The hepatocyte nuclear factor-3/forkhead transcription regulatory family in development, inflammation, and neoplasia

A high-concentrate diet provokes inflammatory responses by downregulating Forkhead box protein A2 (FOXA2) through epigenetic modifications in the liver of dairy cows

A high-concentrate diet has been reported to promote an inflammatory response in dairy cows. The purpose of this study was to clarify the effect of the high-concentrate (HC) diet on hepatic Forkhead box protein A2 (FOXA2) expression and uncover the molecular mechanisms in inflammatory responses in the liver. The results showed that the HC diet reduced the ruminal fluid pH and elevated the secretion of SAA3, IL-1α, and IL-8 and reduced that of IL-10 in peripheral blood plasma. Compared with the low-concentrate (LC) group, the concentration of myeloperoxidase (MPO) was higher in the liver of dairy cows in the HC group. In addition, the relative mRNA expression of acute phase proteins (HP, SAA3, and LBP), proinflammatory cytokines (TNFα, IL-1α, IL-1β, IL-8), TLR4, MyD88, TRAF6, TRIF, IκBα, p65, p38 and JNK1 was upregulated and that of IL-10 was downregulated in the liver of the HC group. Consistently, the protein abundance of TLR4, TNFα and phosphorylation of proteins involved in NF-κB (IκBα and p65) and MAPK (p38 and JNK) pathways were significantly increased in the HC group compared with the LC group. And both the mRNA and protein abundance of FOXA2 were downregulated in the HC group. Further epigenetic analysis results demonstrated that chromatin compaction and DNA hypermethylation contributed to inhibiting FOXA2 expression, in which the demethylase ten-eleven translocation 1 (TET1) and histone deacetylase 3 (HDAC3) might participate. Overall, these findings demonstrated that the high-concentrate diet triggered inflammatory cascades and downregulated FOXA2 by epigenetic modifications in the liver of dairy cows.

Trefoil Factor Family (TFF) Peptides and Their Links to Inflammation: A Re-evaluation and New Medical Perspectives

Trefoil factor family peptides (TFF1, TFF2, TFF3), together with mucins, are typical exocrine products of mucous epithelia. Here, they act as a gastric tumor suppressor (TFF1) or they play different roles in mucosal innate immune defense (TFF2, TFF3). Minute amounts are also secreted as endocrine, e.g., by the immune and central nervous systems. As a hallmark, TFF peptides have different lectin activities, best characterized for TFF2, but also TFF1. Pathologically, ectopic expression occurs during inflammation and in various tumors. In this review, the role of TFF peptides during inflammation is discussed on two levels. On the one hand, the expression of TFF1-3 is regulated by inflammatory signals in different ways (upstream links). On the other hand, TFF peptides influence inflammatory processes (downstream links). The latter are recognized best in various Tff-deficient mice, which have completely different phenotypes. In particular, TFF2 is secreted by myeloid cells (e.g., macrophages) and lymphocytes (e.g., memory T cells), where it modulates immune reactions triggering inflammation. As a new concept, in addition to lectin-triggered activation, a hypothetical lectin-triggered inhibition of glycosylated transmembrane receptors by TFF peptides is discussed. Thus, TFFs are promising players in the field of glycoimmunology, such as galectins and C-type lectins.

Hepatocyte nuclear factor-4α regulates expression of the serotonin transporter in intestinal epithelial cells

The serotonin transporter (SERT) functions to regulate the availability of serotonin (5-HT) in the brain and intestine. An intestine-specific mRNA variant arising from a unique transcription start site and alternative promoter in the SERT gene has been identified (iSERT; spanning exon 1C). A decrease in SERT is implicated in several gut disorders, including inflammatory bowel diseases (IBD). However, little is known about mechanisms regulating the iSERT variant, and a clearer understanding is warranted for targeting SERT for the treatment of gut disorders. The current studies examined the expression of iSERT across different human intestinal regions and investigated its regulation by HNF4α (hepatic nuclear factor-4α), a transcription factor important for diverse cellular functions. iSERT mRNA abundance was highest in the human ileum and Caco-2 cell line. iSERT mRNA expression was downregulated by loss of HNF4α (but not HNF1α, HNF1β, or FOXA1) in Caco-2 cells. Overexpression of HNF4α increased iSERT mRNA concomitant with an increase in SERT protein. Progressive promoter deletion and site-directed mutagenesis revealed that the HNF4α response element spans nucleotides -1,163 to -1150 relative to the translation start site. SERT mRNA levels in the intestine were drastically reduced in the intestine-specific HNF4α-knockout mice relative to HNF4αFL/FL mice. Both HNF4α and SERT mRNA levels were also downregulated in mouse model of ileitis (SAMP) compared with AKR control mice. These results establish the transcriptional regulation of iSERT at the gut-specific internal promoter (hSERTp2) and have identified HNF4α as a critical modulator of basal SERT expression in the intestine.

Functionally analyzing the important roles of hepatocyte nuclear factor 3 (FoxA) in tumorigenesis

Transcriptional factors (TFs) play a central role in governing gene expression under physiological conditions including the processes of embryonic development, metabolic homeostasis and response to extracellular stimuli. Conceivably, the aberrant dysregulations of TFs would dominantly result in various human disorders including tumorigenesis, diabetes and neurodegenerative diseases. Serving as the most evolutionarily reserved TFs, Fox family TFs have been explored to exert distinct biological functions in neoplastic development, by manipulating diverse gene expression. Recently, among the Fox family members, the pilot roles of FoxAs attract more attention due to their functions as both pioneer factor and transcriptional factor in human tumorigenesis, particularly in the sex-dimorphism tumors. Therefore, the pathological roles of FoxAs in tumorigenesis have been well-explored in modulating inflammation, immune response and metabolic homeostasis. In this review, we comprehensively summarize the impressive progression of FoxA functional annotation, clinical relevance, upstream regulators and downstream effectors, as well as valuable animal models, and highlight the potential strategies to target FoxAs for cancer therapies.

MAPK/FoxA2-mediated cigarette smoke-induced squamous metaplasia of bronchial epithelial cells

Objective

To explore the effect of cigarette smoke (CS) on the development of squamous metaplasia in human airway epithelial cells and the role of MAPK- and FoxA2-signaling pathways in the process.

Materials and methods

In an in vitro study, we treated the bronchial epithelial cell line BEAS2B with CS extract, followed by treatment with the ERK inhibitor U0126, the JNK inhibitor SP600125, or the p38 inhibitor SB203580. In vivo, we used a CS-induced rat model. After treatment with CS with or without MAPK inhibitors for 90 days, lung tissues were harvested. p-ERK, p-p38 and p-JNK protein levels in cells and lung tissue were measured using enzyme-linked immunosorbent assays, mRNA- and protein-expression profiles of FoxA2, E-cadherin, CD44, and ZO1 were measured using quantitative real-time polymerase chain reaction and Western blotting, respectively, and morphological changes in bronchial epithelial cells were observed using lung-tissue staining.

Results

In both the in vitro and in vivo studies, phosphorylation of the ERK1/2, JNK, and p38 proteins was significantly increased (P<0.05) and mRNA and protein expression of E-cadherin and FoxA2 significantly decreased (P<0.05) compared with the control group. ERK, JNK, and p38 inhibitors reversed the CS-extract-induced changes in E-cadherin, CD44, and ZO1 mRNA and protein expression (P<0.05), decreased p-ERK, p-p38, and p-JNK protein levels in cells and lung tissue, suppressed bronchial epithelial hyperplasia and local squamous metaplasia, and decreased FoxA2 expression.

Conclusion

MAPK and FoxA2 mediate CS-induced squamous metaplasia. MAPK inhibitors upregulate FoxA2, resulting in a reduction in the degree of squamous metaplasia.

