Stoichiometry of heparin binding to basic fibroblast growth factor

Fibroblast growth factors (FGFs) strongly bind to heparin and are thereby stabilized against deactivation and proteolytic cleavage. We have investigated the interactions of basic fibroblast growth factor (bFGF) with low- and high-molecular-weight heparin using size exclusion chromatography with on-line light scattering, absorbance, and refractive index detection. When heparin-bFGF mixtures with excess heparin are chromatographed using eluant that does not contain heparin, essentially all the protein is seen to elute as a complex with the heparin, indicating strong binding such that the complex does not dissociate significantly during chromatography (approximately 20 min). Combining the data from the light scattering, absorbance, and refractive index chromatograms allows us to determine the molecular weight of the protein component of the complex, and therefore to measure the number of bFGF molecules bound per heparin. A series of samples were prepared with a constant concentration of bFGF and variable amounts of a low-molecular-weight heparin (LMWH, M(r) = approximately 5000). At bFGF: heparin ratios above 1.5, a mix of complexes containing 3, 2, and 1 bFGF molecules is observed, with an average of 2.2 bFGF molecules per complex. Since the amount of bFGF incorporated into complexes implies an average of 2.5 +/- 0.3 bFGF molecules per heparin, there is only one heparin molecule per complex. The coexistence of complexes of different size when bFGF is in excess implies that the LMWH molecules are heterogeneous with respect to their ability to bind bFGF. When a high-molecular-weight heparin (HMWH, M(r) = 15,000) is used, complexes averaging 6.3 bFGF molecules per HMWH molecule are seen, while the overall amount of bFGF appearing in complexes implies six to seven sites per HMWH. These data show that the protein molecules can be packed very closely together. Both types of heparin give a heparin mass of 2300 Da per bFGF binding site, which corresponds approximately to an octasaccharide.

Characteristics of human immunodeficiency virus and chlorpromazine induced antiphospholipid antibodies: effect of beta 2 glycoprotein I on binding to phospholipid

OBJECTIVE

To investigate the nature of the target epitope for human immunodeficiency virus (HIV) and chlorpromazine (CPZ) induced antiphospholipid antibodies (aPL) by evaluating the effect of the aPL cofactor (beta 2 glycoprotein I) on phospholipid binding and to compare this with known binding patterns of infection induced and autoimmune aPL.

METHODS

aPL positive sera from 17 patients with HIV and 16 patients with schizophrenia treated with CPZ were tested and compared with aPL positive sera from 20 patients with syphilis and 35 with autoimmune disease. Both the sera and either IgG fractions prepared by affinity chromatography or IgM fractions prepared by euglobulin precipitation and gel filtration were tested for binding to cardiolipin (CL) in ELISA in the presence and absence of purified human beta 2 glycoprotein I (beta 2-GPI). Competition studies evaluated biotinylated CPZ IgM aPL binding and the effect on this of added aPL, placental anticoagulant protein I--a phospholipid binding protein that inhibits autoimmune aPL--and CL vesicles.

RESULTS

HIV IgG aPL binding to CL was inhibited by beta 2-GPI (51-53%), like syphilis IgG aPL and in contrast to autoimmune IgG aPL. CPZ IgM aPL, like autoimmune IgM aPL, bound more efficiently in the presence of beta 2-GPI, with binding increases of 31-149%. Binding of biotinylated CPZ IgM aPL to CL was competitively inhibited by autoimmune IgG aPL (47%) and CPZ aPL (92%) but not by HIV IgG aPL or normal IgG. Placental anticoagulant protein I and CL vesicles completely prevented binding of CPZ IgM aPL to CL (100 and 96% inhibition, respectively).

CONCLUSIONS

Findings indicate that CPZ aPL resembles the autoimmune aPL, whereas aPL found in HIV infection do not appear to be of autoimmune type.

