Transcriptional networks in the liver: hepatocyte nuclear factor 6 function is largely independent of Foxa2

ERα prevents tumorigenesis of both liver and breast cancer cells through CCN5

Estrogen receptor alpha (ERα)-mediated estrogen signaling has also shown to prevent hepatic tumorigenesis in mice. Consistent with this, hormone replacement therapy with estrogen supplementation dramatically reduced the risk of hepatocellular carcinoma. Silencing of ERα is also a key event for the transformation of ERα-positive breast cancer cells into malignant triple-negative breast cancer cells. However, the mechanisms underlying ERα-mediated prevention of both hepatic and mammary tumorigenesis in humans are still unclear. Here, we present a functional genomics study of ERα targeting by comparing human liver cancer cells with human breast cancer cells using "loss or gain of function" genetic assays of ERα in vitro and in vivo. We discover that cellular communication network factor 5 (CCN5) is a direct downstream target of ERα; ERα suppresses growth and prevents tumorigenesis and malignant transformation of both liver and breast cancer cells through CCN5 in humans. The ERα-CCN5 regulatory axis functions as suppressors for both hepatic and mammary tumors, which is a common mechanism of preventing tumorigenesis for both liver cancer and breast cancer in humans.

Interconnections between circadian clocks and metabolism

Circadian rhythms evolved through adaptation to daily light/dark changes in the environment; they are believed to be regulated by the core circadian clock interlocking feedback loop. Recent studies indicate that each core component executes general and specific functions in metabolism. Here, we review the current understanding of the role of these core circadian clock genes in the regulation of metabolism using various genetically modified animal models. Additionally, emerging evidence shows that exposure to environmental stimuli, such as artificial light, unbalanced diet, mistimed eating, and exercise, remodels the circadian physiological processes and causes metabolic disorders. This Review summarizes the reciprocal regulation between the circadian clock and metabolism, highlights remaining gaps in knowledge about the regulation of circadian rhythms and metabolism, and examines potential applications to human health and disease.

Regulation of the Pancreatic Exocrine Differentiation Program and Morphogenesis by Onecut 1/Hnf6

BACKGROUND & AIMS

The Onecut 1 transcription factor (Oc1, a.k.a. HNF6) promotes differentiation of endocrine and duct cells of the pancreas; however, it has no known role in acinar cell differentiation. We sought to better understand the role of Oc1 in exocrine pancreas development and to identify its direct transcriptional targets.

METHODS

Pancreata from Oc1^Δpanc (Oc1^fl/fl;Pdx1-Cre) mouse embryos and neonates were analyzed morphologically. High-throughput RNA-sequencing was performed on control and Oc1-deficient pancreas; chromatin immunoprecipitation sequencing was performed on wild-type embryonic mouse pancreata to identify direct Oc1 transcriptional targets. Immunofluorescence labeling was used to confirm the RNA-sequencing /chromatin immunoprecipitation sequencing results and to further investigate the effects of Oc1 loss on acinar cells.

RESULTS

Loss of Oc1 from the developing pancreatic epithelium resulted in disrupted duct and acinar cell development. RNA-sequencing revealed decreased expression of acinar cell regulatory factors (Nr5a2, Ptf1a, Gata4, Mist1) and functional genes (Amylase, Cpa1, Prss1, Spink1) at embryonic day (e) 18.5 in Oc1^Δpanc samples. Approximately 1000 of the altered genes were also identified as direct Oc1 targets by chromatin immunoprecipitation sequencing, including most of the previously noted genes. By immunolabeling, we confirmed that Amylase, Mist1, and GATA4 protein levels are significantly decreased by P2, and Spink1 protein levels were significantly reduced and mislocalized. The pancreatic duct regulatory factors Hnf1β and FoxA2 were also identified as direct Oc1 targets.

CONCLUSIONS

These findings confirm that Oc1 is an important regulator of both duct and acinar cell development in the embryonic pancreas. Novel transcriptional targets of Oc1 have now been identified and provide clarity into the mechanisms of Oc1 transcriptional regulation in the developing exocrine pancreas. Oc1 can now be included in the gene-regulatory network of acinar cell regulatory genes. Oc1 regulates other acinar cell regulatory factors and acinar cell functional genes directly, and it can also regulate some acinar cell regulatory factors (eg, Mist1) indirectly. Oc1 therefore plays an important role in acinar cell development.

Notch Inhibition Enhances Cardiac Reprogramming by Increasing MEF2C Transcriptional Activity

Conversion of fibroblasts into functional cardiomyocytes represents a potential means of restoring cardiac function after myocardial infarction, but so far this process remains inefficient and little is known about its molecular mechanisms. Here we show that DAPT, a classical Notch inhibitor, enhances the conversion of mouse fibroblasts into induced cardiac-like myocytes by the transcription factors GATA4, HAND2, MEF2C, and TBX5. DAPT cooperates with AKT kinase to further augment this process, resulting in up to 70% conversion efficiency. Moreover, DAPT promotes the acquisition of specific cardiomyocyte features, substantially increasing calcium flux, sarcomere structure, and the number of spontaneously beating cells. Transcriptome analysis shows that DAPT induces genetic programs related to muscle development, differentiation, and excitation-contraction coupling. Mechanistically, DAPT increases binding of the transcription factor MEF2C to the promoter regions of cardiac structural genes. These findings provide mechanistic insights into the reprogramming process and may have important implications for cardiac regeneration therapies.

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Notch activation is a barrier for GHMT-induced cardiac cell reprogramming

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Notch blockade by DAPT improves GHMT-induced cardiac reprogramming

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DAPT increases sarcomere organization, calcium flux, and beating in GHMT reprogramming

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DAPT enhances transcriptional activity of MEF2C in GHMT reprogramming

Inflammation-Induced Expression and Secretion of MicroRNA 122 Leads to Reduced Blood Levels of Kidney-Derived Erythropoietin and Anemia

BACKGROUND & AIMS

Anemia is associated commonly with acute and chronic inflammation, but the mechanisms of their interaction are not clear. We investigated whether microRNA 122 (MIR122), which is generated in the liver and is secreted into the blood, is involved in the development of anemia associated with inflammation.

