Identification of a transthyretin enhancer site that selectively binds the hepatocyte nuclear factor-3 beta isoform

The upstream proximal region of the transthyretin (TTR) promoter and a distal enhancer are sufficient to drive liver-specific expression of the TTR gene, as demonstrated by experiments in transgenic mice. Previous analyses have characterized the binding of a number of liver-enriched transcription factors of the TTR promoter including hepatocyte nuclear factors one (HNF-1), HNF-4, and three distinct HNF-3 proteins (alpha, beta, and gamma), which are members of the winged helix (fork head) family. The TTR enhancer was shown to bind members of the CCAAT/enhancer binding protein (C/EBP) family at two distinct sites (TTR-2 and TTR-3), and an oligonucleotide containing the activation protein one (AP-1) binding sequence competed for recognition to a third enhancer site (TTR-1). In this study, we have carried out a detailed analysis of the transcription factors that recognize the TTR enhancer elements (TTR-1, TTR-2, and TTR-3 oligonucleotide sequences). Analysis of the TTR-1 site demonstrates that the putative AP-1 site in the TTR enhancer binds a ubiquitously expressed factor that is distinct from the AP-1 family of proteins. Next we demonstrate, via gel shift analysis, that the TTR-3 site is recognized by the C/EBP family in liver nuclear extracts. We also show that whereas the TTR-2 enhancer site is capable of binding recombinant C/EBP proteins, it does not bind C/EBP proteins from liver nuclear extracts. The TTR-2 site does, however, contain a variant HNF-3 recognition sequence that exclusively binds the HNF-3 beta isoform. Mutation of this HNF-3 beta-specific recognition sequence caused reductions in TTR enhancer activity. We had previously observed a 95% decrease in HNF-3 alpha expression and a 20% reduction in HNF-3 beta expression in acute phase livers, which correlated with a 60% decrease in TTR gene transcription. We propose that the HNF-3 beta-specific binding site in the TTR enhancer may play a role in maintaining TTR gene expression during the acute phase response in spite of the dramatic reduction in HNF-3 alpha protein levels.

Management of delayed edema formation after fibrinolytic therapy for intracerebral hematomas: preliminary experimental data

OBJECTIVE

Fibrinolytic therapy for spontaneous intracerebral hemorrhage using recombinant tissue plasminogen activator (rtPA) is considered a viable alternative to microsurgical hematoma removal. However, experimental data suggest that rtPA is neurotoxic and evokes a late perihematomal edema. We present preliminary data focusing on the avoidance of late edema formation after lysis of an intracerebral hematoma in a porcine model.

METHODS

Twenty pigs underwent placement of a frontal intracerebral hematoma with a minimum volume of 1 mL. Half of the pigs were subjected to rtPA clot lysis and MK-801 injection for blockage of the NMDA receptor-mediated rtPA-enhanced excitotoxic pathway. The remaining 10 pigs received desmoteplase (DSPA) for clot lysis, which is known to be a less neurotoxic fibrinolytic agent than rtPA. MRI on the day of surgery and on postoperative days 4 and 10 was used to assess hematoma and edema volumes.

RESULTS

Late edema formation could be prevented in both the MK-801/rtPA and DSPA pigs.

CONCLUSION

The benefits of fibrinolytic therapy for intracerebral hematomas appear to be counterbalanced by late edema formation. MK-801 infusion as an adjunct to rtPA lysis, or the use of DSPA instead of rtPA, prevents late edema and therefore has the potential to further improve results after clot lysis.

Anterior thalamic nucleus stimulation for epilepsy

One option for treatment of medically refractory debilitating epilepsy is stimulation of the anterior thalamic nucleus, which projects via the cingulate gyrus to limbic structures and neocortex. In this chapter we describe the technique for anterior thalamic deep brain stimulation and report outcomes of early series of patients. The prospective double-blind randomized Stimulation of the Anterior Nucleus of the Thalamus for Epilepsy (SANTE) trial will evaluate the efficacy of this technique for epilepsy treatment.

Endocrine dysfunction following traumatic brain injury: mechanisms, pathophysiology and clinical correlations

Despite growing recognition among those who provide care for traumatic brain injury patients, endocrine dysfunction following brain injury is an often under-recognized phenomenon. From historical reports one would conclude that endocrine dysfunctions hardly ever occurs following trauma to the head. However, recent studies suggest that a significant proportion of patients suffer some degree of hypopituitarism. To date, there are no clear predicting factors identifying patients at risk for developing hormonal disturbances and thus no parameters exist for screening. Several retrospective analyses and literature reviews, and more recently, a few longitudinal studies of brain injured patients have been performed.