Densimetric determination of equilibrium binding of sucrose octasulfate with basic fibroblast growth factor

Fibroblast growth factors (FGFs) strongly bind to heparin and are thereby stabilized against deactivation and proteolytic cleavage. Sucrose octasulfate (SOS), which has a chemical structure resembling the repeating unit of heparin, has also been shown to enhance stability of basic FGF against thermal denaturation and to induce a small conformational change. We have examined SOS binding to bFGF using equilibrium dialysis. The difference in SOS concentration across the dialysis membrane was measured using a precision density meter, since the density of SOS differs greatly from that of water. With care, this densimetric technique can measure binding with a precision of +/- 0.1 mol/mol using about 2 mg/ml of protein. These results show that the binding saturates at 2 mol of SOS per mole of bFGF as the SOS concentration increases to 3.6 mM or higher. The effect of SOS on the thermal stability of bFGF was examined using denaturation at a constant heating rate, by both turbidity and differential scanning calorimetry. Since the thermal denaturation is irreversible, the temperature where aggregation abruptly increases was taken to indicate the onset of denaturation. This temperature increased by approximately 12 degrees C as the SOS concentration increased from 0.018 to 3.6 mM and remained constant above 3.6 mM, consistent with our binding data if the binding is specific to the native state.

Acid-induced unfolding of brain-derived neurotrophic factor results in the formation of a monomeric "a state"

Recombinant human brain-derived neurotrophic factor in acid undergoes a slow loss of tertiary structure as monitored by both near-UV circular dichroism and fluorescence, and appears to retain some secondary structure, as monitored by far-UV circular dichroism and Fourier transform infrared spectroscopy. This loss of tertiary structure parallels a decrease in the weight average molecular weight, from dimer to monomer, when examined using light scattering. Increasing the temperature accelerates this slow reaction. This process may be described most simply as N2 in equilibrium with 2D where N and D are the native and denatured forms of the protein, respectively. However, the acid denaturation strongly depends on the protein concentration, with higher concentration resulting in a lower rate and extent of denaturation. This suggests that the more complicated mechanism N2 in equilibrium with 2N in equilibrium with 2D more accurately describes the denaturation, where the dissociation into a native monomer is the rate-limiting step, and the conversion of N to D occurs relatively rapidly. Size-exclusion chromatography (at neutral pH) at several points during denaturation further demonstrated that the amount of tertiary structure remaining paralleled the dimer concentration and also that the monomer form was long-lived, remaining as monomer during the course of the chromatography. Size-exclusion chromatography and sedimentation velocity determination indicated that the acid-denatured form is a compact molecule. On the basis of the above data, the acid-denatured form may be considered to be a monomeric compact intermediate A state with no tertiary structure but considerable secondary structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Refolding of brain-derived neurotrophic factor from guanidine hydrochloride: kinetic trapping in a collapsed form which is incompetent for dimerization

We have studied the pathway and kinetics of refolding of recombinant human brain-derived neurotrophic factor (BDNF), which is a very tightly-associated dimer in its native state. When BDNF unfolded in 6 M guanidine hydrochloride is diluted 20-fold into phosphate-buffered saline, a partially folded intermediate is rapidly formed (< 1 min). Circular dichroism and fluorescence spectroscopy show that this intermediate has extensive secondary structure, but no well-defined tertiary structure. Size-exclusion chromatography with light scattering detection shows that it is compact and monomeric, and therefore corresponds to what is often called a "collapsed form" or "molten globule". This collapsed form disappears with a half-time of approximately 30 min, simultaneously with the appearance of native dimers, without accumulation of monomeric species with a native tertiary structure. Remarkably, the monomer-dimer association constant of the collapsed form is approximately 10(10) weaker than the native structure, and it has a low tendency to form large aggregates. Given the very large hydrophobic surface present at the dimer interface of nerve growth factor (and presumably in BDNF), these results indicate that these hydrophobic groups are not exposed in the collapsed form, and that it is therefore quite dissimilar from the native structure. A significant conformational change in the collapsed form is necessary to re-expose these hydrophobic groups to form the dimer interface, making this the rate-limiting step in reaching the native conformation.

Do patients with antiphospholipid syndrome have autoantibodies to beta 2-glycoprotein I?

