Helicobacter pylori culture supernatant inhibits binding and proliferative response of human gastric cells to epidermal growth factor: implications for H.pylori interference with ulcer healing?

Helicobacter pylori (H. pylori) infection of gastric mucosa is strongly associated with gastritis and peptic ulcer disease. However, the mechanisms of the ulcerogenic action of H. pylori and/or the interference of H. pylori with ulcer healing are unknown. Through binding to its receptor, epidermal growth factor (EGF) accelerates cells migration and triggers epithelial cell proliferation which are both important for the healing of gastroduodenal ulcers. H. pylori seems to interfere with ulcer healing, but the cellular and molecular targets and mechanisms of these actions have not been elucidated. In the present study, we tested the effect of H. pylori culture supernatant (dialyzed to remove molecules smaller than 10 kD) on EGF binding to its receptor and on the proliferative response of human gastric Kato III cells to EGF. H. pylori culture supernatant significantly reduced specific binding of EGF to its receptor and reduced EGF-stimulated gastric cell proliferation. Since ulcer healing requires epithelial cell proliferation and cell migration (re-epithelialization), which are both triggered by EGF binding to its receptor, the alteration in these mechanisms by H. pylori product may be the basis of H. pylori-induced interference with ulcer healing.

Formation of an active dimer during storage of interleukin-1 receptor antagonist in aqueous solution

The degradation products of recombinant human interleukin-1 receptor antagonist (rhIL-1ra) formed during storage at 30 degrees C in aqueous solution were characterized. Cationic exchange chromatography of the stored sample showed two major, new peaks eluting before (P1) and after (L2) the native protein, which were interconvertible. Size-exclusion chromatography and electrophoresis documented that both the P1 and L2 fractions were irreversible dimers, formed by noncovalent interactions. A competition assay with interleukin-1 indicated that on a per monomer basis the P1 and L2 dimers retained about two-thirds of the activity of the native monomer. Infrared and far-UV circular dichroism spectroscopies showed that only minor alterations in secondary structure arose upon the formation of the P1 dimer. However, alteration in the near-UV circular dichroism spectrum suggested the presence of disulfide bonds in the P1 dimer, which are absent in the native protein. Mass spectroscopy and tryptic mapping, before and after carboxymethylation, demonstrated that the P1 dimer contained an intramolecular disulfide bond between Cys-66 and Cys-69. Although conversion of native protein to the P1 dimer was irreversible in buffer alone, the native monomer could be regained by denaturing the P1 dimer with guanidine hydrochloride and renaturing it by dialysis, suggesting that the intramolecular disulfide bond does not interfere with refolding. Analysis of the time course of P1 formation during storage at 30 degrees C indicated that the process followed first-order, and not second-order, kinetics, suggesting that the rate-limiting step was not dimerization. It is proposed that a conformational change in the monomer is the rate-limiting step in the formation of the P1 dimer degradation product. Sucrose stabilized the native monomer against this process. This result can be explained by the general stabilization mechanism for this additive, which is due to its preferential exclusion from the protein surface.

Prostanoid receptors of murine NIH 3T3 and RAW 264.7 cells. Structure and expression of the murine prostaglandin EP4 receptor gene

Prostaglandin endoperoxide H synthase-1 (PGHS-1) is expressed constitutively in murine NIH 3T3 cells and RAW 264.7 cells. PGHS-2 is inducibly expressed in these cells following stimulation with serum or bacterial lipopolysaccharide (LPS), respectively. Reverse transcription-polymerase chain reaction (RT-PCR) analysis established that a variety of G protein-linked and peroxisomal proliferator-activated prostanoid receptors are expressed in both of these cell types. The levels of the EP2 and EP4 prostaglandin E2 (PGE2) receptors and the prostaglandin I2 receptor were changed in these cells by serum or LPS stimulation. Quantitative RT-PCR indicated that the mRNA for the murine EP4 receptor, the butaprost-insensitive PGE2 receptor that couples to Gs, increases 1.5-3-fold in response to serum (NIH 3T3) or LPS (RAW 264.7) with a time course approximating the induction of PGHS-2 expression. To study expression of the EP4 receptor we isolated the mouse EP4 receptor gene; the gene is 10 kilobase pairs (kb) in length and, like other known prostanoid receptor genes, contains three exons and two introns. The first intron is 0.5 kb and is located 16 base pairs (bp) downstream of the translational start site. This is a different location than that of the first introns of other prostanoid receptor genes. The second intron is located immediately following the sixth transmembrane domain at the same position as the second intron of the thromboxane A2 receptor, prostaglandin D2 receptor, prostaglandin I2 receptor, and one of the PGE2 (EP1) receptor genes. A major transcriptional start was detected at -142 bp upstream of the translational start. There are a variety of putative cis-acting elements within 1.5 kb upstream of the translational start site and within the first intron. Promoter analyses of the EP4 receptor gene promoter in RAW 264.7 cells indicated that there is a constitutive negative regulatory region between -992 and -928 bp, a constitutive positive region between -928 and -554 bp, and an LPS/serum-responsive region between -554 and -116 bp.

