Monoclonal antibodies specific for non-glycosylated porcine prolactin and for pituitary porcine prolactin

Regulation and distribution of squirrel monkey chorionic gonadotropin and secretogranin II in the pituitary

Secretogranin II (SgII) is a member of the granin family of proteins found in neuroendocrine and endocrine cells. The expression and storage of SgII in the pituitary gland of Old World primates and rodents have been linked with those of luteinizing hormone (LH). However, New World primates including squirrel monkeys do not express LH in the pituitary gland, but rather CG is expressed. If CG takes on the luteotropic role of LH in New World primates, SgII may be associated with the expression and storage of CG in the pituitary gland. The goal of this study was to evaluate the regulation and distribution of CG and SgII in the squirrel monkey. A DNA fragment containing approximately 750 bp of squirrel monkey SgII promoter was isolated from genomic DNA and found to contain a cyclic-AMP response element that is also present in the human SgII promoter and important for GnRH responsiveness. The squirrel monkey and human SgII promoters were similarly activated by GnRH in luciferase reporter gene assays in LβT2 cells. Double immunofluorescence microscopy demonstrated close association of SgII and CG in gonadotrophs of squirrel monkey pituitary gland. These results suggest that CG and SgII have a similar intercellular distribution and are coregulated in squirrel monkey pituitary gland.

A sensitive sandwich ELISA for buffalo prolactin

Two murine monoclonal antibodies have been developed against the buffalo prolactin (buPRL). These were designated as 1501 and 1504. Using two MAbs and anti-buPRL rabbit serum, an analysis was performed for the development of a sandwich ELISA (sELISA). The 1504/buPRL/anti-buPRL rabbit serum system was found feasible for sELISA. The sELISA had a sensitivity of 156 pg/mL. The buffalo serum sample showed a parallelism with the standard curve. The intra- and inter-assay coefficients of variance were 8.4% and 9.06%, respectively. These data proved the validity of the assay.

Epitope mapping of monoclonal antibodies to bovine prolactin

The epitopes recognized by three monoclonal antibodies generated to sheep prolactin were determined by evaluating their cross-reactivities by immunodot analysis with 14 mutants of bovine prolactin, in which individual amino acids had been deleted or substituted. Mutations were made throughout the molecule and included disruption of the amino-terminal, carboxyl-terminal, and central disulfide loops. Lack of immunoreactivity was taken as an indication that the site of mutation was part of the epitope. Antibody 6F11 reacted with all bovine prolactin mutants tested, except those in which the carboxyl-terminal cysteine (position 199) was substituted by a serine. Antibodies 5G2 and 4C10 reacted with all of the bovine prolactin mutants, except those in which the amino-terminal cysteine (position 4) was substituted by a serine. Western blot analysis of sheep, squirrel monkey, and rat prolactins with the monoclonal antibodies revealed that 5G2 and 4C10 were specific for sheep prolactin, whereas antibody 6F11 cross-reacted with prolactins from all three species. The mitogenic activity of sheep or rat prolactin in the Nb2 bioassay was determined in the presence of the antibodies to determine whether the epitopes were part of the functional domains of these prolactins. The bioactivity of sheep prolactin (0.4 ng/ml) was unaffected by the monoclonal antibodies [0.01-1 microgram immunoglobulin G (IgG)/ml], whereas the bioactivity of rat prolactin (1.25 ng/ml) was inhibited by 6F11 with an apparent 50% inhibitory concentration of 0.25 microgram IgG/ml. These results indicate that monoclonal antibodies 5G2 and 4C10 cross-react with a species-specific region of the amino-terminal disulfide loop of bovine prolactin.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and biochemical properties of four forms of glycosylated porcine prolactin

