Glycosylated ovine prolactin

A cautionary tale: Alien prolactins may induce lesser, no, or opposite effects to homologous hormone!

Cost and availability have often dictated the use of heterologous/alien prolactins in experiments, particularly in vivo. The assumption has been that what is initiated in the target cell is representative of the homologous hormone since many heterologous mammalian prolactins bind to and activate rodent receptors. Here, we examined gene expression in mouse liver in response to a 7-day treatment with recombinant mouse prolactin (mRecPRL), recombinant ovine prolactin (oRecPRL) and pituitary extract ovine prolactin (oPitPRL). Having established mouse ribosomal protein S9 as the most stable reference gene in the liver in the absence and presence of prolactin treatment, we examined expression of the two most highly expressed prolactin receptors (PRLRs) and three members of the Cyp3a group of cytochrome P450 isoenzymes by qRTPCR. For short form (SF) 3 PRLR, mRecPRL doubled expression while for oRecPRL and oPitPRL expression was only 1.3-fold control. For the long form (LF) PRLR, changes were similar to those seen for SF 3 PRLR, such that the SF3:LF PRLR ratio remained the same. Expression of the Cyp3as was also dependent on the prolactin origin and, although mRecPRL always stimulated, the other PRLs caused varying results. Compared to control, Cyp3a16 was stimulated 12-fold by mRecPRL, 3-fold by oRecPRL, and 6-fold by oPitPRL. For Cyp3a41, mRecPRL was 3.7-fold control, oRecPRL was without effect, and oPitPRL was 2-fold control. Importantly, for Cyp3a44, mRecPRL stimulated 2-fold, whereas both oRecPRL and oPitPRL had an opposite, inhibitory effect, with expression at 0.5-fold control. We conclude that homologous hormone had the largest stimulatory effect on expression of all measured genes and that by contrast heterologous hormone showed reduced activity, no activity, or opposite activity, depending on the gene being analyzed. Thus, experimentation using alien heterologous PRL may lead to inaccurate conclusions.

Critical Review on Physiological and Molecular Features during Bovine Mammary Gland Development: Recent Advances

The mammary gland is a unique organ with the ability to undergo repeated cyclic changes throughout the life of mammals. Among domesticated livestock species, ruminants (cattle and buffalo) constitute a distinct class of livestock species that are known milk producers. Cattle and buffalo contribute to 51 and 13% of the total milk supply in the world, respectively. They also play an essential role in the development of the economy for farming communities by providing milk, meat, and draft power. The development of the ruminant mammary gland is highly dynamic and multiphase in nature. There are six developmental stages: embryonic, prepubertal, pubertal, pregnancy, lactation, and involution. There has been substantial advancement in our understanding of the development of the mammary gland in both mouse and human models. Until now, there has not been a thorough investigation into the molecular processes that underlie the various stages of cow udder development. The current review sheds light on the morphological and molecular changes that occur during various developmental phases in diverse species, with a particular focus on the cow udder. It aims to explain the physiological differences between cattle and non-ruminant mammalian species such as humans, mice, and monkeys. Understanding the developmental biology of the mammary gland in molecular detail, as well as species-specific variations, will facilitate the researchers working in this area in further studies on cellular proliferation, differentiation, apoptosis, organogenesis, and carcinogenesis. Additionally, in-depth knowledge of the mammary gland will promote its use as a model organ for research work and promote enhanced milk yield in livestock animals without affecting their health and welfare.

Changes in post-translational modifications of prolactin during development and reproductive cycles in the chicken

Changes in proportion of glycosylated prolactin in the anterior pituitary glands of chickens were assessed using one- and two-dimensional western blotting analysis during the perihatch stage of embryos and reproductive cycles. Multiple isoforms of prolactin were detected by one-dimensional analysis and glycosylated (G) and non-glycosylated (NG) isoforms were identified by N-glycosidase and neuraminidase treatment. Increases of ratio of G to NG isoforms were observed in both embryonic stages and reproductive cycles by the one-dimensional analysis. Although a similar tendency of increase of proportion of G prolactin was obtained, different values of proportion were observed between one-dimensional and two-dimensional analysis. Since two-dimensional analysis may better resolve isoforms differing slightly in molecular size of G prolactin, the results from two-dimensional analysis may reflect the actual proportion of prolactin isoforms. Furthermore, isoforms differing in isoelectric points were detected after N-glycosidase and neuraminidase treatment. These results indicate that prolactin may also be additionally post-translationally modified such as by phosphorylation. Thus function and biological activity of prolactin were, at least in part, regulated by post-translational modification in the various physiological stages.