The cut-homeodomain transcriptional activator HNF-6 is coexpressed with its target gene HNF-3 beta in the developing murine liver and pancreas

Murine hepatocyte nuclear factor-3 beta (HNF-3 beta) protein is a member of a large family of developmentally regulated transcription factors that share homology in the winged helix/fork head DNA binding domain and that participate in embryonic pattern formation. HNF-3 beta also mediates cell-specific transcription of genes important for the function of hepatocytes, intestinal and bronchiolar epithelial, and pancreatic acinar cells. We have previously identified a liver-enriched transcription factor, HNF-6, which is required for HNF-3 beta promoter activity and also recognizes the regulatory region of numerous hepatocyte-specific genes. In this study we used the yeast one-hybrid system to isolate the HNF-6 cDNA, which encodes a cut-homeodomain-containing transcription factor that binds with the same specificity as the liver HNF-6 protein. Cotransfection assays demonstrate that HNF-6 activates expression of a reporter gene driven by the HNF-6 binding site from either the HNF-3 beta or transthyretin (TTR) promoter regions. We used interspecific backcross analysis to determine that murine Hnf6 gene is located in the middle of mouse chromosome 9. In situ hybridization studies of staged specific embryos demonstrate that HNF-6 and its potential target gene, HNF-3 beta, are coexpressed in the pancreatic and hepatic diverticulum. More detailed analysis of HNF-6 and HNF-3 beta's developmental expression patterns provides evidence of colocalization in hepatocytes, intestinal epithelial, and in the pancreatic ductal epithelial and exocrine acinar cells. The expression patterns of these two transcription factors do not overlap in other endoderm-derived tissues or the neurotube. We also found that HNF-6 is also abundantly expressed in the dorsal root ganglia, the marginal layer, and the midbrain. At day 18 of gestation and in the adult pancreas, HNF-6 and HNF-3 beta transcripts colocalize in the exocrine acinar cells, but their expression patterns diverge in other pancreatic epithelium. HNF-6, but not HNF-3 beta, expression continues in the pancreatic ductal epithelium, whereas only HNF-3 beta becomes restricted to the endocrine cells of the islets of Langerhans. We discuss these expression patterns with respect to specification of hepatocytes and differentiation of the endocrine and exocrine pancreas.

Hepatocyte nuclear factor 3/fork head homolog 11 is expressed in proliferating epithelial and mesenchymal cells of embryonic and adult tissues

The hepatocyte nuclear factor 3alpha (HNF-3alpha) and 3beta proteins have homology in the winged helix/fork head DNA binding domain and regulate cell-specific transcription in hepatocytes and in respiratory and intestinal epithelia. In this study, we describe two novel isoforms of the winged helix transcription factor family, HNF-3/fork head homolog 11A (HFH-11A) and HFH-11B, isolated from the human colon carcinoma HT-29 cell line. We show that these isoforms arise via differential splicing and are expressed in a number of epithelial cell lines derived from tumors (HT-29, Caco-2, HepG2, HeLa, A549, and H441). We demonstrate that differentiation of Caco-2 cells toward the enterocyte lineage results in decreased HFH-11 expression and reciprocal increases in HNF-3alpha and HNF-3beta mRNA levels. In situ hybridization of 16 day postcoitus mouse embryos demonstrates that HFH-11 expression is found in the mesenchymal and epithelial cells of the liver, lung, intestine, renal cortex, and urinary tract. Although HFH-11 exhibits a wide cellular expression pattern in the embryo, its adult expression pattern is restricted to epithelial cells of Lieberkühn's crypts of the intestine, the spermatocytes and spermatids of the testis, and the thymus and colon. HFH-11 expression is absent in adult hepatocytes, but its expression is reactivated in proliferating hepatocytes at 4, 24, and 48 h after partial hepatectomy. Consistent with these findings, we demonstrate that HFH-11 mRNA levels are stimulated by intratracheal administration of keratinocyte growth factor in adult lung and its expression in an adult endothelial cell line is reactivated in response to oxidative stress. These experiments show that the HFH-11 transcription factor is expressed in embryonic mesenchymal and epithelial cells and its expression is reactivated in these adult cell types by proliferative signals or oxidative stress.

The transcriptional activator hepatocyte nuclear factor 6 regulates liver gene expression

The hepatocyte nuclear factor 3(alpha) (HNF-3(alpha)), -3(beta), and -3(gamma) proteins share homology in the winged-helix/fork head DNA binding domain and mediate hepatocyte-enriched transcription of numerous genes whose expression is necessary for organ function. In this work, we identify a liver-enriched transcription factor, HNF-6, which recognizes the -138 to -126 region of the HNF-3(beta) promoter and binds the original HNF-3 site of the transthyretin promoter (-94 to -106). We show that HNF-6 and HNF-3 possess different DNA binding specificities by competition and methylation interference studies and are immunologically distinct. Site-directed mutagenesis of the HNF-6 sites in the HNF-3(beta) and transthyretin promoters diminishes reporter gene expression, suggesting that HNF-6 activates transcription of these promoters. Using the HNF-6 binding sequence DHWATTGAYTWWD (where W = A or T, Y = T or C, H is not G, and D is not C) determined by sequence comparison and methylation interference, we predicted that HNF-6 will bind to 22 additional hepatocyte-enriched genes. Of these potential target genes, we selected seven of the HNF-6 binding sequences and demonstrated that they bind the HNF-6 protein. These include promoter sequences from alpha-2 urinary globulin, alpha-1 antitrypsin, cytochrome P-450 2C13, L-type 6-phosphofructo-2-kinase, mouse major urinary protein, tryptophan oxygenase, and alpha-fetoprotein genes. HNF-6 binding activity was also found in the intestinal epithelial cell line HT29, and potential HNF-6 binding sites were present in intestinal sucrase isomaltase, cdx-2 homeodomain protein, and intestinal fatty acid binding protein promoter regions. These studies suggest that HNF-6 may regulate hepatocyte-specific genes and may play a role in epithelial cell differentiation of gut endoderm via regulation of HNF-3(beta).

