Binding sites for lactogenic and somatogenic hormones from rabbit mammary gland and liver

Purification of DNA-binding proteins using biotin/streptavidin affinity systems

Short fragments of DNA-either natural or formed from oligonucleotides-containing a high-affinity site for a DNA-binding protein provide a powerful tool for purification. The biotin/streptavidin purification system is based on the tight and essentially irreversible complex that biotin forms with streptavidin. In this procedure, a DNA fragment is prepared that contains a high-affinity binding site for the protein of interest, and a molecule of biotinylated nucleotide is then incorporated into one of the ends of the DNA fragment. The protein of interest binds to the DNA, and then this complex binds (via the biotin moiety) to the tetrameric protein streptavidin. Next, the protein/biotinylated fragment/streptavidin ternary complex is efficiently isolated by adsorption onto a biotin-containing resin. Since streptavidin is multivalent, it is able to serve as a bridge between the biotinylated DNA fragment and the biotin-containing resin. Proteins remaining in the supernatant are removed by washing, and the resin-bound protein is then eluted with a high-salt buffer. An alternate protocol describes a microcolumn method that is useful for larger volumes of biotin-cellulose resin. This method is also used to elute the protein in as small a volume (i.e., as high a concentration) as possible. Another variation on the basic procedure is provided in which streptavidin-agarose is employed.

Methods in neuroendocrine histopathology, a methodological overview

Light microscopy is still the main tool in diagnostic histopathology, though it does not always lead to a definitive diagnosis. It has therefore been a constant ambition to develop methods which can add further information to the diagnosis. In endocrine pathology, a major problem has been to distinguish between neuroendocrine and non-neuroendocrine tumours. The silver stains, such as the Bodian, Grimelius and Sevier-Munger methods, were the first useful "general neuroendocrine" markers. Electron microscopy can also be useful for identifying neuroendocrine tumours. A further step forward was the introduction of histochemical fluorescence methods, as these could identify biogenic amines. With the introduction of immunohistochemical techniques, tumours could be characterized in a more specific way regarding peptide hormones and biogenic amines content, proliferation factors, hormone receptors, etc. Another method, DNA cytometry, has been used mainly in predicting the prognosis. In situ hybridization can be a useful complement to the histopathological diagnosis when other methods have failed to demonstrate the neuroendocrine nature of the tumour. Some endocrine tumours, especially the well-differentiated ones, still cause diagnostic problems in predicting tumour behaviour, why further complementary methods would be of great value.

Thrombomodulin enhances the invasive activity of mouse mammary tumor cells

Thrombomodulin (TM) is a thrombin receptor on the surface of endothelial cells that converts thrombin from a procoagulant to an anticoagulant. Thrombin promotes invasion by various tumor cells, and positive or negative correlations are found between the expression of TM and tumorigenesis in some patients. In this study, we used an invasion assay to investigate the effect of TM on the invasive activity of a mouse mammary tumor cell line, MMT cells, and the effects of TM were compared with those of thrombin as a positive control. In the presence of 1% fetal calf serum (FCS), TM significantly stimulated MMT cell invasion in a dose-dependent manner, resulting in an approximately 3-fold increase at 1-10 pg/ml over the untreated control. Thrombin also caused a similar degree of stimulation at 50 ng/ml. Since thrombin activity was detected in the components of the assay system, an invasion assay was also performed in a thrombin-activity-depleted assay system constructed to eliminate the effect of thrombin activity; TM (10 pg/ml) plus thrombin (1 pg/ml) stimulated invasion by approximately 3.5-fold in this assay system. Hirudin, a specific thrombin inhibitor, inhibited stimulation by TM as well as by thrombin in both the presence and absence of 1% FCS. Investigations of the effects of TM on proliferation, adhesion and chemotaxis to clarify the mechanism of stimulation by TM revealed that TM does not affect proliferation or adhesion in the presence of 1% FCS, but stimulates chemotaxis by approximately 2.3-fold. Similar results were obtained in experiments using thrombin. TM (10 pg/ml) plus thrombin (1 pg/ml), on the other hand, stimulated chemotaxis by approximately 2.3-fold in the thrombin-activity-depleted assay system. Binding studies using [125I]-thrombin revealed that the cells have specific saturable binding sites for thrombin. These results show that TM stimulates the invasive activity of MMT cells, probably by acting as a cofactor for the thrombin-stimulated invasion of the cells via its receptor and lowering the effective concentration of thrombin. The findings also indicate that the stimulation of invasive activity in the presence of 1% FCS and in the thrombin-activity-depleted assay system may mainly be mediated by the stimulation of chemotaxis.