Gene of rat Ca2+/calmodulin-dependent protein kinase II alpha isoform -- its cloning and whole structure

The gene encoding the alpha isoform of rat Ca2+/calmodulin-dependent protein kinase II was cloned, and its exon-intron organization was analyzed. The coding region of cDNA consists of 18 exons spanning more than 50 kilobase pairs. Each of the discrete functional units, such as the ATP-binding site, the autophosphorylation site responsible for Ca2+-independent activity, the calmodulin-binding site, and link structure is encoded by a single exon. The largest and smallest exons consist of 229 and 41 base pairs, respectively. All splice junction sequences flanking the introns conform to the consensus splice junction sequence and the GT-AG splice rule.

Colorimetric ELISA measurement of specific mRNA on immobilized-oligonucleotide-coated microtiter plates by reverse transcription with biotinylated mononucleotides

In this study, alpha-globin mRNA was captured on plastic plates to which alpha-globin-specific oligonucleotides had been covalently immobilized; the captured mRNA was immediately reverse-transcribed into cDNA in the presence of biotinylated dUTP. Addition of alkaline phosphatase-conjugated streptavidin to react with the biotin was followed by addition of substrate (p-nitrophenyl phosphate), and the resulting colorimetric development was measured at 405 nm. Because multiple biotin molecules are incorporated into cDNA during reverse transcription, and because synthesized cDNA is more stable than mRNA, we could successfully quantify by conventional colorimetry the amount of alpha-globin mRNA on the plate within a linear range of 100 pg to 10 ng. This is more sensitive than conventional Northern blotting. Therefore, the present method may be applicable to measurements of specific mRNAs in various test materials.

Colorimetric ELISA measurement of specific mRNA on immobilized-oligonucleotide-coated microtiter plates by reverse transcription with biotinylated mononucleotides

In this study, alpha-globin mRNA was captured on plastic plates to which alpha-globin-specific oligonucleotides had been covalently immobilized; the captured mRNA was immediately reverse-transcribed into cDNA in the presence of biotinylated dUTP. Addition of alkaline phosphatase-conjugated streptavidin to react with the biotin was followed by addition of substrate (p-nitrophenyl phosphate), and the resulting colorimetric development was measured at 405 nm. Because multiple biotin molecules are incorporated into cDNA during reverse transcription, and because synthesized cDNA is more stable than mRNA, we could successfully quantify by conventional colorimetry the amount of alpha-globin mRNA on the plate within a linear range of 100 pg to 10 ng. This is more sensitive than conventional Northern blotting. Therefore, the present method may be applicable to measurements of specific mRNAs in various test materials.

Disulfide structure and N-glycosylation sites of an extracellular domain of granulocyte-colony stimulating factor receptor