Transcriptional Responses in the Murine Spleen after Toxoplasma gondii Infection: Inflammasome and Mucus-Associated Genes

The spleen plays an important role in coordinating both adaptive and innate immune responses. Here, the transcriptional response to T. gondii infection in the murine spleen was characterized concerning inflammasome sensors (two different models: seven days after oral or four weeks after intraperitoneal infection). Additionally, Tff1^KO and Tff3^KO mice were investigated because TFF genes are often upregulated during inflammation. The expression of the pattern-recognition receptors Nlrp3, Nlrp12, and Nlrp1a was significantly increased after infection. This increase was diminished in Tff1^KO and Tff3^KO mice pointing towards a positive regulation of the inflammatory response by Tff1 and Tff3. Furthermore, the transcription of Tff1 (encoding a motogenic lectin) and other secretory genes was analyzed, i.e., gastrokines (Gkn), IgG Fc binding protein (Fcgbp), and the mucin Muc2. The corresponding gene products belong to an interactome protecting mucous epithelia. Tff1 was significantly induced after infection, which might increase the motility of immune cells. In contrast, Gkn3, Fcgbp, and Muc2 were downregulated seven days after oral infection; whereas four weeks after i.p. infection only Gkn3 remained downregulated. This might be an indication that Gkn3, Fcgbp, and Muc2 are involved in the transient disruption of the splenic architecture and its reorganization, which is characteristic after T. gondii infection.

Epigenetic reprogramming of the germ cell nuclear factor gene is required for proper differentiation of induced pluripotent cells

Somatic cells have been reprogrammed into induced pluripotent stem (iPS) cells that recapitulate the pluripotent nature of embryonic stem (ES) cells. Reduced pluripotency and variable differentiation capacities have hampered progress with this technology for applications in regeneration medicine. We have previously shown that germ cell nuclear factor (Gcnf) is required for the repression of pluripotency genes during ES cell differentiation and embryonic development. Here we report that iPS cell lines, in which the Gcnf gene was properly reprogrammed, allowing expression of Gcnf, repress pluripotency genes during subsequent differentiation. In contrast, iPS clones in which the Gcnf gene was not reprogrammed maintained pluripotency gene expression during differentiation and did not differentiate properly either in vivo or in vitro. These mal-reprogrammed cells recapitulated the phenotype of Gcnf knockout (Gcnf(-/-)) ES cells. Reintroduction of Gcnf into either the Gcnf negative iPS cells or the Gcnf(-/-) ES cells rescued repression of Oct4 during differentiation. Our findings establish a key role for Gcnf as a regulator of iPS cell pluripotency gene expression. It also demonstrates that reactivation of the Gcnf gene may serve as a marker to distinguish completely reprogrammed iPS cells from incompletely pluripotent cells, which would make therapeutic use of iPS cells safer and more practical as it would reduce the oncogenic potential of iPS cells.

Expression of Drosophila forkhead transcription factors during kidney development

The Drosophila forkhead (Dfkh) family of transcription factors has over 40 family members. One Dfkh family member, BF2 (aka FoxD1), has been shown, by targeted disruption, to be essential for kidney development. In order to determine if other Dfkh family members were involved in kidney development and to search for new members of this family, reverse transcriptase polymerase chain reaction (RT-PCR) was performed using degenerate primers of the consensus sequence of the DNA binding domain of this family and developing rat kidney RNA. The RT-PCR product was used to probe RNA from a developing rat kidney (neonatal), from a 20-day old kidney, and from an adult kidney. The RT-PCR product hybridized only to a developing kidney RNA transcript of ∼2.3 kb (the size of BF2). A lambda gt10 mouse neonatal kidney library was then screened, using the above-described RT-PCR product as a probe. Three lambda phage clones were isolated that strongly hybridized to the RT-PCR probe. Sequencing of the RT-PCR product and the lambda phage clones isolated from the developing kidney library revealed Dfkh BF2. In summary, only Dfkh family member BF2, which has already been shown to be essential for nephrogenesis, was identified in our screen and no other candidate Dfkh family members were identified.

The transcription factor FOXM1 (Forkhead box M1): proliferation-specific expression, transcription factor function, target genes, mouse models, and normal biological roles

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor, which stimulates cell proliferation and exhibits a proliferation-specific expression pattern. Accordingly, both the expression and the transcriptional activity of FOXM1 are increased by proliferation signals, but decreased by antiproliferation signals, including the positive and negative regulation by protooncoproteins or tumor suppressors, respectively. FOXM1 stimulates cell cycle progression by promoting the entry into S-phase and M-phase. Moreover, FOXM1 is required for proper execution of mitosis. Accordingly, FOXM1 regulates the expression of genes, whose products control G1/S-transition, S-phase progression, G2/M-transition, and M-phase progression. Additionally, FOXM1 target genes encode proteins with functions in the execution of DNA replication and mitosis. FOXM1 is a transcriptional activator with a forkhead domain as DNA binding domain and with a very strong acidic transactivation domain. However, wild-type FOXM1 is (almost) inactive because the transactivation domain is repressed by three inhibitory domains. Inactive FOXM1 can be converted into a very potent transactivator by activating signals, which release the transactivation domain from its inhibition by the inhibitory domains. FOXM1 is essential for embryonic development and the foxm1 knockout is embryonically lethal. In adults, FOXM1 is important for tissue repair after injury. FOXM1 prevents premature senescence and interferes with contact inhibition. FOXM1 plays a role for maintenance of stem cell pluripotency and for self-renewal capacity of stem cells. The functions of FOXM1 in prevention of polyploidy and aneuploidy and in homologous recombination repair of DNA-double-strand breaks suggest an importance of FOXM1 for the maintenance of genomic stability and chromosomal integrity.

6p25 microdeletion: white matter abnormalities in an adult patient

We report on a 41-year-old woman of normal intelligence with a complicated past medical history including unilateral profound hearing loss, unilateral Axenfeld-Rieger anomaly, and leukoencephalopathy. She was referred to an adult neurology clinic because of a previous diagnosis of multiple sclerosis, which was non-responsive to multiple medications. Due to her complicated past medical history, the medical genetics service was consulted. She was found to have a chromosome 6p25.3-6p25.2 deletion on SNP array. This report highlights chromosome 6p subtelomeric deletions as a possible underlying cause for periventricular white matter abnormalities in an adult. It emphasizes the importance of genetic testing in an adult with leukoencephalopathy and congenital anomalies.

Allele-specific transactivation of matrix metalloproteinase 7 by FOXA2 and correlation with plasma levels in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a complex disease with poorly understood etiology. Previously, we reported upregulation of matrix metalloproteinase 7 (MMP7) in both lung and peripheral blood of IPF patients. Here we report evidence for genetic correlation of plasma levels and promoter polymorphisms (rs11568818 and rs11568819) of MMP7 in a well-characterized IPF cohort. Both the AA genotype of rs11568818 and the CT genotype of rs11568819 were found to be significantly associated with higher MMP7 plasma levels. These associations were observed only in IPF patients and not in healthy controls. The G-to-A transition of rs11568818 resulted in a novel binding site for the forkhead box A2 (FOXA2) transcription factor, a key regulator of embryonic lung development and proper function of the mature lung. In vitro, this transition led to increased sensitivity of the MMP7 promoter to FOXA2. In IPF lungs, FOXA2 was localized in the nucleus of epithelial cells that expressed MMP7 in the cytoplasm. These results suggest that increased sensitivity of the polymorphic MMP7 promoter to FOXA2 provides one of the genetic bases for the upregulation of MMP7 in IPF.