Purification of DNA-binding proteins using biotin/streptavidin affinity systems

This unit presents purification protocols that exploit the tight and essentially irreversible complex that biotin forms with streptavidin. A DNA fragment containing a high-affinity binding site for the protein of interest is prepared and a molecule of biotinylated nucleotide is incorporated into one of the ends of the DNA fragment. The protein of interest is allowed to bind to the high-affinity recognition site present in the biotinylated fragment. The tetrameric protein streptavidin is then bound to the biotinylated end of the DNA fragment. Next, the protein/biotinylated fragment/streptavidin ternary complex is efficiently removed by adsorption onto a biotin-containing resin. Since streptavidin is multivalent, it is able to serve as a bridge between the biotinylated DNA fragment and the biotin-containing resin. Proteins remaining in the supernatant are washed away under conditions that maximize the stability of the DNA-protein complex. Finally, the protein of interest is eluted from the resin with a high-salt buffer. Both batch and column formats are presented, as is a protocol for the use of streptavidin-agarose. A support protocol describes a mobility shift assay for detecting sequence-specific DNA-binding proteins.

Oriented immobilization of biologically active proteins as a tool for revealing protein interactions and function

The advantages of oriented immobilization of biologically active proteins are good steric accessibilities of active binding sites and increased stability. This not only may help to increase the production of preparative procedures but is likely to promote current knowledge about how the living cells or tissues operate. Protein inactivation starts with the unfolding of the protein molecule by the contact of water with hydrophobic clusters located on the surface of protein molecules, which results in ice-like water structure. Reduction of the nonpolar surface area by the formation of a suitable biospecifc complex or by use of carbohydrate moieties thus may stabilize proteins. This review discusses oriented immobilization of antibodies by use of immobilized protein A or G. The section about oriented immobilization of proteins by use of their suitable antibodies covers immobilization of enzymes utilizing their adsorption on suitable immunosorbents prepared using monoclonal or polyclonal antibodies, preparation of bioaffinity adsorbent for the isolation of concanavalin A and immobilization of antibodies by use of antimouse immunoglobulin G, Fc-specific (i.e. specific towards the constant region of the molecule). In the further section immobilization of antibodies and enzymes through their carbohydrate moieties is described. Oriented immobilization of proteins can be also based on the use of boronate affinity gel or immobilized metal ion affinity chromatography technique. Biotin-avidin or streptavidin techniques are mostly used methods for oriented immobilization. Site-specific attachment of proteins to the surface of solid supports can be also achieved by enzyme, e.g., subtilisin, after introduction a single cysteine residue by site-directed mutagenesis.

Identification and characterization of growth hormone receptors in snakehead fish (Ophiocephalus argus cantor) liver

The specific binding of 125I-labeled fish growth hormone (GH) to hepatic membranes prepared from several freshwater fish was assessed. A high level of growth hormone receptor (GHR) was detected on the hepatic membranes of the snakehead fish (Ophiocephalus argus Cantor). Scatchard analysis of the binding data showed a single class of high affinity binding site with a binding affinity (Ka) of 1.45 +/- 0.23 x 10(9) M-1 and a binding capacity (Bmax) of 198 +/- 57 fmol/mg protein. The binding was specific for fish GH and was saturable. In addition, the specific binding was temperature- and time-dependent, reaching a steady state after 16 hr of incubation at 25 degrees . The molecular weight of GHR as measured by Sephadex G-200 column chromatography and Western blot analysis using a monoclonal antibody (Mab263) against GHR was found to be 200-400 and 90-93 kDa, respectively. Two bands at 65 and 89 kDa were identified in ligand crosslinking studies of membrane receptors. A sensitive teleost GH radioreceptor assay (RRA) was developed, using recombinant fish GH and a membrane preparation from snakehead fish liver, capable of measuring bioactive GH in fish sera or other samples.

Primary spinal epidural manifestation of malignant lymphoma

The clinical, histological and immunomorphological data in 19 cases of primary spinal epidural manifestation of malignant lymphomas collected between 1974 and 1994 are reported. The age of the patients varied between 11 and 87 years with a mean age of 56.3 years. There was a slight male predominance (11:8). In most cases, the onset of the clinical symptoms was rapid. The preferential tumour localization was the epidural space related to the thoracal vertebral bone. In each case, decompressive laminectomy was performed. The tumours were histologically and immunomorphologically classified as B-cell lymphomas (14 of 19), T-cell lymphomas (3 of 19) and anaplastic plasmacytoma (1 of 19). Except for one case, post-operative staging did not reveal anything other than epidural manifestation of the malignant lymphoma. The vertebral bone, however, was involved in seven cases. Irradiation alone, or in combination with chemotherapy, was performed as additional therapy. The post-operative survival time was variable.