High positive anticardiolipin antibody tests have been associated with recurrent thrombosis and pregnancy loss. Although these antibodies were believed to bind negatively charged phospholipids, recent reports have suggested that a serum protein, beta 2-glycoprotein I (beta 2-GPI), may be the true antigen for these antibodies. To resolve this issue, we compared binding of 75 anticardiolipin-positive and 71 anticardiolipin-negative serum samples from patients with rheumatic diseases to beta 2-GPI by using an enzyme-linked immunosorbent assay (ELISA). Serum samples from 30 healthy blood donors and 10 laboratory personnel were used as normal controls. We found no difference in binding between the three groups of serum samples. In addition, when binding to beta 2-GPI coated plates was compared with binding to ELISA plates without beta 2-GPI (blank), no difference was observed. Finally, binding of anticardiolipin-positive serum samples to plates coated with cardiolipin-beta 2-GPI mixture varied directly with the cardiolipin concentrations. Based on these findings, we conclude that anticardiolipin-positive serum samples do not bind beta 2-GPI.

Familial tumoral calcinosis. A clinical, histopathologic, and ultrastructural study with an analysis of its calcifying process and pathogenesis

We describe histopathologic and ultrastructural changes in tumoral calcinosis (TC) occurring in seven siblings from a single family. Tumoral calcinosis appears to be triggered by bleeding followed by aggregation of foamy histiocytes. These in turn are transformed, with participation of collagenolysis, into cystic cavities lined by osteoclast-like giant cells and histiocytes--the lesion resembling adventitious bursae. Movement and friction, forces generated from the periarticular location of the TC lesions, putatively are key to this transformation. Concomitantly, two calcifying events develop, possibly driven by concurrent hyperphosphatemia or endogenous hypervitaminosis D. One occurs on membranous fragments in antiprotease-containing large cytoplasmic vesicles within osteoclast-like giant cells and mononuclear cells lining the TC cavities; the second, in the TC locules on membranous and cellular debris derived from cavity-lining cells and erythrocytes. The TC cavities ultimately fill with calcified material, losing their synovial-like lining, become encapsulated by fibrous tissue, and ossify. Hydroxyapatite may gain entrance to capillary lumens and embolize to the lung. We conclude that TC represents a disordered reparative process that often is exaggerated because episodes of bleeding, caused by TC-induced vascular injury, provoke development of new lesions. The capricious response of TC to treatment is correlated with its morphologic features.

Rickettsia australis infection: a murine model of a highly invasive vasculopathic rickettsiosis

A mouse model of spotted fever group rickettsiosis, in which disease results from disseminated rickettsial infection of endothelial cells and vascular damage, was developed by intravenous inoculation of 6- to 8-week-old, male, Balb/c mice with Rickettsia australis. Animals developed progressively severe vasculitis, interstitial pneumonia, and multifocal hepatic necrosis. These lesions correlated with early disseminated infection of endothelial cells followed by growth and invasion of rickettsiae into perivascular cells. The dose of 2 x 10(6) organisms was uniformly lethal. Serum interleukin- (IL) 1, IL-6, and interferon (IFN) increased by day 3 and tumor necrosis factor (TNF) on day 5. TNF, IL-6, and IFN declined on day 7. Spleen cells responded to Rickettsia australis antigen by producing IFN, TNF, IL-1, and IL-6 on day 5, followed by lower quantities of these cytokines on day 7. Despite the production of antibodies, IFN, TNF, IL-1, and IL-6, a lethal outcome occurred frequently. A decreased ability to secrete IL-2 suggests an element of infection-associated immunosuppression.

Non-linear epitopes of the large subunit of Ku autoantigen recognized by monoclonal and autoantibodies

Sera from certain patients with SLE, scleroderma and other autoimmune diseases react with the two subunits of the Ku protein: 86 and 70 kDa. Previous experiments indicated that a region of 40 amino acids near the C-terminus of the 86 kDa subunit between amino acids 667 and 708 was critical for binding of monoclonal and some autoimmune antibodies. In the present study, a series of additional 5' deletions and site-specific mutations in the critical region were produced and the immunoreactivities of the recombinant proteins were examined. ELISA and immunoblot analyses showed that three non-competing monoclonal antibodies specific for the 86 kDa subunit require stretches of amino acids significantly longer than 40 amino acids for reactivity, suggesting that the antigen is recognized in a folded state with perhaps more than one contact point. The reactivities of 12 of 24 anti-Ku positive autoimmune sera screened depended on the same amino acid sequences required for binding of the monoclonal antibodies, site-specific mutations reduced the reactivities of monoclonal and autoantibodies in a similar way. Preincubation of native Ku protein with the monoclonal antibodies shifted the electrophoretic mobility of Ku protein-DNA complex, suggesting that these monoclonal antibodies bind to epitopes on the surface of the native Ku protein. Taken together, the results from the deletion and site-directed mutagenesis demonstrate that both monoclonal and autoantibodies recognize non-linear epitopes of the 86 kDa polypeptide. These findings indicate that in a large portion of patients the anti-Ku autoimmune response is similar to the normal immune response to the Ku antigen in mice.

