Coordinate accumulation of the mRNAs for the alpha, beta, and gamma chains of rat fibrinogen following defibrination

Liver gene regulation of hemostasis-related factors is altered by experimental snake envenomation in mice

Few studies have addressed gene expression of hemostasis-related factors during acute thrombo-hemorrhagic diseases. Bites by the lanced-headed viper Bothrops jaracaca induce rapid hemostatic disturbances in victims, leading to systemic bleedings, thrombocytopenia and consumption coagulopathy. Although circulating levels of coagulation factors recover rapidly after administration of specific antivenom therapy, it is unclear if B. jararaca venom (BjV) upregulates the mRNA synthesis of hepatic hemostasis-related factors, or if the recovery occurs under basal conditions after the neutralization of venom components by antivenom. Thus, we aimed to investigate if BjV regulates gene expression of important hemostasis-related factors synthetized by the liver. On that account, Swiss mice were injected with saline or BjV (1.6 mg/kg b.w, s.c.), and after 3, 6 and 24 h blood samples and liver fragments were collected to analyze mRNA expression by real-time qPCR. Increased gene expression of fibrinogen chains, haptoglobin and STAT3 was observed during envenomation, particularly at 3 and 6 h. At 24h, mRNA levels of F10 were raised, while those of Serpinc1, Proc and Adamts13 were diminished. Surprisingly, F3 mRNA levels were steadily decreased at 3 h. Gene expression of Thpo, F7, F5 Tfpi, Mug1 was unaltered. mRNA levels of Vwf, P4hb, F8, F2, Plg, and Serpinf2 were minimally altered, but showed important associations with Nfkb1 gene expression. In conclusion, snakebite envenomation upregulates hepatic mRNA synthesis particularly of fibrinogen chains, and acute-phase markers. This response explains the fast recovery of fibrinogen levels after antivenom administration to patients bitten by B. jararaca snakes.

Virus host protein interaction network analysis reveals that the HEV ORF3 protein may interrupt the blood coagulation process

Hepatitis E virus (HEV) is endemic worldwide and a major cause of acute liver disease in developing countries. However, the molecular mechanisms of liver pathology and clinical disease are not well understood for HEV infection. Open reading frame 3 (ORF3) of HEV encodes a small phosphoprotein, which is assumed to be involved in liver pathology and clinical disease. In this study, the interactions between the HEV ORF3 protein and human proteins were investigated using a stringent, high-throughput yeast two-hybrid (Y2H) analysis. Thirty two proteins were shown to interact with genotype 1 ORF3, 28 of which have not been reported previously. These novel interactions were evaluated by coimmunoprecipitation of protein complexes from transfected cells. We found also that the ORF3 proteins of genotype 4 and rabbit HEV interacted with all of the human proteins identified by the genotype 1 ORF3 protein. However, the putative ORF3 protein derived from avian HEV did not interact with the majority of these human proteins. The identified proteins were used to infer an overall interaction map linking the ORF3 protein with components of the host cellular networks. Analysis of this interaction map, based on functional annotation with the Gene Ontology features and KEGG pathways, revealed an enrichment of host proteins involved in complement coagulation, cellular iron ion homeostasis and oxidative stress. Additional canonical pathway analysis highlighted the enriched biological pathways relevant to blood coagulation and hemostasis. Consideration of the clinical manifestations of hepatitis E reported previously and the results of biological analysis from this study suggests that the ORF3 protein is likely to lead to an imbalance of coagulation and fibrinolysis by interacting with host proteins and triggering the corresponding pathological processes. These results suggest critical approaches to further study of the pathogenesis of the HEV ORF3 protein.

