of Nkx2.8 in HCC cell lines inhibits cell proliferation and colony formation.

Conclusions

Our data indicated that Nkx2.8 plays important roles in the development and progression of HCC and might be a valuable prognostic biomarker and potential therapeutic target for HCC.

Molecular characterization and functional analysis of sheep thyroid transcription factor-1

Thyroid transcription factor-1 (TTF-1), a member of the Nkx2 family of homeodomain-containing proteins, is involved in binding to and in activating the promoters of several important genes in the thyroid, lungs, and brain, and in regulating expression of these tissue-specific genes. We investigated potential roles of sheep (Ovis aries) TTF-1 in regulating cell fate and organ morphogenesis and in controlling puberty and reproductive capability of females. We amplified and cloned the sheep TTF-1 full-length DNA for the first time, analyzed its functional domains and regions, predicted molecular structure of its homeodomain and DNA-binding sites, and examined its expression in pituitary, brain, thyroid gland, ovary, and hypothalamus. We found that sheep TTF-1 has a high degree of homologous identity with that of other mammals, and it has several important domains including domain N, DNA-binding domain, domain C, TN-domain, domain I, and NK2-SD. The DNA-binding domain of sheep TTF-1 has 10 potential DNA-binding sites and is a novel mammalian homeodomain that shows considerable sequence homology with the corresponding rat homeodomain. Several functional regions in sheep TTF-1 share high sequence identity with rat TTF-1, indicating that these regions may have the same activity as in the rat. Expression of TTF-1 in several specific tissues implies that sheep TTF-1 in involved in sheep sexual development and reproductive capability. These results suggest a role of sheep TTF-1 in enhancing sheep reproduction performance and we propose it as a candidate gene for selection.

Role of epigenetic aberrations in the development and progression of human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most lethal and prevalent cancers in humans. The molecular mechanisms leading to the development of HCC are extremely complicated and consist of prominent genetic, genomic, and epigenetic alterations. This review summarizes the current knowledge of the role of epigenetic aberrations, including changes in DNA methylation, histone modifications, and expression of microRNAs in the pathogenesis of HCC. It also emphasizes that identification of the underlying epigenetic alterations that drive cell transformation and promote development and progression of HCC is crucially important for understanding mechanisms of hepatocarcinogenesis, its detection, therapeutic intervention, and prevention.

The tumor-suppressor gene Nkx2.8 suppresses bladder cancer proliferation through upregulation of FOXO3a and inhibition of the MEK/ERK signaling pathway

Invasive bladder cancer is a lethal disease for which effective prognostic markers as well as potential therapy targets are still lacking. Nkx2.8 (Nk2 homeobox 8), a novel member of the NK-2 gene family, was reported to play an important role in the development and progression of human cancer. Herein, we reported that Nkx2.8 was markedly reduced in bladder cancer tissues compared with matched adjacent normal urothelial tissues. Nkx2.8 levels were inversely correlated with advanced T classification, N classification, tumor multiplicity, high proliferation index (Ki-67) and poor survival of patients. Furthermore, we found that overexpression of Nkx2.8 in bladder cancer cells significantly inhibited cell proliferation in vitro and in vivo, whereas silencing Nkx2.8 dramatically enhanced cell proliferation. Moreover, we demonstrated that overexpression of Nkx2.8 resulted in G(1)/S phase arrest, accompanied by upregulation of p27(Kip1), downregulation of cyclin D1 and p-FOXO3a and inhibition of MEK/ERK pathway activity. Meanwhile, silencing Nkx2.8 led to acceleration of G(1)/S transition, downregulation of p27(Kip1), upregulation of cyclin D1 and p-FOXO3a and increase of MEK/ERK pathway activity. These findings suggest that Nkx2.8 plays a potential tumor suppressor role in bladder cancer progression and represents a valuable clinical prognostic marker of this disease.

Mutational spectrum in the cardiac transcription factor gene NKX2.5 (CSX) associated with congenital heart disease

Heterozygous mutations in the human transcription factor gene NKX2.5 are associated with either isolated or combined congenital heart disease (CHD), primarily secundum atrial septal defect-II (ASD-II), ventricular septal defect (VSD) or tetralogy of Fallot (TOF). Thus, NKX2.5 has an important role at different stages of cardiac development. The frequency of NKX2.5 mutations in a broader phenotypic spectrum of CHD is not completely determined. Here, we report the identification of two novel mutations in the NKX2.5 gene in a screening of 121 patients with a broad spectrum of CHDs. However, mutations were only associated with familial ASD-II and in both, patients also showed atrioventricular (AV) block. We found one missense mutation (R190L) in two siblings with ASD-II and a frame-shift mutation (A255fsX38) at the C-terminus in a mother and daughter. In addition, a single patient with hypoplastic left heart syndrome (HLHS) had the reported sequence variant R25C. Importantly, sporadic cases of CHD that share phenotypic aspects of NKX2.5 mutation carriers were negative for genetic analysis. Thus, even important for cardiac development, germline mutations in NKX2.5 are rare in patients with sporadic CHD and genetic and/or pathophysiologic heterogeneity is likely for sporadic forms of CHD.