Role of Foxa1 in regulation of bcl2 expression during oxidative-stress-induced apoptosis in A549 type II pneumocytes

Forkhead box protein A1 (Foxa1) is an evolutionarily conserved winged helix transcription factor that was traditionally considered to be involved in embryonic development and cell differentiation. However, little is known about the role of Foxa1 in oxidative-stress-induced apoptosis. In this study, hydrogen peroxide (H(2)O(2))-induced apoptosis, upregulation of Foxa1, and the role of Foxa1 in the regulation of bcl2 gene expression were studied in A549 type II pneumocytes. H(2)O(2) upregulated Foxa1 mRNA and protein in a time- and dose-dependent manner. Overexpression of Foxa1 promoted apoptosis, whereas Foxa1 deficiency, induced by antisense oligonucleotides, decreased A549 cell apoptosis induced by H(2)O(2), as shown by flow cytometry. Moreover, Foxa1 overexpression decreased the expression of bcl2, while Foxa1 depletion increased the expression of bcl2. Electrophoretic mobility shift assay and chromatin immunoprecipitation revealed that Foxa1 bound to bcl2 promoter, and H(2)O(2) promoted its DNA binding activity. Luciferase reporter showed that Foxa1 also decreased the transcription activity of bcl2 promoter under normal conditions and oxidative stress. These results indicate that Foxa1 plays a pro-apoptotic role by inhibiting the expression of anti-apoptotic gene bcl2.

The expression and prognosis of FOXO3a and Skp2 in human hepatocellular carcinoma

The forkhead box proteins (FOXO proteins) comprise a large family of functionally diverse transcription factors involved in cellular proliferation, transformation, differentiation and longevity. Recently, ubiquitination and proteasome degradation of FOXO3a have been reported. In this study, we investigated the role of FOXO3a and Skp2 in human hepatocellular carcinoma progression. Immunohistochemical analysis was performed on formalin-fixed paraffin sections of 91 specimens. Furthermore in vitro, western-blot analysis and protein stabilization studies were used to study the relationship between FOXO3a and Skp2. We found that the expression of FOXO3a was negatively related with Skp2 expression (r = -0.583; p < 0.05) and FOXO3a expression correlated significantly with histological grade (p = 0.000), cirrhosis (p = 0.015), and tumor size (p = 0.043) while Skp2 expression correlated significantly with histological grade (p = 0.000) and tumor size (p = 0.005). Kaplan-Meier analysis revealed that survival curves of low versus high expressers of FOXO3a and Skp2 showed a highly significant separation in HCC (p < 0.01). Our results suggested that FOXO3a and Skp2 may be considered to be important prognosis in human hepatocellular carcinoma. In vitro studies suggested that the degradation of FOXO3a may dependent on the expression of Skp2 in the proliferated Huh7 cells.

A combination of HNF-4 and Foxo1 is required for reciprocal transcriptional regulation of glucokinase and glucose-6-phosphatase genes in response to fasting and feeding

Glucokinase (GK) and glucose-6-phosphatase (G6Pase) regulate rate-limiting reactions in the physiologically opposed metabolic cascades, glycolysis and gluconeogenesis, respectively. Expression of these genes is conversely regulated in the liver in response to fasting and feeding. We explored the mechanism of transcriptional regulation of these genes by nutritional condition and found that reciprocal function of HNF-4 and Foxo1 plays an important role in this process. In the GK gene regulation, Foxo1 represses HNF-4-potentiated transcription of the gene, whereas it synergizes with HNF-4 in activating the G6Pase gene transcription. These opposite actions of Foxo1 concomitantly take place in the cells under no insulin stimulus, and such gene-specific action was promoter context-dependent. Interestingly, HNF-4-binding elements (HBEs) in the GK and G6Pase promoters were required both for the insulin-stimulated GK gene activation and insulin-mediated G6Pase gene repression. Indeed, mouse in vivo imaging showed that mutating the HBEs in the GK and G6Pase promoters significantly impaired their reactivity to the nutritional states, even in the presence of intact Foxo1-binding sites (insulin response sequences). Thus, in the physiological response of the GK and G6Pase genes to fasting/feeding conditions, Foxo1 distinctly decodes the promoter context of these genes and differently modulates the function of HBE, which then leads to opposite outcomes of gene transcription.

Anaphase-promoting complex/cyclosome-CDH1-mediated proteolysis of the forkhead box M1 transcription factor is critical for regulated entry into S phase

The forkhead box M1 (FoxM1) transcription factor is overexpressed in many cancers, and in mouse models it is required for tumor progression. FoxM1 activates expression of the cell cycle genes required for both S and M phase progression. Here we demonstrate that FoxM1 is degraded in late mitosis and early G(1) phase by the anaphase-promoting complex/cyclosome (APC/C) E3 ubiquitin ligase. FoxM1 interacts with the APC/C complex and its adaptor, Cdh1. Expression of Cdh1 stimulated degradation of the FoxM1 protein, and depletion of Cdh1 resulted in stabilization of the FoxM1 protein in late mitosis and in early G(1) phase of the cell cycle. Cdh1 has been implicated in regulating S phase entry. We show that codepletion of FoxM1 inhibits early S phase entry observed in Cdh1-depleted cells. The N-terminal region of FoxM1 contains both destruction box (D box) and KEN box sequences that are required for targeting by Cdh1. Mutation of either the D box sequence or the KEN box sequence stabilized FoxM1 and blocked Cdh1-induced proteolysis. Cells expressing a nondegradable form of FoxM1 entered S phase rapidly following release from M phase arrest. Together, our observations show that FoxM1 is one of the targets of Cdh1 in late M or early G(1) phase and that its proteolysis is important for regulated entry into S phase.

Embryological origin of airway smooth muscle

Airway smooth muscle (SM) develops from local mesenchymal cells located around the tips of growing epithelial buds. These cells gradually displace from distal to proximal position alongside the bronchial tree, elongate, and begin to synthesize SM-specific proteins. Mechanical tension (either generated by cell spreading/elongation or stretch), as well as epithelial paracrine factors, regulates the process of bronchial myogenesis. The specific roles of many of these paracrine factors during normal lung development are currently unknown. It is also unknown how and if mechanical and paracrine signals integrate into a common myogenic pathway. Furthermore, as with vascular SM and other types of visceral SM, we are just beginning to elucidate the intracellular signaling pathways and the genetic program that controls lung myogenesis. Here we present what we have learned so far about the embryogenesis of bronchial muscle.

Crystal structure of the human FOXO3a-DBD/DNA complex suggests the effects of post-translational modification

FOXO3a is a transcription factor of the FOXO family. The FOXO proteins participate in multiple signaling pathways, and their transcriptional activity is regulated by several post-translational mechanisms, including phosphorylation, acetylation and ubiquitination. Because these post-translational modification sites are located within the C-terminal basic region of the FOXO DNA-binding domain (FOXO-DBD), it is possible that these post-translational modifications could alter the DNA-binding characteristics. To understand how FOXO mediate transcriptional activity, we report here the 2.7 A crystal structure of the DNA-binding domain of FOXO3a (FOXO3a-DBD) bound to a 13-bp DNA duplex containing a FOXO consensus binding sequence (GTAAACA). Based on a unique structural feature in the C-terminal region and results from biochemical and mutational studies, our studies may explain how FOXO-DBD C-terminal phosphorylation by protein kinase B (PKB) or acetylation by cAMP-response element binding protein (CBP) can attenuate the DNA-binding activity and thereby reduce transcriptional activity of FOXO proteins. In addition, we demonstrate that the methyl groups of specific thymine bases within the consensus sequence are important for FOXO3a-DBD recognition of the consensus binding site.

