Characterization of a Monoclonal Antibody, D73H, that Maps to a Highly Conserved Region on Fibrinogen Bβ Chain

The primary structure of fibrinogen is highly conserved across species, yet often times monoclonal antibodies produced against the fibrinogen of one species will not crossreact with the fibrinogen of another. Herein, we describe the production and characterization of murine MAb, D73H, raised against human fibrinogen. D73H crossreacts with a highly conserved epitope on the Bβ chain of fibrinogen from human, rat, bovine, guinea pig, and mouse. Western blotting revealed that D73H reacted with the Bβ chain of plasmin fragment D, localizing its epitope to Bβ134-461. A 7 kDa band was identified by D73H in Western blots of reduced fibrinogen CNBr-fragments. N-terminal sequencing mapped this fragment to Bβ243-253, further localizing the epitope to Bβ243-305. In silico analysis indicated that Bβ243-305 is predominantly hydrophilic, and surface probability prediction indicated three potential antigenic determinants corresponding to Bβ252-258, Bβ262-269, and Bβ279-286. Further in silico analysis of the crystal structure of fibrinogen fragment D-D indicated that Bβ262-269 (FGRKWDPY) is predominantly α-helical and located on the surface of the molecule adjacent to a bend imposed in the β chain at residue 260, which is near the junction between the rigid coiled-coil domain and the globular C-terminus. A synthetic peptide corresponding to Bβ261-272 competitively inhibited the binding of D73H to the Bβ chain of denatured intact fibrinogen and reduced and denatured Bβ chain in Western blots, experimentally proving the validity of these predictive algorithms. Together these data indicate that, although plasmin resistant, Bβ chain residues Bβ261-272 comprising the D73H epitope are highly conserved across species, surface exposed, and immunogenic.

Heterologous expression of Streptococcus mutans Cnm in Lactococcus lactis promotes intracellular invasion, adhesion to human cardiac tissues and virulence

In S. mutans, the expression of the surface glycoprotein Cnm mediates binding to extracellular matrix proteins, endothelial cell invasion and virulence in the Galleria mellonella invertebrate model. To further characterize Cnm as a virulence factor, the cnm gene from S. mutans strain OMZ175 was expressed in the non-pathogenic Lactococcus lactis NZ9800 using a nisin-inducible system. Despite the absence of the machinery necessary for Cnm glycosylation, Western blot and immunofluorescence microscopy analyses demonstrated that Cnm was effectively expressed and translocated to the cell wall of L. lactis. Similar to S. mutans, expression of Cnm in L. lactis enabled robust binding to collagen and laminin, invasion of human coronary artery endothelial cells and increased virulence in G. mellonella. Using an ex vivo human heart tissue colonization model, we showed that Cnm-positive strains of either S. mutans or L. lactis outcompete their Cnm-negative counterparts for tissue colonization. Finally, Cnm expression facilitated L. lactis adhesion and colonization in a rabbit model of infective endocarditis. Collectively, our results provide unequivocal evidence that binding to extracellular matrices mediated by Cnm is an important virulence attribute of S. mutans and confirm the usefulness of the L. lactis heterologous system for further characterization of bacterial virulence factors.

Cnm is a major virulence factor of invasive Streptococcus mutans and part of a conserved three-gene locus

Cnm, a collagen- and laminin-binding protein present in a subset of Streptococcus mutans strains, mediates binding to extracellular matrices (ECM), intracellular invasion and virulence in the Galleria mellonella model. Antibodies raised against Cnm were used to confirm expression and the cell surface localization of Cnm in the highly invasive OMZ175 strain. Sequence analysis identified two additional genes (cnaB and cbpA) encoding putative surface proteins immediately upstream of cnm. Inactivation of cnaB and cbpA in OMZ175, individually or in combination, did not decrease the ability of this highly invasive and virulent strain to bind to different ECM proteins, invade human coronary artery endothelial cells (HCAEC), or kill G. mellonella. Similarly, expression of cnaB and cbpA in the cnm(-) strain UA159 revealed that these genes did not enhance Cnm-related phenotypes. However, integration of cnm in the chromosome of UA159 significantly increased its ability to bind to collagen and laminin, invade HCAEC, and kill G. mellonella. Moreover, the presence of antibodies against Cnm nearly abolished the ability of OMZ175 to bind to collagen and laminin and invade HCAEC, and significantly protected G. mellonella against OMZ175 infection. We concluded that neither CnaB nor CbpA is necessary for the expression of Cnm-related traits. We also provided definitive evidence that Cnm is an important virulence factor and a suitable target for the development of novel preventive and therapeutic strategies to combat invasive S. mutans strains.

Anticancer Role of PPARgamma Agonists in Hematological Malignancies Found in the Vasculature, Marrow, and Eyes

The use of targeted cancer therapies in combination with conventional chemotherapeutic agents and/or radiation treatment has increased overall survival of cancer patients. However, longer survival is accompanied by increased incidence of comorbidities due, in part, to drug side effects and toxicities. It is well accepted that inflammation and tumorigenesis are linked. Because peroxisome proliferator-activated receptor (PPAR)-gamma agonists are potent mediators of anti-inflammatory responses, it was a logical extension to examine the role of PPARgamma agonists in the treatment and prevention of cancer. This paper has two objectives: first to highlight the potential uses for PPARgamma agonists in anticancer therapy with special emphasis on their role when used as adjuvant or combined therapy in the treatment of hematological malignancies found in the vasculature, marrow, and eyes, and second, to review the potential role PPARgamma and/or its ligands may have in modulating cancer-associated angiogenesis and tumor-stromal microenvironment crosstalk in bone marrow.

Invasion of human coronary artery endothelial cells by Streptococcus mutans OMZ175

INTRODUCTION

Dissemination of oral bacteria into the bloodstream has been associated with eating, oral hygiene, and dental procedures; including tooth extraction, endodontic treatment, and periodontal surgery. Recently, studies identified Streptococcus mutans, the primary etiological agent of dental caries, as the most prevalent bacterial species found in clinical samples from patients who underwent heart valve and atheromatous plaque surgery.

METHODS

By using antibiotic protection assays, we tested the capacity of 14 strains of S. mutans to invade primary human coronary artery endothelial cells (HCAEC).

RESULTS

Serotype e strain B14 and serotype f strain OMZ175 of S. mutans were able to efficiently invade HCAEC. Among the tested strains, serotype f S. mutans OMZ175 was the most invasive, whereas strains of serotype c S. mutans, the most prevalent serotype in dental plaque, were not invasive. Based on its high invasion rate, we further investigated the invasive properties of serotype f OMZ175. Using transmission electron microscopy and antibiotic protection assays we demonstrate that S. mutans OMZ175 is capable of attaching to the HCAEC surface, entering the cells and surviving in HCAEC for at least 29 h.