SET/MYND Lysine Methyltransferases Regulate Gene Transcription and Protein Activity

The SET and MYND (SMYD) family of lysine methyltransferases is defined by a SET domain that is split into two segments by a MYND domain, followed by a cysteine-rich post-SET domain. While members of the SMYD family are important in the SET-mediated regulation of gene transcription, pathological consequences have also been associated with aberrant expression of SMYD proteins. The last decade has witnessed a rapid increase in the studies and corresponding understanding of these highly impactful enzymes. Herein, we review the current body of knowledge related to the SMYD family of lysine methyltransferases and their role in transcriptional regulation, epigenetics, and tumorigenesis.

One allele's loss is another's gain: alterations of NKX2-8 in non-small cell lung cancer

Large-scale genetic changes such as loss or gain of chromosomes are important drivers of solid tumor carcinogenesis. Recent technological advances in genomic profiling have allowed quantitative detection of gene copy numbers, leading to identification of the 14q13.3 gene locus as functionally important in non-small cell lung cancers.

Zhx2 and Zbtb20: novel regulators of postnatal alpha-fetoprotein repression and their potential role in gene reactivation during liver cancer

The mouse alpha-fetoprotein (AFP) gene is abundantly expressed in the fetal liver, normally silent in the adult liver but is frequently reactivated in hepatocellular carcinoma. The basis for AFP expression in the fetal liver has been studied extensively. However, the basis for AFP reactivation during hepatocarcinogenesis is not well understood. Two novel factors that control postnatal AFP repression, Zhx2 and Zbtb20, were recently identified. Here, we review the transcription factors that regulate AFP in the fetal liver, as well as Zhx2 and Zbtb20, and raise the possibility that the loss of these postnatal repressors may be involved in AFP reactivation in liver cancer.

Both gene amplification and allelic loss occur at 14q13.3 in lung cancer

PURPOSE

Because loss of Nkx2-8 increases lung cancer in the mouse, we studied suppressive mechanisms in human lung cancer.

EXPERIMENTAL DESIGN

NKX2-8 is located within 14q13.3, adjacent to its close relative TTF1/NKX2-1. We first analyzed LOH of 14q13.3 in forty-five matched human lung cancer and control specimens. DNA from tumors with LOH was then analyzed with high-density single-nucleotide polymorphism (SNP) arrays. For correlation with this genetic analysis, we quantified expression of Nkx2-8 and TTF1 mRNA in tumors. Finally, suppressive function of Nkx2-8 was assessed via colony formation assays in five lung cancer cell lines.

RESULTS

Thirteen of forty-five (29%) tumors had LOH. In six tumors, most adenocarcinomas, LOH was caused by gene amplification. The 0.8-Mb common region of amplification included MBIP, SFTA, TTF1, NKX2-8, and PAX9. In 4 squamous or adenosquamous cancers, LOH was caused by deletion. In three other tumors, LOH resulted from whole chromosome mechanisms (14(-), 14(+), or aneuploidy). The 1.2-Mb common region of deletion included MBIP, SFTA, TTF1, NKX2-8, PAX9, SLC25A21, and MIPOL1. Most tumors had low expression of Nkx2-8. Nevertheless, sequencing did not show NKX2-8 mutations that could explain the low expression. TTF1 overexpression, in contrast, was common and usually independent of Nkx2-8 expression. Finally, stable transfection of Nkx2-8 selectively inhibited growth of H522 lung cancer cells.

CONCLUSIONS

14q13.3, which contains NKX2-8, is subject to both amplification and deletion in lung cancer. Most tumors have low expression of Nkx2-8, and its expression can inhibit growth of some lung cancer cells.

A novel functional DEC1 promoter polymorphism -249T>C reduces risk of squamous cell carcinoma of the head and neck