Effective method for synthetic peptide immobilization that increases the sensitivity and specificity of ELISA procedures

A procedure is described for the immobilization of synthetic peptide antigens on a plastic solid phase for performing ELISA. The use of a streptavidin-biotinylated peptide system for coating microplates with peptide antigen markedly increased both the sensitivity and the specificity compared to a standard ELISA based on synthetic peptides. The procedure was used for the detection of HIV-1-specific antibodies.

The preparation of biotinyl-epsilon-aminocaproylated forms of the vasoactive intestinal polypeptide (VIP) as probes for the VIP receptor

Vasoactive intestinal polypeptide (VIP) was biotinyl-epsilon-aminocaproylated using sulfosuccinimidyl-6-(biotinamido) hexanoate thereby producing a series of products that were separated by high performance liquid chromatography (HPLC). Seven VIP-derivatives were isolated and the number and location of biotinyl-epsilon-aminocaproylation was determined by a combination of enzymatic degradation and plasma desorption mass spectrometry (PDMS). Receptor binding experiments with the VIP biotinyl-epsilon-aminocaproylated derivatives revealed IC50 values for the monobiotinyl-epsilon-aminocaproylated peptides that were 1.3-3.2 times higher than for natural VIP. All isolated biotinyl-epsilon-aminocaproylated derivatives possess VIP-like bioactivity as shown by an assay measuring pancreatic juice secretion in cat, VIP biotinyl-epsilon-aminocaproylated in position lysine being almost equipotent with natural VIP.

Biotinylated derivative of a human brain lectin: synthesis and use in affinoblotting for endogenous ligand studies

Coupling of biotin to an endogenous lectin yields a probe which can be used for selective nonradioactive detection of complementary endogenous ligands. To exemplify practical applications of this type of compounds, we have synthesized and characterized a biotinylated derivative of a beta-galactoside-specific human brain lectin. Proteins which bind this lectin can be located on nitrocellulose sheets after electrophoretic transfer from gradient polyacrylamide gels, by sequential incubation with biotinylated probes and streptavidin-peroxidase, with visualization by an insoluble reaction product (affinoblotting). Biotinylated galactoside-binding plant lectins were used in the same way to visualize human brain glycoproteins, and their binding specificity was compared with that of human brain lectin. The results obtained by means of these different probes showed the usefulness of the endogenous lectin derivative to actually identify its endogenous partners. Thus this approach may find extended applications in the study of biological activities of vertebrate lectins in homologous systems, i.e., with lectins and ligands coming from the same tissue origin.

A new method of detecting hormone-binding proteins electroblotted onto glass fiber filter: juvenile hormone-binding proteins from grasshopper hemolymph

We have developed a new method to identify juvenile hormone (JH)-binding proteins blotted onto glass fiber filter (GFF) after electrophoretic separation. Insect JH regulates reproduction in the two-striped grasshopper, Melanoplus bivittatus. A number of proteins are involved in the delivery of JH from its site of synthesis to the nuclei of fat body cells where it acts to induce vitellogenesis. To identify JH binding proteins, hemolymph was separated by PAGE, electroblotted onto GFF, and incubated in [10-3H]JH-III. The amount of hormone bound by blotted proteins increased with the amount of protein on the filter, was competitively displaced by excess non-labeled hormone, and was affiliated with individual bands on fluorograms of proteins blotted after electrophoretic separation. GFF etched with trifluoroacetic acid was better than nitrocellulose, Zeta Probe, cellulose acetate or unetched GFF. Phosphate (pH 6.0-7.3) or Tris buffers (pH 7.3-8.0) worked equally well for the procedure. Unbound hormone was easily removed by short washes in buffer, and adequate binding for detection was achieved in a 15 min incubation. Preliminary data suggest that this technique may be used to detect receptors, carriers, and binding proteins of steroid hormones.

Synthesis of a biotinylated, iodinatable, and photoactivatable probe for angiotensin receptors

We propose here a biotinyl-aminohexanoyl-[Ala1, Phe(4N3)8]angiotensin II analog as a radioiodinatable and photoactivatable probe for covalent labeling, detection and isolation of angiotensin receptors. A combination of solid phase and minimum-protection segment-coupling strategy using hexafluorophosphate of (benzotriazol-1-yloxy)tris(dimethylamino)phosphonium (BOP) as a coupling reagent is proposed for the synthesis of this probe. Optimized yields were obtained by HPLC monitoring of all reactions. A complete n.m.r. study suggests an extended conformation of this molecule, allowing a simultaneous recognition of receptor and avidin. The probe binds with high affinity (Kd = 2 nM) to angiotensin II receptors from rat liver membranes.