Fibrinogen gene regulation

The Aα, Bβ and γ polypeptide chains of fibrinogen are encoded by a three gene cluster on human chromosome four. The fibrinogen genes (FGB-FGA-FGG) are expressed almost exclusively in hepatocytes where their output is coordinated to ensure a sufficient mRNA pool for each chain and maintain an abundant plasma fibrinogen protein level. Fibrinogen gene expression is controlled by the activity of proximal promoters which contain binding sites for hepatocyte transcription factors, including proteins which influence fibrinogen transcription in response to acute-phase inflammatory stimuli. The fibrinogen gene cluster also contains cis regulatory elements; enhancer sequences with liver activities identified by sequence conservation and functional genomics. While the transcriptional control of this gene cluster is fascinating biology, the medical impetus to understand fibrinogen gene regulation stems from the association of cardiovascular disease risk with high level circulating fibrinogen. In the general population this level varies from about 1.5 to 3.5 g/l. This variation between individuals is influenced by genotype, suggesting there are genetic variants contributing to fibrinogen levels which reside in fibrinogen regulatory loci. A complete picture of how fibrinogen genes are regulated will therefore point towards novel sources of regulatory variants. In this review we discuss regulation of the fibrinogen genes from proximal promoters and enhancers, the influence of acute-phase stimulation, post-transcriptional regulation by miRNAs and functional regulatory variants identified in genetic studies. Finally, we discuss the fibrinogen locus in light of recent advances in understanding chromosomal architecture and suggest future directions for researching the mechanisms that control fibrinogen expression.

ORF3 protein of hepatitis E virus interacts with the Bbeta chain of fibrinogen resulting in decreased fibrinogen secretion from HuH-7 cells

The ORF3 protein of hepatitis E virus (HEV), the precise cellular functions of which remain obscure, was used in a yeast two-hybrid screen to identify its cellular binding partners. One of the identified interacting partners was fibrinogen Bbeta protein. The ORF3-fibrinogen Bbeta interaction was verified by co-immunoprecipitation and fluorescence resonance energy transfer in mammalian cells. Fibrinogen is a hepatic acute-phase protein and serves as a central molecule that maintains host homeostasis and haemostasis during an acute-phase response. Metabolic labelling of ORF3-transfected HuH-7 cells showed that secreted as well as intracellular levels of fibrinogen were decreased in these cells compared with vector-transfected controls. Northern hybridization and RT-PCR analyses revealed that the mRNA levels of all three chains of fibrinogen, Aalpha, Bbeta and gamma, were transcriptionally downregulated in ORF3-transfected cells. The constitutive expression of fibrinogen genes can be significantly upregulated by interleukin (IL)-6, an important mediator of liver-specific gene expression during an acute-phase response. Transcription of fibrinogen genes after IL-6 stimulation was less in ORF3-expressing cells compared with controls. This report adds one more biological function to, and advances our understanding of, the cellular role of the ORF3 protein of HEV. The possible implications of these findings in the virus life cycle are discussed.

Fibrin structure and wound healing

Fibrinogen and fibrin play an important role in blood clotting, fibrinolysis, cellular and matrix interactions, inflammation, wound healing, angiogenesis, and neoplasia. The contribution of fibrin(ogen) to these processes largely depends not only on the characteristics of the fibrin(ogen) itself, but also on interactions between specific-binding sites on fibrin(ogen), pro-enzymes, clotting factors, enzyme inhibitors, and cell receptors. In this review, the molecular and cellular biology of fibrin(ogen) is reviewed in the context of cutaneous wound repair. The outcome of wound healing depends largely on the fibrin structure, such as the thickness of the fibers, the number of branch points, the porosity, and the permeability. The binding of fibrin(ogen) to hemostasis proteins and platelets as well as to several different cells such as endothelial cells, smooth muscle cells, fibroblasts, leukocytes, and keratinocytes is indispensable during the process of wound repair. High-molecular-weight and low-molecular-weight fibrinogen, two naturally occurring variants of fibrin, are important determinants of angiogenesis and differ in their cell growth stimulation, clotting rate, and fibrin polymerization characteristics. Fibrin sealants have been investigated as matrices to promote wound healing. These sealants may also be an ideal delivery vehicle to deliver extra cells for the treatment of chronic wounds.

Association of increased levels of fibrinogen and the -455G/A fibrinogen gene polymorphism with chronic periodontitis

BACKGROUND

Fibrinogen is one of the acute-phase proteins whose levels are elevated during periodontal disease. Recent studies suggest that excessive fibrinogen production might play a role in upregulating host immune responses. In addition, there is a relationship between the -455G/A polymorphism (HaeIII) in the 5' flanking region of the beta-fibrinogen gene promoter and increased fibrinogen levels. In this study, we investigated the distribution of the -455G/A polymorphism and the relationship of this specific genotype to fibrinogen levels in periodontitis patients.