An extracellular domain containing 603 amino acid residues of human granulocyte-colony stimulating factor receptor was expressed in Chinese hamster ovary cells. The affinity-purified material has previously been shown to dimerize when combined with the ligand. In this paper we have characterized the primary structure of this active receptor. Laser desorption mass spectrometry of the purified receptor showed a broad peak at a molecular weight of 84,000, ranging from 77,000 to 91,000. The molecular weight heterogeneity is due to glycosylation. Since the molecular weight based on the amino acid sequence is 67,322, by subtraction the carbohydrate content is approximately 17,000. Disulfide structure of the receptor was determined by peptide mapping in the absence and presence of reducing agent. Sequence and mass spectral analyses of these peptides showed the receptor to contain eight disulfide bonds and three free cysteines. These disulfide bonds are consistent with the known domain motifs of the receptor in that no interdomain disulfides were present. One of the three free cysteines is reactive with alkylating agents, while the others are less reactive, probably being buried in the interior of the molecule. Blocking the free cysteines did not affect the ligand binding. Carbohydrate moieties are somewhat evenly spaced throughout the molecule, at eight different N-glycosylation sites, some of which show heterogeneity in their compositions. Glycosylation seems necessary for stabilizing the molecule against disulfide-linked oligomerization of the receptor, indicating that the free cysteine residues become reactive for oxidation and disulfide exchange upon deglycosylation.

Indomethacin treatment during initial period of acetic acid-induced rat gastric ulcer healing promotes persistent polymorphonuclear cell-infiltration and increases future ulcer recurrence. Possible mediation of prostaglandins

The study was performed to examine whether indomethacin administered during the initial period of acetic acid-induced gastric ulcer healing affects future ulcer recurrence. Gastric ulcers were produced in rats by subserosal injection of acetic acid. Indomethacin (1 mg/kg/day, orally) administered either alone or concomitant with ornoprostil (50 micrograms/kg/day, orally) was started on the fourth day and continued for 56 days. In rats whose ulcer healed at the 90th day after production of ulcer, endoscopy was done every 30 days to examine recurrence of ulcer. Gastric specimens were obtained 10, 30, 60, 90, and 240 days after ulcer production for histology, to quantitate the height of regenerated mucosa, thickness of fibrous tissue, degree of polymorphonuclear cell infiltration, and PAS-positive cells. Cumulative ulcer recurrence rate was significantly higher in rats initially treated with indomethacin than in controls. Increased polymorphonuclear cell infiltration was the major histologic abnormality persisting after cessation of indomethacin. Ornoprostil reversed these abnormalities caused by indomethacin. In conclusion, the administration of indomethacin during the initial period of the ulcer healing promoted persistent polymorphonuclear cell infiltration and increased ulcer recurrence rates, possibly via a prostaglandin-dependent mechanism.

Size-exclusion chromatography with on-line light-scattering, absorbance, and refractive index detectors for studying proteins and their interactions

Techniques of using size-exclusion chromatography (SEC) with on-line light-scattering, uv absorbance, and refractive index detectors to characterize the polypeptide molecular weights of simple proteins or glycoproteins or to determine the stoichiometry of protein complexes are described. Two unique advantages of this approach over conventional SEC are that the molecular weight measurement is independent of elution position and can exclude the contributions from carbohydrates. When a protein or complex contains no carbohydrates, a two-detector method, i.e., light scattering combined with refractive index, can be used to calculate the molecular weight. When a protein contains carbohydrates, a three-detector method is used to calculate the molecular weight of polypeptide alone. Finally, a self-consistent three-detector method is used to determine the stoichiometry of a protein complex containing carbohydrates. Example applications for all these methodologies are described.

ErbB receptor activation, cell morphology changes, and apoptosis induced by anti-Her2 monoclonal antibodies

A panel of mAbs were generated against the purified soluble form of erbB2/Her2 receptor, corresponding to the extracellular region of the receptor, and examined for their ability to mimic the receptor ligand. Some of the mAbs strongly induced tyrosine phosphorylation of 180-185 kDa proteins, including not only Her2 but also Her3 and Her4 receptors, when they were expressed on the surface of breast cancer cells. These mAbs do not cross-react with Her3 or Her4 as demonstrated by competition study. Receptor phosphorylation was also observed with the cell lines transfected with Her2 or a chimeric receptor consisting of the extracellular domain of Her2 and the transmembrane and cytoplasmic domains of epidermal growth factor receptor. Selected mAbs were tested for their ability to change cell morphology, and one specific mAb, mAb74, induced cell morphology changes and apoptosis.