DISCUSSION

Our findings highlight a potential role for S. mutans in the pathogenesis of certain cardiovascular diseases.

Fibrinogen synthesized by cancer cells augments the proliferative effect of fibroblast growth factor-2 (FGF-2)

BACKGROUND

Fibroblast growth factor (FGF)-2 is a critical growth factor in normal and malignant cell proliferation and tumor-associated angiogenesis. Fibrinogen and fibrin bind to FGF-2 and modulate FGF-2 functions. Furthermore, we have shown that extrahepatic epithelial cells are capable of endogenous production of fibrinogen.

OBJECTIVE

Herein we examined the role of fibrinogen and FGF-2 interactions on prostate and lung adenocarcinoma cell growth in vitro.

METHODS

Cell proliferation was measured by (3)H-thymidine uptake and the specificity of FGF-2-fibrinogen interactions was measured using wild-type and mutant FGF-2s, fibrinogen gamma-chain (FGG) RNAi and co-immunoprecipitation. Metabolic labeling, immunopurification and fluorography demonstrated de novo fibrinogen production.

RESULTS

FGF-2 stimulated DU-145 cell proliferation, whereas neither FGF-2 nor fibrinogen affected the growth of PC-3 or A549 cells. Fibrinogen augmented the proliferative effect of FGF-2 on DU-145 cells. The role of fibrinogen in FGF-2-enhanced DNA synthesis was confirmed using an FGF-2 mutant that exhibits no binding affinity for fibrinogen. FGG transcripts were present in PC-3, A549 and DU-145 cells, but only PC-3 and A549 cells produced detectable levels of intact protein. RNAi-mediated knockdown of FGG expression resulted in decreased production of fibrinogen protein and inhibited (3)H-thymidine uptake in A549 and PC-3 cells by 60%, which was restored by exogenously added fibrinogen. FGF-2 and fibrinogen secreted by the cells were present in the medium as a soluble complex, as determined by coimmunoprecipitation studies.

CONCLUSIONS

These data indicate that endogenously synthesized fibrinogen promotes the growth of lung and prostate cancer cells through interaction with FGF-2.

Plasma fibrinogen gamma' chain content in the thrombotic microangiopathy syndrome

BACKGROUND

Human fibrinogen gamma chain variants, termed gamma' chains, contain a unique 20-residue sequence after gamma chain residue 407 that ends at gamma'427, and is designated gamma'(427L). Full-length (FL) gamma'(427L) chains are constituents of a fibrin-dependent thrombin inhibitory system known as antithrombin I, whereas a gamma' chain processed in vivo, termed gamma'(423P), lacks the C-terminal tetrapeptide EDDL, and does not bind thrombin. Together, the gamma'(423P) and gamma'(427L) chains comprise the total plasma fibrinogen gamma' chain content.

OBJECTIVES

Lowered plasma gamma' chain content (i.e. gamma' chain-containing fibrinogen/total fibrinogen ratio) has been shown to correlate with susceptibility to venous thrombosis, thus prompting this study on the total and FL gamma' chain content in 45 subjects with thrombotic microangiopathy (TMA), a disorder characterized by microvascular thrombosis.

METHODS

We measured by enzyme-linked immunosorbent assay the total gamma' chain-containing fibrinogen/total fibrinogen (Total gamma'-fgn/Total fgn) ratio and the FL gamma' chain-containing fibrinogen/total fibrinogen (FL gamma'-fgn/Total fgn) ratio in these plasmas and in healthy subjects (n = 87).

RESULTS

In healthy subjects, the mean Total gamma'-fgn/Total fgn ratio was 0.127, whereas the FL gamma'-fgn/Total fgn ratio was somewhat lower at 0.099 (P < 0.0001), a difference reflecting the presence of gamma'(423P) chains. In TMA plasmas, both the Total gamma'-fgn and FL gamma'-fgn/Total fgn ratios (0.099 and 0.084, respectively) were lower than those of their healthy subject counterparts (P < 0.0001).

CONCLUSIONS

These findings in TMA suggest that reductions in the gamma' chain content indicate reduced antithrombin I activity that may contribute to microvascular thrombosis in TMA.

Fibrinogen binding potentiates FGF-2 but not VEGF induced expression of u-PA, u-PAR, and PAI-1 in endothelial cells

Endothelial cell responses at sites of injury occur in a fibrin matrix and are regulated by growth factors including those of the FGF and VEGF families. The pericellular proteolytic balance is important in these responses, and FGF-2 and VEGF up-regulate endothelial cell u-PA, u-PAR and PAI-1. Because both VEGF and FGF-2 bind to fibrinogen, we have examined the capacity of fibrinogen to modulate the up-regulation of these proteins by FGF-2 and VEGF. Confluent cultures of endothelial cells were exposed to FGF-2, VEGF, and fibrinogen or to combinations of growth factors with fibrinogen. Changes in mRNA levels of u-PA, u-PAR and PAI-1 were measured by Northern blot. FGF-2 increased u-PA, u-PAR, and PAI-1 mRNA, but there was a significantly greater induction when fibrinogen was added to FGF-2 at all concentrations. The potentiation by fibrinogen was particularly evident at an FGF-2 concentration of 0.1 ng mL(-1), which resulted in non-significant change in transcript levels by itself, but significantly increased up to 2.6-fold with fibrinogen. VEGF also increased endothelial cell expression of u-PA, u-PAR and PAI-1, but this effect was not potentiated by fibrinogen. Addition of LM609, a monoclonal antibody to alphaVbeta3, significantly inhibited induction of u-PA mRNA and activity by fibrinogen-bound FGF-2 compared to FGF-2. A monoclonal antibody to FGFR1 also inhibited u-PA mRNA expression induced by fibrinogen-bound FGF-2. We conclude that fibrinogen increases the capacity of FGF-2, but not of VEGF, to up-regulate u-PA, u-PAR, and PAI-1 in endothelial cells and that fibrinogen-bound FGF-2 requires alphaVbeta3 binding to up-regulate endothelial cell u-PA.

Fibrinogen modulates gene expression in wounded fibroblasts

Fibrinogen (FBG) has long been regarded as serving essentially a hemostatic role by its conversion from a soluble, plasma protein to an insoluble fibrin gel. However, several extrahepatic sites of FBG biosynthesis have been identified. Indeed, we have demonstrated that both lung epithelial cell derived and plasma FBG assemble into the extracellular matrix (ECM) of epithelial cells and fibroblasts. In this report, we determined that FBG assembly into the ECM is a cell dependent step that occurs in the absence of de novo protein synthesis. Using an in vitro model of wound repair, we examined the role of FBG in modulating gene expression. Data collected from cDNA array analysis indicated that FBG downregulates steady state levels of fibronectin mRNA, whereas cyclin D1 mRNA levels were upregulated in fibroblasts. Taken together, these data suggest that FBG may function independently of hemostasis in cellular adhesive interactions to modulate cellular signaling processes during wound repair.