METHODS

We characterized the primary transcript of the human liver-specific MIR122 using Northern blot, quantitative real-time polymerase chain reaction, and 3' and 5' rapid amplification of cDNA ends analyses. We studied regulation of MIR122 in human hepatocellular carcinoma cell lines (Huh7 and HepG2) as well as in C57BL/6 and mice with disruption of the tumor necrosis factor (Tnf) gene. Liver tissues were collected and analyzed by bioluminescence imaging or immunofluorescence. Inflammation in mice was induced by lipopolysaccharide (LPS) or by cerulein injections. Mice were given 4 successive injections of LPS, leading to inflammation-induced anemia. Steatohepatitis was induced with a choline-deficient, high-fat diet. Hemolytic anemia was stimulated by phenylhydrazine injection. MIR122 was inhibited in mice by tail-vein injection of an oligonucleotide antagonist of MIR122. MicroRNA and messenger RNA levels were determined by quantitative real-time polymerase chain reaction.

RESULTS

The primary transcript of MIR122 spanned 5 kb, comprising 3 exons; the third encodes MIR122. Within the MIR122 promoter region we identified a nuclear factor-κB binding site and showed that RELA (NF-κB p65 subunit), as well as activators of NF-κB (TNF and LPS), increased promoter activity of MIR122. Administration of LPS to mice induced secretion of MIR122 into blood, which required TNF. Secreted MIR122 reached the kidney and reduced expression of erythropoietin (Epo), which we identified as a MIR122 target gene. Injection of mice with an oligonucleotide antagonist of MIR122 increased blood levels of EPO, reticulocytes, and hemoglobin. We found an inverse relationship between blood levels of MIR122 and EPO in mice with acute pancreatitis or steatohepatitis, and also in patients with acute inflammation.

CONCLUSION

In mice, we found that LPS-induced inflammation increases blood levels of MIR122, which reduces expression of Epo in the kidney; this is a mechanism of inflammation-induced anemia. Strategies to block MIR122 in patients with inflammation could reduce the development or progression of anemia.

HNF6 and Rev-erbα integrate hepatic lipid metabolism by overlapping and distinct transcriptional mechanisms

In this study, Zhang et al. investigated the role of hepatic nuclear factor 6 (HNF6) in adult liver metabolism. The results demonstrate that deletion of HNF6 in livers of adult C57Bl/6 mice leads to fatty liver and that HNF6 and Rev-erbα can coordinately regulate hepatic lipid metabolism.

Hepatocyte nuclear factor 6 (HNF6) is required for liver development, but its role in adult liver metabolism is not known. Here we show that deletion of HNF6 in livers of adult C57Bl/6 mice leads to hepatic steatosis in mice fed normal laboratory chow. Although HNF6 is known mainly as a transcriptional activator, hepatic loss of HNF6 up-regulated many lipogenic genes bound directly by HNF6. Many of these genes are targets of the circadian nuclear receptor Rev-erbα, and binding of Rev-erbα at these sites was lost when HNF6 was ablated in the liver. While HNF6 and Rev-erbα coordinately regulate hepatic lipid metabolism, each factor also affects additional gene sets independently. These findings highlight a novel mechanism of transcriptional repression by HNF6 and demonstrate how overlapping and distinct mechanisms of transcription factor function contribute to the integrated physiology of the liver.

Onecut transcription factors in development and disease

Developmental processes are remarkably well conserved among species, and among the most highly conserved developmental regulators are transcription factor families. The Onecut transcription factor family consists of three members known for their single "cut" DNA-binding domain and an aberrant homeodomain. The three members of the Onecut family are highly conserved from Drosophila to humans and have significant roles in regulating the development of diverse tissues derived from the ectoderm or endoderm, where they activate a number of gene families. Of note, the genetic interaction between Onecut family members and Neurogenin genes appears to be essential in multiple tissues for proper specification and development of unique cell types. This review highlights the importance of the Onecut factors in cell fate specification and organogenesis, highlighting their role in vertebrates, and discusses their role in the maintenance of cell fate and prevention of disease. We cover the essential spatial and temporal control of Onecut factor expression and how this tight regulation is required for proper specification and subsequent terminal differentiation of multiple tissue types including those within the retina, central nervous system, liver and pancreas. Beyond development, Onecut factors perform necessary functions in mature cell types; their misregulation can contribute to diseases such as pancreatic cancer. Given the importance of this family of transcription factors in development and disease, their consideration in essential transcription factor networks is underappreciated.

Galectin 3 regulates HCC cell invasion by RhoA and MLCK activation

Hepatocellular carcinoma (HCC) carries a poor prognosis with no effective treatment available other than liver transplantation for selected patients. Vascular invasion of HCC is one of the most important negative predictor of survival. As the regulation of invasion of HCC cells is not well understood, our aim was to study the mechanisms by which galectin 3, a β-galactosidase-binding lectin mediates HCC cell migration. HCC was induced by N-diethylnitrosamine in wild-type and galectin 3(-/-) mice, and tumor formation, histology, and tumor cell invasion were assessed. The galectin 3(-/-) mice developed significantly smaller tumor burden with a less invasive phenotype than the wild-type animals. Galectin 3 was upregulated in the wild-type HCC tumor tissue, but not in the surrounding parenchyma. Galectin 3 expression in HCC was induced by NF-κB transactivation as determined by chromatin immunoprecipitation assays. In vitro studies assessed the pro-migratory effects of galectin 3. The migration of hepatoma cells was significantly decreased after transfection by the galectin 3 siRNA and also after using the Rho kinase inhibitor Y-27632. The reorganization of the actin cytoskeleton, RhoA GTPase activity and the phosphorylation of MLC2 (myosin light chain 2) were decreased in the galectin 3 siRNA-transfected cells. In addition, in vitro and in vivo evidence showed that galectin 3 deficiency reduced hepatoma cell proliferation and increased their apoptosis rate. In conclusion, galectin 3 is an important lectin that is induced in HCC cells, and promotes hepatoma cell motility and invasion by an autocrine pathway. Targeting galectin 3 therefore could be an important novel treatment strategy to halt disease progression.