Induction of alpha-helix in the beta-sheet protein tumor necrosis factor-alpha: thermal- and trifluoroethanol-induced denaturation at neutral pH

The unfolding and refolding of alpha-helical proteins has been extensively studied, demonstrating formation of intermediate structures which retain the native-like alpha-helix but lack the tertiary structure. Studies on the folding of proteins consisting primarily of beta-sheet are interesting since, unlike the alpha-helix, the beta-sheet requires the formation of peptide hydrogen bonds between two or more polypeptide segments which may be far apart in the linear sequence. Here we have studied the unfolding of the beta-sheet-containing protein tumor necrosis factor-alpha (TNF-alpha). This protein exists as a symmetric trimer in solution. Murine TNF-alpha begins to melt at 60 degrees C and unfolds to a soluble structure with a transition midpoint of 66 degrees C. This reaction is irreversible. This unfolded form contains a considerable amount of (approximately 30%) alpha-helix, as determined by circular dichroism. Human TNF-alpha begins to melt at 60 degrees C and precipitates concurrently with unfolding, such that there is no soluble protein present by 70 degrees C. The secondary and tertiary structures of murine TNF-alpha unfold simultaneously, suggesting that unfolding from the native to the unfolded state occurs cooperatively. The thermal-induced denaturation is very insensitive to protein concentration, indicating that trimer to monomer conversion, if it occurs, is not rate-limiting. Trifluoroethanol induces alpha-helix in both human and murine TNF-alpha, further demonstrating the propensity of TNF-alpha to form alpha-helix. The different behavior of human versus murine TNF-alpha upon thermal unfolding is due to differences in the solubility of the unfolded protein, the murine form being more soluble. These results indicate that TNF-alpha can form alpha-helix when the long range interactions conferred by the native structure are removed during unfolding.

Induction of alpha-helix in the beta-sheet protein tumor necrosis factor-alpha: acid-induced denaturation

Acid-induced unfolding of proteins often results in an intermediate structure, called the molten globule structure or "A" state, which retains at least partial secondary structure but lacks a rigid tertiary structure. Acid-induced unfolding has been studied extensively for alpha-helical proteins, while few studies have been done on proteins containing only beta-strands. Tumor necrosis factor-alpha (TNF-alpha) is a trimer in which the individual subunits consist of antiparallel beta-sheet, organized into a jellyroll beta-sandwich. We have found previously [Narhi et al. (1996) Biochemistry 35, 11447-11453] that thermal denaturation of TNF-alpha results in an aggregate which contains a substantial amount of alpha-helix and that the addition of trifluoroethanol induces alpha-helix in both murine and human TNF-alpha. Here we show that acid also can induce alpha-helix in these proteins. At acidic pH (below 4), both human and murine TNF-alpha convert to a monomeric form, as determined by sedimentation and diffusion constants obtained from sedimentation velocity experiments. The sedimentation coefficient indicated that this monomer was only slightly expanded relative to the native state. Near-UV circular dichroic (CD) analysis showed a loss of tertiary structure. These structural features coincide with the notion that the acid-induced structure of TNF-alpha is a molten globule. What is unique in this protein is that TNF-alpha acquires alpha-helical structure, which is not present in the native structure as determined by both CD and Fourier transform infrared spectroscopy. Even more surprising is that TNF-alpha at pH 3.3 undergoes a very gradual noncooperative change in secondary structure upon heating, which results in an increase in alpha-helical content. At pH 2.2 in the absence of salt, TNF-alpha shows considerable alpha-helix, although heating does not change the spectrum. At pH 2.2, physiological salt decreases the amount of alpha-helix at ambient temperature, and upon heating, we see the noncooperative increase in alpha-helix as observed at pH 3.3 with low salt. The addition of salt at low pH induces reassociation but to a range of oligomers rather than a unique trimer structure. This acid-induced formation of an alpha-helical monomer of TNF-alpha may be related to its known interaction with lipid bilayers.