Tumors and fibrinogen. The role of fibrinogen as an extracellular matrix protein

The progression of a tumor from benign and localized to invasive and metastatic growth is the major cause of poor clinical outcome in cancer patients. Much like in a healing wound, the deposition of fibrin(ogen), along with other adhesive glycoproteins, into the extracellular matrix (ECM) serves as a scaffold to support binding of growth factors and to promote the cellular responses of adhesion, proliferation, and migration during angiogenesis and tumor cell growth. Inappropriate synthesis and deposition of ECM constituents is linked to altered regulation of cell proliferation, leading to tumor cell growth and malignant transformation. Fibrin deposition occurs within the stroma of a majority of tumor types. In contrast, abundant FBG, not fibrin, is present within the stroma of breast cancers. It is thought to originate from exudation of plasma FBG and subsequent deposition into the tumor stroma and not endogenous synthesis and secretion of FBG by breast tumor cells. However, we show that MCF-7 human breast cancer cells synthesize and secrete FBG polypeptides, suggesting that the origin of FBG in the stroma of breast carcinoma may be due to endogenous synthesis and deposition. Moreover, FBG assembles into ECM as conformationally altered FBG, not as fibrin. Studies in our laboratory demonstrate that FBG alters the ability of breast cancer cells to migrate. Together, the results of studies from our laboratory, as well as the laboratories of others, indicate that the presence of fibrin(ogen) within the tumor stroma likely affects the progression of tumor cell growth and metastasis. This review focuses on FBG within tumors and its relationship with other tumor constituents, ultimately focusing on the role of FBG in breast cancer.

Fibrinogen naples I (B beta A68T) nonsubstrate thrombin-binding capacities

Fibrinogen Naples I (Bbeta A68T) is characterized by defective thrombin binding and fibrinopeptide cleavage at the fibrinogen substrate site in the E domain. We evaluated the fibrinogen of three homozygotic members of this kindred (II.1, II.2, II.3) who have displayed thrombophilic phenotypes and two heterozygotic subjects (I.1, I.2) who were asymptomatic. Electron microscopy of Naples I fibrin networks showed relatively wide fiber bundles, probably due to slowed fibrin assembly secondary to delayed fibrinopeptide release. We evaluated 125I-thrombin binding to the fibrin from subjects I.1, I.2, II.1, and II.2 by Scatchard analysis with emphasis on the high-affinity site in the D domain of fibrin(ogen) molecules containing a gamma chain variant termed gamma'. Homozygotic subjects II.1 and II.2 showed virtually absent low-affinity binding, consistent with the Bbeta A68T mutation, whereas heterozygotes I.1 and I.2 showed only moderately reduced low-affinity binding. The homozygotes also showed impaired high-affinity thrombin binding, whereas that of the heterozygotes was nearly the same as normal. Genomic sequencing of the gamma' coding sequence (I.2, II.2), ELISA measurements of two gamma' chain epitopes (L2B, gamma'409-412, and IF10, gamma'417-427) (I.2, II.1, II.2, II.3), and mass spectrometry of Naples I fibrinogen (II.2) showed no differences from normal, thus indicating that there were no abnormal structural modifications of the gamma' chain residues in Naples I fibrinogen. However, thrombin reportedly utilizes both of its available exosites for binding to high- and low-affinity sites on normal fibrin, suggesting that binding is cooperative. Thus, reduced high-affinity thrombin binding to homozygotic Naples I fibrin may be related to the absence of low-affinity binding sites.

Integrin alphavbeta3-mediated endocytosis of immobilized fibrinogen by A549 lung alveolar epithelial cells

Fibrinogen (FBG), together with its polymerized form fibrin, modulates cellular responses during wound repair and tissue remodeling. Thus, we sought to determine whether A549 lung epithelial type II-like cells would endocytose insoluble, surface-bound FBG as a potential mechanism of alveolar matrix remodeling. Surface-bound FBG was endocytosed into either lysosomes or late endosomes by A549 cells through arg-gly-asp-dependent binding to alphavbeta3 but not alpha5beta1 integrin receptors. Soluble FBG added to confluent monolayers of A549 cells was not endocytosed. Unlike the uptake of the extracellular matrix glycoproteins vitronectin and thrombospondin by other cell types, endocytosis of FBG by A549 cells was neither inhibited by heparin nor dependent on binding to cell-surface heparan sulfate proteoglycans. FBG did not colocalize with endocytosed transferrin, whereas dextran showed partial colocalization with FBG in endocytic vesicles, suggesting nonclathrin-mediated endocytosis. Inhibition of actin filament polymerization blocked endocytosis of both dextran and FBG but not transferrin, providing further support that FBG is endocytosed via a nonclathrin pathway. Disruption of actin polymerization inhibited integrin-mediated cell spreading, which contributed to an overall reduction in FBG clearance that was most likely due to reduced cell migration and associated pericellular proteolysis. Trasylol inhibition of extracellular plasmin activity did not inhibit endocytosis of FBG. The endocytosed FBG was degraded to trichloroacetic acid-soluble fragments that showed an electrophoretic pattern distinctly different from plasmin-degraded FBG. Together, these results suggest that endocytosis of matrix-associated FBG by alveolar epithelial cells may be involved in the processes of alveolar tissue repair and matrix remodeling.

The charge-heterogeneity of human fibrinogen as investigated by 2D electrophoresis

The charge-heterogeneity of human plasma fibrinogen subunit chains was characterized by two-dimensional electrophoresis (2DE). Western blotting with antibodies specific for the gamma-chain demonstrated that the gamma-chains focus at varying isoelectric points (pI). This microheterogeneity was also observed in fibrinogen secreted from hepatocytic cells and in recombinant fibrinogen expressed in Chinese hamster ovary (CHO) cells. Further, covalent gammagamma-dimerization by FXIIIa was not influenced by the charge-heterogeneity, and removal of the carbohydrate did not reduce the number of gamma-chain pI variants. These observations suggest that the microheterogeneity of the gamma-chain is a multifactorial phenomenon that is not due to physiologic modification of the glycoprotein in circulation.