Nuclear receptor-mediated alleviation of alcoholic fatty liver by polyphenols contained in alcoholic beverages

To elucidate the effect of the polyphenols contained in alcoholic beverages on the metabolic stress induced by ethanol consumption, four groups of mice were fed for five weeks on Lieber's diet with or without ethanol, with ethanol plus ellagic acid, and with ethanol plus trans-resveratrol. Alcoholic fatty liver was observed in the group fed the ethanol diet but not in those fed the ethanol plus polyphenol diets. Liver transcriptome analysis revealed that the addition of the polyphenols suppressed the expression of the genes related to cell stress that were up-regulated by ethanol alone. Conversely, the polyphenols up-regulated the genes involved in bile acid synthesis, unsaturated fatty acid elongation, and tetrahydrofolate synthesis that were down-regulated by ethanol alone. Because parts of these genes were known to be regulated by the constitutive androstane receptor (CAR), we performed the same experiment in the CAR-deficient mice. As a result, fatty liver was observed not only in the ethanol group but also with the ethanol plus polyphenol groups. In addition, there was no segregation of the gene expression profiles among these groups. These results provide a molecular basis for the prevention of alcohol-induced stress by the polyphenols in alcoholic beverages.

Foxa2 and H2A.Z mediate nucleosome depletion during embryonic stem cell differentiation

Nucleosome occupancy is fundamental for establishing chromatin architecture. However, little is known about the relationship between nucleosome dynamics and initial cell lineage specification. Here, we determine the mechanisms that control global nucleosome dynamics during embryonic stem (ES) cell differentiation into endoderm. Both nucleosome depletion and de novo occupation occur during the differentiation process, with higher overall nucleosome density after differentiation. The variant histone H2A.Z and the winged helix transcription factor Foxa2 both act to regulate nucleosome depletion and gene activation, thus promoting ES cell differentiation, whereas DNA methylation promotes nucleosome occupation and suppresses gene expression. Nucleosome depletion during ES cell differentiation is dependent on Nap1l1-coupled SWI/SNF and INO80 chromatin remodeling complexes. Thus, both epigenetic and genetic regulators cooperate to control nucleosome dynamics during ES cell fate decisions.

Foxa1 and Foxa2 are essential for sexual dimorphism in liver cancer

Hepatocellular carcinoma (HCC) is sexually dimorphic in both rodents and humans, with significantly higher incidence in males, an effect that is dependent on sex hormones. The molecular mechanisms by which estrogens prevent and androgens promote liver cancer remain unclear. Here, we discover that sexually dimorphic HCC is completely reversed in Foxa1- and Foxa2-deficient mice after diethylnitrosamine-induced hepatocarcinogenesis. Coregulation of target genes by Foxa1/a2 and either the estrogen receptor (ERα) or the androgen receptor (AR) was increased during hepatocarcinogenesis in normal female or male mice, respectively, but was lost in Foxa1/2-deficient mice. Thus, both estrogen-dependent resistance to and androgen-mediated facilitation of HCC depend on Foxa1/2. Strikingly, single nucleotide polymorphisms at FOXA2 binding sites reduce binding of both FOXA2 and ERα to their targets in human liver and correlate with HCC development in women. Thus, Foxa factors and their targets are central for the sexual dimorphism of HCC.

Transcriptional control of hepatocyte differentiation

The liver is the largest glandular organ in the body and plays a central role in controlling metabolism. During hepatogenesis, complex developmental processes must generate an array of cell types that are spatially arranged to generate a hepatic architecture that is essential to support liver function. The processes that control the ultimate formation of the liver are diverse and complex and in many cases poorly defined. Much of the focus of research during the past three decades has been on understanding how hepatocytes, which are the predominant liver parenchymal cells, differentiate during embryogenesis. Through a combination of mouse molecular genetics, embryology, and molecular biochemistry, investigators have defined a myriad of transcription factors that combine to control formation and function of hepatocytes. Here, we will review the major discoveries that underlie our current understanding of transcriptional regulation of hepatocyte differentiation.

The nucleosome map of the mammalian liver

Binding to nucleosomal DNA is critical for 'pioneer' transcription factors such as the winged-helix transcription factors Foxa1 and Foxa2 to regulate chromatin structure and gene activation. Here we report the genome-wide map of nucleosome positions in the mouse liver, with emphasis on transcriptional start sites, CpG islands, Foxa2 binding sites and their correlation with gene expression. Despite the heterogeneity of liver tissue, we could clearly discern the nucleosome pattern of the predominant liver cell, the hepatocyte. By analyzing nucleosome occupancy and the distributions of heterochromatin protein 1 (Hp1), CBP (also known as Crebbp) and p300 (Ep300) in Foxa1- and Foxa2-deficient livers, we find that the maintenance of nucleosome position and chromatin structure surrounding Foxa2 binding sites is independent of Foxa1 and Foxa2.

Inhibition of the liver enriched protein FOXA2 recovers HNF6 activity in human colon carcinoma and liver hepatoma cells

Recently, we demonstrated that the transcription factors HNF6 and FOXA2 function as key regulators in human colorectal liver metastases. To better understand their proposed inhibitory crosstalk, the consequences of functional knockdown of FOXA2 on HNF6 and C/EBPα activity were investigated in the human colon Caco-2 and HepG2 carcinoma cell lines. Specifically, siRNA-mediated gene silencing of FOXA2 repressed transcript expression by >80%. This resulted in a statistically significant 6-, 3-, 4-, and 8-fold increase in mRNA expression of HNF6 and of genes targeted by this transcription factor, e.g., HSP105B, CYP51, and C/EBPα, as determined by qRT-PCR. Thus, functional knockdown of FOXA2 recovered HNF6 activity. Furthermore, with nuclear extracts of Caco-2 cells no HNF6 DNA binding was observed, but expression of HNF1α, FOXA2, FOXA3, and HNF4α protein was abundant. We therefore transfected a plasmid encoding HNF6 into Caco-2 cells but also employed a retroviral vector to transfect HNF6 into HepG2 cells. This resulted in HNF6 protein expression with DNA binding activity being recovered as determined by EMSA band shift assays. Furthermore, by flow cytometry the consequences of HNF6 expression on cell cycle regulation in transfected cells was studied. Essentially, HNF6 inhibited cell cycle progression in the G2/M and G1 phase in Caco-2 and HepG2 cell lines, respectively. Here, proliferation was reduced by 80% and 50% in Caco-2 and HepG2 cells, respectively, as determined by the BrdU labeling assay. Therefore functional knockdown of FOXA2 recovered HNF6 activity and inhibited growth of tumor-cells and may possibly represent a novel therapeutic target in primary and secondary liver malignancies.