Glycosylation characteristics of the mouse liver lactogenic receptor

The structural characteristics and glycosylation properties of the lactogenic receptor were examined in 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS)-solubilized plasma membranes from female mouse liver. The specific binding of the radioiodinated human growth hormone [( 125I]hGH) was displaced with an equivalent potency by both hGH and prolactin. After a mild neuraminidase treatment, this binding was increased by 40%, as a result of an increase in receptor affinity. Affinity chromatography on immobilized lectins revealed that the [125I]hGH-receptor complexes were specifically retained and eluted from ricin lectin-agarose, concanavalin A and lentil lectin, indicating the presence of N-linked glycans. Covalent cross-linking of solubilized [125I]hGH-receptor complexes with disuccinimidyl suberate, followed by analysis by sodium dodecyl sulfate-gel electrophoresis (SDS-PAGE) under reducing conditions, and autoradiography resulted in the appearance of two bands with apparent Mr approximately 62,000 and approximately 100,000. The labelling of these bands was prevented by unlabelled hGH or ovine prolactin (oPrl) but not by bovine growth hormone (bGH). Neuraminidase treatment of the two receptor forms resulted in increased electrophoretic mobility which was inhibited by simultaneous addition of sialyl-lactose, a neuraminidase substrate. The both cross-linked forms were unaffected by endoglycosidase H, while endoglycosidase F decreased the molecular weight of each of the forms by about 8000 Da, yielding bands at Mr approximately 54,000 and approximately 92,000. In conclusion, taking into account that hGH is a Mr 22,000 polypeptide, the two forms of the receptor correspond to glycoproteins of Mr approximately 40,000 and approximately 78,000, respectively. They contain polypeptide backbones of Mr approximately 32,000 and approximately 70,000, and complex N-linked oligosaccharide chains with terminal sialic acid residues which could be involved in receptor binding affinity.

Quantitative determination of staphylococcal enterotoxin A by an enzyme-linked immunosorbent assay using a combination of polyclonal and monoclonal antibodies and biotin-streptavidin interaction

A sandwich enzyme-linked immunosorbent assay to detect staphylococcal enterotoxin A (SEA) was developed by using monoclonal antibodies (MAb) to SEA as primary capture antibodies. The antigen was detected with purified rabbit anti-SEA antibody as the secondary antibody. The secondary antibody was identified by direct conjugation with biotin or via biotinylated sheep F(ab')2 fragments to rabbit antibody. The biotin was then reacted with avidin-alkaline phosphatase (AP) conjugate, avidin-biotin-AP conjugated complex, or streptavidin-AP conjugate. The enzyme was identified by using p-nitrophenylphosphate. The incorporation of the avidin-biotin-AP conjugated complex or streptavidin-AP conjugate augmented the sensitivity 32-fold over that of the enzyme-linked immunosorbent assay without these reagents. Controls were run by substitution of the anti-SEA MAb with unrelated MAb of the same isotype. Sample values were considered positive when the A405 exceeded those of the negative controls by 3 standard deviations (greater than 99% confidence interval). The toxin could be quantitated with purified SEA standards through linear regression analysis with lower detection limits of 4 ng/ml (r = 0.99) and 0.25 ng/ml (r greater than or equal to 0.98). Concentrations of protein A up to 10 micrograms/ml did not cause interference. Analyses of crude growth extracts of SEA-secreting strains of Staphylococcus aureus were reproducible and were expressed in terms of 95% confidence intervals. Lack of cross-reactivity was seen with extracts of other toxigenic and nontoxigenic strains of S. aureus. The assay can be completed in one working day, provided that MAb-coated plates are available.

Enhanced immunodetection of blotted house dust mite protein allergens on nitrocellulose following blocking with Tween 20

The effect of blocking nitrocellulose membranes with the nonionic detergent Tween 20 on the detection, by protein blotting, of IgE-binding to house dust mite Dermatophagoides pteronyssinus allergens has been investigated. Tween blocking led to enhanced immunodetection of allergens despite removal of proteins from the membrane when compared to protein blocking agents which did not displace transferred components. The enhancement varied with the different mite components and, for one in particular, antigen Der p II, an increase of more than 100-fold in IgE antibody binding occurred despite a concurrent loss of more than 90% of Der p II from the membrane. Both the enhancement of binding and loss of components from the membrane were dependent upon the time course of blocking and the concentration of Tween used.

Phagocytosis in Dictyostelium discoideum is inhibited by antibodies directed primarily against common carbohydrate epitopes of a major cell-surface plasma membrane glycoprotein