Cytokine regulation of the liver transcription factor hepatocyte nuclear factor-3 beta is mediated by the C/EBP family and interferon regulatory factor 1

Three distinct hepatocyte nuclear factor-3 (HNF-3) proteins (alpha, beta, and gamma) regulate the transcription of numerous liver-enriched genes. The HNF-3 proteins bind DNA via a homologous winged helix motif common to a number of proteins known to be critical for determination events in embryogenesis. We have demonstrated previously that two binding sites in the -184 HNF-3 beta promoter are recognized by widely distributed factors and that there is also a critical autoregulatory site, we identified a binding site for a cell-specific factor, LF-H3 beta, that may function in restricting HNF-3 beta gene expression to hepatocytes. Our present study demonstrates that members of the C/EBP and proline and acidic amino acid-rich subfamilies of basic region leucine zipper transcription factors bind the LF-H3 beta site, and cotransfection of HepG2 cells shows that these factors are able to activate an HNF-3 beta promoter reporter construct. The LF-H3 beta-C/EBP binding sequence also confers HNF-3 beta promoter stimulation in response to interleukin (IL)-1 and IL-6. Upstream of this HNF-3 beta proximal promoter region, an IFN-stimulated response element core sequence (-231 to -210) was found that mediates transcriptional induction by IFN-gamma but not IFN-alpha. Gel mobility supershift assay demonstrates that an IFN-gamma-induced protein-DNA complex is disrupted by an antibody specific for interferon regulatory factor-1/interferon-stimulated gene factor-2. Consistent with this finding, we observed that IFN-gamma induction requires ongoing protein synthesis. Surprisingly, the effect of the three cytokines (IL-1, IL-6, and IFN-gamma) in combination as assayed by the same model is not synergistic. HNF-3beta joins the C/EBP family on the list of liver-enriched transcription factors, the expression of which is modulated by cytokines.

Decreased expression of hepatocyte nuclear factor 3 alpha during the acute-phase response influences transthyretin gene transcription

Three distinct hepatocyte nuclear factor 3 (HNF-3) proteins (alpha, beta, and gamma) are known to regulate the transcription of numerous liver-specific genes. The HNF-3 proteins bind to DNA as monomers through a winged-helix motif, which is also utilized by a number of developmental regulators, including the Drosophila homeotic fork head (fkh) protein. We have previously characterized a strong-affinity HNF-3S site in the transthyretin (TTR) promoter region which is essential for expression in human hepatoma (HepG2) cells. In the current study, we identify an activating protein 1 (AP-1) site which partially overlaps the HNF-3S sequence in the TTR promoter. We show that in HepG2 cells the AP-1 sequence confers 12-O-tetradecanoylphorbol-13-acetate inducibility to the TTR promoter and contributes to normal TTR transcriptional activity. We also demonstrate that the HNF-3 proteins and AP-1 bind independently to the TTR AP-1-HNF-3 site, and cotransfection experiments suggest that they do not cooperate to activate an AP-1-HNF-3 reporter construct. In addition, 12-O-tetradecanoylphorbol-13-acetate exposure of HepG2 cells results in a reciprocal decrease in HNF-3 alpha and -3 gamma expression which may facilitate interaction of AP-1 with the TTR AP-1-HNF-3 site. In order to explore the role of HNF-3 in the liver, we have examined expression patterns of TTR and HNF-3 during the acute-phase response and liver regeneration. Partial hepatectomy produced minimal fluctuation in HNF-3 and TTR expression, suggesting that HNF-3 expression is not influenced by proliferative signals induced during liver regeneration. In acute-phase livers, we observed a dramatic reduction in HNF-3 alpha expression which correlates with a decrease in the expression of its target gene, the TTR gene. Furthermore, consistent with previous studies, the acute-phase livers are induced for c-jun but not c-fos expression. We propose that the reduction in TTR gene expression during the acute phase is likely due to lower HNF-3 alpha expression levels and that the induction of primarily c-jun homodimers, which are poor transcriptional activators, is insufficient to maintain normal TTR expression levels. We also discuss the role of reduced HNF-3 alpha expression in mediating decreased transcription of HNF-3 target genes which respond negatively to cytokine signalling.