METHODS

In order to assess the -455G/A polymorphism, restriction fragment length polymorphism (RFLP) analysis with HaeIII enzyme was performed in the promoter region of the beta-fibrinogen gene. This was carried out on 79 chronic periodontitis patients as compared to 75 periodontally healthy subjects, matched to age, gender, and race. Fibrinogen levels were determined by the radial immunodiffusion assay (RID).

RESULTS

The frequency of homozygocity for the rare allele of the beta-fibrinogen gene (H2H2) was 13% for the periodontitis patients and 3% for the control group (P = 0.01). The distributions of H1H1 and H1H2 genotypes were 48% and 39% in the patient group and 70% and 27% in the control group, respectively. Chi-square analysis indicated that the distribution of these genotypes between the 2 groups was significantly different (P = 0.01). Fibrinogen levels were significantly higher in the patient group (2,496.5 mg/l +/- 105) compared to the control group (2,250.0 mg/l +/- 118.3) after adjusting for age, gender, and smoking status (P = 0.04). Consistent with previous reports, in our study population, those subjects with the H2H2 genotype had significantly higher fibrinogen levels (3,005.7 mg/l +/- 182.5) compared to subjects with the H1H1 genotype (2,325.0 mg/l +/- 91.6) or H1H2 genotype (2,438.0 mg/l +/- 117.4) (P = 0.001). Furthermore, the H1H2 and H2H2 genotypes were found at a higher frequency among periodontitis patients than controls. The odds ratios (OR) for these genotypes were 3.26 (95% confidence interval [CI]: 1.25 to 8.53) for the H1H2 genotype and 6.41 (95% CI: 1.15 to 35.83) for the H2H2 genotype as compared to individuals with the H1H1 genotype, after adjusting for age, gender, and smoking status.

CONCLUSIONS

The results indicate that a higher percentage of chronic periodontitis patients exhibit genotypes associated with higher plasma fibrinogen levels than healthy individuals. Furthermore, periodontitis patients have significantly higher fibrinogen levels compared to healthy individuals. The presence of H1H2 or H2H2 genotypes as well as elevated fibrinogen levels, in conjunction with other factors, may put individuals at higher risk of having periodontal disease, or may result from periodontal infection-genetic interactions.

Effect of genetic background and diet on plasma fibrinogen in mice. Possible relation with susceptibility to atherosclerosis

Many epidemiological studies suggest that elevated plasma fibrinogen concentrations form one of the most important independent risk factors in blood for cardiovascular disease and particularly atherosclerosis in humans. To clarify the effect of genetic factors, diets and their interactions on plasma fibrinogen concentrations, we examined plasma fibrinogen levels in four strains of mice, which differ in their susceptibility to cholesterol-induced atherosclerosis. When maintained on basal diet, two strains 129/J and C3H/HeJ exhibited a significantly higher plasma fibrinogen concentration (2.1 and 1.9 mg/ml) than C57BL/6J and BALB/C strains (1.5 and 1.4 mg/ml). The strongest and most rapid (1 week) increase of plasma fibrinogen (by all semi-synthetic diets) is observed in C57BL/6J mice, which are known to be highly susceptible to diet-induced atherosclerosis. After a period of 8 weeks an increase in plasma fibrinogen of approximately 30-50% was observed in all strains on all semi-synthetic diets. Remarkably, no increase was observed in the fibrinogen Aalpha- Bbeta- and gamma-chain mRNA levels in the liver on the same diets. These mRNA levels were even decreased by approximately 20-50% in all strains on an extremely atherogenic diet. It was found that: genetic background determines the plasma fibrinogen levels on basal diet; plasma fibrinogen levels are altered by diet; the extent of these changes depends on the genetic background: surprisingly, this increase of fibrinogen in plasma is independent of transcription; the diet-induced increase of fibrinogen was very fast in the very highly atherosclerosis-susceptible strain C57BL/6J having a low basal fibrinogen level, and very slow in the atherosclerosis-resistant strain C3H/HeJ having a high basal fibrinogen level. It might be concluded that it is the kinetics of the response of fibrinogen to diet rather than the actual level, which relates to atherosclerosis susceptibility.