Genome-wide search identifies Ccnd2 as a direct transcriptional target of Elf5 in mouse mammary gland

Background

The ETS transcription factor Elf5 (also known as ESE-2) is highly expressed in the mammary gland and plays an important role in its development and differentiation. Indeed studies in mice have illustrated an essential role for Elf5 in directing alveologenesis during pregnancy. Although the molecular mechanisms that underlie the developmental block in Elf5 null mammary glands are beginning to be unraveled, this investigation has been hampered by limited information about the identity of Elf5-target genes. To address this shortcoming, in this study we have performed ChIP-cloning experiments to identify the specific genomic segments that are occupied by Elf5 in pregnant mouse mammary glands.

Results

Sequencing and genomic localization of cis-regulatory regions bound by Elf5 in vivo has identified several potential target genes covering broad functional categories. A subset of these target genes demonstrates higher expression levels in Elf5-null mammary glands suggesting a repressive functional role for this transcription factor. Here we focus on one putative target of Elf5, the Ccnd2 gene that appeared in our screen. We identify a novel Elf5-binding segment upstream of the Ccnd2 gene and demonstrate that Elf5 can transcriptionally repress Ccnd2 by directly binding to the proximal promoter region. Finally, using Elf5-null mammary epithelial cells and mammary glands, we show that loss of Elf5 in vivo leads to up regulation of Ccnd2 and an altered expression pattern in luminal cells.

Conclusions

Identification of Elf5-targets is an essential first step in elucidating the transcriptional landscape that is shaped by this important regulator. Our studies offer new toolbox in examining the biological role of Elf5 in mammary gland development and differentiation.

Transcriptional regulation of glucose sensors in pancreatic β-cells and liver: an update

Pancreatic β-cells and the liver play a key role in glucose homeostasis. After a meal or in a state of hyperglycemia, glucose is transported into the β-cells or hepatocytes where it is metabolized. In the β-cells, glucose is metabolized to increase the ATP:ADP ratio, resulting in the secretion of insulin stored in the vesicle. In the hepatocytes, glucose is metabolized to CO(2), fatty acids or stored as glycogen. In these cells, solute carrier family 2 (SLC2A2) and glucokinase play a key role in sensing and uptaking glucose. Dysfunction of these proteins results in the hyperglycemia which is one of the characteristics of type 2 diabetes mellitus (T2DM). Thus, studies on the molecular mechanisms of their transcriptional regulations are important in understanding pathogenesis and combating T2DM. In this paper, we will review a recent update on the progress of gene regulation of glucose sensors in the liver and β-cells.

C/EBPalpha regulates SIRT1 expression during adipogenesis

SIRT1 plays an important role in adipogenesis, but how SIRT1 is regulated in adipogenesis is largely unknown. In this study, we show that both SIRT1 protein and mRNA levels were increased along with CCAAT/enhancer-binding protein alpha (C/EBPalpha) during adipocyte differentiation. C/EBPalpha, but not C/EBPalphap30, activated SIRT1 promoter in both HeLa cells and 3T3-L1 preadipocytes. Furthermore, C/EBPalpha upregulated SIRT1 mRNA and protein levels in HeLa cells and increased SIRT1 expression in a p53-independent manner in Soas2 cells. In preadipocytes, ectopic expression of C/EBPalpha upregulated SIRT1 protein level and knockdown of C/EBPalpha led to the decrease of SIRT1 protein level. Moreover, by promoter deletion analysis, gel shift assay and chromatin immunoprecipitation, we found that C/EBPalpha bound to the SIRT1 promoter at a consensus C/EBPalpha binding site. These data demonstrate that C/EBPalpha regulates SIRT1 expression during adipogenesis by directly binding to the SIRT1 promoter.

Identification of interacting transcription factors regulating tissue gene expression in human

BACKGROUND

Tissue gene expression is generally regulated by multiple transcription factors (TFs). A major first step toward understanding how tissues achieve their specificity is to identify, at the genome scale, interacting TFs regulating gene expression in different tissues. Despite previous discoveries, the mechanisms that control tissue gene expression are not fully understood.

RESULTS

We have integrated a function conservation approach, which is based on evolutionary conservation of biological function, and genes with highest expression level in human tissues to predict TF pairs controlling tissue gene expression. To this end, we have identified 2549 TF pairs associated with a certain tissue. To find interacting TFs controlling tissue gene expression in a broad spatial and temporal manner, we looked for TF pairs common to the same type of tissues and identified 379 such TF pairs, based on which TF-TF interaction networks were further built. We also found that tissue-specific TFs may play an important role in recruiting non-tissue-specific TFs to the TF-TF interaction network, offering the potential for coordinating and controlling tissue gene expression across a variety of conditions.

CONCLUSION

The findings from this study indicate that tissue gene expression is regulated by large sets of interacting TFs either on the same promoter of a gene or through TF-TF interaction networks.

Identification of known and novel pancreas genes expressed downstream of Nkx2.2 during development

BACKGROUND

The homeodomain containing transcription factor Nkx2.2 is essential for the differentiation of pancreatic endocrine cells. Deletion of Nkx2.2 in mice leads to misspecification of islet cell types; insulin-expressing beta cells and glucagon-expressing alpha cells are replaced by ghrelin-expressing cells. Additional studies have suggested that Nkx2.2 functions both as a transcriptional repressor and activator to regulate islet cell formation and function. To identify genes that are potentially regulated by Nkx2.2 during the major wave of endocrine and exocrine cell differentiation, we assessed gene expression changes that occur in the absence of Nkx2.2 at the onset of the secondary transition in the developing pancreas.

RESULTS

Microarray analysis identified 80 genes that were differentially expressed in e12.5 and/or e13.5 Nkx2.2-/- embryos. Some of these genes encode transcription factors that have been previously identified in the pancreas, clarifying the position of Nkx2.2 within the islet transcriptional regulatory pathway. We also identified signaling factors and transmembrane proteins that function downstream of Nkx2.2, including several that have not previously been described in the pancreas. Interestingly, a number of known exocrine genes are also misexpressed in the Nkx2.2-/- pancreas.

CONCLUSIONS

Expression profiling of Nkx2.2-/- mice during embryogenesis has allowed us to identify known and novel pancreatic genes that function downstream of Nkx2.2 to regulate pancreas development. Several of the newly identified signaling factors and transmembrane proteins may function to influence islet cell fate decisions. These studies have also revealed a novel function for Nkx2.2 in maintaining appropriate exocrine gene expression. Most importantly, Nkx2.2 appears to function within a complex regulatory loop with Ngn3 at a key endocrine differentiation step.