Using a water-soluble, reversible biotinylating reagent, we retrieved three surface-exposed proteins from a complex mixture of crude membrane proteins. The compound, sulfosuccinimidyl 2-(biotinamido)ethyl-1-3'-dithiopropionate (sulfo-NHS-SS-biotin), which has a cleavable disulfide bond, was used to label Dictyostelium discoideum amebae. Cells were lysed and a crude membrane preparation was isolated and solubilized with Triton X-100. Biotinylated molecules were bound to immobilized streptavidin and then eluted from the affinity matrix with dithiothreitol. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that out of the original complex mixture of detergent-solubilized membrane proteins, three major species at 130, 100, and 77 kDa were specifically bound and eluted with thiol reagents. These three proteins were glycoproteins (gp) since they bound concanavalin A. As demonstrated by one-dimensional peptide mapping, the retrieved gp130 and gp100 also were present in specialized plasma membrane subdomains called contact regions which are regions of cell-cell cohesion isolated from aggregated, developed amebae. This finding provides preliminary evidence that the two proteins may be involved in cell-cell interactions during both the vegetative and aggregation stages of the D. discoideum life cycle. The retrieved gp130 species has a relative mobility on SDS-gels similar to that of gp126, a surface-exposed glycoprotein. gp126 has been suggested to play roles both as a phagocytosis receptor and as a cohesion molecule (C.M. Chadwick, J.E. Ellison, and D.R. Garrod, (1984) Nature (London) 307, 646). To test if the retrieved gp130 was the same as gp126, a polyclonal antiserum was raised against gel-purified, endoglycosidase F-treated gp130. The immune serum recognized epitopes, apparently carbohydrates, present on many D. discoideum membrane proteins. Univalent IgG fragments from this antiserum inhibited phagocytosis, suggesting that anti-carbohydrate activity was responsible for the functional inhibition of phagocytosis.

Axonal transport in the garfish optic nerve: comparison with the olfactory system

Fast and slow axonal transports were studied in the optic nerve of the garfish and compared with previous studies on the olfactory nerve. The composition of fast-transport proteins was very similar in the two nerves. Although the velocity of fast transport was slightly lower in the optic nerve, there was a linear increase in velocity with temperature in both nerves. As in the olfactory nerve, only a single wave of slow-transport protein radioactivity moves along the nerve. The velocity of slow transport also increased linearly with temperature, but the coefficient was less than in the olfactory system. The composition of slow transport in the optic nerve was significantly different from that in the olfactory nerve, a finding reflecting the different cytoskeletal constituents of the two types of axons. The slow wave could be differentiated into several subcomponents, with the order of velocities being a 105-kilodalton protein and actin greater than tubulins and clathrin greater than fodrin much greater than neurofilaments. It can be concluded that the temperature dependence of fast and slow axonal transport in different nerves reflects the influence of temperature on the individual polypeptides constituting the various transport phases. The garfish optic nerve preparation may be advantageous for studies of axonal transport in retinal ganglion cell axons, because its great length avoids the complications of having to study transport in the optic tract or in material accumulating at the tectum.

Cloning and expression of the rat prolactin receptor, a member of the growth hormone/prolactin receptor gene family

The primary structure of the rat liver prolactin receptor has been deduced from a single complementary DNA clone. The sequence begins with a putative 19 amino acid signal peptide followed by the 291 amino acid receptor that includes a single 24 amino acid transmembrane segment. In spite of the fact that the prolactin receptor has a much shorter cytoplasmic region than the growth hormone receptor, there is strong localized sequence identity between these two receptors in both the extracellular and cytoplasmic domains, suggesting that the two receptors originated from a common ancestor.

tRNA-mediated labelling of proteins with biotin. A nonradioactive method for the detection of cell-free translation products

We have developed a new method for the rapid and sensitive detection of cell-free translation products. Biotinylated lysine is incorporated into newly synthesized proteins by means of lysyl-tRNA that is modified in the epsilon-position. After electrophoresis in a dodecyl sulfate gel and blotting onto nitrocellulose, the translation products can be identified by probing with streptavidin and biotinylated alkaline phosphatase, followed by incubation with a chromogenic enzyme substrate. The non-radioactive labelling by biotin approaches in its sensitivity that obtained by radioactive amino acids. The products are absolutely stable and can be rapidly identified. The new method has been tested with different mRNAs in the cell-free translation systems of wheat germ and reticulocytes. Neither the interaction of secretory proteins with the signal recognition particle nor the in vitro translocation across the endoplasmic reticulum membrane or core glycosylation of nascent polypeptides are prevented by the incorporation of biotinylated lysine residues. The results indicate that both the ribosome and the endoplasmic reticulum membrane permit the passage of polypeptides carrying bulky groups attached to the amino acids (by atomic models it was estimated that the size of the side chain of lysine changes from approximately equal to 0.8 nm to approximately equal to 2 nm after modification.