Human DEC1 (deleted in esophageal cancer 1) gene is located on chromosome 9q, a region frequently deleted in various types of human cancers, including squamous cell carcinoma of the head and neck (SCCHN). However, only one epidemiological study has evaluated the association between DEC1 polymorphisms and cancer risk. In this hospital-based case-control study, four potentially functional single-nucleotide polymorphisms -1628 G>A (rs1591420), -606 T>C [rs4978620, in complete linkage disequilibrium with -249T>C (rs2012775) and -122 G>A(rs2012566)], c.179 C>T p.Ala60Val (rs2269700) and 3' untranslated region-rs3750505 as well as the TP53 tumor suppressor gene codon 72 (Arg72Pro, rs1042522) polymorphism were genotyped in 1111 non-Hispanic Whites SCCHN patients and 1130 age-and sex-matched cancer-free controls. After adjustment for age, sex and smoking and drinking status, the variant -606CC (i.e. -249CC) homozygotes had a significantly reduced SCCHN risk (adjusted odds ratio = 0.71, 95% confidence interval = 0.52-0.99) compared with the -606TT homozygotes. Stratification analyses showed that a reduced risk associated with the -606CC genotype was more pronounced in subgroups of non-smokers, non-drinkers, younger subjects (defined as ≤57 years), carriers of the TP53 Arg/Arg (rs1042522) genotype, patients with oropharyngeal cancer or late-stage SCCHN. Further in silico analysis revealed that the -249 T-to-C change led to a gain of a transcription factor-binding site. Additional functional analysis showed that the -249T-to-C change significantly enhanced transcriptional activity of the DEC1 promoter and the DNA-protein-binding activity. We conclude that the DEC1 promoter -249 T>C (rs2012775) polymorphism is functional, modulating susceptibility to SCCHN among non-Hispanic Whites.

DNA amplification is a ubiquitous mechanism of oncogene activation in lung and other cancers

Chromosomal translocation is the best-characterized genetic mechanism for oncogene activation. However, there are documented examples of activation by alternate mechanisms, for example gene dosage increase, though its prevalence is unclear. Here, we answered the fundamental question of the contribution of DNA amplification as a molecular mechanism driving oncogenesis. Comparing 104 cancer lines representing diverse tissue origins identified genes residing in amplification 'hotspots' and discovered an unexpected frequency of genes activated by this mechanism. The 3431 amplicons identified represent approximately 10 per hematological and approximately 36 per epithelial cancer genome. Many recurrently amplified oncogenes were previously known to be activated only by disease-specific translocations. The 135 hotspots identified contain 538 unique genes and are enriched for proliferation, apoptosis and linage-dependency genes, reflecting functions advantageous to tumor growth. Integrating gene dosage with expression data validated the downstream impact of the novel amplification events in both cell lines and clinical samples. For example, multiple downstream components of the EGFR-family-signaling pathway, including CDK5, AKT1 and SHC1, are overexpressed as a direct result of gene amplification in lung cancer. Our findings suggest that amplification is far more common a mechanism of oncogene activation than previously believed and that specific regions of the genome are hotspots of amplification.

ZHX2 is a repressor of alpha-fetoprotein expression in human hepatoma cell lines

The zinc-fingers and homeoboxes 2 (ZHX2) protein was shown previously to be involved in postnatal repression of α-fetoprotein (AFP) in mice. More recently, loss of ZHX2 expression was often found in human hepatcellular carcinoma (HCC), where AFP is frequently reactivated. Using HepG2 and HepG2.2.15, which express high AFP levels, we show that ZHX2 overexpression significantly decreases of AFP secretion in a dose dependent manner. Furthermore, using LO2 and SMMC7721 cells, which express low AFP levels, we use siRNA inhibition to show that AFP is de-repressed when ZHX2 levels are reduced. This represents the first direct evidence that ZHX2 represses AFP. Co-transfections of ZHX2 and AFP-luciferase reporter genes demonstrate ZHX2 repression is governed by the AFP promoter and requires intact HNF1 binding sites. These data support the idea that ZHX2 contributes to AFP repression in the liver after birth and may also be involved in AFP reactivation in liver cancer.

Array CGH analysis of copy number variation identifies 1284 new genes variant in healthy white males: implications for association studies of complex diseases

The discovery of copy number variation in healthy individuals is far from complete, and owing to the resolution of detection systems used, the majority of loci reported so far are relatively large ( approximately 65%>10 kb). Applying a two-stage high-resolution array comparative genomic hybridization approach to analyse 50 healthy Caucasian males from northern France, we discovered 2208 copy number variants (CNVs) detected by more than one consecutive probe. These clustered into 1469 CNV regions (CNVRs), of which 721 are thought to be novel. The majority of these are small (median size 4.4 kb) and most have common boundaries, with a coefficient of variation less than 0.1 for 83% of endpoints in those observed in multiple samples. Only 6% of the CNVRs analysed showed evidence of both copy number losses and gains at the same site. A further 6089 variants were detected by single probes: 48% of these were observed in more than one individual. In total, 2570 genes were seen to intersect variants: 1284 in novel loci. Genes involved in differentiation and development were significantly over-represented and approximately half of the genes identified feature in the Online Mendelian Inheritance in Man database. The biological importance of many genes affected, along with the well-conserved nature of the majority of the CNVs, suggests that they could have important implications for phenotype and, thus, be useful for association studies of complex diseases.

