Purification of rabbit mammary prolactin receptor by acidic elution from a prolactin affinity column

Leptin expression in the fetus and placenta during mouse pregnancy

During pregnancy, leptin concentrations in the maternal circulation are elevated in both humans and rodents but decrease to pre-pregnancy levels at birth, suggesting a role for leptin in the maintenance of pregnancy. Synthesis of leptin by the human placenta is established but whether the murine placenta synthesizes leptin remains controversial. The aims of this study were to determine (a) if the mouse wild-type placenta expresses the ob gene using Reverse Transcription-Polymerase Chain Reaction (RT-PCR) and (b) whether the mouse fetus and placenta contribute to the significant increase of leptin in the maternal circulation during pregnancy. The mouse placenta did not express the ob gene at a level that could be readily detected using RT-PCR. Moreover, both maternal gain in weight and undetectable concentrations of leptin in sera in leptin-deficient ob/ob mothers bearing heterozygote (ob/+) fetuses suggested that the mouse fetus and placenta do not make a significant contribution to the dramatic increase in maternal plasma concentrations of leptin during late gestation. It is therefore concluded that neither fetal- nor placental-derived leptin modulates maternal weight gain during pregnancy.

Expression and purification of recombinant polyomavirus VP2 protein and its interactions with polyomavirus proteins

Recombinant polyomavirus VP2 protein was expressed in Escherichia coli (RK1448), using the recombinant expression system pFPYV2. Recombinant VP2 was purified to near homogeneity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, electroelution, and Extracti-Gel chromatography. Polyclonal serum to this protein which reacted specifically with recombinant VP2 as well as polyomavirus virion VP2 and VP3 on Western blots (immunoblots) was produced. Purified VP2 was used to establish an in vitro protein-protein interaction assay with polyomavirus structural proteins and purified recombinant VP1. Recombinant VP2 interacted with recombinant VP1, virion VP1, and the four virion histones. Recombinant VP1 coimmunoprecipitated with recombinant VP2 or truncated VP2 (delta C12VP2), which lacked the carboxy-terminal 12 amino acids. These experiments confirmed the interaction between VP1 and VP2 and revealed that the carboxyterminal 12 amino acids of VP2 and VP3 were not necessary for formation of this interaction. In vivo VP1-VP2 interaction study accomplished by cotransfection of COS-7 cells with VP2 and truncated VP1 (delta N11VP1) lacking the nuclear localization signal demonstrated that VP2 was capable of translocating delta N11VP1 into the nucleus. These studies suggest that complexes of VP1 and VP2 may be formed in the cytoplasm and cotransported to the nucleus for virion assembly to occur.

Expression and ligand binding characterization of the beta-subunit (p75) ectodomain of the interleukin-2 receptor

The baculovirus-mediated eukaryotic insect cell expression system was used to prepare large quantities of the beta-subunit ectodomain of the high-affinity interleukin-2 receptor (IL-2R beta x). We describe the expression, purification, and biophysical characterization of this ligand binding domain. The human cDNA encoding IL-2R beta x was inserted into baculovirus transfer vectors. High titer recombinant baculovirus was produced in Spodoptera frugiperda (Sf9) insect cells, and the viral supernatants were subsequently used to infect monolayers of Trichoplusia ni (High Five) insect cells in serum-free culture. Maximal expression of the recombinant protein excreted into the cell culture supernatants was determined by SDS/PAGE analysis, where a band migrating with an apparent molecular mass of 31 kDa was identified by immunostaining. One-step purification was achieved by affinity chromatography on either a monoclonal antibody (TIC-1) column or an IL-2 column, with a final yield of approximately 5 mg/L of culture supernatant. Interestingly, partial purification was also demonstrated using metal chelate affinity chromatography. Amino-terminal sequence analysis of the protein matched the published sequence. Both equilibrium sedimentation analysis and gel filtration chromatography indicated that IL-2R beta x remains monomeric. Deconvolution of far-UV circular dichroism (CD) spectra indicated the predominant secondary structural element to be beta-sheet, consistent with structural analysis and predictions for other members of the hematopoietic receptor family. A dissociation constant (Kd) for IL-2R beta x in solution of 5.3 x 10(-7) M was calculated from competitive receptor binding assays.(ABSTRACT TRUNCATED AT 250 WORDS)