The human mucin MUC4 is transcriptionally regulated by caudal-related homeobox, hepatocyte nuclear factors, forkhead box A, and GATA endodermal transcription factors in epithelial cancer cells

The human gene MUC4 encodes a large transmembrane mucin that is developmentally regulated and expressed along the undifferentiated pseudostratified epithelium, as early as 6.5 weeks during fetal development. Immunohistochemical analysis of Muc4 expression in developing mouse lung and gastrointestinal tract showed a different spatio-temporal pattern of expression before and after cytodifferentiation. The molecular mechanisms governing MUC4 expression during development are, however, unknown. Hepatocyte nuclear factors (HNF), forkhead box A (FOXA), GATA, and caudal-related homeobox transcription factors (TFs) are known to control cell differentiation of gut endoderm derived-tissues during embryonic development. They also control the expression of cell- and tissue-specific genes and may thus control MUC4 expression. To test this hypothesis, we studied and deciphered the molecular mechanisms responsible for MUC4 transcriptional regulation by these TFs. Experiments using small interfering RNA, cell co-transfection, and site-directed mutagenesis indicated that MUC4 is regulated at the transcriptional level by CDX-1 and -2, HNF-1 alpha and -1 beta, FOXA1/A2, HNF-4 alpha and -4 gamma, and GATA-4, -5, and -6 factors in a cell-specific manner. Binding of TFs was assessed by chromatin immunoprecipitation, and gel-shift assays. Altogether, these results demonstrate that MUC4 is a target gene of endodermal TFs and thus point out an important role for these TFs in regulating MUC4 expression during epithelial differentiation during development, cancer, and repair.

Regulation of hepatitis B virus transcription and replication by liver-enriched transcriptional factors

Hepatotropism is a prominent feature of hepatitis B virus (HBV). Cell lines of nonhepatic origin do not independently support HBV replication. In this review, we show that the nuclear hormone receptors, hepatocyte nuclear factor 4 and retinoid X receptor plus peroxisome proliferator-activated receptor, support HBV replication in nonhepatic cells by controlling pregenomic RNA synthesis, indicating that these liver-enriched transcription factors control a unique molecular switch restricting viral tropism. In contrast, hepatocyte nuclear factor 3 antagonizes nuclear hormone receptor-mediated viral replication, demonstrating distinct regulatory roles for these liver-enriched transcription factors.

The forkhead box M1 transcription factor contributes to the development and growth of mouse colorectal cancer

BACKGROUND & AIMS

In this study, we used Forkhead Box m1b (Foxm1b) transgenic mice and conditional Foxm1 knock-out mice to examine the role of Foxm1 in colon cancer development and proliferation.

METHODS

To induce mouse colorectal cancer, we used a single intraperitoneal injection of azoxymethane (AOM) followed by three 1-week cycles of 2.5% dextran sodium sulfate (DSS) water, each cycle separated by 2 weeks. For these colon tumor studies, we used either Rosa26-Foxm1b transgenic mice that ubiquitously expressed the human Foxm1b complementary DNA or mice in which the Foxm1 fl/fl targeted allele was deleted in colonic epithelial cells using the gut-specific Villin-Cre recombinase transgene (Villin-Cre). Colorectal tumor number and bromodeoxyuridine labeling were determined in Rosa26-Foxm1b mice, Villin-Cre Foxm1-/-, mice and wild-type mice after 12 weeks of AOM/DDS exposure. We also used Foxm1 small interfering RNA-depleted human DLD1 and mouse CT26 colon cancer cell lines to examine DNA replication and anchorage-independent growth.

RESULTS

After 12 weeks of treatment with AOM/DSS, Rosa26 Foxm1b transgenic mice showed an increase in the number and size of colorectal tumors compared with wild-type mice. Likewise, a significant reduction in the development and growth of colorectal tumors was found in Villin-Cre Foxm1-/- mice compared with Foxm1 fl/fl mice after AOM/DSS treatment, which was associated with decreased expression of cyclin A2, cyclin B1, survivin, and T-cell factor 4 genes. Moreover, Foxm1-depleted colon cancer cell lines showed reduced DNA replication and anchorage-independent growth.

CONCLUSIONS

These studies suggest that Foxm1 is critical for the proliferation and growth of colorectal cancer.

FoxO1 is required for the regulation of preproglucagon gene expression by insulin in pancreatic alphaTC1-9 cells

Forkhead/winged helix box gene, group O-1 (FoxO1) is a member of a family of nuclear transcription factors regulated by insulin-dependent phosphorylation and implicated in the development of the endocrine pancreas. We show here firstly that FoxO1 protein is expressed in both primary mouse islet alpha and beta cells. Examined in clonal alphaTC1-9 cells, insulin caused endogenous FoxO1 to translocate from the nucleus to the cytoplasm. Demonstrating the importance of nuclear exclusion of FoxO1 for the inhibition of preproglucagon gene expression, FoxO1 silencing by RNA interference reduced preproglucagon mRNA levels by >40% in the absence of insulin and abolished the decrease in mRNA levels elicited by the hormone. Electrophoretic mobility shift assay and chromatin immunoprecipitation revealed direct binding of FoxO1 to a forkhead consensus binding site, termed GL3, in the preproglucagon gene promoter region, localized -1798 bp upstream of the transcriptional start site. Deletion or mutation of this site diminished FoxO1 binding and eliminated transcriptional regulation by glucose or insulin. FoxO1 silencing also abolished the acute regulation by insulin, but not glucose, of glucagon secretion, demonstrating the importance of FoxO1 expression in maintaining the alpha-cell phenotype.

Expression of the forkhead transcription factor FoxN4 in progenitor cells in the developing Xenopus laevis retina and brain

Forkhead proteins are involved in gene regulation in a large variety of developmental situations. Several forkhead gene products are expressed in the developing eye and brain. Here we characterize the expression of FoxN4 during Xenopus development. We report that FoxN4 is expressed in the eye from the earliest stages of specification through retinal maturation. FoxN4 is also expressed in the pallium, optic tectum, isthmus, reticular formation, and in cells lining the ventricle of the tadpole brain.

Induced trefoil factor family 1 expression by trans-differentiating Clara cells in a murine asthma model

Asthma is a chronic inflammatory disease of the airways that is accompanied by goblet cell metaplasia and mucus hypersecretion. Trefoil factor family (TFF) peptides represent major secretory products of the respiratory tract and are synthesized together with mucins. In the murine lung, TFF2 is mainly expressed, whereas TFF1 transcripts represent only a minor species. TFF peptides are well known for their motogenic and anti-apoptotic effects, and they modulate the inflammatory response of bronchial epithelial cells. Here, an established mouse model of asthma was investigated (i.e., exposure to Aspergillus fumigatus [AF] antigens). RT-PCR analysis of lung tissue showed elevated levels particularly of TFF1 transcripts in AF-sensitized/challenged animals. In contrast, transcripts encoding Clara cell secretory protein (CCSP/CC10) were strongly diminished in these animals. For comparison, the expression of the goblet cell secretory granule marker mCLCA3/Gob-5, the mucins Muc1-Muc6 and Muc19, and the secretoglobins ScgB3A1 and ScgB3A2, as well as the mammalian ependymin-related gene MERP2, were monitored. Immunohistochemistry localized TFF1 mainly in cells with a mixed phenotype (e.g., TFF1-positive cells stain with the lectin wheat germ agglutinin (WGA), which recognizes mucins characteristic of goblet cells). In addition, these cells express CCSP/CC10, a Clara cell marker. When compared with mucins or CCSP/CC10, TFF1 was stored in a different population of secretory granules localized at the more basolateral portion of these cells. Thus, the results presented indicate for the first time that allergen exposure leads to the trans-differentiation of Clara cells toward a TFF1-expressing mucous phenotype.