Characterization of a monoclonal antibody, D73H, that maps to a highly conserved region on fibrinogen Bbeta chain

The primary structure of fibrinogen is highly conserved across species, yet often times monoclonal antibodies produced against the fibrinogen of one species will not crossreact with the fibrinogen of another. Herein, we describe the production and characterization of murine MAb, D73H, raised against human fibrinogen. D73H crossreacts with a highly conserved epitope on the Bbeta chain of fibrinogen from human, rat, bovine, guinea pig, and mouse. Western blotting revealed that D73H reacted with the Bbeta chain of plasmin fragment D, localizing its epitope to Bbeta134-461. A 7 kDa band was identified by D73H in Western blots of reduced fibrinogen CNBr-fragments. N-terminal sequencing mapped this fragment to Bbeta243-253, further localizing the epitope to Bbeta243-305. In silico analysis indicated that Bbeta243-305 is predominantly hydrophilic, and surface probability prediction indicated three potential antigenic determinants corresponding to Bbeta252-258, Bbeta262-269, and Bbeta279-286. Further in silico analysis of the crystal structure of fibrinogen fragment D-D indicated that Bbeta262-269 (FGRKWDPY) is predominantly alpha-helical and located on the surface of the molecule adjacent to a bend imposed in the beta chain at residue 260, which is near the junction between the rigid coiled-coil domain and the globular C-terminus. A synthetic peptide corresponding to Bbeta261-272 competitively inhibited the binding of D73H to the Bbeta chain of denatured intact fibrinogen and reduced and denatured Bbeta chain in Western blots, experimentally proving the validity of these predictive algorithms. Together these data indicate that, although plasmin resistant, Bbeta chain residues Bbeta261-272 comprising the D73H epitope are highly conserved across species, surface exposed, and immunogenic.

Fibrinogen assembly, secretion, and deposition into extracellular matrix by MCF-7 human breast carcinoma cells

A hallmark of breast carcinoma is the deposition of fibrinogen (FBG) without subsequent conversion to fibrin in the tumor stroma. In this study, the ability of the MCF-7 human breast cancer epithelial cell line to synthesize, secrete, and deposit FBG into the extracellular matrix (ECM) was examined. Whereas MCF-7 cells produced low levels of intact FBG, abundant levels of FBG intermediate complexes or degraded Aalpha, Bbeta, and gamma chain polypeptides were observed. Most of the Bbeta chain was degraded and missing an NH2-terminal peptide fragment. Reverse transcription-PCR analysis indicated that only gamma chain mRNA was present in detectable steady-state levels, although Southern hybridization revealed that the FBG Aalpha, Bbeta, and gamma chain genes were intact in MCF-7 cells. Immunostaining showed that extracellular FBG was bound to the surface of MCF-7 cells in a punctate pattern, reminiscent of receptor binding, rather than a fibrillar pattern characteristic of mature ECM. A similar punctate pattern of staining was observed when MCF-7 FBG was added to fibroblasts that normally assemble exogenous FBG into an extensive, fibrillar ECM, suggesting that MCF-7 cells are defective in assembly of a fibrillar ECM. The loss of FBG Bbeta chain NH2-terminal peptides may contribute to the lack of intact FBG assembly in MCF-7 cells, which may further affect its ability to assemble FBG into a fibrillar ECM. Taken together, the data suggest that endogenous synthesis and secretion of FBG is, at least in part, the source of FBG deposition in the ECM of breast cell carcinomas.

Post-transcriptional regulation of endothelial cell plasminogen activator inhibitor-1 expression during R. rickettsii infection

Intracellular infection of endothelial cells with Rickettsia rickettsii results in increased steady-state levels of plasminogen activator inhibitor-1 (PAI-1) mRNA. Control mechanisms governing such increased expression in response to this novel stimulus have not been defined. In this study, we compared the stability of PAI-1 mRNA in infected and uninfected endothelial cells (EC) and explored the requirement for de novo host cell protein synthesis in the infection-induced increase of steady-state levels. The half-life of PAI-1 mRNA, which is constitutively expressed in cultured EC, increased from 18 h in uninfected EC to greater than 30 h in EC infected for 24 h, a time point at which increases in steady-state PAI-1 mRNA levels are noted. There was no change in stability of gamma-actin due to infection. Nuclear run-on studies revealed no apparent increase in transcription rate at 4, 18 and 24 h. R. rickettsii -induced increase in PAI-1 mRNA was blocked by the eukaryotic protein synthesis inhibitor, cycloheximide, which suggests that this response requires de novo host cell protein synthesis. These results provide evidence that post-transcriptional control mechanisms are operative in the regulation of PAI-1 during R. rickettsii infection.

Cell type-specific regulation of fibrinogen expression in lung epithelial cells by dexamethasone and interleukin-1beta

Our recent studies demonstrating the expression of fibrinogen (FBG) by an alveolar type II cell line stimulated with proinflammatory mediators and also in the inflamed pulmonary epithelium of animals with Pneumocystis carinii pneumonia suggest that extrahepatic FBG participates in the local acute phase response (APR) to infection and subsequent wound repair. However, the mechanisms that regulate extrahepatic FBG expression are poorly understood. This study compares the regulation of hepatic and pulmonary FBG expression by mediators of the APR, interleukin (IL)-6, IL-1beta, and dexamethasone (DEX), a synthetic glucocorticoid. Northern blotting and metabolic labeling studies revealed that IL-6 with or without DEX upregulates gammaFBG messenger RNA and protein, whereas IL-1beta inhibits gammaFBG expression in human lung (A549) and liver (HepG2) epithelial cells. In contrast, the addition of DEX relieved the IL-1beta-mediated inhibition of FBG expression in lung epithelial cells only; this response is termed "DEX rescue." Studies with cycloheximide indicate that only DEX rescue required de novo protein synthesis. Nuclear run-on analysis revealed no increase in gammaFBG transcription by DEX treatment. Although DEX treatment alone increased the stability of gammaFBG transcripts in lung cells, this effect was not observed in the presence of IL-1beta. Together, these results suggest that pre-existing transcription factors mediate the effects of IL-6 with or without DEX, DEX, and IL-1beta on gammaFBG gene expression in lung and liver cells. Also, the data suggest that DEX induces new protein synthesis of an inhibitor of IL-1beta signal transduction to effectively "rescue" FBG production in lung but not liver epithelial cells. This cell type-specific stimulation of FBG production by glucocorticoids to overcome IL-1beta inhibition may promote pulmonary wound repair mechanisms.

Molecular characterization of KEX1, a kexin-like protease in mouse Pneumocystis carinii

Expression screening of a Pneumocystis carinii-infected mouse lung cDNA library with specific monoclonal antibodies (mAbs) led to the identification of a P. carinii cDNA with extensive homology to subtilisin-like proteases, particularly fungal kexins and mammalian prohormone convertases. The 3.1 kb cDNA contains a single open reading frame encoding 1011 amino acids. Structural similarities to fungal kexins in the deduced primary amino acid sequence include a putative proenzyme domain delineated by a consensus autocatalytic cleavage site (Arg-Glu-Lys-Arg), conserved Asp, His, Asn and Ser residues in the putative catalytic domain, a hydrophobic transmembrane spanning domain, and a carboxy-terminal cytoplasmic domain with a conserved tyrosine motif thought to be important for localization of the protease in the endoplasmic reticulum and/or Golgi apparatus. Based on these structural similarities and the classification of P. carinii as a fungus, the protease was named KEX1. Southern blotting of mouse P. carinii chromosomes localized kex1 to a single chromosome of approximately 610 kb. Southern blotting of restriction enzyme digests of genomic DNA from P. carinii-infected mouse lung demonstrated that kex1 is a single copy gene. The function of kexins in other fungi suggests that KEX1 may be involved in the post-translational processing and maturation of other P. carinii proteins.