Liver regeneration: alternative epithelial pathways

Loss of hepatic tissue triggers a regenerative response in the whole organ. Under typical normal conditions, all hepatic cells (epithelial: hepatocytes and biliary epithelial cells; non-epithelial: stellate cells, macrophages and endothelial cells) undergo one to three rounds of replication to establish the original number of cells and restore organ size. The review summarizes the literature of regenerative patterns in situations in which proliferation of either hepatocytes or biliary epithelial cells is inhibited. The evidence strongly suggests that under these circumstances, hepatocytes or biliary epithelial cells can function as facultative stem cells for each other and replenish the inhibited cellular compartment by a process of transdifferentiation, involving complex signaling pathways. These pathways are activated under experimental conditions in rodents and in fulminant hepatitis associated with liver failure in humans. Mechanistic analysis of these pathways has implications for liver biology and for potential therapeutic modalities in human liver disease.

Liver regeneration: alternative epithelial pathways

Loss of hepatic tissue triggers a regenerative response in the whole organ. Under typical normal conditions, all hepatic cells (epithelial: hepatocytes and biliary epithelial cells; non-epithelial: stellate cells, macrophages and endothelial cells) undergo one to three rounds of replication to establish the original number of cells and restore organ size. The review summarizes the literature of regenerative patterns in situations in which proliferation of either hepatocytes or biliary epithelial cells is inhibited. The evidence strongly suggests that under these circumstances, hepatocytes or biliary epithelial cells can function as facultative stem cells for each other and replenish the inhibited cellular compartment by a process of transdifferentiation, involving complex signaling pathways. These pathways are activated under experimental conditions in rodents and in fulminant hepatitis associated with liver failure in humans. Mechanistic analysis of these pathways has implications for liver biology and for potential therapeutic modalities in human liver disease.

Establishment of intestinal identity and epithelial-mesenchymal signaling by Cdx2

We demonstrate that conditional ablation of the homeobox transcription factor Cdx2 from early endoderm results in the replacement of the posterior intestinal epithelium with keratinocytes, a dramatic cell fate conversion caused by ectopic activation of the foregut/esophageal differentiation program. This anterior homeotic transformation of the intestine was first apparent in the early embryonic Cdx2-deficient gut by a caudal extension of the expression domains of several key foregut endoderm regulators. While the intestinal transcriptome was severely affected, Cdx2 deficiency only transiently modified selected posterior Hox genes and the primary enteric Hox code was maintained. Further, we demonstrate that Cdx2-directed intestinal cell fate adoption plays an important role in the establishment of normal epithelial-mesenchymal interactions, as multiple signaling pathways involved in this process were severely affected. We conclude that Cdx2 controls important aspects of intestinal identity and development, and that this function is largely independent of the enteric Hox code.

Foxa1 and Foxa2 regulate bile duct development in mice

The forkhead box proteins A1 and A2 (Foxa1 and Foxa2) are transcription factors with critical roles in establishing the developmental competence of the foregut endoderm and in initiating liver specification. Using conditional gene ablation during a later phase of liver development, we show here that deletion of both Foxa1 and Foxa2 (Foxa1/2) in the embryonic liver caused hyperplasia of the biliary tree. Abnormal bile duct formation in Foxa1/2-deficient liver was due, at least in part, to activation of IL-6 expression, a proliferative signal for cholangiocytes. The glucocorticoid receptor is a negative regulator of IL-6 transcription; in the absence of Foxa1/2, the glucocorticoid receptor failed to bind to the IL-6 promoter, causing enhanced IL-6 expression. Thus, after liver specification, Foxa1/2 are required for normal bile duct development through prevention of excess cholangiocyte proliferation. Our data suggest that Foxa1/2 function as terminators of bile duct expansion in the adult liver through inhibition of IL-6 expression.

Foxa2-dependent hepatic gene regulatory networks depend on physiological state

Bile acids are powerful detergents produced by the liver to aid in the absorption of dietary lipids. We recently reported a novel role for Foxa2 in bile acid metabolism. The winged helix transcription factor Foxa2 is required to prevent intrahepatic cholestasis and liver injury in mice fed a cholic acid-enriched diet. Here, we use functional genomics to study how Foxa2 regulates its targets in a cholic acid-dependent manner. We found that multiple signaling pathways essential for the hepatic response to acute liver injury are impaired in livers of Foxa2-deficient mice, suggesting that the deletion of Foxa2 in the hepatocyte affects the liver on a large scale. We also discovered distinct feed-forward regulatory loops controlling Foxa2-dependent targets in a cholic acid-dependent or -independent manner. We show that Foxa2 interacts with different transcription factors to achieve gene expression responses appropriate for each physiologic state.

Notch signaling controls liver development by regulating biliary differentiation

In the mammalian liver, bile is transported to the intestine through an intricate network of bile ducts. Notch signaling is required for normal duct formation, but its mode of action has been unclear. Here, we show in mice that bile ducts arise through a novel mechanism of tubulogenesis involving sequential radial differentiation. Notch signaling is activated in a subset of liver progenitor cells fated to become ductal cells, and pathway activation is necessary for biliary fate. Notch signals are also required for bile duct morphogenesis, and activation of Notch signaling in the hepatic lobule promotes ectopic biliary differentiation and tubule formation in a dose-dependent manner. Remarkably, activation of Notch signaling in postnatal hepatocytes causes them to adopt a biliary fate through a process of reprogramming that recapitulates normal bile duct development. These results reconcile previous conflicting reports about the role of Notch during liver development and suggest that Notch acts by coordinating biliary differentiation and morphogenesis.

Elf5 conditional knockout mice reveal its role as a master regulator in mammary alveolar development: failure of Stat5 activation and functional differentiation in the absence of Elf5

The transcription factor Elf5 plays an important role in mammary gland development. However, because of the embryonic lethality of Elf5 straight knockout mice, prior studies have been limited to experiments with Elf5 haploinsufficient animals, overexpression systems or transplants. Here, we have utilized K14-Cre to generate mammary-gland specific Elf5 conditional knockout mice. During pregnancy, Elf5-null mammary epithelium completely failed to initiate alveologenesis, and a characteristic of virgin ductal epithelial cells persisted postpartum. We demonstrate that the loss of Elf5 leads to the absence of alveolar secretory markers confirming previous published data. Interestingly, the developmental block due to a lack of Elf5 could not be restored by multiple gestations. Elf5-null mammary epithelial cells also display disorganized cell structures as evident by altered cell polarities, which might be the cause for collapsed lumina. We observe reduced levels of Stat5 and attenuated Stat5 activity as measured by p-Stat5 levels both in Elf5-null mammary glands as well as cultured mammary epithelial cells. This data suggests that the failure of alveolar and lactogenic differentiation due to the loss of Elf5 is mediated in part due to impaired Stat5 activity. In support of this hypothesis, we show by ChIP experiments that Stat5a promoter contains a conserved Elf5-binding site that is occupied by Elf5 in mammary glands. Mammary epithelia lacking Elf5 exhibited downregulation of several other critical genes involved in alveologenesis, suggesting Elf5 as a master regulator in alveolar development. We propose a model for Elf5-mediated alveolar development, in which Elf5 regulates the expression of key mediators of the PrlR/Jak2/Stat5 signaling pathway.