Purification of PRL receptors from toad kidney: comparisons with rabbit mammary PRL receptors

The binding characteristics of the prolactin (PRL) receptors present in toad (Bufo marinus) kidneys were investigated and compared to those of PRL receptors present in rabbit mammary glands. The molecular characteristics of the Triton X-100 solubilized renal and mammary PRL receptors were assessed by gel filtration and by migration analysis on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) after affinity labeling of the binding sites with 125I-human growth hormone. Similar results were obtained for both receptors. Partial purification of the toad PRL receptor could be achieved by affinity chromatography. The molecular weight of this purified receptor could be determined by analysis on SDS-PAGE. With the use of a polyclonal antiserum raised against a purified preparation of rabbit mammary PRL receptor, one or several antigenic epitope(s) could be identified on the core of the toad renal PRL receptor. In conclusion, although the structure and the biological role(s) of PRL have substantially changed during evolution, the receptor for this hormone has retained many of its structural features as could be assessed between an amphibian and a mammalian species on functionally different target tissues.

Characterization of a biotin-conjugated ovine prolactin ligand

Ovine prolactin was biotinylated with N-hydroxysuccinimidobiotin. Biotinylation was proportional to the molar ratio of reactants. Gel electrophoresis of the biotinylated derivative revealed little or no change in migration, but isoelectric focusing showed an acidic shift when compared to oPRL. Biotinylated ovine prolactin (B-oPRL) was detected by anti-oPRL antiserum and avidin-fluorescein-isothiocyanate (FITC) on protein blots. Competitive binding assays using 125I-B-oPRL and 125I-oPRL revealed: (a) similar dissociation constants and ID50 values for binding to anti-oPRL antibodies; (b) similar dissociation constants and maximum binding values for binding to liver membrane preparations; and (c) similar dissociation curves for displacement by several pituitary hormones. In contrast, binding of biotinylated oPRL to Nb2 node cells was reduced by approximately 70% and its bioreactivity was only 10% of that of oPRL. Our results indicate that biotinylation of oPRL does not alter its binding characteristics as measured by radioimmunoassay and radioreceptor assay using hepatic lactogenic receptors, but decreases its binding and bioreactivity when measured in Nb2 lymphoma cells. Assuming that N-hydroxysuccinimidobiotin interacts with reactive free amino groups of oPRL, our results suggest that these groups are essential for binding and bioreactivity of the molecule in the Nb2 lymphoma cell system.

Design of angiotensin II derivatives suitable for indirect affinity techniques: potential applications to receptor studies

The design of angiotensin II (A II)-derived probes suitable for indirect affinity techniques is presented. Biotin or dinitrophenyl moieties have been added at the N-terminus of A II, through aminohexanoic acid as spacer arm, to generate (6-biotinylamido)-hexanoyl-AII (Bio-Ahx-AII) and dinitrophenyl- aminohexanoyl-AII (Dnp-Ahx-AII). Monoiodinated and highly labeled radioiodinated forms of these probes have been prepared. The two bifunctional ligands displayed high affinities for rat liver A II receptors (Kd values in the nanomolar range) and their secondary acceptors: streptavidin and monoclonal anti-Dnp antibodies respectively. Bio-Ahx-AII and Dnp-Ahx-AII behaved as agonists on several AII-sensitive systems. Based on these structural assessments, the parent photoactivable azido probe: Bio-Ahx-(Ala1,Phe(4N3)8)A II. A II was synthesized and proved to possess similar biological properties than the non-azido compound. The hepatic A II receptor could be covalently labeled by the radioiodinated probe, with a particularly high yield (15-20%); SDS-polyacrylamide gel electrophoresis of solubilized complexes revealed specific labeling of a 65 Kdaltons binding unit, in agreement with previous data obtained with other azido AII-derived compounds. The potential applications of these probes are: i) receptor purification by combination of its photoaffinity labeling and adsorption of biotin-tagged solubilized hormone-receptor complexes on avidin gels. ii) cell labeling and sorting. iii) histochemical receptor visualization.

Binding of prolactin and monoclonal antibody to prolactin receptors immobilized on a nitrocellulose membrane filter

Mammary prolaction (PRL) receptors in 3-[(3-cholamidopropyl)dimethylammonio]propanesulfonic acid (Chaps) extract were immobilized on a nitrocellulose (NC) filter, and a binding assay using the filter-bound receptors was carried out in the absence of detergent. PRL binding to the receptors was dependent on the quantity of the receptors and the PRL added to the filters. The filter-bound receptors retained the specificity of binding to peptide hormones. Scatchard analysis showed that the number of PRL receptors and the dissociation constant for PRL binding are essentially unchanged after immobilization on a NC filter, indicating that the PRL binding site does not participate in the binding to the NC filter and is equally available for PRL binding. The monoclonal antibody (MAb) against the PRL receptor was able to bind specifically to the Chaps-solubilized and filter-bound PRL receptors, as shown by curvilinear Scatchard plots. Immobilization on NC filters permits direct detection and characterization of the soluble PRL receptor using labeled PRL or MAb.