Silencing SMYD3 in hepatoma demethylates RIZI promoter induces apoptosis and inhibits cell proliferation and migration

AIM: To investigate the role of SMYD3 in hepatocellular carcinoma (HCC) development and progression and to verify whether its regulation activity was through RIZ1 inactivation.

METHODS: Expression of SMYD3 in HCC cell lines and tissues were measured; silencing of SMYD3 by RNA interference (RNAi) was effectuated, hepatoma cell proliferation, migration and apoptosis were tested, with RIZ1 CpG promoter methylation, and corresponding mRNA expression were investigated.

RESULTS: SMYD3 over-expression in HCC was associated with RIZ1 hypermethylation and mRNA down-expression. Suppression of SMYD3 expression de-methylated RIZ1 CpG promoter (P < 0.01) and increased RIZ1 mRNA expression (P < 0.01). Consequently, SMYD3 down-expression with RIZ1 de-methylation strongly inhibited hepatoma cell growth (MTT inhibitory rates: Pgenesil-1-s1 60.95% ± 7.97%, Pgenesil-1-s2 72.14% ± 9.68% vs Pgenesil-1-hk 6.89% ± 4.12%, P < 0.01) and migration (Pgenesil-1-s1 4.24% ± 1.58%, Pgenesil-1-s1 4.87% ± 0.73% vs Pgenesil-1 19.03% ± 4.63%, Pgenesil-1-hk 19.95% ± 5.21%, P < 0.01) and induced apoptosis (FCM subG1 phase Pgenesil-1-s1 19.07% ± 1.78%, Pgenesil-1-s2 17.68% ± 2.36% vs Pgenesil-1 0.47% ± 0.12%, Pgenesil-1-hk 1.46% ± 0.28%, P < 0.01. TUNEL-positive cells: Pgenesil-1-s1 40.24% ± 5.18%, Pgenesil-1-s2 38.48% ± 4.65% vs Pgenesil-1 2.18% ± 1.34%, Pgenesil-1-hk 2.84% ± 1.22%, P < 0.01) in HepG2 cells.

CONCLUSION: These results demonstrate that SMYD3 plays a critical role in the carcinogenesis and progression of HCC. The proliferation, migration induction and apoptosis inhibition activities of SMYD3 may be mediated through RIZ1 CpG promoter hypermethylation.

Loss of Nkx2.8 deregulates progenitor cells in the large airways and leads to dysplasia

Nkx2.8, a homeodomain transcription factor, has been characterized in liver cancer and in the developing central nervous system. We now show that this factor is also expressed in the lung, where it localizes in adults to a discrete population of tracheobronchial basal cells. To target the mouse gene, the first exon was replaced by a LacZ marker gene joined to the intact 5'-untranslated region. Marker expression was observed throughout the lower respiratory tract, beginning on E11 in a few cells of the distal lung buds. The region of expression then spread upward. By neonatal day 1, expression was greatest in the large airways and the Nkx2.8-/- mice exhibited generalized tracheobronchial hyperplasia. Bromodeoxyuridine (BrdUrd) labeling studies showed that a higher rate of bronchial cell proliferation persisted at 6 to 8 months. In adults, Nkx2.8 marker expression decreased with progressive differentiation into ciliated and secretory cells. The cell localizations and patterns of coexpression with BrdUrd and differentiation markers suggest a progenitor relationship: the cells that most strongly express Nkx2.8 seem to function as tracheobronchial stem cells. Moreover, Nkx2.8 acts to limit the number of these progenitor cells because the marker-expressing population was greatly expanded in Nkx2.8-/- mice. Increased proliferation and an altered progenitor relationship caused progressive bronchial pathology, which manifested as widespread dysplasia in the large airways of 1-year-old Nkx2.8-/- mice.

AUF1-like protein binds specifically to DAS cis-acting element that regulates mouse alpha-fetoprotein gene expression

Alpha-fetoprotein (AFP) is one of the major serum proteins in the early life of mammals. We have previously identified a novel cis-acting element designated as DAS at the 5'-flanking region of the AFP gene and demonstrated that the DAS sequence can be specifically recognized by nuclear protein DAP-II in AFP-producing hepatoma cells and retinoic acid (RA)-induced AFP-producing F9 cells. In this study, we used DNA affinity chromatography to purify the DAP-II proteins from the nuclear extracts (NE) of RA-treated F9 cells. The purified DAP-II complex mainly contained five proteins, with molecular weights of 45, 42, 32, 30, and 20 kDa, respectively. The identification of these proteins was determined by MALDI-TOF mass spectrometric analysis and a database search. These proteins were found to belong to the AUF1 RNA-binding protein family. Protein (30 kDa), one of five proteins in an isolated DAP-II complex, was matched with amino acid sequence highly similar to muAUF1-3. The expression of this protein is inducible by RA, and the pattern of the protein expression is the same as DAP-II proteins in F9 cells after treatment with RA during differentiation. Our results suggest that the 30-kDa protein is a novel isoform of AUF1 family and is the main component of the DAP-II complex that binds to the DAS sequence.