Extracti-Gel D chromatography is a simple, efficient method for removing digitonin during receptor purification: application to the kappa 1 opioid receptor

Digitonin is widely used for extracting active neurotransmitter receptors from membranes. However, its low critical micellar concentration has made its removal from samples problematic. Here we report that digitonin can be efficiently removed (> 90%) from solution using Extracti-Gel D, a detergent-absorbing matrix. Active kappa 1 opioid receptors solubilized from brain survive Extracti-Gel D chromatography with a recovery of 50-55% and 25% dilution by added volume. The loss of receptor and the dilution, however, are compensated for to a large extent by the disinhibition of binding that results from the removal of digitonin. Extracti-Gel D chromatography had little or no effect on the apparent equilibrium dissociation constant for [3H]U-69,593 binding to the kappa 1 receptor. We conclude that Extracti-Gel D column chromatography is a simple, highly efficient and practical method for markedly reducing the concentration of digitonin in biological samples. Application of the procedure should allow characterization of digitonin-solubilized receptors with minimal complications from bound digitonin and extend the usefulness of digitonin to studies going beyond the initial stages of receptor purification.

Single-channel characteristics of a purified bovine renal amiloride-sensitive Na+ channel in planar lipid bilayers

We have purified an amiloride-inhibitable Na+ channel protein from bovine renal papillae using ion-exchange and immunoaffinity chromatography. In the present study, these purified Na+ channels were reconstituted into planar lipid bilayers, and their single-channel characteristics were studied. We observed both large- and small-conductance Na(+)-selective ion channels in planar lipid bilayers. Single-channel conductance for the large- and small-conductance channels saturated as a function of Na+ concentration. These relations could be fitted by a simple Langmuir isotherm with a Michaelis constant of 55 and 45 mM and a maximum open-state conductance of 56 or 8.4 pS, respectively. Both channels were perfectly cation selective, with a Na(+)-to-K+ permeability ratio of 6.7:1 for the large channel and 7.8:1 for the small channel, and their open single-channel current-voltage relations were linear when bathed with symmetrical Na+ solutions. The percent open time of the reconstituted large or small channels varied between 10 and 50% or 1 and 20%, respectively. After application of amiloride, both the large- and small-conductance Na+ channels were inhibited in a dose-dependent manner.

Purification and characterization of a high-affinity binding protein for pancreatic-type phospholipase A2

A high-affinity and specific binding site for mammalian group I phospholipase A2 (PLA2-I) was found on the membranes of bovine corpus luteum. Affinity labeling experiments revealed that PLA2-I binds to a single polypeptide with a mass of 190-200 kDa. The PLA2-I binding protein in the membranes was solubilized in an active form with n-octyl beta-D-thioglucoside, and then purified approx. 16,000-fold. The purification procedures consisted of diethylaminoethyl-Sephacel chromatography, PLA2-I-affinity gel chromatography and gel-filtration high-performance liquid chromatography on a TSKgel G3,000SWXL column. The final preparation migrated as a single molecular species of 190 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and identification of the 190 kDa protein as the PLA2-I binding protein was demonstrated by ligand blotting analysis. The purified protein possessed a binding capacity with high affinity and specificity for a mammalian mature type of PLA2-I. Treatment of the purified material with N-glycosidase F resulted in increased mobility of the protein on SDS-PAGE as well as considerable abolition of the PLA2-I binding activity, thus suggesting the requirement of the carbohydrate moiety of the PLA2-I binding protein for receptor-ligand interactions.

VIP receptors from porcine liver: high yield solubilization in a GTP-insensitive form

Vasoactive intestinal peptide (VIP) receptors were solubilized from porcine liver membranes using CHAPS. The binding of 125I-VIP to solubilized receptors was reversible, saturable and specific. Scatchard analysis indicated the presence of one binding site with a Kd of 6.5 +/- 0.3 nM and a Bmax of 1.20 +/- 0.15 pmol/mg protein. Solubilized and membrane-bound receptors displayed the same pharmacological profile since VIP and VIP-related peptides inhibited 125I-VIP binding to both receptor preparations with the same rank order of potency e.g. VIP greater than helodermin greater than rat GRF greater than rat PHI greater than secretin greater than human GRF. GTP inhibited 125I-VIP binding to membrane-bound receptors but not to solubilized receptors supporting functional uncoupling of VIP receptor and G protein during solubilization. Affinity labeling of solubilized and membrane-bound VIP receptors with 125I-VIP revealed the presence of a single molecular component with Mr 55,000 in both cases. It is concluded that VIP receptors from porcine liver can be solubilized with a good yield, in a GTP-insentive, G protein-free form. This represents a major advance towards the purification of VIP receptors.