Four isoforms of glycosylated prolactin (G-pPRL) were isolated from porcine pituitary glands by affinity chromatography and concanavalin A-Sepharose, based upon differences in their affinity for the lectin. Structural analysis indicated differences in the carbohydrate units of the four G-pPRLs. N-glycanase treatment cleaved the oligosaccharide from the G-pPRLs, establishing N-linked glycosylation. The binding of G-pPRLs to receptors from lactating rabbit mammary glands was only 3-8% that of nonglycosylated pPRL (NG-pPRL). The immunological crossreactivity of the G-pPRLs varied from 36 to 65% that of NG-pPRL. When tested in the pigeon crop sac bioassay, G-pPRLs were only 11-40% as active as NG-pPRL. The metabolic clearance rate of one of the G-pPRLs was slower and another faster than that of NG-pPRL. We conclude that there are several forms of G-PRL of variable immuno- and bio-potencies in the porcine pituitary, and that the current radioimmunoassay for the hormone does not measure the actual bioactivity.

Carbohydrate-dependent epitope mapping of human thyrotropin

To probe possible effects of carbohydrate chains in the conformation of pituitary glycoprotein hormones, two radiolabeled derivatives of human thyroid-stimulating hormone (hTSH), either partially deglycosylated in the beta-subunit or fully deglycosylated in both the alpha- and beta-subunits, were compared to the native hormone for binding to monoclonal as well as polyclonal antibodies. Monoclonal antibodies were screened for their ability to bind the intact hormone (anti-hTSH), hTSH and its free alpha-subunit (anti-alpha) or its free beta-subunit (anti-beta). A panel of 14 monoclonal antibodies directed against at least eight out of the 12 epitopes known to be present in the hormone was tested in solid-phase assays for their capacity to bind intact and deglycosylated forms of hTSH. All of them displayed identical recognition of native and partially deglycosylated 125I-hTSH. In contrast, binding of fully deglycosylated 125I-hTSH to anti-hTSH and anti-beta antibodies was dramatically lost while that of anti-alpha was preserved. This clearly indicates that most of the epitopes specific for subunit association as well as those present on the beta-subunit are glycosylation dependent. No alteration was found in antibody recognition following deglycosylation of free individual subunits, indicating that the carbohydrate effect can only occur in the combined dimer. Using polyclonal antisera raised against the International Reference Preparations, we found that the deglycosylated hormone could be bound by the anti-beta antiserum although at a much lower dilution than the native antigen, suggesting the presence of at least one glycosylation-independent epitope in the beta-subunit. Competitive binding assays revealed that deglycosylated hTSH is 5 times less immunoreactive toward the anti-beta compared to the anti-alpha antiserum. The current data thus demonstrate the presence of the glycosylation-independent epitopes in the alpha-subunit of hTSH and the localization of most of the glycosylation-dependent domains in the beta-subunit.

Phosphorylated variant of bovine prolactin

Bovine pituitary explants and cell cultures were incubated with [32P]orthophosphate. Extracts were prepared from the explants and analyzed by sodium dodecyl sulfate-containing acrylamide gel electrophoresis and autoradiography revealing a phosphoprotein that co-migrated with authentic bovine prolactin. Clonal antibodies to bovine prolactin were produced, purified and used to prepare affinity columns. Extracts of [32P]orthophosphate-labeled explants and cells or media were applied to prolactin affinity columns and a radiolabeled protein was eluted with a pH 2.8 wash. The eluted protein was identified as prolactin by co-migration with standard on gel electrophoresis and by amino acid analysis. Treatment of immunoaffinity-purified pituitary prolactin with alkaline phosphatase reduced the phosphate associated with prolactin in a time-dependent manner, indicating a covalent phosphate linkage. Autoradiography of gels revealed prolactin from explants, cells and their associated media to be a phosphoprotein. A phosphorylated variant of bovine prolactin is synthesized and secreted in both explant and cell cultures.