Transcription factors and congenital heart defects

Although there have been important advances in diagnostic modalities and therapeutic strategies for congenital heart defects (CHD), these malformations still lead to significant morbidity and mortality in the human population. Over the past 10 years, characterization of the genetic causes of CHD has begun to elucidate some of the molecular causes of these defects. Linkage analysis and candidate-gene approaches have been used to identify gene mutations that are associated with both familial and sporadic cases of CHD. Complementation of the human studies with developmental studies in mouse models provides information for the roles of these genes in normal development as well as indications for disease pathogenesis. Biochemical analysis of these gene mutations has provided further insight into the molecular effects of these genetic mutations. Here we review genetic, developmental, and biochemical studies of six cardiac transcription factors that have been identified as genetic causes for CHD in humans.

Family members p53 and p73 act together in chromatin modification and direct repression of alpha-fetoprotein transcription

Aberrant expression of the alpha-fetoprotein (AFP) gene is a diagnostic tumor marker of hepatocellular carcinoma. We find that AFP gene expression is repressed by the TP53 family member p73 during normal hepatic development and when p73alpha or p73beta is introduced into cultured hepatoma cells that express AFP. Transient co-transfection of p53 family members showed that p53 and transactivating (TA)-p73, but not TA-p63, repress endogenous AFP transcription additively or independently. p53-independent functions of p73 are further supported by delayed, p73-associated compensation of AFP repression during development of the p53-null mouse. Chromatin immunoprecipitation assays of normal and p53-null mouse liver tissue showed that TA-p73 binds at a previously identified p53 repressor site (-860/-830) within the distal promoter of AFP at a level equivalent to p53 in wild type liver, with increased binding of TA-p73 to chromatin in the absence of p53. Sequential chromatin immunoprecipitation analyses revealed that TA-p73 and p53 bind simultaneously to their shared regulatory site in wild type liver. Like the founding family member p53, TA-p73 represses AFP expression by chromatin structure alteration, targeting reduction of acetylated histone H3 lysine 9 and increased dimethylated histone H3 lysine 9 levels. However, chromatin-bound TA-p73 is associated with elevated di- and tri-methylated histone H3 lysine 4 levels in p53-null liver and hepatoma cells, concomitant with a reduced ability to repress transcription compared with p53.

Afr2 regulation occurs cell-autonomously in vitro but is not conferred on episomal DNA in transient assays

Oncofetal antigens such as alpha-fetoprotein (AFP) are expressed in regenerating liver. The level of AFP gene expression during liver regeneration is regulated by the unlinked, autosomal gene, Alpha-fetoprotein regulator 2 (Afr2). C3H/HeJ (Afr2A/A) mice express 10-fold higher levels of AFP than C57BL/6J (Afr2B/B) mice. Here we show that primary hepatocytes isolated from C3H/HeJ and C57BL/6J mice exhibit differential expression of the endogenous AFP gene, which was attributed to the Afr2 gene locus and indicative of a cell-autonomous mechanism. We show that the Afr2-Response Element (ARE), between 1010 and 838 base pairs upstream of the AFP transcriptional start site, did not modulate reporter gene expression in transfection assays of Hep G2, Hep 3B, Hepa 1.6, and HeLa cell lines. Reporter gene expression in transiently transfected primary hepatocytes was also ARE-independent. Finally, gene expression from reporter constructs delivered by hydrodynamics-based transfection to the livers of C3H/HeJ and C57BL/6J mice after CCl4-induced liver regeneration was ARE-independent. In conclusion, ARE-dependent transcription was not found in transient assays performed in three different systems, two of which retained regulation of the endogenous AFP gene, suggesting that the ARE may not function as a simple transcription factor recognition site.

SMYD3 encodes a histone methyltransferase involved in the proliferation of cancer cells

Colorectal and hepatocellular carcinomas are some of the leading causes of cancer deaths worldwide, but the mechanisms that underly these malignancies are not fully understood. Here we report the identification of SMYD3, a gene that is over-expressed in the majority of colorectal carcinomas and hepatocellular carcinomas. Introduction of SMYD3 into NIH3T3 cells enhanced cell growth, whereas genetic knockdown with small-interfering RNAs (siRNAs) in cancer cells resulted in significant growth suppression. SMYD3 formed a complex with RNA polymerase II through an interaction with the RNA helicase HELZ and transactivated a set of genes that included oncogenes, homeobox genes and genes associated with cell-cycle regulation. SMYD3 bound to a motif, 5'-CCCTCC-3', present in the promoter region of downstream genes such as Nkx2.8. The SET domain of SMYD3 showed histone H3-lysine 4 (H3-K4)-specific methyltransferase activity, which was enhanced in the presence of the heat-shock protein HSP90A. Our findings suggest that SMYD3 has histone methyltransferase activity and plays an important role in transcriptional regulation as a member of an RNA polymerase complex. Furthermore, activation of SMYD3 may be a key factor in human carcinogenesis.