Enhanced glucose synthesis in three-dimensional hepatocyte collagen matrix

Three-dimensional (3D) cell culture model offers a unique opportunity to study hepatocytes that require extracellular matrix to keep the cells at the differentiated state. In this report, we cultured isolated mouse hepatocytes in a 3D collagen matrix system and developed a protocol to measure glucose production at 3h, 6h, 18h and 24h after culture. The results demonstrated that hepatocytes cultured under 3D collagen matrix condition consistently produced glucose at 240-290 mg/10(6) cells for up to 24h. Contrarily, hepatocytes cultured under traditional monolayer condition produced less than 50 mg/10(6) cells glucose. We demonstrated higher expression of phosphoenolpyruvate carboxykinase (PEPCK), a key enzyme for the synthesis of glucose from pyruvate, and CCAAT/enhancer-binding protein alpha (C/EBPalpha), an important liver-specific transcription factor, under the 3D collagen matrix culture condition in comparison to the monolayer condition. Thus, the 3D collagen matrix system preserved metabolic function of hepatocytes and can be used as an in vitro model for studying hepatocyte glucose production and gluconeogenesis.

FoxF1 and FoxL1 link hedgehog signaling and the control of epithelial proliferation in the developing stomach and intestine

The hedgehog (Hh) signaling pathway is a key component of cross-talk during vertebrate gut development, involving endodermally secreted Sonic (Shh) and Indian hedgehog (Ihh) proteins that directly signal to adjacent mesoderm. Here we show that the closely linked mesenchymal forkhead transcription factors Foxf1 and Foxl1 are part of this signaling cascade. Analysis of conserved non-coding sequences surrounding Foxf1 and Foxl1 identified seven Gli binding sites, with two sites near Foxl1 being identical among mammalian, bird, fish, and amphibian species. In vitro experiments indicate that Gli2 binds to these Gli sites, several of which are critical for Gli2-mediated activation of a luciferase reporter in 293 cells. In addition, we demonstrate occupancy of one of these elements by Gli proteins in the intestine in vivo using chromatin immunoprecipitation. Furthermore, expression of both Foxf1 and Foxl1 is reduced in the Gli2/Gli3 mutant gut. These results provide compelling evidence that Foxf1 and Foxl1 are mediators of the Hh (endoderm) to mesoderm signaling pathway.

Endocrine and gene expression changes following forced swim stress exposure during cocaine abstinence in mice

RATIONALE

Stress can reinstate previous cocaine-seeking long after drug is no longer present. However, little is known regarding the effect of chronic drug exposure and subsequent drug abstinence on responsivity to stress.

OBJECTIVE

To determine the effect of acute (24-h) and prolonged (14-day) drug-free periods in cocaine-experienced mice on behavioral, endocrine, and molecular outputs following stress exposure.

MATERIALS AND METHODS

Mice were administered a cocaine binge (15 mg/kg, every hour for 3h) for 2 weeks. Following a 24-h or 14-day drug-free period, stress responsivity, along with levels of anxiety, were measured using the forced swim test and elevated zero maze, respectively. In addition, alterations in the levels of plasma corticosterone, corticotrophin-releasing factor (CRF) mRNA, brain-derived neurotrophic factor (BDNF) mRNA, and histone acetylation at their respective promoters were examined following stress exposure.

RESULTS

At both acute and prolonged abstinence time points, behavioral measures were essentially unaltered; however, cocaine-experienced mice exhibited an augmented corticosterone response to the forced swim stress compared to saline-treated mice. Stress exposure increased BDNF mRNA levels in the ventral tegmental area (VTA) and nucleus accumbens (NAc) only in cocaine-experienced mice following a prolonged, but not acute, drug-free period. Increased BDNF mRNA in the NAc was associated with an increase in acetylated histone 3 (AcH3) at the BDNF I promoter. CRF mRNA levels were increased in the amygdala (AMYG); however, this was not associated with alterations in histone acetylation at the promoter.

CONCLUSION

These results demonstrate that drug history and prolonged abstinence can alter the endocrine and molecular responses to stress, which may facilitate the reinstatement of drug-seeking behaviors.

Hepatocyte-specific ablation of Foxa2 alters bile acid homeostasis and results in endoplasmic reticulum stress

Production of bile by the liver is crucial for the absorption of lipophilic nutrients. Dysregulation of bile acid homeostasis can lead to cholestatic liver disease and endoplasmic reticulum (ER) stress. We show by global location analysis ('ChIP-on-chip') and cell type-specific gene ablation that the winged helix transcription factor Foxa2 is required for normal bile acid homeostasis. As suggested by the location analysis, deletion of Foxa2 in hepatocytes in mice using the Cre-lox system leads to decreased transcription of genes encoding bile acid transporters on both the basolateral and canalicular membranes, resulting in intrahepatic cholestasis. Foxa2-deficient mice are strikingly sensitive to a diet containing cholic acid, which results in toxic accumulation of hepatic bile salts, ER stress and liver injury. In addition, we show that expression of FOXA2 is markedly decreased in liver samples from individuals with different cholestatic syndromes, suggesting that reduced FOXA2 abundance could exacerbate the injury.