Biological activities of glycosylated and nonglycosylated porcine prolactin

Nonglycosylated and glycosylated porcine prolactin (PRL) were separated using concanavalin A-Sepharose CL-6B column chromatography and tested for mitogenic and lactogenic activities, as well as immunoaffinity and receptor binding characteristics compared to total (nonseparated) porcine PRL. Mitogenic activity, using Nb2 lymphoma cells, was 4- and 50-fold greater (P less than 0.01) for total PRL than nonglycosylated and glycosylated PRL, respectively. Glycosylated PRL had 64% higher (P less than 0.05) lactogenic activity than nonglycosylated or total PRL. In a homologous radioimmunoassay (RIA), displacement was greatest for total, followed by the nonglycosylated and glycosylated forms of PRL. Competitive inhibition of porcine [125I]-(total) PRL by radioinert total, nonglycosylated and glycosylated PRL in a homologous radioreceptor assay (RRA) indicated similar Ka values for total and nonglycosylated PRL, but different receptor numbers, while radioinert glycosylated PRL had a higher Ka, but bound fewer receptors. Therefore, glycosylated porcine PRL has greater lactogenic activity and higher binding affinity despite decreased mitogenicity, while nonglycosylated PRL had characteristics similar to total PRL. Results from the homologous RRA and the Nb2 assay suggest that both forms of PRL are necessary to achieve biological effects similar to those for total PRL. The two forms of PRL may have individual and collective effects, while changes in the ratio between these forms may influence physiologically diverse effects of PRL on target tissues.

A monoclonal antibody which inhibits the biological activity of rat prolactin, but not prolactin from other species

Monoclonal antibodies generated to ovine prolactin were screened for their ability to neutralize the biological activity of prolactin from several species. By Western blot analysis, antibody 6F11 cross-reacted strongly with prolactin in homogenates of anterior pituitary glands from squirrel monkey, sheep and rat. In addition, this antibody (1 micrograms IgG/ml) completely inhibited the lactogenic activity of serum or purified prolactin (0.5 ng/ml) from rat, but not prolactin from any other source, in the Nb2 lymphoma bioassay. 6F11 cross-reacted with purified ovine and rat prolactin by enzyme-linked immunosorbentassay (ELISA) and Western blot analysis with similar affinities, suggesting that the 6F11 epitope was common to these peptides. Another monoclonal antibody (17D9, 35 ng IgG/ml) showed the opposite selectivity, completely inhibiting the activity of 0.3 ng/ml ovine prolactin, but not 0.5 ng/ml rat prolactin, in the Nb2 assay. Thus, we have identified monoclonal antibodies which cross-react with both ovine and rat prolactin, but selectively neutralize the lactogenic activity of prolactin from only one species.

Presence of tyrosine-O-sulfate in sheep pituitary prolactin

When the metabolically obtained 35S-labelled sheep pituitary prolactin-rich fraction was subjected to chemical deglycosylation the radioactivity was retained in the immunoprecipitable prolactin. 35S-labelled prolactin-rich pituitary extract was fractionated on SDS-PAGE and protein was extracted from prolactin positive bands. When the extracted 35S-labelled prolactin was hydrolysed by alkali and then chromatographed on a thin layer of silica, it showed the presence of a radioactive compound which had an Rf value identical to the standard Tyr-O-SO4 synthesized and characterized in our laboratory.

Receptor binding and Nb2 cell mitogenic activities of glycosylated vs. unglycosylated porcine prolactin

Purified fractions of glycosylated (pGPrl) and unglycosylated (pUGPrl) porcine prolactin were prepared by affinity chromatography on Concanavalin A-Sepharose. The relative binding activities of these two forms of prolactin for receptors from porcine mammary, adrenal cortex and rabbit mammary, as well as their Nb2 cell mitogenic activity were determined. In both the porcine mammary and adrenal cortex receptor binding assays pGPrl had a 2-3 fold lower activity than pUGPrl. In the rabbit mammary binding assay pGPrl had a about a 5 fold lower activity than pUGPrl. Similarly, pGPrl had only about 20% of the activity of pUGPrl in the Nb2 cell proliferation assay.