Crystal structure of the human FOXK1a-DNA complex and its implications on the diverse binding specificity of winged helix/forkhead proteins

Interleukin enhancer binding factor (ILF) is a human transcription factor and a new member of the winged helix/forkhead family. ILF can bind to purine-rich regulatory motifs such as the human T-cell leukemia virus-long terminal region and the interleukin-2 promoter. Here we report the 2.4 A crystal structure of two DNA binding domains of ILF (FOXK1a) binding to a 16-bp DNA duplex containing a promoter sequence. Electrophoretic mobility shift assay studies demonstrate that two ILF-DNA binding domain molecules cooperatively bind to DNA. In addition to the recognition helix recognizing the core sequences through the major groove, the structure shows that wing 1 interacts with the minor groove of DNA, and the H2-H3 loop region makes ionic bonds to the phosphate group, which permits the recognition of DNA. The structure also reveals that the presence of the C-terminal alpha-helix in place of a typical wing 2 in a member of this family alters the orientation of the C-terminal basic residues (RKRRPR) when binding to DNA outside the core sequence. These results provide a new insight into how the DNA binding specificities of winged helix/forkhead proteins may be regulated by their less conserved regions.

Role of the CCAAT/enhancer-binding protein NFATc2 transcription factor cascade in the induction of secretory phospholipase A2

Inflammatory cytokines such as interleukin-1 and tumor necrosis factor-alpha modulate a transcription factor cascade in the liver to induce and sustain an acute and systemic defense against foreign entities. The transcription factors involved include NF-kappaB, STAT, and CCAAT/enhancer-binding protein (C/EBP). Whether the NFAT group of transcription factors (which was first characterized as playing an important role in cytokine gene expression in the adaptive response in immune cells) participates in the acute-phase response in hepatocytes is not known. Here, we have investigated whether NFAT is part of the transcription factor cascade in hepatocytes during inflammatory stress. We report that interleukin-1 or tumor necrosis factor-alpha increases expression of and activates NFATc2. C/EBP-mediated NFATc2 induction is temporally required for expression of type IIA secretory phospholipase A2. NFATc2 is also required for expression of phospholipase D1 and the calcium-binding protein S100A3. Thus, a C/EBP-NFATc2 transcription factor cascade provides an additional means to modulate the acute-phase response upon stimulation with inflammatory cytokines.

Recapitulation of in vivo gene expression during hepatic differentiation from murine embryonic stem cells

Hepatic differentiation at the molecular level is poorly understood, mainly because of the lack of a suitable model. Recently, using adherent monoculture conditions, we demonstrated the direct differentiation of hepatocytes from embryonic stem (ES) cells. In this study, we exploited the direct differentiation model to compare the gene expression profiles of ES cell-derived hepatocytes with adult mouse liver using DNA microarray technology. The results showed that the ES cell-derived hepatocyte gene expression pattern is very similar to adult mouse liver. Through further analysis of gene ontology categories for the 232 most radically altered genes, we found that the significant categories related to hepatic function. Furthermore, through the use of small interfering RNA technology in vitro, hepatocyte nuclear factor 3beta/FoxA2 was identified as having an essential role in hepatic differentiation. These results demonstrate that ES cell-derived hepatocytes recapitulate the gene expression profile of adult mouse liver to a significant degree and indicate that our direct induction system progresses via endoderm differentiation. In conclusion, our system closely mimics in vivo hepatic differentiation at the transcriptional level and could, therefore, be useful for studying the molecular basis of hepatocyte differentiation per se.

Compensatory roles of Foxa1 and Foxa2 during lung morphogenesis

Foxa1 and Foxa2 are closely related family members of the Foxa group of transcription factors that are coexpressed in subsets of respiratory epithelial cells throughout lung morphogenesis. Shared patterns of expression, conservation of DNA binding, and transcriptional activation domains indicate that they may serve complementary functions in the regulation of gene expression during lung morphogenesis. Whereas branching morphogenesis of the fetal lung occurs normally in the Foxa2Delta/Delta and Foxa1-/- mice, deletion of both Foxa1 and Foxa2 (in Foxa2Delta/Delta, Foxa1-/- mice) inhibited cell proliferation, epithelial cell differentiation, and branching. Dilation of terminal lung tubules and decreased branching were observed as early as embryonic day 12.5. Foxa1 and Foxa2 regulated Shh (sonic hedgehog) and Shh-dependent genes in the respiratory epithelial cells that influenced the expression of genes in the pulmonary mesenchyme that are required for branching morphogenesis. Epithelial cell differentiation, as indicated by lack of expression of surfactant protein B, surfactant protein C, the Clara cell secretory protein, and Foxj1, was inhibited. Foxa family members regulate signaling and transcriptional programs required for morphogenesis and cell differentiation during formation of the lung.

A Transcriptional Profiling Study of CCAAT/Enhancer Binding Protein Targets Identifies Hepatocyte Nuclear Factor 3β as a Novel Tumor Suppressor in Lung Cancer

We showed previously that CCAAT/enhancer binding protein alpha (C/EBP alpha), a tissue-specific transcription factor, is a candidate tumor suppressor in lung cancer. In the present study, we have performed a transcriptional profiling study of C/EBP alpha target genes using an inducible cell line system. This study led to the identification of hepatocyte nuclear factor 3beta (HNF3 beta), a transcription factor known to play a role in airway differentiation, as a downstream target of C/EBP alpha. We found down-regulation of HNF3 beta expression in a large proportion of lung cancer cell lines examined and identified two novel mutants of HNF3 beta, as well as hypermethylation of the HNF3 beta promoter. We also developed a tetracycline-inducible cell line model to study the cellular consequences of HNF3 beta expression. Conditional expression of HNF3 beta led to significant growth reduction, proliferation arrest, apoptosis, and loss of clonogenic ability, suggesting additionally that HNF3 beta is a novel tumor suppressor in lung cancer. This is the first study to show genetic abnormalities of lung-specific differentiation pathways in the development of lung cancer.

Role of hepatocyte nuclear factor 3γ in the expression of human CYP2C genes

Hepatocyte nuclear factor 3 gamma (HNF-3 gamma) is an important transcription factor for the maintenance of specific liver functions. However, its relevance in the expression of human cytochrome P450 (CYP) genes has not yet been explored. Several HNF3 putative binding sites can be identified in human CYP2C 5'-flanking regions. Gene reporter experiments with proximal promoters revealed that HNF-3 gamma transactivated CYP2C8, CYP2C9, and CYP2C19 (25-, 4-, and 4-fold, respectively), but it did not transactivate CYP2C18. However, overexpression of HNF-3 gamma in hepatoma cells by means of a recombinant adenovirus induced CYP2C9, CYP2C18, and CYP2C19 mRNA (4.5-, 20-, and 50-fold, respectively) but did not activate endogenous CYP2C8. The lack of effect of HNF-3 gamma on endogenous CYP2C8 could be reversed by treating cells with the deacetylase inhibitor, trichostatin A, suggesting the existence of chromatin condensation around functional HNF3 elements in this gene. We conclude that HNF3 gamma is an important transcription factor for the hepatic-specific expression of human CYP2C genes. Our results also evidence that efficient transfection tools, such as adenoviral vectors, may be decisive for assessing the role of transcription factor on chromatin organized genes.