Global analysis of in vivo Foxa2-binding sites in mouse adult liver using massively parallel sequencing

Foxa2 (HNF3β) is a one of three, closely related transcription factors that are critical to the development and function of the mouse liver. We have used chromatin immunoprecipitation and massively parallel Illumina 1G sequencing (ChIP–Seq) to create a genome-wide profile of in vivo Foxa2-binding sites in the adult liver. More than 65% of the ∼11.5 k genomic sites associated with Foxa2 binding, mapped to extended gene regions of annotated genes, while more than 30% of intragenic sites were located within first introns. 20.5% of all sites were further than 50 kb from any annotated gene, suggesting an association with novel gene regions. QPCR analysis demonstrated a strong positive correlation between peak height and fold enrichment for Foxa2-binding sites. We measured the relationship between Foxa2 and liver gene expression by overlapping Foxa2-binding sites with a SAGE transcriptome profile, and found that 43.5% of genes expressed in the liver were also associated with Foxa2 binding. We also identified potential Foxa2-interacting transcription factors whose motifs were enriched near Foxa2-binding sites. Our comprehensive results for in vivo Foxa2-binding sites in the mouse liver will contribute to resolving transcriptional regulatory networks that are important for adult liver function.

Cis-regulatory modules in the mammalian liver: composition depends on strength of Foxa2 consensus site

Foxa2 is a critical transcription factor that controls liver development and plays an important role in hepatic gluconeogensis in adult mice. Here, we use genome-wide location analysis for Foxa2 to identify its targets in the adult liver. We then show by computational analyses that Foxa2 containing cis-regulatory modules are not constructed from a random assortment of binding sites for other transcription factors expressed in the liver, but rather that their composition depends on the strength of the Foxa2 consensus site present. Genes containing a cis-regulatory module with a medium or weak Foxa2 consensus site are much more liver-specific than the genes with a strong consensus site. We not only provide a better understanding of the mechanisms of Foxa2 regulation but also introduce a novel method for identification of different cis-regulatory modules involving a single factor.

Expansion of adult beta-cell mass in response to increased metabolic demand is dependent on HNF-4alpha

The failure to expand functional pancreatic beta-cell mass in response to increased metabolic demand is a hallmark of type 2 diabetes. Lineage tracing studies indicate that replication of existing beta-cells is the principle mechanism for beta-cell expansion in adult mice. Here we demonstrate that the proliferative response of beta-cells is dependent on the orphan nuclear receptor hepatocyte nuclear factor-4alpha (HNF-4alpha), the gene that is mutated in Maturity-Onset Diabetes of the Young 1 (MODY1). Computational analysis of microarray expression profiles from isolated islets of mice lacking HNF-4alpha in pancreatic beta-cells reveals that HNF-4alpha regulates selected genes in the beta-cell, many of which are involved in proliferation. Using a physiological model of beta-cell expansion, we show that HNF-4alpha is required for beta-cell replication and the activation of the Ras/ERK signaling cascade in islets. This phenotype correlates with the down-regulation of suppression of tumorigenicity 5 (ST5) in HNF-4alpha mutants, which we identify as a novel regulator of ERK phosphorylation in beta-cells and a direct transcriptional target of HNF-4alpha in vivo. Together, these results indicate that HNF-4alpha is essential for the physiological expansion of adult beta-cell mass in response to increased metabolic demand.

The hepatocyte nuclear factor 6 (HNF6) and FOXA2 are key regulators in colorectal liver metastases

The molecular causes leading to secondary liver malignancies are unknown. Here we report regulation of major hepatic nuclear factors in human colorectal liver metastases and primary colonic cancer. Notably, the genes coding for HNF6, HNF1beta, and C/EBPgamma were selectively regulated in liver metastases. We therefore studied protein expression of regulated transcription factors and found unacetylated HNF6 to be a hallmark of colorectal liver metastases. For its known interaction with HNF6, we investigated expression of FOXA2, which we found to be specifically induced in colorectal liver metastases. By electromobility shift assay, we examined DNA binding of disease regulated transcription factors. Essentially, no HNF6 DNA binding was observed. We also searched for sequence variations in the DNA binding domains of HNF6, but did not identify any mutation. Furthermore, we probed for expression of 28 genes targeted by HNF6. Mostly transcript expression was repressed except for tumor growth. In conclusion, we show HNF6 protein expression to be driven by the hepatic environment. Its expression is not observed in healthy colon or primary colonic cancer. HNF6 DNA binding is selectively abrogated through lack of post-translational modification and interaction with FOXA2. Targeting of FOXA2 and HNF6 may therefore enable mechanism-based therapy for colorectal liver metastases.

EPConDB: a web resource for gene expression related to pancreatic development, beta-cell function and diabetes

EPConDB () is a public web site that supports research in diabetes, pancreatic development and beta-cell function by providing information about genes expressed in cells of the pancreas. EPConDB displays expression profiles for individual genes and information about transcripts, promoter elements and transcription factor binding sites. Gene expression results are obtained from studies examining tissue expression, pancreatic development and growth, differentiation of insulin-producing cells, islet or beta-cell injury, and genetic models of impaired beta-cell function. The expression datasets are derived using different microarray platforms, including the BCBC PancChips and Affymetrix gene expression arrays. Other datasets include semi-quantitative RT–PCR and MPSS expression studies. For selected microarray studies, lists of differentially expressed genes, derived from PaGE analysis, are displayed on the site. EPConDB provides database queries and tools to examine the relationship between a gene, its transcriptional regulation, protein function and expression in pancreatic tissues.

Mitogen-activated protein kinase-mediated disruption of enhancer-promoter communication inhibits hepatocyte nuclear factor 4alpha expression

Hepatocyte nuclear factor 4 (HNF-4) is a key member of the transcription factor network regulating hepatocyte differentiation and function. Activation of the HNF-4 gene involves physical interaction between a distant enhancer and the proximal promoter region, bound by distinct sets of transcription factors. Here we report that, upon mitogen-activated protein (MAP) kinase activation, HNF-4 expression is downregulated in human hepatoma cells. This effect is mediated by the loss of CEBPalpha expression. During MAP kinase signaling, the recruitment of HNF-3beta and HNF-1alpha to the HNF-4 enhancer and RNA polymerase II to the proximal HNF-4 promoter was compromised. CBP, Brg1, and TFIIB were also dissociated from the HNF-4 regulatory regions, and the enhancer-promoter complex was disrupted. Interestingly, the extent of nucleosome acetylation did not decrease at either regulatory region, and HNF-6 and HNF-1alpha, as well as components of the TFIID, remained associated with the proximal promoter during the repressed state. The results point to an absolute requirement of enhancer-promoter communication for maintaining the active state of the HNF-4 gene and provide evidence for a molecular bookmarking mechanism, which may contribute to the prevention of permanent silencing of the locus during the repressed state.