A SAF binding site in the promoter region of human gamma-fibrinogen gene functions as an IL-6 response element

Expression of fibrinogen is highly induced during inflammation, and such abnormal expression of this protein is considered as a major cardiovascular risk factor. IL-6 is one of the main mediators of abnormal expression of fibrinogen leading to the pathogenic conditions. Transient transfection and EMSA were performed to investigate the molecular mechanism of IL-6-induced gamma-fibrinogen gene expression in hepatic cells. Using progressively deleted 5' fragments of the gamma-fibrinogen promoter coupled to chloramphenicol acetyltransferase gene, an IL-6 responsive element located between positions -273 and -259 was identified. Mutation of this element abrogates IL-6 responsiveness of the gamma-fibrinogen promoter. Interaction of this promoter with a zinc finger transcription factor, serum amyloid A activating factor (SAF)-1, was demonstrated by EMSA. Furthermore, overexpression of wild-type SAF-1 in transfected liver cells can increase transcription of the gamma-fibrinogen promoter. These data show that transcription factor SAF-1 is involved in the regulation of IL-6-mediated induction of the human gamma-fibrinogen gene in liver cells.

Efficacy of bothropic antivenom and its IgG(T) fraction in restoring fibrinogen levels of Bothrops jararaca envenomed mice

Bothropic antivenom and its IgG(T) fraction, administered 4 h after experimental envenoming by Bothrops jararaca in Swiss mice, were compared for their abilities to restore fibrinogen 24 or 48 h after treatment. IgG(T) was able to normalise fibrinogen levels as efficiently as conventional antivenom. As IgG(T) also neutralises most anti-toxic activities of Bothrops venom, our results suggest that IgG(T) could be a better alternative treatment for envenoming due to the reduced amount of extraneous proteins, which may facilitate the induction of early adverse reactions.

Enhanced secretion of ApoB by transfected HepG2 cells overexpressing fibrinogen

HepG2 cells stably transfected with cDNA-encoding single fibrinogen chains overexpress fibrinogen and have increased (4-fold) secretion of apolipoprotein B. Overexpression of fibrinogen does not affect the secretion of three representative acute-phase proteins but causes a small increase in albumin secretion. Enhanced apolipoprotein B secretion is due to less intracellular degradation and not to increased expression. The increased secretion of apolipoprotein B is independent of the acute-phase response, since stimulation of fibrinogen gene expression by interleukin 6 did not affect secretion. HepG2 cells overexpressing fibrinogen chains had increased 3-hydroxy-3-methylglutaryl coenzyme A reductase mRNA levels, enhanced cholesterol production but normal levels of triglyceride and phospholipid synthesis and of sterol response binding proteins. These results, that associate overexpression of fibrinogen with enhance apolipoprotein B secretion, may be significant since epidemiological studies indicate that elevated levels of fibrinogen and lipids are independent risk factors in coronary artery disease.

Changes in mRNA levels of fibrinogen subunit polypeptides in rats defibrinogenated with batroxobin

Batroxobin is a snake venom that is a thrombinlike enzyme used for clinical treatment. We analyzed hepatic mRNA levels for fibrinogen subunit polypeptides and prothrombin by reverse transcription-polymerase chain reaction as well as coagulation and fibrinolysis factors in plasma 1, 3, 5 and 24 hours after Batroxobin treatment (3 BU/100 g) in rats. The mRNA levels of alpha- and beta-chains of fibrinogen were significantly increased with decreases in plasma fibrinogen, alpha2-plasmin inhibitor, and plasminogen levels, while the mRNA levels for prothrombin remained unchanged. These results suggest that fibrinogen mRNA synthesis is regulated by plasma fibrinogen levels in Batroxobin-induced defibrinogenated rats.