Sequence-specific DNA binding by the vnd/NK-2 homeodomain of Drosophila

The ventral nervous system defective (vnd)/NK-2 homeodomain and some flanking amino acid residues were expressed in Escherichia coli, purified to homogeneity, and the protein was covalently coupled to Sepharose. Oligodeoxynucleotides that contained 16-bp random sequences were purified by vnd/NK-2 affinity column chromatography, cloned, and sequenced. The consensus nucleotide sequence of the vnd/NK-2 homeodomain binding site was shown to be T(T/C)AAGTG(G/C). The apparent equilibrium dissociation constant (K(D)) of the vnd/NK-2 homeodomain for the consensus sequence is 1.9 x 10(-10) M. In addition, results of competition between oligodeoxynucleotides for binding to the vnd/NK-2 homeodomain and determination of the apparent K(D) values of oligodeoxynucleotides that differ from the consensus sequence by only a single base pair demonstrate that the four central nucleotides, AAGT, in this sequence play a major role in determining the affinity of binding.

Regulation of alpha-fetoprotein expression by Nkx2.8

The alpha-fetoprotein (AFP) gene is an important model of developmental gene silencing and neoplastic gene reactivation. Nkx2.8 is a divergent homeodomain factor originally cloned through its binding to the promoter-coupling element (PCE), a regulatory region upstream of the AFP promoter that mediates stimulation by distant enhancers. Nkx2.8 is the only developmentally regulated factor that has been associated with AFP gene expression. Fetoprotein transcription factor, an orphan nuclear receptor, has also been shown to bind the PCE but is not developmentally regulated. The binding specificities of both families of transcription factor were determined, and overlapping sites for each were defined in the PCE. After modification of nuclear extract and gel shift analysis procedures, Nkx2.8 was identified in six AFP-positive cell lines. Transient-transfection analysis did not show transcriptional stimulation by Nkx2.8 or other active NK2 factors, which only interfered with gene expression. However, two sets of analysis demonstrated the relationship of Nkx2.8 to AFP expression: chromatin immunoprecipitation demonstrated that Nkx2.8 bound to the active AFP promoter, and antisense inhibition of Nkx2.8 mRNA translation selectively reduced expression of both the endogenous human AFP gene and transfected reporters containing the rat AFP promoter.

The mouse alpha-fetoprotein promoter is repressed in HepG2 hepatoma cells by hepatocyte nuclear factor-3 (FOXA)

The mouse alpha-fetoprotein gene is expressed at high levels in the fetal liver and is transcriptionally silenced at birth. The repression is governed, at least in part, by the 250 base pair (bp) AFP promoter. We show here that the AFP promoter is dramatically repressed by HNF3 in HepG2 hepatoma cells. This repression is governed by the region between -205 and -150. Furthermore, this fragment can confer HNF3-mediated repression on a heterologous promoter. The repression is abolished by a mutation that is centered at -165. EMSA analyses using in vivo and in vitro synthesized proteins indicate that HNF3 proteins do not bind DNA from the -205 to -150 region. We propose that HNF3 represses AFP promoter activity through indirect mechanisms that modulate the binding or activity of a liver-enriched factor that interacts with the -165 region of the AFP promoter.

The mouse fetoprotein transcription factor (FTF) gene promoter is regulated by three GATA elements with tandem E box and Nkx motifs, and FTF in turn activates the Hnf3beta, Hnf4alpha, and Hnf1alpha gene promoters