The carboxyl terminus of Pneumocystis carinii glycoprotein A encodes a functional glycosylphosphatidylinositol signal sequence

Pneumocystis carinii pneumonia is a hallmark disease associated with AIDS. An abundant glycoprotein, termed gpA, on the surface of P. carinii is considered an important factor in host-parasite interactions. The primary structure of ferret P. carinii gpA contains a carboxyl-terminal sequence characteristic of a signal for glycosylphosphatidylinositol (GPI) anchors. Here we report the capacity for this gpA carboxyl sequence to direct attachment of a secreted protein, human growth hormone (hGH), to the membranes of COS cells. A control fusion protein (hGHDAF37) was obtained which, under the direction of the GPI signal from decay accelerating factor, directs hGH cell surface expression. A construct (phGH2-1A30) was created similar to hGHDAF37 by fusing hGH to the putative GPI signal sequence encoded in the terminal 30 residues from a ferret P. carinii gpA cDNA clone. By indirect immunofluorescent staining, hGH was detected on the surface of COS cells transfected with phGH2-1A30; this surface location was confirmed by confocal laser cytometry. Metabolic labeling with [3H]ethanolamine and subsequent immunopurification of hGH from cells transfected with phGH2-1A30 confirmed that a lipid moiety characteristic of a conventional GPI anchor was linked covalently to hGH, and cell surface hGH2-1A30 fusion protein was sensitive to enzymatic cleavage by phosphatidylinositol-phospholipase C. Furthermore, hGH2-1A30 recombinant protein cofractionated with 5'-nucleotidase, a classical GPI-anchored membrane marker. Together, these results indicate that the carboxyl-terminal residues of ferret P. carinii gpA constitute a biologically functional GPI consensus domain, thus providing a potential mechanism for antigenic variation of P. carinii gpA during P. carinii pneumonia.

Induction of fibrinogen expression in the lung epithelium during Pneumocystis carinii pneumonia

Pneumocystis carinii is an important pulmonary pathogen responsible for morbidity and mortality in patients with AIDS. The acute-phase response (APR), the primary mechanism used by the body to restore homeostasis following infection, is characterized by increased levels of circulating fibrinogen (FBG). Although the liver is the primary site of increased FBG synthesis during the APR, we unexpectedly discovered that FBG is synthesized and secreted by lung alveolar epithelial cells in vitro during an inflammatory stimulus. Therefore, we sought to determine whether lung epithelial cells produce FBG in vivo using animal models of P. carinii pneumonia (PCP). Inflammation was noted by an influx of macrophages to P. carinii-infected alveoli. Northern hybridization revealed that gamma-FBG mRNA increased two- to fivefold in P. carinii-infected lung tissue, while RNA in situ hybridization demonstrated increased levels of gamma-FBG mRNA in the lung epithelium. Immunoelectron microscopy detected lung epithelial cell-specific production of FBG, suggesting induction of a localized inflammatory response resembling the APR. A systemic APR was confirmed by a two- to fivefold upregulation of the levels of hepatic gamma-FBG mRNA in animals with PCP, resulting in a corresponding increase in levels of FBG in plasma. Furthermore, immunoelectron microscopy revealed the presence of FBG at the junction of cell membranes of trophic forms of P. carinii organisms aggregated along the alveolar epithelium. These results implicate FBG in the pathogenesis of PCP in a manner similar to that of the adhesive glycoproteins fibronectin and vitronectin, which are known to participate in intra-alveolar aggregation of organisms and adherence of P. carinii to the lung epithelium.

Molecular characterization of mouse Pneumocystis carinii surface glycoprotein A

Since the mouse offers an easily manipulated experimental animal model for the study of the immunopathogenesis of pneumonia caused by the opportunist Pneumocystis carinii, we cloned and characterized cDNAs encoding an abundant, immunogenic surface antigen termed glycoprotein A (gpA) from mouse P. carinii. A cDNA library was constructed in bacteriophage lambda gt11 from P. carinii-infected mouse lung poly(A+) RNA. Using a nucleic acid probe derived from a conserved region of the mouse P. carinii gpA structural gene, cDNAs encoding gpA were identified. A composite full-length gpA coding sequence was assembled from two overlapping cDNA clones. A DNA element homologous to the rat P. carinii upstream conserved sequence (UCS) was identified at the 5' end of several of the mouse P. carinii gpA cDNA clones, just upstream of the sequences encoding gpA structural gene isoforms. Using primer extension analysis, two neighboring putative transcriptional start sites were located on UCS-gpA mRNAs approximately 25 and 30 nt, respectively, upstream of the most 5' gpA cDNA clone isolated, suggesting a 5' UCS of 489 or 494 nucleotides in mouse P. carinii gpA. A comparative alignment of the composite mouse P. carinii gpA deduced amino acid sequence with gpA homologs from rat, human and ferret P. carinii demonstrated 156 identical residues, including 46 cysteines, further supporting the hypothesis for conserved secondary structure, as well as function, for gpA from all P. carinii.

Antigenic properties of recombinant glycosylated and nonglycosylated Pneumocystis carinii glycoprotein A polypeptides expressed in baculovirus-infected insect cells

Since a continuous culture system is not yet available for the opportunistic fungal pathogen Pneumocystis carinii, obtaining suitable amounts of purified P. carinii antigens free of mammalian-host lung contaminants is difficult. Hence, production of recombinant antigen possessing epitopes found in native P. carinii antigens is critical for immunological studies. We utilized the baculovirus expression vector system (BEVS) in insect cells to determine whether B-cell epitopes present in the protein core of a native P. carinii surface glycoprotein were conserved in the recombinant polypeptide, and to investigate its glycosylation by insect cells. B-cell epitopes were retained, but the insect cells appeared to hyperglycosylate the recombinant protein.

Transcriptional regulation of endothelial cell tissue factor expression during Rickettsia rickettsii infection: involvement of the transcription factor NF-kappaB

The vascular endothelial cell (EC) is a primary target of infection with Rickettsia rickettsii, the etiologic agent of Rocky Mountain spotted fever. Changes in gene transcription elicited by intracellular infection, including EC expression of the coagulation pathway initiator known as tissue factor (TF), may contribute to the vascular pathology observed during disease. Nuclear run-on analysis of uninfected and infected, cultured human endothelial cells revealed that the rate of TF mRNA transcription is enhanced more than twofold at 3 h following infection, thus coinciding with increased steady-state levels of TF mRNA. TF mRNA remained relatively unstable during infection, with a half-life of 1.6 h. The eukaryotic protein synthesis inhibitor cycloheximide did not block R. rickettsii-induced increase in TF mRNA levels and actually resulted in its superinduction, thus revealing that de novo synthesis of host cell protein was not prerequisite to this transcriptional response. Involvement of the transcription factor NF-kappaB in R. rickettsii-induced TF expression was demonstrated by using two unrelated inhibitors of NF-kappaB activation. The antioxidant pyrrolidinedithiocarbamate and the proteasome inhibitor N-tosyl-L-phenylalanine chloromethyl ketone blocked expression of TF mRNA and activity during infection. This study demonstrates that R. rickettsii infection results in transcriptional activation of the TF gene and that this response involves activation of the transcription factor NF-kappaB.