Fibrin(ogen)-related antigens in rabbits experimentally infected with rabbit haemorrhagic disease virus

We investigated fibrin(ogen)-related antigens in liver tissues of rabbits infected with rabbit haemorrhagic disease (RHD) virus. Fibrin(ogen)-related antigens were detected in the sinusoids of liver at six hours post infection (pi). At 18 hours pi, the antigens were clearly detected in the hepatocytes infiltrated with heterophils rather than in the sinusoid. In the rabbits that spontaneously died (30 hours pi), fibrin(ogen)-related antigens were detected in both degenerating and some intact hepatocytes. They were also expressed in the necrotic foci of hepatocytes infiltrated by heterophils. By immunoprecipitation fibrin(ogen)-related antigens were extracted from the infected liver homogenates and analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis and Western blot analysis. There was an increase in fibrinogen and A alpha polypeptide chains in the liver homogenates from rabbits sacrificed at 18 and 24 hours pi, including those that died. Disseminated intravascular coagulation developed after progress of degeneration and necrosis of hepatocytes in RHD. It is assumed that the resultant consumption of fibrinogen triggers replenishment of fibrinogen by hepatocytes.

Selective loss of the hepatic phenotype due to the absence of a transcriptional activation pathway

Liver-enriched trans-acting factors hepatocyte nuclear factor-1 alpha (HNF1 alpha) and -4 (HNF4) are components of a transcriptional activation pathway that is thought to play a major role in hepatic gene activation. We previously described the isolation and characterization of distinct classes of hepatoma variants which lack the HNF4-->HNF1 alpha pathway (1). In order to determine the influence of the HNF4-->HNF1 alpha pathway on hepatic gene expression, genetic rescue experiments were done using hepatoma variant line H11 as a model system. Results suggest that this pathway is required for basal expression of a number of endogenous hepatocyte-specific genes. Complementation groups were established by fusion of H11 cells with other variant lines. Lastly, introduction of human chromosome 20 (containing the HNF4 locus) or randomly-marked human chromosomes into H11 cells failed to rescue the hepatic phenotype, suggesting that what appears to be a 'simple' defect may involve multiple genetic loci.

Characterization of the 5'-flanking region of the gene for the alpha chain of human fibrinogen

The 5'-flanking region of the gene coding for the alpha chain of human fibrinogen was isolated, sequenced, and characterized. The principal site of transcription initiation was determined by primer extension analysis and the RNase protection assay and shown to be at an adenine residue located 55 nucleotides upstream from the initiator methionine codon, or 13,399 nucleotides down-stream from the polyadenylation site of the gene coding for the gamma chain. Transient expression of constructs containing sequentially deleted 5'-flanking sequences of the alpha chain gene fused to the chloramphenicol acetyltransferase reporter gene showed that the promoter was liver-specific and inducible by interleukin 6 (IL-6). The shortest DNA fragment with significant promoter activity and full response to IL-6 stimulation encompassed the region from -217 to +1 base pairs (bp). Although six potential IL-6 responsive sequences homologous to the type II IL-6 responsive element were present, a single sequence of CTGGGA localized from -122 to -127 bp was shown to be a functional element in IL-6 induction. A hepatocyte nuclear factor 1 (HNF-1) binding site, present from -47 to -59 bp, in combination with other upstream elements, was essential for liver-specific expression of the gene. A functional CCAAT/enhancer binding protein site (C/EBP, -134 to -142 bp) was also identified within 217 bp from the transcription initiation site. An additional positive element (-1393 to -1133 bp) and a negative element (-1133 to -749 bp) were also found in the upstream region of the alpha-fibrinogen gene.

Resolution of spontaneous bleeding events but failure of pregnancy in fibrinogen-deficient mice

To explore the role of the key coagulation factor, fibrinogen, in development, hemostasis, wound repair, and disease pathogenesis, we disrupted the fibrinogen A alpha chain gene in mice. Homozygous, A alpha chain-deficient (A alpha-/-) mice are born normal in appearance, and there is no evidence of fetal loss of these animals based on the Mendelian pattern of transmission of the mutant A alpha chain allele. All of the component chains of fibrinogen (A alpha, B beta, and gamma) are immunologically undetectable in the circulation of both neonatal and adult A alpha-/- mice, and blood samples fail to either clot or support platelet aggregation in vitro. Overt bleeding events develop shortly after birth in approximately 30% of A alpha-/- mice, most frequently in the peritoneal cavity, skin, and soft tissues around joints. Remarkably, most newborns displaying signs of bleeding ultimately control the loss of blood, clear the affected tissues, and survive the neonatal period. Juveniles and young adult A alpha-/- mice are predisposed to spontaneous fatal abdominal hemorrhage, but long-term survival is variable and highly dependent on genetic background. The periodic rupture of ovarian follicles in breeding-age A alpha-/- females does not appear to significantly diminish life expectancy relative to males; however, pregnancy uniformly results in fatal uterine bleeding around the tenth day of gestation. Microscopic analysis of spontaneous lesions found in A alpha-/- mice suggests that fibrin(ogen) plays a fundamental role in the organization of cells at sites of injury.