Immunological relationship and binding capacity of prolactin receptors in cytosolic and membrane fractions of rabbit mammary gland

We have recently identified and partially characterized a specific lactogen binding protein in rabbit mammary gland cytosol. In this report, studies using pregnant or lactating rabbits are described which further characterize the cytosolic lactogen binding protein in relation to the membrane-bound lactogen receptor. The data show that in pregnant or lactating rabbits the binding capacity (fmol/mg protein) of membranes is at least double that of the cytosol preparation although when expressed on a tissue content basis (fmol/g tissue) there was no membrane-cytosol difference in receptor number. Treatment of lactating rabbits with CB-154, however, caused a marked increase (100-150%) in the binding capacity of membrane-bound receptors with comparatively little effect (+20%) on the cytosolic lactogram binding protein. There was also a marked difference in the association constants for 125I-hGH, with the cytosolic lactogen binding protein exhibiting a 6-fold higher affinity than the membrane-bound receptor. Three anti-prolactin receptor monoclonal antibodies (M110, A82 (antagonists) and A917 (agonist) have also been used to assess the relative immunological characteristics of the cytosolic lactogen binding protein and the membrane lactogen receptor. Each monoclonal antibody was able to inhibit the specific binding of 125I-hGH to both membranes and cytosol in a dose-dependent manner. However, the order of potency was not identical being M110 greater than A917 greater than A82 in membranes and M110 greater than A82 greater than A917 in cytosol. A917 was at least 10 times more active in membranes than cytosol whereas A82 was at least 10 times more active in cytosol.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunological recognition of the prolactin receptor: identification of a single binding unit of molecular weight approximately 42,000

Different polyclonal and monoclonal antibodies against the rabbit mammary prolactin (PRL) receptor were previously obtained that totally inhibited PRL binding in the rabbit mammary gland. Only polyclonal antibodies were shown to immunoprecipitate preformed PRL--receptor complexes in solubilized mammary membranes suggesting that they also recognized domains outside of the PRL binding site of the receptor. When partially purified PRL receptor preparations from both rabbit and pig mammary tissues were iodinated, immunoprecipitated and subsequently analyzed by SDS--PAGE, a single component of molecular weight approximately 42,000 was specifically recognized by all the anti-PRL receptor antibodies. This unit was the only component immunoprecipitated by the monoclonal antibody M 110. Its identification was not impaired by using reducing or non-reducing conditions. Moreover, a further purification of the [125I]-labeled receptor preparations from both species by a second PRL affinity chromatography selected a single binding unit of the same molecular weight. In contrast, polyclonal antibodies immunoprecipitated additional components apart from the 42,000 unit, especially one unit of molecular weight 70,000-80,000 in both species. We conclude that rabbit and pig mammary PRL receptors exhibit striking immunological similarities. Both contain a single binding unit of molecular weight approximately 42,000 that is not linked to other units via disulfide bridges. This binding unit could be associated with a larger component of MW 70,000-80,000 in the holo receptor.

Purification of prolactin receptors from sow mammary gland and polyclonal antibody production

After solubilization with Triton X-100 or 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate (CHAPS), prolactin receptors from mammary crude membranes of primiparous lactating sows (pretreated with bromocriptine) have been purified by affinity chromatography using ovine prolactin or a monoclonal antibody against rabbit prolactin receptor. Comparative analysis of these two methods of purification demonstrated that use of an immunoaffinity step allowed a great improvement of receptor yield (40%) compared to the hormone affinity method (10%). In addition, partially purified fractions obtained by immunoaffinity appeared more homogeneous and had much higher specific activity. Affinity labelling of prolactin receptors from crude membranes or solubilized extracts with iodinated ovine prolactin, followed by electrophoretic analysis (SDS-PAGE) and autoradiography, revealed one binding unit of approximately 45 kDa. When partially purified receptor preparations were labelled with 125I, submitted to an additional affinity chromatography and analyzed by SDS-PAGE, prolactin receptors appeared as a single form having a molecular weight of 42-45 kDa, which is not associated with itself or other subunits by disulfide linkages. Partially purified fractions were used to produce anti-prolactin receptor serum from goats. These polyclonal antibodies were able to completely inhibit the binding of lactogenic hormones in sow and rabbit mammary membranes. They were also able to recognize hormone-receptor complexes, but more specifically in sow mammary gland. These antisera could inhibit prolactin binding to its receptors in several organs of various species, suggesting that prolactin receptors shared numerous antigenic similarities between species and particularly between sow and rabbit. These similarities appeared to be located essentially on the part of the molecule more specifically involved in the recognition of the hormone.

A cell-free analysis of the endocytic pathway

The molecular control of the endocytic pathway is poorly understood. To obtain this information requires the use of cell-free systems which faithfully recreate the various endocytic events as they occur in the intact cell. Here I describe our approach to elucidating the mechanism which controls the fusion between different vesicles on the pathway.