Induction of antiphospholipid autoantibodies by immunization with beta 2 glycoprotein I (apolipoprotein H)

A subset of patients with systemic lupus erythematosus has autoantibodies to acidic phospholipids. Since lipids are poor immunogens, the mechanism responsible for the induction of these antibodies is unclear. Immunization of a normal rabbit and normal mice with purified human beta 2-glycoprotein I (apolipoprotein H) resulted in the production of high levels of two non-cross-reactive antibody populations, anti-apolipoprotein H, and antiphospholipid. The antiphospholipid antibodies had binding specificities indistinguishable from autoantibodies obtained from human and murine lupus. These findings suggest a novel mechanism for the induction of antiphospholipid autoantibodies.

[A research on the quality of radix Astragali]

Milkvetch root (Radix Astragali) and its likes were determined in their contents of trace elements, total extracts and astragalin A. The result showed there was some relationship between the drug quality, trace-element contents, difference of species, growing areas and on-the-spot processing methods.

[An immunohistochemical and ultrastructural survey on smooth muscle tumors of the alimentary tract]

33 cases of smooth muscle tumors of the alimentary tract were analysed. Among them, 18 cases showed positive reaction to desmin, including one out of two cases of esophageal neoplasms, 6 out of 11 cases of gastric neoplasms, 5 from 12 cases of small intestinal neoplasms, 6 from 8 cases of large intestinal neoplasms, 14 out of 21 cases of benign tumors as well as sarcomas in grade I, and 4 from 12 cases of sarcomas in grade II and III (only mild positive result obtained in grade II and III-sarcomas). S-100 protein staining was performed in 27 cases and positive reaction was obtained only in five. Among them, 2 cases showed prominent positive reaction. 20 cases were studied by electron microscopy, and cytoplasmic myofilaments as well as dense bodies were demonstrated in 7 cases. All of them were the benign neoplasm or sarcoma in grade I. The conclusion is that most stromal tumors of the digestive system are originating from the smooth muscle, except very few cases are neurogenic in origin.

Siderotic cerebral macrophages in the acquired immunodeficiency syndrome

Excessive hemosiderin-laden perivascular macrophages have been described in the brains of patients with the acquired immunodeficiency syndrome (AIDS) who underwent autopsy; its meaning remains unclear. In the brains of 53 patients with AIDS who consecutively underwent autopsy, we quantified the abnormality, elucidated its relationship to the pathologic features of AIDS, and asked if there was some relationship to endogenous iron storage and transport proteins in brain macrophages and microglia. The number of perivascular siderotic macrophages was significantly increased in patients with AIDS compared with age-matched control subjects. Macrophage siderosis was strongly correlated with the presence of disseminated mycobacterial infection and vacuolar myelopathy at autopsy; a generalized wasting (cachexia) also was related significantly. Many other pathologic abnormalities were not related, including putative human immunodeficiency virus-specific neuropathologic changes such as multinucleated cells and myelin pallor. Activated macrophages and microglial cells in the central nervous system had dense intracytoplasmic accumulation of ferritin (iron storage protein) in AIDS and non-AIDS patients. These results suggest that siderosis of cerebral macrophages is related to an ill-defined nonspecific systemic imbalance associated with the breakdown of abundant stores of endogenous intracellular ferritin. Understanding chronic "secondary" effects of human immunodeficiency virus type 1 infection will become increasingly important as improved survival in patients with AIDS is realized.