Fetoprotein transcription factor (FTF) is an orphan nuclear receptor that activates the alpha(1)-fetoprotein gene during early liver developmental growth. Here we sought to define better the position of FTF in transcriptional cascades leading to hepatic differentiation. The mouse FTF gene was isolated and assigned to chromosome 1 band E4 (one mFTF pseudogene was also found). Exon/intron mapping shows an mFTF gene structure similar to that of its close homologue SF1, with two more N-terminal exons in the mFTF gene; exon mapping also delimits several FTF mRNA 5'- and 3'-splice variants. The mFTF transcription initiation site was located in adult liver at 238 nucleotides from the first translation initiator codon, with six canonical GATA, E box, and Nkx motifs clustered between -50/-140 base pairs (bp) from the cap site; DNA/protein binding assays also pinpointed an HNF4-binding element at +36 bp and an FTF-binding element at -257 bp. Transfection assays and point mutations showed that the mFTF promoter is activated by GATA, HNF4alpha, FTF, Nkx, and basic helix-loop-helix factors, with marked cooperativity between GATA and HNF4alpha. A tandem GATA/E box activatory motif in the proximal mFTF promoter is strikingly similar to a composite motif coactivated by differentiation inducers in the hematopoietic lineage; a tandem GATA-Nkx motif in the distal mFTF promoter is also similar to a composite motif transducing differentiation signals from transforming growth factor-beta-like receptors in the cardiogenic lineage. Three genes encoding transcription factors critical to early hepatic differentiation, Hnf3beta, Hnf4alpha, and Hnf1alpha, each contain dual FTF-binding elements in their proximal promoters, and all three promoters are activated by FTF in transfection assays. Direct DNA binding action and cooperativity was demonstrated between FTF and HNF3beta on the Hnf3beta promoter and between FTF and HNF4alpha on the Hnf1alpha promoter. These combined results suggest that FTF is an early intermediary between endodermal specification signals and downstream genes that establish and amplify the hepatic phenotype.

Identification of an enhancer and an alternative promoter in the first intron of the alpha-fetoprotein gene

In this study we have characterized a positive regulatory region located in the first intron of the alpha-fetoprotein (AFP) gene. We show that the enhancer activity of the region depends on a 44 bp sequence centered on a CACCC motif. The sequence is the target of the two zinc fingers transcription factors BKLF and YY1. The introduction of a mutation destroying the CACCC box impairs the binding of BKLF but improves that of YY1. Moreover, the mutated sequence behaves as a negative control element, suggesting that BKLF behaves as a positive factor and that YY1 is a negative one. We also demonstrate the existence of a novel, tissue-specific AFP mRNA isoform present in the yolk sac and fetal liver which initiates from an alternative promoter located approximately 100 bp downstream of the enhancer element. The transcriptional start site controlled by this new promoter (called P2), was mapped to 66 bp downstream of a TATA box. A putative AUG translation site in-frame with exon 2 of the classical gene was found 295 bp downstream of the transcription start site. Like the traditional AFP promoter (P1), the P2 promoter is active in the yolk sac and fetal liver. Embryonic stem cells with an AFP knock-in gene containing either the P2 promoter or deleted for it were isolated and comparative analysis of embryonic bodies derived from these cells suggests that the P2 promoter contributes to early expression of the AFP gene.

Distant enhancers stimulate the albumin promoter through complex proximal binding sites

The albumin-alpha-fetoprotein locus epitomizes the main features of transcriptional regulation of fetal and adult hepatocyte-specific genes: developmentally regulated promoters and strong distant enhancers. Full enhancer activity required only a proximal albumin-promoter region containing the TATA box, hepatic nuclear factor 1 (HNF1), and nuclear factor Y (NF-Y) sites. Deletion of the HNF1 site abrogated enhancer and promoter activity, whereas methylation of the site reduced all activity by about 3-fold. Deletion of the NF-Y site attenuated activity by about half, but much of the activity could be replaced by juxtaposition of an upstream region (designated distal element IV). Gel shift and competition analysis demonstrated that binding of architectural factors overlapped NF-Y binding. Moreover, a mutation that eliminated NF-Y binding but only minimally perturbed the surrounding region did not affect enhancer function. In plasmids with a second promoter, the enhancers simultaneously stimulated both albumin and alpha-fetoprotein promoters with minimal competition, but surprisingly some mutations in the albumin promoter attenuated expression from both promoters, whereas another uncoupled their expression. With single promoters, the function of the proximal promoter region was controlled by three parameters in the following hierarchy: HNF1 binding > local architecture > NF-Y binding, but integrated two-promoter function had a much greater dependence on NF-Y.

Intramolecular control of transcriptional activity by the NK2-specific domain in NK-2 homeodomain proteins

The developmentally important homeodomain transcription factors of the NK-2 class contain a highly conserved region, the NK2-specific domain (NK2-SD). The function of this domain, however, remains unknown. The primary structure of the NK2-SD suggests that it might function as an accessory DNA-binding domain or as a protein-protein interaction interface. To assess the possibility that the NK2-SD may contribute to DNA-binding specificity, we used a PCR-based approach to identify a consensus DNA-binding sequences for Nkx2.2, an NK-2 family member involved in pancreas and central nervous system development. The consensus sequence (T(C)(T)AAGT(G)(A)(G)(C)TT) is similar to the known binding sequences for other NK-2 homeodomain proteins, but we show that the NK2-SD does not contribute significantly to specific DNA binding to this sequence. To determine whether the NK2-SD contributes to transactivation, we used GAL4-Nkx2. 2 fusion constructs to map a powerful transcriptional activation domain in the C-terminal region beyond the conserved NK2-SD. Interestingly, this C-terminal region functions as a transcriptional activator only in the absence of an intact NK2-SD. The NK2-SD also can mask transactivation from the paired homeodomain transcription factor Pax6, but it has no effect on transcription by itself. These results demonstrate that the NK2-SD functions as an intramolecular regulator of the C-terminal activation domain in Nkx2.2 and support a model in which interactions through the NK2-SD regulate the ability of NK-2-class proteins to activate specific genes during development.