Partial purification and characterization of bovine mammary gland prolactin receptor

Prolactin (PRL) receptors from the mammary gland of the lactating cow were solubilized with 3-[(3-cholamidopropyl)dimethylamonio]-1-propane sulfonate (CHAPS). Affinite chromatography on human growth hormone (hGH) coupled to Affi-Gel 10 resulted in over 500-fold purification, as compared to microsomal fractions. Scatchard analysis of the binding of hGH indicated an increase in the affinity constant of 2.5-fold after solubilization and of further 2-fold after the affinity purification. The specific binding activity of the affinity-purified fraction was 9000 fmol hGH/mg protein. Complexes of Triton X-100-solubilized receptors with [125I]hGH were analyzed by gel filtration on Sephadex G-150, in the presence of Triton X-100. A minor fraction of the complexes eluted as high molecular weight (Mr) aggregates, whereas a major fraction eluted as a 150 kDa peak. Assuming a contribution of approximately 30% to the Mr by the bound detergent and a hormone: receptor ratio of 1:1 in the complex, a Mr of 80-85 kDa can be calculated for the receptor molecule. Affinity labelling of the receptor with [125I]hGH revealed a Mr of 37 +/- 0.5 kDa (n = 7) for the binding subunit. Specific high Mr aggregates were also observed after crosslinking; however, the size of the labelled species was not affected by reducing agents. Homologous and heterologous competitive binding studies with ovine PRL (oPRL) or hGH revealed a considerably higher affinity for hGH as compared to oPRL. The competitive displacement patterns obtained with oPRL or hGH as tracers were similar, indicating that both hormones bound to the same receptor sites with different affinities. A similar difference in affinity was retained by the affinity-purified receptors.

Purification and characterization of ovarian LH/hCG and prolactin receptors

We have purified the luteinizing hormone (LH)/human choriogonadotropin (hCG) receptor to homogeneity by sequential affinity column on wheat germ lectin-Sepharose and hCG-Sepharose. The method was designed to allow also the purification of lactogen receptor from the initial starting material. Comparable purification of lactogen receptor can be attained using Con A-Sepharose as initial step. The purified LH/hCG receptor was identified as a single protein of Mr = 75,000 on SDS gel electrophoresis. The lactogen receptor is composed of two dissimilar active subunits of Mr 88,000 and 40,000, the latter probably being an integral part of the larger form. Comparison of Mr's derived from SDS gels with those from fast performance liquid chromatography suggested that the native LH holoreceptor is present in a dimeric form, while the lactogen receptor seems to be composed of aggregates that could represent dimeric or trimeric forms of holoreceptor Mr 80,000. Cross-linking studies performed after binding of hCG (radiolabeled in the individual subunits) to the purified LH/hCG receptor indicated that the hCG alpha-subunit undergoes predominant interaction with the receptor molecule. The influence of the beta-subunit in this interaction seems to occur mainly through its association with the alpha-subunit, presumably by conferring specificity to the alpha-subunit for its interaction with the receptor. The alpha-subunit, which is identical within species, has an important role in the receptor binding interaction and biological activity of glycoprotein hormones.

Immunohistochemical procedures for the demonstration of peptide- and tyrosine hydroxylase-containing nerve fibers in cryostat sections of unfixed rapidly frozen tissue stored for long periods of time. A study on heart tissue

Traditional protocols for the immunohistochemical localization of peptides and tyrosine hydroxylase (TH) in nerve fibers in cryostat sections require the tissue to be thoroughly fixed and rinsed and to be processed for the cryostat sectioning and the immunohistochemical staining more or less directly after freezing. In the present study it was tested whether also unfixed, rapidly frozen tissue, conforming to guinea pig and bovine heart specimens, can be used for the visualization of neuropeptides [neuropeptide Y (NPY) and substance P (S P)] and TH in cryostat sections. The following observations were made: 1) NPY-immunoreactive (IR) and S P-IR nerve fibers could be clearly identified in both fixed and unfixed sections of this type of tissue. 2) TH-IR nerve fibers could be detected in unfixed tissue if the sections were post-fixed with aldehydes by the use of a two-step fixation process related to a sudden change of pH. However, the outlines of the nerve fibers were sometimes diffuse. 3) Storage of unfixed tissue for periods of up to 2.5 years at-80 degrees C did not lead to a decrease in immunoreactivity. 4) Somewhat higher concentrations of primary antibodies had to be used for sections of unfixed tissue than for sections of fixed tissue when the FITC method was used. This waste of antibodies was partly overcome by use of the biotin-streptavidin method. The glyoxylic acid induced catecholamine(CA)-fluorescence method for demonstration of sympathetic nerve fibers was also applied and was found to give optimal results after storage of tissue for up to 2.5 years.(ABSTRACT TRUNCATED AT 250 WORDS)