Characterization of keratinocyte growth factor binding to heparin and dextran sulfate

Binding of keratinocyte growth factor (KGF) with heparin (molecular weight of 5000) and dextran sulfate (molecular weight of 8000) was studied using an online monitoring of size-exclusion chromatography with light scattering, refractive index, and uv absorbance detectors. This technique allows the determination of the molecular weight of KGF eluting as complexes with the above polymers. When mixtures of KGF with heparin were injected into the column, two peaks of heparin/KGF complexes were observed. The first peak corresponded to, on average, 3.4 KGF per complex and the second peak to an average of about 2 KGF per complex. These results suggest that the heparin/ KGF complex is heterogeneous, consisting of 1,2,3, and 4 KGF molecules per complex. To calculate the number of heparin molecules in these complexes, the rate of disappearance of free KGF was determined as heparin was added. The average number of KGF bound to 1 mol of heparin was calculated to be about 2 mol, suggesting that only one heparin molecule is present in these complexes. The heparin binding of two KGF mutants, i.e., (C1, 15S)KGF (with substitutions of serine for cysteines 1 and 15) and d28KGF (lacking 28 N-terminal amino acid residues), was essentially identical to that of the native sequence KGF. A similar experiment was carried out for KGF binding to dextran sulfate. The molecular weight of the complex corresponded to 2 to 2.6 KGF molecules per complex. The rate of disappearance of free KGF as the dextran sulfate added showed 2-3 mol of KGF bound to 1 mol of dextran sulfate, consistent with the idea that the complex contains only 1 dextran sulfate molecule.

Complete sequence, subunit structure, and complexes with pancreatic alpha-amylase of an alpha-amylase inhibitor from Phaseolus vulgaris white kidney beans

The complete amino acid sequence of a white kidney bean (Phaseolus vulgaris) alpha-amylase inhibitor (PHA-I), which is composed of two kinds of glycopolypeptide subunits, alpha and beta, was established by conventional methods. The polypeptide molecular weight of PHA-I determined by the light-scattering technique, considered together with the sequence molecular weights revealed for the subunits, indicated that PHA-I has the subunit stoichiometry of (alpha beta)2 complex. Inhibition test of PHA-I with increasing amounts of porcine pancreatic alpha-amylase (PPA) suggested that an inactive 2:1 complex is formed between PPA and PHA-I. In fact, two complexes differing from each other in the molar ratio of PPA to PHA-I were separated by gel filtration, and molecular weight estimation by the light-scattering technique confirmed that they are complexes of PHA-I with one or two PPA molecules. The binding of PPA to PHA-I appeared to follow simple binomial statistics, suggesting that two binding sites on PHA-I are independent and of high affinity for PPA.

Native and non-native structure in a protein-folding intermediate: spectroscopic studies of partially reduced IGF-I and an engineered alanine model

The structure of a metastable folding intermediate of human insulin-like growth factor I (IGF-I) and an engineered model are investigated by circular dichroism and two-dimensional 1H NMR spectroscopy. The intermediate, which contains two of three native disulfide bonds, was trapped by acid quenching and isolated by reverse-phase HPLC. The reduced cysteine residues were mapped to residues 47 and 52 (corresponding to A6-A11 in insulin). In the native state this disulfide bridge anchors an adjoining amphipathic alpha-helix (helix 2; residues 42 to 49) against the hydrophobic core. Comparison of CD and 1H-NMR spectra demonstrates that the acid-quenched intermediate is partially folded and contains elements of native secondary and tertiary structure. Spectra are similar to those of an equilibrium model in which the reduced cysteine residues are replaced by alanine. Complete 1H-NMR sequential assignment of the alanine model has been obtained and demonstrates that removal of the disulfide bond is associated with local unfolding of the adjoining alpha-helix. Native secondary structure (including helices 1 and 3) is otherwise retained and defines a folded subdomain. Long-range nuclear Overhauser effects (NOE) within this subdomain are similar to those of native IGF-I; no non-native NOE is observed. Our results support the hypothesis that folding of the insulin motif is directed by a subset of native structural elements and that these elements form at an early step in the pathway. Formation of helix 2, despite its prominence in the native state, is likely to represent a late step. Hydrophobic collapse of this segment appears to precede helix formation.

[Extracorporeal shock wave lithotripsy in an 8-month-old infant]

An 8-month-old boy who presented with pyrexia and vomiting was referred to the pediatric clinic of Kitasato University Hospital. He was found to have hematuria, proteinuria and pyuria. Abdominal X-ray film showed calcification suggesting renal staghorn calculus in the bilateral kidneys. At 10-months and 11-months, we succeeded in treating him with extracorporeal shock wave lithotripsy (ESWL) without complications.