The alpha-fetoprotein promoter is the target of Afr1-mediated postnatal repression

The alpha-fetoprotein (AFP) gene is transcribed at high levels in the fetal liver and is repressed at birth, leading to low but detectable levels of AFP mRNA in the adult liver. This repression is regulated, in part, by a locus that is unlinked to AFP called Alpha-fetoprotein regulator 1 (Afr1). Previous studies showed that Afr1 regulation is independent of the AFP enhancers but requires the 1-kb AFP promoter/repressor region. Here, we demonstrate that a transgene with the 250-bp AFP promoter region linked to AFP enhancer element EII is expressed in the fetal liver and is postnatally repressed. In addition, this transgene is regulated by Afr1. These data indicate that the promoter is involved in postnatal AFP repression. Furthermore, we provide a high-resolution map of the Afr1 locus on mouse chromosome 15.

The role of Sp family members, basic Kruppel-like factor, and E box factors in the basal and IFN-gamma regulated expression of the human complement C4 promoter

The fourth component of human complement (C4) is a serum protein that is expressed in the liver and other organs. The promoter region of the C4 gene has been analyzed in reporter gene assays in two cell lines that represent hepatic (HepG2) and monocytic (U937) lineages. Analysis indicated that regions important for basal transcription in HepG2 cells included Sp1 and E box sites within the first 100 bp upstream of the transcription initiation site but not the nuclear factor-1 site important in the control of the mouse C4 gene. Also, a region encompassing -468 to -310 was able to repress activity 2-fold. However, when a CACCC or GT box sequence at -140 was mutated the repressive activity of the upstream region resulted in almost no activity. The -140 region consists of a series of four closely positioned GT boxes that were shown to bind Sp1, Sp3, and basic Krupple-like factor in EMSA. This novel two-part regulatory element may be involved in the regulated expression of C4. However, IFN-gamma a major activator of C4 expression did not signal through this two-part regulatory element. We were able to map the position of an IFN-gamma responsive element in U937. IFN-gamma was able to increase transcription by up to 20-fold with mutations in the E box sequence at -78 to -73, thus completely abolishing induction. We conclude that the E box binding factors, which appear to be distinct from upstream stimulatory factors 1 and 2, are totally responsible for IFN-gamma induction of C4.

Alpha-fetoprotein gene regulation: lessons from transgenic mice

The mouse alpha-fetoprotein (AFP) gene provides an excellent model system to study developmental gene activation and different aspects of liver-specific transcriptional control. AFP is activated early in hepatogenesis, repressed post-natally, and can be reactivated during liver regeneration and in hepatocellular carcinomas. Transgenic studies have also revealed that AFP enhancers, when linked individually to a heterologous promoter, can confer zonal control in the adult liver. Continued transgenic studies, combined with analysis using in vitro and tissue culture systems, will help elucidate mechanisms of transcriptional regulation during liver development and hepatocarcinogenesis.

Retinoic acid mediates down-regulation of the alpha-fetoprotein gene through decreased expression of hepatocyte nuclear factors

alpha-Fetoprotein (AFP), a protein highly induced during fetal liver development, is down-regulated by retinoids in the human hepatoma cell line Hep3B, in contrast to up-regulation observed in other cell types. Previously, we have documented that such up-regulation involves direct effects through cis-retinoid X receptor-binding sites in the AFP enhancer. In this report, we show a distinctive effect of all-trans-retinoic acid (RA) in Hep3B cells. RA caused a marked decrease in AFP transcripts. Deletion analysis of the upstream regulatory region of the AFP gene revealed that cis-acting sites required for down-regulation resided near the promoter. Gel mobility shift assays for factors binding to key elements in the AFP promoter region demonstrated that hepatocyte nuclear factor (HNF) 1 binding was diminished in nuclear extracts from RA-treated cells. In addition, HNF4, which is not known to bind to the AFP promoter but does regulate HNF1, was also diminished. The levels of HNF1 and HNF4 mRNA were also decreased following RA treatment. AFP promoter-chloramphenicol acetyltransferase transient transfection assays demonstrated that the level of HNF1 had a direct impact on basal transcription as well as RA-mediated down-regulation of the AFP gene, and that co-transfection of HNF1 and HNF4, but not transfection of either factor alone, reversed the RA-mediated inhibition. Taken together these data point to an interaction among the RA, HNF1, and HNF4 signals, which is reflected in decreased expression of AFP.