Transcriptional regulation of the Xenopus laevis B beta fibrinogen subunit gene by glucocorticoids and hepatocyte nuclear factor 1: analysis by transfection into primary liver cells

The blood-clotting protein fibrinogen is composed of three subunits, designated A alpha, B beta, and gamma, which are encoded by a family of related genes. As part of the acute-phase response, expression of the fibrinogen genes is coordinately regulated in the liver by glucocorticoids. To understand the factors underlying this hormonal response, we have examined control of transcription from fibrinogen gene fragments transfected into hepatocytes from the frog Xenopus laevis. This analysis is the first in any species to define transcriptional regulatory elements for the fibrinogen genes by transfection into primary liver cells, rather than liver-derived cell lines. A transfection vector was constructed containing the Xenopus B beta gene transcription start site and 1293 bp of the 5' flanking sequence linked to the firefly luciferase gene. When this construct was transfected into primary liver parenchymal cells, luciferase expression was induced approximately 14-fold by glucocorticoids, an increase similar to the transcriptional stimulation of the endogenous B beta subunit gene. DNA fragments with as little as 284 bases of upstream sequence retained full hormone responsiveness. This region contains a sequence resembling the canonical glucocorticoid response element (GRE) at bases -148 to -162. Deletions or specific point mutations eliminating this putative GRE led to complete loss of glucocorticoid inducibility. Physical association of the steroid hormone receptor with this functional GRE was demonstrated with a truncated form of the rat glucocorticoid receptor containing the DNA-binding domain. A second possible GRE at positions -526 to -540 was not hormone-responsive, in either the presence or the absence of the more proximal GRE. The regulatory region also has a sequence similar to the binding site for a liver-specific transcription factor, hepatocyte nuclear factor 1 (HNF-1), at positions -120 to -132. Specific point mutations in the HNF-1-binding site, in a construct containing a wild-type GRE, reduced promoter activity by a factor of 10, while stimulation by glucocorticoids was retained. Binding studies confirmed specific interaction between this site and the transcription factor HNF-1 alpha from mouse. Thus, we have identified a GRE sufficient to account for full glucocorticoid inducibility and an HNF-1 site close to the promoter that are major determinants of transcriptional control of the Xenopus fibrinogen B beta subunit gene in cells from normal liver tissue.

Genetic factors determining thrombosis and fibrinolysis

Raised plasma levels of fibrinogen, factor VIIc, and plasminogen activator inhibitor-1 (PAI-1) are associated with an increased risk of ischemic heart disease. Levels of these proteins are determined in part by environmental influences such as smoking and dietary fat intake. However, genetic variation explains much of the interindividual variation in plasma levels of these proteins not accounted for by environmental factors. We previously investigated the DNA variation at the fibrinogen gene locus and showed that BclI restriction fragment length polymorphism (RFLP) of the beta-fibrinogen gene is associated with between-person differences in plasma fibrinogen levels. This RFLP is unlikely to be the functional base change itself, since it lies downstream of the gene. The rate-limiting step in the production of the mature fibrinogen molecule in the human hepatoma cell-line HepG2 is the synthesis of the beta-polypeptide chain, which in turn is influenced by the amount of messenger (mRNA) available. One possibility is that BclI RFLP is in linkage disequilibrium with a base change in the region of the beta-gene controlling synthesis of its mRNA and ultimately of fibrinogen protein. We identified a base change in the 5'-flanking region of the beta-fibrinogen gene that is in linkage disequilibrium with the BclI RFLP, that is associated with plasma fibrinogen levels, and that may be involved in control of fibrinogen gene expression. For the factor VII gene, we identified a polymorphism, detected after Msp I digestion of polymerase chain reaction (PCR)-amplified genomic DNA, that is strongly associated with factor VII coagulant activity (factor VIIc). The base change that creates the Msp I polymorphism is a G to A substitution, leading to the replacement of arginine (Arg) with glutamine (Gln) in the protein product of the M2 allele. In a sample of 284 men from the United Kingdom the frequency of the Gln allele (M2 loss of cutting site) is 0.1, and individuals of genotype Arg/Gln have factor VIIc levels 22% below the sample mean. In this sample, the Msp I genotype was found to be the strongest predictor of factor VIIc, accounting for 20.2% of the variance, with cholesterol accounting for an additional 3.5%. Three individuals homozygous for the Gln allele had both low factor VIIc and low factor VII protein concentrations. The conformation of the factor VII Gln may be different from that of the Arg protein, affecting its intracellular processing, secretion, turnover in plasma, or activity.(ABSTRACT TRUNCATED AT 400 WORDS)