Thrombin cleavage-independent deposition of fibrinogen in extracellular matrices

Lung epithelial cells (A549) synthesize and secrete fibrinogen (FBG) in vitro when stimulated with interleukin-6 and dexamethasone. This FBG secretion is polarized in the basolateral direction, suggesting that FBG is a component of the extracellular matrix (ECM). Immunofluorescent staining of A549 cells showed a fibrillar pattern of FBG, similar to the staining detected using antibodies against the matrix constituents, collagen type IV and fibronectin (FN). The same pattern of staining was detected using antibodies against fibrinopeptides A and B, as well as with the T2G1 monoclonal antibody against the fibrin-specific epitope, beta15-21. Matrix staining was unaltered in the presence of the thrombin inhibitor, hirudin, or the plasmin inhibitor, aprotinin, consistent with the interpretation that matrix deposition of FBG does not require such enzymatic action. Metabolic labeling studies confirmed that FBG secreted from A549 cells or deposited into the ECM showed no evidence of thrombin or plasmin proteolytic processing or of transglutaminase-mediated covalent cross-linking (gamma-gamma dimers or alpha-polymers). Incubation of either A549 cell-derived or purified plasma FBG with cultures of human foreskin fibroblasts resulted in FBG deposition in the ECM that colocalized with matrix fibrils containing endogenously produced FN and laminin (LN). Binding of FBG to this exogenously produced matrix was unaltered by inhibition of thrombin and plasmin action, yet also exhibited exposure of the fibrin-specific epitope, beta15-21. The majority (approximately 70%) of newly synthesized and secreted FBG is bound to the cell surface as determined by its trypsin-sensitivity. Cell surface-bound FBG is initially deoxycholate-soluble, which, over time, becomes incorporated in the deoxycholate-insoluble ECM in a similar fashion to FN. These data suggest that matrix incorporation requires the binding of secreted FBG to cell-associated matrix assembly sites. However, unlike FN, FBG in the ECM is composed of the dimeric protamer (A alpha/B beta/gamma gamma) and not high molecular weight polymers indicative of fibrin. This study provides evidence that deposition of FBG in both endogenous and exogenously produced matrices results in conformational changes that occur independently of thrombin cleavage. This matrix-bound FBG, on which unique cell-reactive domains are likely exposed, could augment cellular response mechanisms evoked during injury and inflammation.

Polarized secretion of fibrinogen by lung epithelial cells

The lung epithelium has recently been identified as a novel site of fibrinogen (FBG) biosynthesis. A coordinated upregulation of A alpha, B beta, and gamma chain FBG gene transcription occurs upon stimulation of A549 lung epithelial cells with dexamethasone (DEX) and the proinflammatory mediator interleukin-6 (IL-6). Subsequently, the cells synthesize and secrete fully assembled FBG. This study addresses the polarity of such FBG secretion by A549 cells cultured on polycarbonate membrane filters. After induction with IL-6 and DEX, cells were metabolically labeled, and FBG was immunopurified from the apical and basolateral chambers. Analysis by gel electrophoresis revealed that A549 cells secreted newly synthesized FBG in a polarized manner, with the majority (80%) of FBG secreted basolaterally. Consistent with this observation, immunoelectron microscopy using Protein A-gold labeling showed FBG within secretory vesicles in close proximity to the basolateral aspect of the A549 cell membrane. Polarized secretion was microtubule-dependent since depolymerization using colchicine significantly reduced the basolateral component of secretion, causing intracellular retention of FBG. These data provide evidence that FBG is secreted by lung alveolar epithelial cells vectorially toward the basement membrane, which may reflect in vivo processes associated with local injury, inflammation, and repair mechanisms.

Heparin-binding domain of fibrin mediates its binding to endothelial cells

Spreading of human umbilical vein endothelial cells (ECs) on fibrin requires thrombin cleavage of fibrinopeptide B (FPB) and subsequent exposure of the new beta 15-42 N-terminus. To further understand the interactions between ECs and fibrin beta 15-42 sequences, binding of fibrin(ogen) to EC monolayers was measured with polyclonal anti-fibrinogen (FBG) in parallel with monoclonal anti-FBG (18C6, beta 1-21; J88B, gamma 63-78) and anti-fibrin (T2G1, beta 15-21) antibodies in an indirect enzyme-linked immunosorbent assay. To accomplish this, large, soluble fragments of fibrin were prepared by cyanogen bromide (CNBr) cleavage (fibrin-CNBr); CNBr-cleaved FBG (FBG-CNBr) served as the control ligand. N-terminal fibrin-CNBr bound to EC monolayers and cells in suspension in a dose-dependent and saturable manner. By contrast, FBG-CNBr bound only 50% as well to EC monolayers, with no significant binding of intact FBG, C-terminal FBG plasmic fragment D, or N-terminal plasmic fragment E, which lacks beta 1-53. ECs bound the peptide beta 15-42-bovine serum albumin (BSA) conjugate but neither a scrambled beta 15-42 peptide conjugate nor conjugates of beta 24-42, beta 18-27, or beta 18-31. Binding of fibrin-CNBr was inhibited 54% by the beta 15-42-BSA conjugate and 17% by the B beta 1-42-BSA conjugate but not by free beta 15-42 peptide or RGDS-cell binding peptide. Binding of fibrin-CNBr was inhibited > 95% by heparin in a concentration-dependent manner; the same concentrations of heparin inhibited binding of beta 15-42-BSA by > 75% but not the dose-dependent binding of fibronection to ECs. These data suggest that in their native conformation, FBG B beta 15-42 sequences are unavailable for binding to ECs and that thrombin-induced exposure of beta 15-42 is required for binding by a heparin-dependent, RGD-independent mechanism at the new N-terminus of fibrin.