435-bp liver regulatory sequence in the liver fatty acid binding protein (L-FABP) gene is sufficient to modulate liver regional expression in transgenic zebrafish

Liver fatty acid binding protein (L-FABP) is a small protein that is thought to play an important role in the intracellular binding and trafficking of long chain fatty acids in the liver. Expression of the gene encoding the zebrafish liver fatty acid binding protein is regulated by a 435-bp distal region (-1944 to -1510) of the L-FABP promoter. The 435-bp sequence is sufficient for gene activation in the liver primordia (or bud) and continues to be active in the adult liver when positioned adjacent to the SV40 basal promoter and linked directly to green fluorescent protein. The 435-bp sequence region has two distinct liver regulatory elements, A (-1944 to -1623) and B (-1622 to -1510), and contains multiple putative consensus binding sites. The element A sequence includes two consensus HFH and one HNF-1alpha site and the element B sequence includes one consensus HNF-3beta site. Deletion of an internal 435-bp fragment (-1944 to -1510) including the A and B elements totally ablated the liver-specific activity of the zebrafish L-FABP gene promoter. Deletion of either of the two elements reduces the liver activity. Mutation of the HNF-1alpha site or either of the two HFH sites in the A element or the HNF-3beta site in the B element significantly altered specificity in the liver primordia of transient expression embryos. The importance of the HNF-1alpha consensus binding site in the A element and the HNF-3beta consensus binding site in the B element within the 435-bp distal region of the L-FABP promoter region suggests that combinatorial interactions between multiple regulatory factors are responsible for the gene expression of L-FABP in the liver.

A family with Axenfeld-Rieger syndrome and Peters Anomaly caused by a point mutation (Phe112Ser) in the FOXC1 gene

PURPOSE

Mutations of the forkhead transcription factor gene FOXC1 result in anterior segment anomalies. No description of the spectrum of defects resulting from a single point mutation of this gene exists in the ophthalmology literature. We have screened all available patients with Axenfeld-Rieger genes (PITX2 and FOXC1). In this report, we clinically characterize the spectrum of ocular and systemic manifestations in one family resulting from a previously reported point mutation (Phe112Ser) in FOXC1.

DESIGN

Observational case series.

METHODS

Ten members of a multigenerational family were examined for signs of glaucoma, anterior segment abnormalities, and systemic features of Axenfeld-Rieger syndrome. The examinations were performed in an ophthalmology examination room or in the patients' homes. Blood was obtained from 10 members and screened for mutations in FOXC1 using direct DNA sequencing.

RESULTS

A single mutation causing a T to C change in codon 112 (Phe112Ser) of FOXC1 was present in six members of the family. Five of these six patients were examined and all demonstrated anterior segment anomalies. One patient had Axenfeld anomaly, one had Rieger syndrome, and one had both Axenfeld anomaly and Peters anomaly. Additionally, some members demonstrated cardiac abnormalities, which may be secondary to their FOXC1 mutation.

CONCLUSIONS

A wide spectrum of clinical phenotypes can result from a single point mutation of FOXC1. This report confirms that Rieger syndrome (with dental and facial abnormalities) can be caused by a mutation in FOXC1. It is also the first report of Peters anomaly being caused by a FOXC1 mutation.

PAX3-FKHR transformation increases 26 S proteasome-dependent degradation of p27Kip1, a potential role for elevated Skp2 expression

PAX3-FKHR is an oncogenic form of the developmental regulator Pax3 transcription factor. PAX3-FKHR results from a t(2,13) chromosomal translocation, a unique genetic marker of alveolar rhabdomyosarcoma. In this study, we showed that ectopic expression of PAX3-FKHR, but not Pax3, in fibroblasts altered cell cycle control and accelerated G(0)/G(1) to S cell cycle transition. PAX3-FKHR-expressing cells had reduced expression of p27(Kip1) protein, a key cell cycle regulator. The reduction in p27(Kip1) levels by PAX3-FKHR resulted from destabilization of p27(Kip1) as shown by cycloheximide treatment and in vivo pulse-chase labeling experiments. The reduced p27(Kip1) protein level in PAX3-FKHR-expressing cells was restored to the level of control cells by treatment with chemical inhibitors that specifically blocked 26 S proteasome activity. Along with the reduction in p27(Kip1) protein, PAX3-FKHR-expressing cells exhibited elevated expression of F-box Skp2 protein, a substrate-specific component of SCF (Skp1-Cullin-F box protein) ligase involved in the cell cycle-dependent control of p27(Kip1) ubiquitination and 26 S proteasome dependent degradation. Finally, we showed that ectopic expression of p27(Kip1) in PAX3-FKHR-expressing cells significantly reduced the proliferation and colony-forming potential of these cells, implicating that down-regulation of p27(Kip1) protein played an active role in the PAX3-FKHR-directed cell transformation.

Solution structure of the DNA-binding domain of interleukin enhancer binding factor 1 (FOXK1a)

Interleukin enhancer binding factor (ILF) binds to the interleukin-2 (IL-2) promoter and regulates IL-2 gene expression. In this study, the 3D structure of the DNA-binding domain of ILF was determined by multidimensional NMR spectroscopy. NMR structure analysis revealed that the DNA-binding domain of ILF is a new member of the winged helix/forkhead family, and that its wing 2 contains an extra alpha-helix. This is the first study to report the presence of a C-terminal alpha-helix in place of a typical wing 2 in a member of this family. This structural difference may be responsible for the different DNA-binding specificity of ILF compared to other winged helix/forkhead proteins. Our deletion studies of the fragments of ILF also suggest that the C-terminal region plays a regulatory role in DNA binding.

Stem cell pluripotency and transcription factor Oct4

Mammalian cell totipotency is a subject that has fascinated scientists for generations. A long lasting question whether some of the somatic cells retains totipotency was answered by the cloning of Dolly at the end of the 20th century. The dawn of the 21st has brought forward great expectations in harnessing the power of totipotentcy in medicine. Through stem cell biology, it is possible to generate any parts of the human body by stem cell engineering. Considerable resources will be devoted to harness the untapped potentials of stem cells in the foreseeable future which may transform medicine as we know today. At the molecular level, totipotency has been linked to a singular transcription factor and its expression appears to define whether a cell should be totipotent. Named Oct4, it can activate or repress the expression of various genes. Curiously, very little is known about Oct4 beyond its ability to regulate gene expression. The mechanism by which Oct4 specifies totipotency remains entirely unresolved. In this review, we summarize the structure and function of Oct4 and address issues related to Oct4 function in maintaining totipotency or pluripotency of embryonic stem cells.

Mechanisms of inhibition of nuclear hormone receptor-dependent hepatitis B virus replication by hepatocyte nuclear factor 3beta

The nuclear hormone receptors hepatocyte nuclear factor 4 (HNF4) and the retinoid X alpha (RXRalpha) plus the peroxisome proliferator-activated receptor alpha (PPARalpha) heterodimer support hepatitis B virus (HBV) replication in nonhepatoma cells. Hepatocyte nuclear factor 3 (HNF3) inhibits nuclear hormone receptor-mediated viral replication. Inhibition of HBV replication by HNF3beta is associated with the preferential reduction in the level of the pregenomic RNA compared with that of precore RNA. Hepatitis B e antigen (HBeAg), encoded by the precore RNA, mediates part of the inhibition of viral replication by HNF3beta. The amino-terminal transcriptional activation domain of HNF3beta is essential for the inhibition of HBV replication. The activation of transcription by HNF3 from HBV promoters downstream from the nucleocapsid promoter appears to contribute indirectly to the reduction in the steady-state level of 3.5-kb HBV RNA, possibly by interfering with the elongation rate of these transcripts. Therefore, transcriptional interference mediated by HNF3 may also regulate HBV RNA synthesis and viral replication.