Diagnosis of borderline adenomas of the stomach by endoscopic mucosal resection

BACKGROUND AND STUDY AIMS

The correct histological diagnosis of gastric borderline adenomas is often difficult, especially in excluding malignancy, since the usual diagnostic methods, such as radiography and histological examination of forceps biopsy specimens, are of limited accuracy. The aim of this study was to retrospectively analyze the value of endoscopic mucosal resection in establishing the correct diagnosis of borderline adenomas.

RESULTS

Fourteen borderline adenomas were finally diagnosed as containing early gastric cancer type IIa (well-differentiated tubular adenocarcinoma) after endoscopic mucosal resection, of the remaining 36 tubular adenomas, six represented mild dysplasia, 24 moderate dysplasia, and six severe dysplasia. Most parts of the 14 adenomas containing early gastric cancers had regions of structural atypia, and cellular atypia was moderate in all. Seven of 14 cancers were completely resected, all patients being tumor-free after a follow-up of 33-61 months.

CONCLUSIONS

These results suggest that diagnosing borderline adenoma on the basis of radiographic and endoscopic-bioptic findings is generally unreliable, because biopsy specimens may not be representative of the entire lesion. Borderline adenomas of the stomach should be completely resected by endoscopic mucosal resection to obtain a final diagnosis and - depending on the size and type of the lesion - possibly also definitive treatment.

Application of N-terminally truncated DNA polymerase from Thermus thermophilus (delta Tth polymerase) to DNA sequencing and polymerase chain reactions: comparative study of delta Tth and wild-type Tth polymerases

N-Terminally truncated DNA polymerase from Thermus thermophilus (delta Tth polymerase) lacking 5'-3' exonuclease activity was used for DNA sequencing and polymerase chain reaction (PCR). In contrast to the high background of the sequencing ladder observed with the wild-type Tth polymerase, delta Tth polymerase gave readable sequencing patterns which extend up to more than 500 bases from the primer site on cycle sequencing and automated sequencing. The delta Tth polymerase was used for the standard and mutagenic PCR, and net amplification of the DNA and the mutations accumulated during PCR were analyzed. Under mutagenic PCR, the mutation rates were 7.0 x 10(-4) (Tth) and 8.3 x 10(-4) (delta Tth) per nucleotide per cycle of amplification, which were 4-9 times higher than the rates under standard PCR.

Dimerization of the extracellular domain of granuloycte-colony stimulating factor receptor by ligand binding: a monovalent ligand induces 2:2 complexes

Granulocyte-colony stimulating factor (G-CSF) binds to a specific cell surface receptor and induces signals for growth and differentiation in cells of granulocyte hematopoietic lineage. In order to understand how G-CSF binding initiates signals into these cells, we have studied its interactions with the entire extracellular domain of the receptor (sG-CSFR). The sG-CSFR was purified from CHO cell conditioned media with a G-CSF affinity column, resting in a preparation fully competent for ligand binding. However, when sG-CSFR was purified by conventional means, i.e., without affinity chromatography, only about half was competent. Therefore, all studies were carried out using affinity-purified material. The sG-CSFR exhibited a weak self-association into a dimer with a dissociation constant of 200microM in the absence of G-CSF. Addition of G-CSF dimerizes the receptor, with a preferred stoichiometry of 2 G-CSF molecules plus 2 receptors. Unexpectedly, receptor-receptor interactions rather than through two receptors binding to the same G-CSF molecule; i.e., G-CSF is a monovalent ligand. G-CSF binding to the receptor monomer occurs with high affinity. The binding of G-CSF also enhances the receptor-receptor dimerization; when G-CSF is bound to both receptors, dimerization is enhanced 2000-fold, while the interaction of a 1:1 receptor-ligand complex with a second ligand-free receptor is enhanced 80-fold. Thus, the mechanism of receptor dimerization is fundamentally different than that of related cytokine receptors such as growth hormone and erythropoietin receptors. Circular dichroic spectra showed a small but significant conformational change of receptor upon binding G-CSF. This is consistent with the idea that G-CSF binding alters the conformation of the receptor, resulting in an increase in receptor-receptor interactions.