HNF-1 shares three sequence motifs with the POU domain proteins and is identical to LF-B1 and APF

The coordinate expression of genes during development and differentiation is thought to be accomplished by common transcription factors operating on the promoters of families of coexpressed genes. HNF-1 is a transcriptional factor involved in the expression of genes in the liver and was originally defined as playing a major role in coordinating the expression of the linked fibrinogen genes. We have isolated cDNA clones for HNF-1 using oligonucleotides prepared to the sequence of the purified protein. The sequence of HNF-1 shares homeo domain, as well as short acidic and basic sequences with the POU family of transcriptional activators. Peptides from the protein interacting with the albumin proximal element, or B box (APF), and the factor interacting with the alpha 1-antitrypsin promoter (LF-B1) are found in the predicted sequence of HNF-1. HNF-1 mRNA is not present in the dedifferentiated hepatoma variant, C2, but reappears upon selection for gluconeogenesis coincident with the re-expression of liver-specific genes. Finally, the mRNA is not present in somatic cell hybrids in which liver-specific gene expression is extinguished. In contrast to earlier published results, we find that in addition to being present in the liver, HNF is expressed in the kidney, intestine, and spleen, but not in other tissues. This pattern of expression mirrors the complex pattern of expression of many genes, such as alpha-fetoprotein, alpha 1-antitrypsin, and fibrinogen, whose promoters contain HNF-1 sites. These data indicate that HNF-1 is a more broadly acting transcription factor than has been indicated by previous work.

Control of plasma fibrinogen levels

It is clear that the control of plasma fibrinogen levels is complex, involving not only many environmental factors such as alcohol intake, smoking habit, age, obesity and the acute phase response, but also genetic factors as shown by the association of the Bcl I RFLP of the beta-fibrinogen gene with plasma fibrinogen levels. The advent of recombinant DNA technology has made the dissection of the different factors controlling plasma fibrinogen levels a valid proposition, and great progress is already being made. The goals of this research are twofold. First, it may be possible to develop DNA tests to identify individuals who, on the basis of their genotype, are at high risk of ischaemic heart disease. Once identified, the subsequent risk of these individuals can be reduced by modifying life-style or by drug therapy to reduce other known risk factors such as cholesterol levels. Second, once the mechanisms controlling fibrinogen concentration are better understood at the molecular level, it may be possible to develop directed therapeutic strategies that will reduce fibrinogen synthesis in a specific manner, an approach that is not possible at present. In the future, such pharmacological agents may have as wide an impact on reducing ischaemic heart disease as cholesterol-lowering drugs do today.

Fibrinogen and albumin synthesis are regulated at the transcriptional level during the acute phase response

During acute inflammation or after administration of monocytic products, an enhanced transcription of the fibrinogen polypeptide genes and a reduced transcription of the albumin gene were observed. The changes in the fibrinogen polypeptide transcriptional rate were found to precede the change in albumin gene transcription. These findings indicate that the altered synthesis of fibrinogen and albumin during inflammation are regulated at the transcriptional level and are most probably mediated by monocytic products (including interleukin-1).