[Biological behavior of smooth muscle tumors of the alimentary tract--a pathological analysis of 501 cases]

501 cases with smooth muscle tumors of the alimentary tract are presented with follow up information. 249 leiomyomas and 252 leiomyosarcomas were analyzed in an attempt to evaluate their biological behavior. All patients with leiomyoma survived except 15 who died of other diseases. In the leiomyosarcoma group, 134 survived and 118 died. The 1-2-3-4-5-10-and over 10 year-survival rates were 80.4%, 62.0%, 48.7%, 41.5%, 36.1%, 30.1% and 15.1%, respectively. The following factors were found to be statistically prognostic, arranged in order of their influence on survival; histologic grade, tumor size, mitotic rate and location of the tumor. Leiomyosarcomas were histologically divided into three grades; the higher the grade, the poorer the prognosis. The prognosis was better when the sarcoma was smaller and became worse when larger, especially over 10 centimetres in diameter. The survival rate decreased with increase in mitotic figure. Patients with leiomyosarcoma in the esophagus or stomach had longer survival than those with lesions in the small or large intestines.

Mapping of epitopes on the 86 kDa subunit of the Ku autoantigen

Patients with rheumatic disorders develop autoantibodies to a nuclear protein antigen termed Ku. The Ku antigen has been identified as a non-histone DNA-binding protein complex composed of two polypeptides: 86 kDa and 70 kDa. Initial competition experiments with four monoclonal antibodies specific for the 86 kDa subunit of Ku protein suggested there was more than one epitope on this polypeptide. To determine the region for these epitopes, cDNA deletions were made from both 5' and 3' ends. The immunoreactivity of the expressed proteins was assayed by immunoblotting. A 40 amino acids region located near the C-terminus of the polypeptide between amino acids 667-708 was essential for binding the monoclonal and autoimmune antibodies. Within this region, we differentiated three epitopes for the monoclonal antibodies. The sequence critical for binding of the autoimmune antibodies was in the same region, between amino acids 689-708. None of the four monoclonal antibodies blocked the binding of the autoantibodies. The implications of these results for the etiology of the anti-Ku autoantibody response are discussed.

Unscheduled DNA synthesis and HPRT mutation in fetal Syrian hamster and human respiratory epithelial cells exposed to ethylnitrosourea

We previously reported that the chromosomes of fetal Syrian hamster respiratory epithelial cells were less stable toward ethylnitrosourea (ENU) than those of comparable human cells. Following this, we compared the sensitivity of genetic materials of the same cell systems to the same mutagen in terms of unscheduled DNA synthesis (UDS) and mutation at HPRT locus (HPRT-). UDS occurred 5 (with 0.1 mg ENU/ml) to 7 (with 0.4 mg ENU/ml) times more frequently in the hamster cells than in the human cells. This much lower UDS frequency in human cells cannot be solely explained by the fact that the human cells possess only a moderately larger (1.6 to 2.9 times) size of intracellular deoxythymidine triphosphate (dTTP) pool than the hamster cells. This finding would thus indicate that the hamster cells actually carry out DNA repair, whether correct or aberrant, more often than the human cells. Moreover, HPRT- was also 5 (at 0.4 mg/ml) to 26 (at 0.8 mg/ml) times more frequent in the hamster cells than in the human cells. Therefore, the current results suggest that the DNA repair mechanisms of the hamster cells are less accurate and more unstable than those of the human cells. Our previous findings with regard to the chromosomal stability give support to this hypothesis.

[Presence of flagellar antigenic subfactors in serotype 1 of Bacillus thuringiensis]

The strain G was isolated from a dead army worm (Leucania separata Walker) in corn field, at Hebei. It has the typical morphological characteristics of Bacillus thuringiensis. The serological analysis showed that the flagellar suspensions of the strain G was agglutinated only by the antisera against the H1 antigen and not by the antisera against the other 22 known H-antigens. The agglutination titre was 1:6,400. The flagellar suspension of the serotype 1, subsp. thuringiensis, was agglutinated by the antiserum against the strain G, with a titre of 1:12,800. However, the cross-saturation of antisera showed that there were different fractions in the H1 antigen. The H antiserum against subsp. thuringiensis still agglutinated with subsp. thuringiensis, having a titre of 1:6,400, even if it was fully saturated by strain G. When it was saturated by subsp. thuringiensis the H antiserum of strain G did not agglutinate by himself. Therefore, the H1 antigen (subsp. thuringiensis) must be divided into subfactors H1alb and strain G antigen is H1a. On the basis of this study, we propose the strain G represents the serotype H1a under the name of Bacillus thuringiensis subsp. hebeiensis.