Stabilization of recombinant human keratinocyte growth factor by osmolytes and salts

Keratinocyte growth factor (KGF) has limited stability in aqueous media, as it undergoes denaturation followed by aggregation at 37 degrees C. Heparin and anionic polymers have been shown to increase the denaturation temperatures and extend the half-life of the monomeric, native form of KGF during storage. These polymers, however, bind more than one protein molecule with high affinity, and such tight complex formation may cause problems for clinical use. In this study, we have tested low molecular weight additives, such as osmolytes and salts, for their effects on the stability of KGF against thermal denaturation and high-temperature storage. Salts such as NaCl, sodium phosphate, ammonium sulfate, and sodium citrate were highly effective in increasing both the denaturation temperature and storage stability. The fact that the same additives stabilize KGF against both stresses is consistent with the idea that the storage stability is determined by denaturation followed by aggregation. Among the osmolytes tested, N,N'-dimethylglycine, trehalose, and sucrose were also effective stabilizers. However, quantitative comparison of the osmolytes tested indicated that their effectiveness on the thermal denaturation and the storage stability is not exactly parallel, suggesting that other factors also contribute to the storage stability.

Dimerization of the extracellular domain of the erythropoietin (EPO) receptor by EPO: one high-affinity and one low-affinity interaction

Although there is considerable evidence that signaling by the erythropoietin (EPO) receptor is initiated when it is dimerized by binding EPO, it has been previously reported that the soluble extracellular domains of the EPO receptor (sEPOR) are not dimerized in the presence of EPO and are able to form only 1:1 complexes with EPO. We have now shown unambiguously by light scattering, sedimentation equilibrium, and titration calorimetry that two molecules of sEPOR can bind to a single EPO monomer but that the binding of the second sEPOR is approximately 1000-fold weaker than that of the first. Because this second binding interaction is quite weak (Kd of approximately 1 microM), the 2:1 sEPOR.EPO complexes are easily dissociated during chromatography (forming the 1:1 complexes reported previously) and cannot be isolated in pure form. Global analysis of the sedimentation equilibrium data has enabled us to determine the binding constants and is consistent with a model in which EPO has two independent binding sites for sEPOR but cannot exclude anticooperative or sequential binding models. The influence of glycosylation of EPO and/or sEPOR on the binding affinities has also been investigated. Titration calorimetry is consistent with the sedimentation data and shows that the weaker binding site has a more negative delta H. The relation of these results to the binding of EPO to membrane-bound receptors and to the phenomenon of apparent high-affinity and low-affinity classes of receptors is discussed.

[Blood pressure and renin in long-term hemodialysis patients]

Blood pressure (BP), plasma active renin concentration (ARC), plasma renin activity (PRA), aldosterone (Aldo), atrial natriuretic peptide (HANP), plasma sodium (Na), plasma potassium (K), total protein (TP), hematocrit (Ht) and body weight (BW) have been measured in 101 patients, including 9 diabetic patients, undergoing hemodialysis for 5 through 278 months. BP, ARC, PRA and HANP correlated inversely with the duration of dialysis. Among 13 patients undergoing hemodialysis for more than 20 years, only one patient received antihypertensive drugs. This finding suggested that relative low ability of renin secretion and a slightly low concentration of HANP causes low blood pressure in long-term dialysis patients. ARC was significantly correlated with PRA, Aldo, Na, TP-A (TP concentration after hemodialysis), Ht(delta)% (difference between before and after hemodialysis) and BW(delta)%. These investigations suggest that the removal of large quantities of water and salt in each dialysis session may cause excessive secretion of renin. Though no relation was demonstrated between ARC and blood pressure in 101 patients, ARC was correlated significantly with blood pressure in 37 non-DM patients undergoing hemodialysis for less than 10 years and was inversely correlated in 55 non-DM patients undergoing hemodialysis for more than 10 years. Therefore, further analysis of other factors that maintain blood pressure, especially in long-term dialysis patients is required. Multiple regression analysis showed that major factors regulating the levels of blood pressure were duration of dialysis, Ht(delta)% and BW(delta)%. During dialysis, we observed significant correlation between ARC(delta)% and Ht(delta)%, but we did not find any correlation between the change in blood pressure and ARC. Furthermore, [correction of Forthermore] we found that caution should be paid to body water control especially in diabetic patients, because of their remarkable fall of BP during dialysis.