Human fibrinogen

The structure and physical properties of human fibrinogen and fibrin are reviewed along with methods for the detection of products of their metabolism. Interactions of human fibrinogen with thrombin, factor XIII, plasminogen, glycoprotein IIb/IIIa, and other proteins are related to their relevance to thrombosis and hemostasis. To the extent information is available, the structural determinants of these interactions are delineated, and kinetic and thermodynamic parameters associated with the interactions are listed. Individual steps in the reaction pathway for the conversion of fibrinogen to cross-linked fibrin are characterized. The altered hemostatic properties of mutational variants of fibrinogen are related to their altered structure. The structures of the genes coding for the polypeptide chains of fibrinogen are discussed along with the current state of knowledge of the control and regulation of fibrinogen synthesis. Fibrinogen catabolism and fibrinolysis are also reviewed.

The adenovirus major late transcription factor activates the rat gamma-fibrinogen promoter

The major late transcription factor (MLTF) is a 46-kilodalton polypeptide that specifically binds to and activates transcription from the major late promoter of adenovirus. The presence of this promoter-specific transcription factor in uninfected HeLa cell extracts suggests that MLTF is also involved in the transcription of cellular genes. This report demonstrates that MLTF specifically stimulates transcription of the rat gamma-fibrinogen gene through a high-affinity binding site. Stimulation of transcription by MLTF was not dependent on the exact position of the MLTF binding site with respect either to the transcription initiation site or to adjacent promoter elements. These results suggest that one of the cellular functions of MLTF is to control gamma-fibrinogen gene expression.

Synthesis of hemopexin and cysteine protease inhibitor is coordinately regulated by HSF-II and interferon-beta 2 in rat hepatoma cells

Rat hepatoma (H-35) cells respond to hepatocyte-stimulating factors by increased expression of major acute phase plasma proteins. The synthesis of hemopexin is stimulated 10-fold by either hepatocyte-stimulating factor-II of human squamous carcinoma cells or hepatocyte-stimulating factor/interferon-beta 2 of activated human blood monocytes. The hormone specificity, time course and dose-dependence of hemopexin regulation is closely correlated with that of cysteine protease inhibitor. The coordinate expression of hemopexin and other type II acute phase proteins suggests the existence of common molecular regulatory mechanisms.

Blood coagulation and coagulation tests

The hemostatic mechanism has evolved to provide efficient protection from traumatic blood loss and yet maintain the blood in a fluid state in the circulation as a whole. Recent advances in biochemistry have provided both detailed understanding of hemostasis and clinically useful coagulation assays to exploit this understanding. Clinicians now have the means to delineate most of the hemostatic problems of clinical significance.

Analysis of fibrinogen genes in patients with congenital afibrinogenemia

Several cDNA clones coding for A alpha, B beta and gamma chains of fibrinogen have been isolated from a human liver cDNA library. They were selected by differential hybridization with probes raised against fractionated liver mRNA (positive probes) and muscle and albumin mRNA (negative probes), then firmly identified by positive hybridization selection. Three of these clones, encoding A alpha, B beta and gamma fibrinogen chain sequences, were further characterized by restriction mapping and used as probes to characterize fibrinogen mRNAs from adult and fetal liver and fibrinogen genes in normal individuals and two afibrinogenemic patients. The results indicate that there is a single copy of the fibrinogen genes which are present and grossly intact in afibrinogenemic DNA.

Sequential comparative hybridizations analyzed by computerized image processing can identify and quantitate regulated RNAs

A method to analyze shifts in the relative abundance of many specific RNAs following any stimulus is presented. Hybridizations of two complex "total" cDNA probes (from the pre- and poststimulus states) to each member of a cDNA library are quantitatively analyzed and mathematically compared by using computer-assisted image processing and statistical analysis of sequential filter hybridizations. Experiments indicate that shifts in abundance between two states can be identified and reproducibly quantitated without purified probes. Direct isolation of recombinant cDNA colonies containing inserts corresponding to regulated RNAs is thus possible. The use of this system is demonstrated for partial analysis of the response in vivo of rat liver to glucocorticoids. Application to other biological systems in which a shift between two states occurs is discussed.