Maintaining HNF6 expression prevents AdHNF3beta-mediated decrease in hepatic levels of Glut-2 and glycogen

The hepatocyte nuclear factor 3 (HNF-3) proteins are members of the Forkhead Box (Fox) family of transcription factors that play important roles in regulating expression of genes involved in cellular proliferation, differentiation, and metabolic homeostasis. In previous studies we increased liver expression of HNF-3beta by using either transgenic mice (transthyretin HNF-3beta) or recombinant adenovirus infection (AdHNF3beta), and observed diminished hepatic levels of glycogen, and glucose transporter 2 (Glut-2), as well as the HNF-6, HNF-3, HNF-1alpha, HNF-4alpha, and C/EBPalpha transcription factors. We conducted the present study to determine whether maintaining HNF-6 protein expression during AdHNF3beta infection prevents reduction of hepatic levels of glycogen and the earlier-mentioned genes. Here, we show that AdHNF3beta- and AdHNF6-infected mouse liver displayed increased hepatic levels of glycogen, Glut-2, HNF-3gamma, HNF-1alpha, and HNF-4alpha at 2 and 3 days postinfection (PI). Furthermore, restoration of hepatic glycogen levels after AdHNF3beta and AdHNF6 coinfection was associated with increased Glut-2 expression. AdHNF6 infection alone caused a 2-fold increase in hepatic Glut-2 levels, suggesting that HNF 6 stimulates in vivo transcription of the Glut-2 gene. DNA binding assays showed that only recombinant HNF-6 protein, but not the HNF-3 proteins, binds to the mouse -185 to -144 bp Glut-2 promoter sequences. Cotransfection assays in human hepatoma (HepG2) cells with either HNF-3 or HNF-6 expression vectors show that only HNF-6 provided significant transcriptional activation of the Glut-2 promoter. In conclusion, these studies show that the hepatic Glut-2 promoter is a direct target for HNF-6 transcriptional activation.

The embryonic stem cell transcription factors Oct-4 and FoxD3 interact to regulate endodermal-specific promoter expression

The POU homeodomain protein Oct-4 and the Forkhead Box protein FoxD3 (previously Genesis) are transcriptional regulators expressed in embryonic stem cells. Down-regulation of Oct-4 during gastrulation is essential for proper endoderm development. After gastrulation, FoxD3 is generally down-regulated during early endoderm formation, although it specifically remains expressed in the embryonic neural crest. In these studies, we have found that Oct-4 and FoxD3 can bind to identical regulatory DNA sequences. In addition, Oct-4 physically interacted with the FoxD3 DNA-binding domain. Cotransfection of Oct-4 and FoxD3 expression vectors activated the osteopontin enhancer, which is expressed in totipotent embryonic stem cells. FoxA1 and FoxA2 (previously HNF-3alpha and HNF-3beta) are Forkhead Box transcription factors that participate in liver and lung formation from foregut endoderm. Although FoxD3 activated the FoxA1 and FoxA2 promoters, Oct-4 inhibited FoxD3 activation of the FoxA1 and FoxA2 endodermal promoters. These data indicate that Oct-4 functions as a corepressor of FoxD3 to provide embryonic lineage-specific transcriptional regulatory activity to maintain appropriate developmental timing.

Multifunctional cytokinesis genes in Schizosaccharomyces pombe

The proper division of cells is essential for the production of viable daughter cells. In plants and fungi, the dividing cell produces a cross-wall or septum that bisects the cytoplasm. For separation of the daughter cells, the septum has to be cleaved. To study the regulation of this process, we isolated mutants defective in septum cleavage. The mutants showed highly pleiotropic phenotypes and defined 17 novel genes. The deduced amino acid sequences of the products of the cloned genes exhibited homologies to various transcription regulators of other organisms. The homologies and the pleiotropic effects of the mutations on sexual development, stress response, mitotic stability, septum initiation and septum placement indicated that these genes affect cell separation indirectly, through multifunctional regulatory modules.

Mechanisms controlling differential promoter-occupancy by the yeast forkhead proteins Fkh1p and Fkh2p: implications for regulating the cell cycle and differentiation

The roles of DNA and Mcm1p interactions in determining the overlapping and distinct functions of the yeast cell cycle regulatory transcription factors Fkh1p and Fkh2p were examined. Full-length recombinant Fkh1p and Fkh2p were purified and their binding to bona fide promoters examined in vitro. Each protein bound a variety of target promoters with similar specificity in vitro, consistent with the observation that these proteins bind common promoters in vivo. However, in vivo, the Fkh1p and Fkh2p occupied different target promoters to different extents, suggesting that each was primarily responsible for controlling a different set of genes. Additional in vitro studies provided a mechanistic explanation for this differential promoter-occupancy. Specifically, the Fkh2p, but not the Fkh1p, was capable of binding cooperatively with Mcm1p. The Mcm1p-Fkh2p cooperative binding was enhanced by, but did not require, the presence of a Mcm1p-binding site within a target promoter. Consistent with these data, Mcm1p was present at Fkh-controlled promoters in vivo regardless of whether they contained Mcm1p-binding sites, suggesting a role for Mcm1p at promoters not thought previously to be under Mcm1p control. Analysis of Fkh1p and Fkh2p binding to promoter targets in vivo by use of mutant strains indicated that the two proteins compete for promoter-occupancy at a number of target promoters. We postulate that Fkh1p and a stable Fkh2p/Mcm1p complex compete for binding to target promoters and that the levels and/or binding activity of Fkh1p, but not Fkh2p, are most limiting for promoter-occupancy in vivo. Interestingly, the in vitro DNA-binding assays, using a variety of promoter targets, revealed that bona fide Fkh target promoters contained two or more Fkh-binding sites that allowed the Fkh1p and Fkh2p proteins to form multiple protein-DNA complexes in vitro. Multiple Fkh-binding sites may be a distinguishing feature of bona fide Fkh promoters in yeast and other organisms.

Forkhead homologue in rhabdomyosarcoma functions as a bifunctional nuclear receptor-interacting protein with both coactivator and corepressor functions

In a search for novel transcriptional intermediary factors for the estrogen receptor (ER), we used the ligand-binding domain and hinge region of ER as bait in a yeast two-hybrid screen of a cDNA library derived from tamoxifen-resistant MCF-7 human breast tumors from an in vivo athymic nude mouse model. Here we report the isolation and characterization of the forkhead homologue in rhabdomyosarcoma (FKHR), a recently described member of the hepatocyte nuclear factor 3/forkhead homeotic gene family, as a nuclear hormone receptor (NR) intermediary protein. FKHR interacts with both steroid and nonsteroid NRs, although the effect of ligand on this interaction varies by receptor type. The interaction of FKHR with ER is enhanced by estrogen, whereas its interaction with thyroid hormone receptor and retinoic acid receptor is ligand-independent. In addition, FKHR differentially regulates the transactivation mediated by different NRs. Transient transfection of FKHR into mammalian cells dramatically represses transcription mediated by the ER, glucocorticoid receptor, and progesterone receptor. In contrast, FKHR stimulates rather than represses retinoic acid receptor- and thyroid hormone receptor-mediated transactivation. Most intriguingly, overexpression of FKHR dramatically inhibits the proliferation of ER-dependent MCF-7 breast cancer cells. Therefore, FKHR represents a bifunctional NR intermediary protein that can act as either a coactivator or corepressor, depending on the receptor type.

Characterization of the mouse islet-specific glucose-6-phosphatase catalytic subunit-related protein gene promoter by in situ footprinting: correlation with fusion gene expression in the islet-derived betaTC-3 and hamster insulinoma tumor cell lines

Glucose-6-phosphatase (G6Pase) is a multicomponent system located in the endoplasmic reticulum comprising a catalytic subunit and transporters for glucose-6-phosphate, inorganic phosphate, and glucose. We have recently cloned a novel gene that encodes an islet-specific G6Pase catalytic subunit-related protein (IGRP) (Ebert et al., Diabetes 48:543-551, 1999). To begin to investigate the molecular basis for the islet-specific expression of the IGRP gene, a series of truncated IGRP-chloramphenicol acetyltransferase (CAT) fusion genes were transiently transfected into the islet-derived mouse betaTC-3 and hamster insulinoma tumor cell lines. In both cell lines, basal fusion gene expression decreased upon progressive deletion of the IGRP promoter sequence between -306 and -66, indicating that multiple promoter regions are required for maximal IGRP-CAT expression. The ligation-mediated polymerase chain reaction footprinting technique was then used to compare trans-acting factor binding to the IGRP promoter in situ in betaTC-3 cells, which express the endogenous IGRP gene, and adrenocortical Y1 cells, which do not. Multiple trans-acting factor binding sites were selectively identified in betaTC-3 cells that correlate with regions of the IGRP promoter identified as being required for basal IGRP-CAT fusion gene expression. The data suggest that hepatocyte nuclear factor 3 may be important for basal IGRP gene expression, as it is for glucagon, GLUT2, and Pdx-1 gene expression. In addition, binding sites for several trans-acting factors not previously associated with islet gene expression, as well as binding sites for potentially novel proteins, were identified.