Solubilization and characterization of a lactogenic receptor from human placental chorion membranes

Prolactin has a wide range of actions, including osmoregulation and the control of mammary gland development and lactation. These effects are mediated through a high-affinity cell surface receptor, which has been well characterized in a number of animal tissues. The molecular characteristics of the human receptor are unknown, however. The present studies were initiated, therefore, to determine the binding and molecular characteristics of the lactogenic receptor of human placental chorion membranes. Subcellular fractionation studies showed that the bulk of the receptor sedimented in the microsomal fraction at 45,000gav. Endogenous ligand was dissociated from the receptor with 3.5 M MgCl2 or 0.05 M acetate buffer (pH 4.8) with preservation of binding activity. The microsomal receptor bound human growth hormone (hGH), human prolactin (hPRL), ovine prolactin (oPRL), and human placental lactogen (hPL) but not non-primate growth hormones, indicating a narrow specificity for lactogenic hormones. The binding was only partially reversible in agreement with the known binding kinetics of animal lactogenic receptors. The receptor was solubilized with 45% yield from the microsomes using 16 mM 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulphonate (CHAPS) detergent-250 mM NaCl, and the binding activity was fully restored by a two-fold dilution in the binding reaction to reveal a KD of 0.8 nM for hGH and a binding capacity of 200 fmol of specifically bound hGH per mg of microsomal protein. Gel filtration chromatography indicated the minimum molecular weight of the ligand-receptor complex was approximately 60,000 daltons, and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of covalently cross-linked 125I-hGH-receptor complexes revealed a molecular size of 58,000 daltons. When account was taken of the contribution of the ligand, a molecular weight of 36,000 for the receptor's binding domain was obtained. These data indicate that the chorion lactogenic receptor has very similar binding and molecular characteristics to the lactogenic receptors from other mammalian species. Chorion membranes are thus a convenient source of material for the further purification and characterization of the human lactogenic receptor.

The effect of cyclosporin A on the growth and prolactin binding to Nb-2 rat lymphoma cells

Cyclosporin A, an immunosuppressive agent, inhibited the prolactin stimulated growth of rat lymphoma Nb-2 cells. In the presence of 1 ng/ml of prolactin, 50% inhibition of growth was at 5 x 10(-6) M and the inhibition was reversible. The Kd of cyclosporin A binding to the Nb-2 cells was 10(-7) M and was independent of prolactin. The Kd of prolactin binding to the Nb-2 cells was 2 x 10(-10) M. Cyclosporin A did not influence the binding of prolactin to the cells and vice versa. The inhibitory effect of cyclosporin A on the growth of Nb-2 cells is due to some step other than the binding of prolactin to the cells.

A filtration assay for solubilized prolactin receptors using polyethyleneimine-treated membrane filters

Free 125I-labeled ovine prolactin can be separated from detergent-solubilized prolactin-receptor complex by filtration on triacetate membrane filters pretreated with polyethyleneimine. Up to 98% of the total 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate solubilized prolactin-receptor complexes from rat liver bound to polyethyleneimine-treated membranes. This simple and rapid technique can be used to quantitate solubilized prolactin-receptor complexes.

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.

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.

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.