[Reaction between monoclonal antibodies to porcine zona pellucida and human and porcine ovary in vitro]

Reaction between monoclonal antibodies to porcine zona pellucida (LPD8, LPC4) and human and porcine ovaries was studied by ABC immunohistochemistry technique in vitro. When slices of human and porcine ovaries were stained with ABC, not only the zona pellucida but also the ovum cytoplasm was stained. Other regions of the ovary, such as granulosa cell, theca cell and connective tissue, could not be stained. These results suggest that the monoclonal antibodies to porcine zona pellucida probably have no direct effect on the endocrine function of ovary, but they may combine with ovum cytoplasm and inhibit follicular growth, so that the number of follicles reduces and endocrine function of the ovary decreases. We do not think that the prospects of continual study on LPD8, LPC4 are good.

[Pathological study of 936 cases of smooth muscle tumor in the alimentary tract]

936 cases of smooth muscle tumor were analysed, including 198 cases in esophagus, 354 in stomach, 243 in small intestine, and 141 in the large bowel. Pathological diagnosis revealed, that there were 468 cases of either leiomyoma or leiomyosarcoma, and the leiomyosarcoma cases had been further divided into three grades. The follow-up data of 191 leiomyomas showed that except 15 patients who died of irrelevant reasons, all the rest survived. Of 252 leiomyosarcoma patients, 138 are still alive and 114 died. The survival rate was 36.1% for 5 years and 30.1% for 10 years. Factors having an effect on the prognosis include sites, sizes, grades of the tumor and the number of mitotic figure in leiomyosarcoma. The authors suggest that mitotic figures (greater than or equal to 2/25HPF); cell anaplasia; density of tumor cell; tumor size (greater than 6cm); presence of necrosis and cystic change and infiltration of tumor cells into the neighbouring tissue may be considered as the criteria for the diagnosis of malignant smooth muscle tumors of the alimentary tract.

cDNA-derived amino acid sequence of the 86-kDa subunit of the Ku antigen

The Ku antigen is a DNA-associated nuclear protein recognized by sera from patients with autoimmune diseases. It consists of two polypeptides of 86 and 70 kDa. cDNA clones encoding the 86-kDa subunit of the Ku antigen were isolated by probing lambda gt11 recombinant cDNA expression libraries with a monoclonal antibody specific for this protein. The amino acid sequence deduced from the cDNA comprises 732 amino acids and corresponds to a protein with molecular weight of 81.914. Nineteen residues at the NH2 terminus determined by protein sequencing corresponded to the sequence deduced from the cDNA. The predicted amino acid sequence contains a region with repeating leucine residues similar to the "leucine zipper" structure observed in the c-myc, v-myc, and c-fos oncogene products. The largest cDNA hybridized to 2.7- and 3.4-kilobase poly(A)+ mRNAs from HeLa cells. The cDNA clones expressed fusion proteins immunoreactive with the monoclonal antibody and sera from patients with autoimmune diseases.

Toxicity and chromosomal damage in fetal Syrian hamster and human pulmonary epithelial cells

In order to test the hypothesis that human chromosomes are more stable than those of rodents, we compared the fetal human and Syrian hamster pulmonary epithelial cell lines for their sensitivity to the induction of cytotoxicity (CT), chromosomal aberrations (CAs) and sister-chromatid exchanges (SCEs). One day after plating, the cells were exposed for 2 h to various doses of ENU dissolved in an exposure medium consisting of McIlvaine buffer, RPMI 1640, and bovine serum albumin. CAs and SCEs were examined in 24-64 post-exposure hours by the standard methods, while CT was determined by cell counts. The frequency of CAs (particularly chromatid exchanges) and that of SCEs showed clear dose dependency and was remarkably higher in the hamster than in the human cells. CT determined in 1 week of post-exposure incubation showed a similar dose response for both cell lines with sharply declining regressions. These results suggest that human chromosomes are indeed more resistant to ENU-inducible aberrations than hamster chromosomes and that CT may not always be directly associated with chromosomal damage.