The promoter of the long variant of collagen XVIII, the precursor of endostatin, contains liver-specific regulatory elements

The endostatin precursor collagen XVIII is expressed at high levels in human livers, the main source being hepatocytes. We have studied the regulatory elements in the promoter 2 of the Col18a1 gene that directs the transcription of the NC1-517 variant of collagen alpha1(XVIII), which is the main form expressed in the liver. The 5'-flanking region of Col18a1 gene was cloned, and a series of 5'-deletions from -3286 bp to +285 bp were linked to the luciferase reporter gene. Transfection experiments in HepG2 cells allowed to identify a silencer-like element containing putative HNF1 and HNF3 sites and activator elements containing stretches of GC-rich sequences. Another putative HNF3 site in close apposition to a NF1/CTF site was localized upstream of the silencer-like element. Cotransfection experiments showed that the Col18a1 promoter 2 was transactivated by Sp1 and HNF3alpha. Gel-shift analyses showed that HNF3, NF1/CTF, and Sp1-like sites specifically recognized nuclear factors. Super-shift experiments indicated that HNF3beta was the major form of HNF3 interacting with the HNF3/NF1 site. The well-differentiated hepatoma cell line mhATFS315 transfected with a truncated form of HNF3beta, which competitively blocks HNF3 transactivating activity, expressed the Col18a1gene at a very low level. Taken together, these data strongly suggest that Col18a1 is a liver-specific gene. Furthermore, gel-shift analyses performed with nuclear factors prepared from well-differentiated hepatocellular carcinomas showed increased HNF3/NF1 binding activity compared with normal livers. Consequently, the precursor of endostatin might be differently expressed according to the differentiated and/or transformed state of hepatocytes.

Proximal promoter of the surfactant protein D gene: regulatory roles of AP-1, forkhead box, and GT box binding proteins

Surfactant protein D (SP-D) plays roles in pulmonary host defense and surfactant homeostasis and is increased following lung injury. Because AP-1 proteins regulate cellular responses to diverse environmental stimuli, we hypothesized that the conserved AP-1 motif (at -109) and flanking sequences in the human SP-D promoter contribute to the regulation of SP-D expression. The AP-1 sequence specifically bound to fra-1, junD, and junB in H441 lung adenocarcinoma nuclear extracts. Mutagenesis of the AP-1 motif in a chloramphenicol acetyltransferase reporter construct containing 285 base pairs of upstream sequence nearly abolished promoter activity, and co-transfection of junD significantly increased wild type but not mutant promoter activity. The sequence immediately downstream of the AP-1 element contained a binding site for HNF-3 (FOXA), and simultaneous mutation of this site (fox-d) and an upstream FoxA binding site (-277, fox-u) caused a 4-fold reduction in chloramphenicol acetyltransferase activity. Immediately upstream of the AP-1-binding site, we identified a GT box-containing positive regulatory element. Despite finding regions of limited homology to the thyroid transcription factor 1-binding site, SP-D promoter activity did not require thyroid transcription factor 1. Thus, transcriptional regulation of SP-D gene expression involves complex interactions with ubiquitous and lineage-dependent factors consistent with more generalized roles in innate immunity.

The thyroid transcription factor 2 (TTF-2) is a promoter-specific DNA-binding independent transcriptional repressor

The thyroid transcription factor TTF-2 is a forkhead-containing protein involved in thyroid-specific gene expression and necessary for thyroid morphogenesis. In this paper, we demonstrate that TTF-2 is able to inhibit the activity of the thyroid-specific transcription factors TTF-1 and Pax-8 only on certain promoters. We identified the minimal protein domain responsible for repressor activity, which behaves as an independent functional domain, and we show that repression by TTF-2 is DNA-binding independent. We suggest that TTF-2 is able to interfere with a specific cofactor required for TTF-1 and Pax-8 activity.

Estrogen modulates HNF-3beta mRNA levels in the developing chick oviduct

Steroid hormones are involved in many physiological processes, including tissue-specific gene expression, homeostasis, and development. The chick oviduct represents an excellent system in which to study many of these events, as it is highly steroid responsive. Here, we report the cloning of chick HNF-3beta from an oviduct cDNA library and its expression pattern in adult tissues and in the developing oviduct in response to estrogen treatment. Overall, cHNF-3beta was expressed at high levels in the immature chick oviduct and lung and, to a lesser extent, in the liver, kidney, and muscle. This expression pattern is divergent from that of mammalian HNF-3beta, which is not expressed in kidney or muscle. Furthermore, several lengths of cHNF-3beta mRNA transcripts were detected that were expressed tissue specifically. Interestingly, cHNF-3beta mRNA levels were differentially influenced by estrogen as a result of a post-transcriptional effect on the cHNF-3beta message in some tissues. Finally, a role for cHNF-3beta is proposed in the estrogen-stimulated differentiation and development of the oviduct, as cHNF-3beta mRNA expression is induced in the early stages of oviduct development and declines as the animal becomes sexually mature.

Atlantic salmon HNF-3/forkhead: cDNA sequence, evolution, expression, and functional analysis

We report the isolation and characterization of a cDNA encoding an HNF-3 family member (as HNF-3) from Atlantic salmon (Salmo salar L). The important functional domains of HNF-3 proteins that have been characterized previously are revealed by segments of high identity along the alignment of the asHNF-3 with winged helix/forkhead amino acid sequences isolated from other species. A comparison of asHNF-3 cDNA and genomic DNA indicated that there were no introns present in the asHNF-3 gene. Expression of asHNF-3 protein in adult salmon tissues was not exclusive to liver but was also present in the pancreas and intestine. An RT-PCR analysis performed on salmon development showed that asHNF3 expression is detectable before gastrulation at the mid blastula transition stage. Functional analysis of the asHNF-3 protein using a characterized HNF-3 consensus binding site demonstrated that the protein can recognize and bind to specific HNF-3 consensus sequences. We also report the identification of a novel HNF3 binding site in the promoter of the Atlantic salmon transferrin gene.

Structure of the Xenopus laevis TFF-gene xP4.1, differentially expressed to its duplicated homolog xP4.2

TFF-peptides (formerly P-domain peptides, trefoil factors) represent major secretory products of mucous epithelia in mammals and amphibia. The nucleotide sequence of a large portion of a gene encoding the TFF-peptide xP4.1 from Xenopus laevis and its genomic organization were determined in the present study. The peptide xP4.1 containing four TFF-domains is thought to represent the functional frog homolog of human TFF2 (formerly hSP). The xP4.1 gene analyzed spans a region of about 7 kb and consists of six exons. Each TFF-domain is encoded by a single exon flanked by type 1 introns typical of shuffled modules. The 5'-upstream region contains a TATA-box, and potential binding sites for hepatocyte nuclear factor 3 and AP-1. Furthermore, the cDNA sequence of a transcript named xP4.2 with 91% similarity to xP4.1 is presented. RT-PCR analysis revealed that xP4.1 and xP4.2 genes are differentially expressed. xP4.1 transcripts are detectable only in the stomach, but not in the esophagus, whereas xP4.2 transcripts are found both in the esophagus and in the stomach with a descending gradient from fundus to antrum.