The interaction of a Trypanosoma cruzi surface protein with Vero cells and its relationship with parasite adhesion

Previous studies have shown that adhesion to fibroblastic cells of cell culture-derived trypomastigotes of Trypanosoma cruzi probably occurs through a ligand-receptor interaction. The results now obtained indicate that solubilization with a mild detergent ('Chaps', 0.8%) of 125I-surface proteins of trypomastigotes, followed by detergent removal and interaction of the solubilized proteins with a monolayer of intact Vero cells, brings about binding to the cells of a parasite surface protein, which exhibits a molecular weight of 83,000 and isoelectric point of 8.1-8.6 upon two-dimensional polyacrylamide gel electrophoresis. This polypeptide was detected in extracts of highly adherent, extracellularly incubated parasites, but not in extracts of poorly adhesive, recently released trypomastigotes. The detergent-free extracts of incubated trypomastigotes inhibit attachment of live parasites to Vero cells, while extracts of fresh trypomastigotes are nearly ineffective. Binding of the parasite polypeptide to the cells is stimulated by parasite trypsinization or activation in the presence of tunicamycin, and it is inhibited by the presence of mannan or by Vero cell trypsinization, thus showing a similar behaviour to that observed for parasite attachment to Vero cells under these conditions. These results suggest that the surface membranes of activated, highly adherent T. cruzi trypomastigotes contain an 83 kDa polypeptide which acts as a lectin-like protein that can interact with the surface of Vero fibroblasts, probably through mannose residues of a glycoprotein receptor of the host cell.

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.

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.

Effect of oxidizing agents on rabbit mammary prolactin receptors

Treatment of rabbit mammary membrane-bound and solubilized prolactin receptors with the oxidizing agents N-chlorobenzene sulfonamide and N-bromosuccinimide resulted in total inactivation of the ability of the receptor to bind prolactin. A similar inactivation was obtained with 2-hydroxy-5-nitrobenzylbromide. The results suggest the possible importance of tryptophan in maintaining the activity of the prolactin receptor.

Studies on dissociation of mouse prolactin from mouse hepatic receptors

The influence of pH, temperature, ethylene glycol, urea, chaotropic anions and excess unlabelled secreted mouse prolactin (smPRL) on the dissociation kinetics of 125I-iodosmPRL from mouse hepatic receptors was investigated. The destabilization of smPRL-receptor complexes by chaotropic anions followed the typical trend of the Hofmeister series: I- greater than Br- greater than Cl- greater than F-. Increasing the temperature of the dissociation reaction from 8 degrees C to 23 degrees C and 30 degrees C caused partial dissociation of 125I-iodosmPRL-receptor complexes. Dissociation of 125I-iodosmPRL from mouse hepatic receptors was pH dependent, with the slowest rate of dissociation occurring at pH 8 and the fastest rate of dissociation occurring at pH 5 and 6. Both ethylene glycol and urea accelerated the rate of dissociation of 125I-iodosmPRL from mouse hepatic receptors in a concentration-dependent manner. Dissociation of 125I-iodosmPRL from mouse hepatic receptors was 6-fold faster in the presence of excess unlabelled smPRL than in its absence. The results of these investigations suggest that both protonation/de-protonation reactions and hydrophobic interactions play important roles in stabilizing the smPRL-receptor complex. In addition, they suggest that cooperative interactions may be involved in the binding of smPRL to mouse hepatic receptors.

Inactivation of rabbit mammary prolactin receptor by N-acetylimidazole

Treatment of rabbit mammary prolactin receptor with N-acetylimidazole resulted in loss of prolactin binding activity. Loss of activity of the particulate receptor was time and concentration dependent with 100 mM reagent causing total inactivation in 10 min. Similar results were obtained with solubilized receptor preparations, but at lower reagent concentrations. The loss of binding activity was due to loss in the number of binding sites. Incubation of the reagent inactivated membranes or soluble receptor with hydroxylamine for 3 hr resulted in 80-90% reactivation of the prolactin binding activity. These results indicate the possible involvement of tyrosyl residue(s) on the receptor in the prolactin-receptor interaction.

Cyclosporin A and rabbit mammary prolactin receptors

The binding of cyclosporin A and ovine prolactin to rabbit mammary gland membranes was determined. CsA bound with a Kd of 2.2 X 10(-6)M whereas prolactin bound with a Kd of 2 X 10(-10)M. The binding of each ligand was an independent event and neither ligand influenced the binding of the other ligand showing that CsA does not inhibit the binding of prolactin to its specific receptor in this system.

The Cuisinart food processor efficiently disaggregates tissues

The Cuisinart Model DLC-7 PRO food processor efficiently disaggregates plant and animal tissues resulting in time savings and often increased yields in the isolated material.