Calcium modulates plasmin cleavage of the fibrinogen D fragment gamma chain N-terminus: mapping of monoclonal antibody J88B to a plasmin sensitive domain of the gamma chain

Plasmin sensitive sites are found on the A alpha, B beta and gamma chains of fibrinogen at regions joining the two C-terminal D fragments with the central E fragment. We have developed a monoclonal antibody (MoAb) reactive with this plasmin sensitive region on the human fibrinogen gamma chain and mapped its epitope. MoAb J88B reacts with gamma chains of both native as well as with reduced and denatured fibrinogen and fibrin, the CNBr fragment of the fibrinogen central domain, plasmin cleaved fragments D, gamma-gamma dimers, but not with plasmic fragments E. These data indicate that J88B maps to the plasmin sensitive domain localized to gamma 63-78. MoAb J88B failed to react with synthetic peptide gamma 70-78, which suggests that the epitope includes the newly exposed N-terminal residues gamma 63-70 of the early plasmic fragment D1A. As calcium has a marked influence on plasmin cleavage of C-terminal sites on the gamma chain, the effects of calcium on modulating plasmin cleavage of D1A to D1 were assessed in the absence or presence of J88B. The results indicated that calcium delays and J88B (+/- calcium) protects the gamma chain from plasmin cleavage at the N-terminus of D1A, suggesting that this enzymatically labile site is calcium-sensitive. Thus, MoAb J88B should prove useful in studies examining the structure of plasmin cleaved fibrinogen and fibrin.

Thrombin cleavage enhances exposure of a heparin binding domain in the N-terminus of the fibrin beta chain

Thrombin (IIa)-cleavage of fibrinogen (FBG) to form polymerized fibrin promotes endothelial cell spreading, proliferation, and von Willebrand factor release, requiring the exposure of the beta 15-42 domain. Studies reported here indicate that IIa-cleavage of fibrinopeptide B enhances exposure of a heparin binding domain at the beta 15-42 neo-N-terminus of fibrin. Crossed immunoelectrophoresis showed heparin-induced mobility shifts indicative of complexing with FBG and with N-terminal CNBr fragments of FBG (NDSK) and of fibrin (IIa-NDSK), but not evidence of heparin complexing with FBG lacking B beta 1-42 or with FBG fragments D and E was seen. Elution from heparin-agarose with a linear gradient of NaCl showed that bound portions of both intact FBG and D fragments eluted below physiologic salt concentrations, whereas E3 fragments lacking B beta 1-53 did not bind. NDSK bound with higher affinity than did intact FBG, whereas binding of IIa-NDSK was maximal in this system. Binding of fibrin(ogen) to heparin agarose was saturable as well as inhibitable in a dose-dependent manner with both FBG and heparin. Scatchard analysis indicated a single class of binding site, with dissociation constants (kd) of 0.3 mumol/L for IIa-NDSK, 0.8 mumol/L for NDSK, and 18 mumol/L for FBG. Immobilized fibrin had twofold more heparin binding sites than did immobilized FBG and required a 5.5-fold higher concentration of heparin to inhibit by 50% the binding of labeled heparin. Together, the results indicate that IIa-cleavage results in enhanced exposure of two heparin binding domains (HBDs) with approximately threefold higher affinity in fibrin than in FBG. Synthetic peptide beta 15-42 showed highest binding to heparin-agarose followed by B beta 1-42, whereas peptides beta 18-31, beta 18-27, and beta 24-42 did not bind. Thus, the primary structure of beta 15-42 is required for specificity of heparin binding. Basic residues within the beta 15-32 region segregate primarily to one side of an alpha-helix in a helical wheel diagram, as is typical for authentic HBDs. Desulfated heparin and heparan sulfate bound more fibrin(ogen) than did other proteoglycans; however, heparin bound sixfold more Ila-NDSK than NDSK. These results confirm that fibrin binds to heparin with higher affinity than does FBG and that fibrin binding is not solely dependent on charge interactions of beta 15-42 with the negatively charged glycosaminoglycan.

Increased expression of plasminogen activator inhibitor-1 in R. rickettsii-infected endothelial cells

Changes in PAI-1 expression in human umbilical vein endothelial cells (HUVEC) were studied following in vitro infection with Rickettsia rickettsii. A 1.8-fold increase in secreted PAI-1 activity occurred in infected versus control cultures (p = 0.03) at 24 h but not at earlier timepoints. A similar increase (1.4-fold) in secreted PAI-1 antigen (p < 0.005) was measured by ELISA. To determine whether this increase was due to increased synthesis of PAI-1, HUVEC were metabolically labeled with 35S-methionine concurrent with R. rickettsii infection. Such infection resulted in a 1.9-fold increase in labeled PAI-1 in the medium at 24 h (p = 0.036). Increase steady-state levels of PAI-1 mRNA were detected as early as 18 h by Northern blot analysis, peaking (5.5-fold) at approximately 24 h. These results indicate that PAI-1 production is increased in RR-infected endothelial cells, an effect that may contribute to the vascular occlusions noted in Rocky Mountain spotted fever.

Cloning and characterization of a lung-specific cDNA corresponding to the gamma chain of hepatic fibrinogen

The gene (gamma FBG) encoding the fibrinogen gamma chain (gamma FBG) has been shown to exhibit both tissue-specific and ubiquitous expression. To confirm the identity of the gamma FBG transcripts expressed in extrahepatic tissue, lung tissue was chosen as a model of extrahepatic gamma FBG gene expression. A ferret lung cDNA clone bank was constructed in lambda gt11 and several positive plaques were isolated using cross-species hybridization with the rat gamma FBG cDNA. Sequence data of the longest clone, designated pFLG gamma 3, was compared at the nucleotide and deduced amino acid (aa) levels with sequences of gamma FBG from other species. The results indicated that the identity of the ferret lung-specific gamma FBG cDNA to pig, rat, bovine and human gamma FBG cDNAs ranged from 78-88%; the similarity of the ferret lung-specific gamma FBG deduced aa sequence ranged from 84-88% across species. Cysteine aa involved in intra- and inter-chain disulfide-bonded secondary and tertiary structure are absolutely conserved in ferret gamma FBG. The putative cell-cell adhesion sites for both platelet alpha IIb beta 3 and intercellular adhesion molecule-1 receptor binding to ferret gamma FBG are > 90% similar to the corresponding sites in the human gamma FBG. The results of Northern hybridization indicated that the ferret lung gamma FBG mRNA was equivalent in size to the liver gamma FBG mRNA; Southern hybridization suggested that ferret gamma FBG is a single-copy gene, as is the gamma FBG of other species. Lung-specific gamma FBG expression was localized to epithelial cells of the large and small airways and chondrocytes by in situ RNA:RNA hybridization. The functional significance of gamma FBG expression in lung is not presently known. Since expression of FBG is up-regulated 2-10-fold in the liver during an inflammatory event, it is possible that lung-specific gamma FBG expression occurs predominantly during lung disease or injury.