Foxa1-deficient mice exhibit impaired insulin secretion due to uncoupled oxidative phosphorylation

Foxa1 (formerly hepatic nuclear factor 3alpha) belongs to the family of Foxa genes that are expressed in early development and takes part in the differentiation of endoderm-derived organs and the regulation of glucose homeostasis. Foxa1-/- pups are growth retarded and hypoglycemic but glucose intolerant in response to an intraperitoneal glucose challenge. However, the mechanism of glucose intolerance in this model has not been investigated. Here, we show that Foxa1-/- islets exhibit decreased glucose-stimulated insulin release in islet perifusion experiments and have significantly reduced pancreatic insulin and glucagon content. Moreover, Foxa1-/- beta-cells exhibit attenuated calcium influx in response to glucose and glyburide, suggesting an insulin secretion defect either at the level or upstream of the ATP-sensitive K+ channel. Intracellular ATP levels after incubation with 10 mmol/l glucose were about 2.5 times lower in Foxa1-/- islets compared with controls. This diminished ATP synthesis could be explained by increased expression of the mitochondrial uncoupling protein uncoupling protein 2 (UCP2) in Foxa1-deficient islets, resulting in partially uncoupled mitochondria. Chromatin immunoprecipitation assays indicate that UCP2 is a direct transcriptional target of Foxa1 in vivo. Thus, we have identified a novel function for Foxa1 in the regulation of oxidative phosphorylation in pancreatic beta-cells.

Plasticity and expanding complexity of the hepatic transcription factor network during liver development

Cross-regulatory cascades between hepatic transcription factors have been implicated in the determination of the hepatic phenotype. Analysis of recruitments to regulatory regions and the temporal and spatial expression pattern of the main hepatic regulators during liver development revealed a gradual increase in complexity of autoregulatory and cross-regulatory circuits. Within these circuits we identified a core group of six transcription factors, which regulate the expression of each other and the expression of other downstream hepatic regulators. Changes in the promoter occupancy patterns during development included new recruitments, release, and exchange of specific factors. We also identified promoter and developmental stage-specific dual regulatory functions of certain factors as an important feature of the network. Inactivation of HNF-4alpha in embryonic, but not in adult, liver resulted in the diminished expression of most hepatic factors, demonstrating that the stability of the network correlates with its complexity. The results illustrate the remarkable flexibility of a self-sustaining transcription factor network, built up by complex dominant and redundant regulatory motifs in developing hepatocytes.

Threshold levels of hepatocyte nuclear factor 6 (HNF-6) acting in synergy with HNF-4 and PGC-1alpha are required for time-specific gene expression during liver development

During liver development, hepatocytes undergo a maturation process that leads to the fully differentiated state. This relies at least in part on the coordinated action of liver-enriched transcription factors (LETFs), but little is known about the dynamics of this coordination. In this context we investigate here the role of the LETF hepatocyte nuclear factor 6 (HNF-6; also called Onecut-1) during hepatocyte differentiation. We show that HNF-6 knockout mouse fetuses have delayed expression of glucose-6-phosphatase (g6pc), which catalyzes the final step of gluconeogenesis and is a late marker of hepatocyte maturation. Using a combination of in vivo and in vitro gain- and loss-of-function approaches, we demonstrate that HNF-6 stimulates endogenous g6pc gene expression directly via a synergistic and interdependent action with HNF-4 and that it involves coordinate recruitment of the coactivator PGC-1alpha. The expression of HNF-6, HNF-4, and PGC-1alpha rises steadily during liver development and precedes that of g6pc. We provide evidence that threshold levels of HNF-6 are required to allow synergism between HNF-6, HNF-4, and PGC-1alpha to induce time-specific expression of g6pc. Our observations on the regulation of g6pc by HNF-6 provide a model whereby synergism, interdependency, and threshold concentrations of LETFs and coactivators determine time-specific expression of genes during liver development.

Core transcriptional regulatory circuitry in human hepatocytes

We mapped the transcriptional regulatory circuitry for six master regulators in human hepatocytes using chromatin immunoprecipitation and high-resolution promoter microarrays. The results show that these regulators form a highly interconnected core circuitry, and reveal the local regulatory network motifs created by regulator–gene interactions. Autoregulation was a prominent theme among these regulators. We found that hepatocyte master regulators tend to bind promoter regions combinatorially and that the number of transcription factors bound to a promoter corresponds with observed gene expression. Our studies reveal portions of the core circuitry of human hepatocytes.

Mechanisms of mutual functional interactions between HNF-4alpha and HNF-1alpha revealed by mutations that cause maturity onset diabetes of the young

Hepatic nuclear factor (HNF)-4alpha and HNF-1alpha are key endodermal transcriptional regulators that physically and functionally interact. HNF-4alpha and HNF-1alpha cooperatively activate genes with binding sites for both factors, whereas suppressive interactions occur at regulatory sequences with a binding site for only one factor. The liver fatty acid binding protein gene (Fabp1) has binding sites for both factors, and chromatin precipitation assays were utilized to demonstrate that HNF-4alpha increased HNF-1alpha Fabp1 promoter occupancy during cooperative transcriptional activation. The HNF4 P2 promoter contains a HNF-1 but not HNF-4 binding site, and HNF-4alpha suppressed HNF-1alpha HNF4 P2 activation and decreased promoter HNF-1alpha occupancy. The apolipoprotein C III (APOC3) promoter contains a HNF-4 but not HNF-1 binding site, and HNF-1alpha suppressed HNF-4alpha APOC3 activation and decreased HNF-4alpha promoter occupancy. Maturity onset diabetes of the young (MODY) as well as defects in hepatic lipid metabolism result from mutations in either HNF-4alpha or HNF-1alpha. We found that MODY missense mutant R127W HNF-4alpha retained wild-type individual Fabp1 activation and bound to HNF-1alpha better than wild-type HNF-4alpha, yet did not cooperate with HNF-1alpha or increase HNF-1alpha Fabp1 promoter occupancy. The R127W mutant was also defective in both suppressing HNF-1alpha activation of HNF4 P2 and decreasing HNF-1alpha promoter occupancy. The HNF-1alpha R131Q MODY mutant also retained wild-type Fabp1 activation and bound to HNF-4alpha as well as the wild type but was defective in both suppressing HNF-4alpha APOC3 activation and decreasing HNF-4alpha promoter occupancy. These results suggest HNF-1alpha-HNF-4alpha functional interactions are accomplished by regulating factor promoter occupancy and that defective factor-factor interactions may contribute to the MODY phenotype.