Cloning and characterization of a conserved region of human and rhesus macaque Pneumocystis carinii gpA

Although the genes encoding Pneumocystis carinii (Pc) glycoprotein A (gpA) display a high degree of host species-specific genotypic diversity, the Pc gpA derived from different host species share defined regions of significant homology in their primary amino acid (aa) structure. Using two degenerate oligodeoxyribonucleotide (oligo) primers corresponding to a conserved Cys region (Cys-primers) of the ferret (F), rat (R) and mouse (M) PcgpA, a 306-bp portion of the human (H) PcgpA was amplified from only one of three known HPc-infected lung samples using PCR. The deduced aa sequence of the HPc PCR product was 72% similar to the corresponding region of a published HPc gpA aa sequence. Because the conserved Cys-primers amplified only one of three samples of HPcgpA, a primer-pair was designed from sequences internal to the Cys-primer sequences of the HPcgpA PCR product (hPc). The hPc primers amplified the expected 254-bp product from each of the three HPc-infected lung DNA samples, suggesting that the Cys-primers may have either amplified a HPcgpA present in fewer copies in the genome of HPc or, alternatively, amplified a gene from an uncommon strain of Pc encoding an isoform variant of gpA not present in the other human isolates analyzed in this report. Restriction analysis of the amplified products demonstrated heterogeneity in the internal sequence, confirming that more than one gpA exists in HPc as well. To determine the relationship of HPcgpA to the gpA of Pc from another primate, the hPc primers were used successfully to amplify a 261-bp product from Pc-infected Rhesus macaque (Rm) lung genomic DNA. These results are consistent with our earlier findings that closely related host species are infected with Pc organisms encoding similar gpA, suggesting that the evolutionary divergence of Pc followed that of the mammalian host species.

Mechanisms of cytopenia in human immunodeficiency virus infection

Human immunodeficiency virus (HIV) infection often has effects on the hematopoietic system which can be distinguished from the concurrent effects of medications or opportunistic infections. Exactly how the virus mediates these effects remains uncertain, but both in vivo and in vitro studies have pointed up possible direct and indirect modes of hematopoietic suppression. Whether a significant fraction of CD34+ cells in vivo are infected with HIV remains controversial, but most studies using in situ polymerase chain reaction techniques would suggest not. Other more indirect modes of hematopoietic cell suppression such as production of autoantibodies, production of other humoral inhibitory factors, T-cell mediated suppression of hematopoiesis, or production of inhibitory or stimulatory cytokines may also be contributory. It is probable that several of these mechanisms may occur simultaneously, and an increased understanding of their role may lead to improved strategies to correct the cytopenias which often accompany HIV disease.

Cloning of the complete coding sequence of rat fibrinogen B beta chain cDNA: interspecies conservation of fibrin beta 15-42 primary structure

After thrombin cleavage, the newly exposed NH2-termini of the beta chains play a role in both fibrin polymerization and fibrin interactions with cells in the process of wound healing. These physiological responses have been shown to be mediated, at least in part, by beta 15-42. To compare the sequence of the beta chain of fibrin across species, the complete coding sequence of the rat fibrinogen B beta chain cDNA was cloned (designated pRB beta 3) and characterized. The sequence newly determined from pRB beta 3 encompassed nucleotides 121-589, encoding residues 9-165 of the mature polypeptide. Significant homology of pRB beta 3 cDNA and deduced amino acid sequences was found when compared with other species' B beta chains. The rat B beta-Arg14-Gly15 thrombin cleavage site is conserved; however, the fibrinopeptide B sequences are only 50% similar when rat is compared with human. In contrast, the beta 15-42 region is 100% similar when allowing for conservative amino acid substitutions. Monoclonal antibodies (MAbs) specific for human fibrinogen B beta 1-21 (1-8C6) and human fibrin beta 15-21 (59D8 and T2G1) failed to cross-react with rat fibrinogen or fibrin by ELISA, respectively, even though thrombin conversion of rat fibrinogen to fibrin was confirmed. MAb 1-8C6 reacted with reduced and denatured human fibrinogen B beta chain by Western blotting, whereas, MAb T2G1 did not blot with reduced and denatured human fibrin beta chain. A comparative analysis of the binding affinity of the human B beta fibrin(ogen) specific MAbs with B beta fibrin(ogen) from several species suggested that amino acid residues preceding and including Arg14-Gly15 are important in the epitope of the B beta 1-21 specific MAb 1-8C6, and that residues Gly15, Leu19 and/or Lys21 play an important role in the epitope shared by the beta 15-21-specific MAbs T2G1 and 59D8.

Intracellular localization of a Trypanosoma cruzi kDNA minicircle transcript using RNA: RNA in situ hybridization

Using RNA: RNA in situ hybridization, the intracellular location of a transcript encoded by and spanning the entire length of a Trypanosoma cruzi kinetoplast DNA minicircle was determined. In axenically cultured T. cruzi epimastigotes, the hybridization signal was restricted to the kinetoplast, which was situated in the perinuclear region of the cell. Following conversion of epimastigotes to culture-derived metacyclic trypomastigotes, the kinetoplast moved to an acentric position in the metacyclic trypomastigote. Again, the hybridization signal co-localized with the position of the kinetoplast. These results suggested that the transcript remained closely associated with the T. cruzi kinetoplast within the mitochondrion in each of the morphological forms. Using specific oligonucleotide probes derived from a cDNA encoding the transcript, the entire native kDNA minicircle encoding the transcript was cloned and its nucleotide sequence was determined. The nucleotide sequence of the intact native minicircle was identical to that of the full-length cDNA corresponding to the minicircle transcript, indicating that the transcript was not modified prior to the time of cDNA synthesis and cloning.

Conserved sequence homology of cysteine-rich regions in genes encoding glycoprotein A in Pneumocystis carinii derived from different host species

Pneumocystis carinii surface glycoprotein A (gpA) exhibits host species-specific phenotypic and genotypic variation. Despite this heterogeneity, the gpAs of P. carinii isolated from different host species appear to be homologous molecules sharing certain biochemical and antigenic characteristics. Using two degenerate oligodeoxyribonucleotide primers corresponding to conserved cysteine regions from ferret and rat P. carinii gpAs, a PCR product of approximately 300 bp was amplified from ferret, rat, and SCID mouse P. carinii-infected lung genomic DNA. Northern (RNA) hybridization revealed a transcript of 3,450 nucleotides in P. carinii-infected SCID mouse lung mRNA, which is similar in size to the transcripts for ferret and rat P. carinii gpAs. Nucleotide sequence analysis of SCID mouse P. carinii gpA subclones derived from the PCR products identified two isoforms, which were 89% identical to each other in the amplified region and 73 and 54% identical to the rat- and ferret-derived P. carinii gpA genes, respectively. Comparison of the deduced amino acid sequences of mouse, ferret, and rat P. carinii gpAs revealed striking similarity in residues adjacent to and including the conserved cysteines. Furthermore, the spacing of two proline residues is invariant, and a potential N-linked glycosylation site is found at a similar position in all of the gpAs. Despite the heterogeneity observed in P. carinii gpAs, the conservation of cysteine residues and adjacent sequences implies similar secondary structure and, most likely, similar function for the gpAs of P. carinii isolated from different host species.