The anterior pituitary gland: lessons from livestock

There has been extensive research of the anterior pituitary gland of livestock and poultry due to the economic (agricultural) importance of physiological processes controlled by it including reproduction, growth, lactation and stress. Moreover, farm animals can be biomedical models or useful in evolutionary/ecological research. There are for multiple sites of control of the secretion of anterior pituitary hormones. These include the potential for independent control of proliferation, differentiation, de-differentiation and/or inter-conversion cell death, expression and translation, post-translational modification (potentially generating multiple isoforms with potentially different biological activities), release with or without a specific binding protein and intra-cellular catabolism (proteolysis) of pituitary hormones. Multiple hypothalamic hypophysiotropic peptides (which may also be produced peripherally, e.g. ghrelin) influence the secretion of the anterior pituitary hormones. There is also feedback for hormones from the target endocrine glands. These control mechanisms show broadly a consistency across species and life stages; however, there are some marked differences. Examples from growth hormone, prolactin, follicle stimulating hormone and luteinizing hormone will be considered. In addition, attention will be focused on areas that have been neglected including the role of stellate cells, multiple sub-types of the major adenohypophyseal cells, functional zonation within the anterior pituitary and the role of multiple secretagogues for single hormones.

Changes in levels of immunoreactive prolactin isoforms during a reproductive cycle in turkey hens

Changes in the ratio between immunoreactive isoforms of prolactin using Western blotting and in the total prolactin content using radioimmunoassay were measured in pituitary glands from turkey hens at different physiological stages. The type of glycosylation (N- or O-linked carbohydrates) was determined using endoglycosidase digestion (N-glycosidase F, O-glycosidase, and neuraminidase). Low levels of prolactin were observed in pituitary glands from sexually immature, out-of-lay, and molting hens. Higher levels were present during the egg-laying period and the highest levels were detected in hens which expressed incubation behavior. Two immunoreactive bands of apparent molecular weights of 24 and 27 kDa were visualized on Western blots, corresponding to the nonglycosylated and glycosylated forms of prolactin, respectively. In pituitary glands from incubating turkey hens, about 70% of the prolactin was glycosylated (27-kDa isoforms), whereas about 60% was glycosylated in immature and in hens during the first egg-laying period. In pituitaries from out-of-lay and molting hens the percentage of glycosylated prolactin was 38 and 33%, respectively. Thus, higher percentages of glycosylated isoforms (27 kDa) were associated with high levels of total prolactin and lower percentages were associated with low levels of prolactin content in the pituitary gland. Digestion of the isoforms with N-glycosidase F resulted in a single band with an apparent molecular weight of 24 kDa. Partial deglycosylation was achieved using neuraminidase, whereas digestion with O-glycosidase had no apparent effect on the isoforms. Thus it appears that the glycosylated isoforms of prolactin have N-linked carbohydrates containing sialic acid.

Sexual dimorphism in the age changes of the pituitary lactotrophs in rats

It is known that aging is associated with alterations in hypothalamic and pituitary functions. In the present study, we have undertaken a quantitative immunohistochemical assessment of the lactotroph cell population as well as prolactin (PRL) secretion, in male and female rats of different ages. Pituitaries from young (3 months), old (20 months) and senescent (29 months) male and female Sprague-Dawley rats were processed for the immunohistochemical detection of lactotrophs. Serum PRL was measured by a homologous RIA. Additionally, the in vitro PRL secretory activity was estimated by perifusion of pituitary cells from senescent animals. Analysis of morphometric parameters revealed age-related changes of PRL cell population in animals of both sexes. The cell density (CD), surface density (SD) and volume density (VD) decreased with age in both male and female rats. However, CD as well as SD appeared to have increased in females when compared to males, either in young or old animals, while VD was higher only in old females. The pituitaries of senescent females displayed chromophobic microadenomas on a background of diffuse PRL cell hyperplasia. Prolactin serum levels showed a marked increase with age in females, but only a modest elevation in males. In senescent females, PRL production per cell was reduced. We conclude that in rats, there exists a clear sexual dimorphism in the age-related changes of pituitary PRL cells.

Glycosylated equine prolactin and its carbohydrate moiety

Glycosylated equine prolactin (G-ePRL) and nonglycosylated ePRL were purified to homogeneity from side fractions obtained during isolation of LH/FSH from horse pituitaries. Both PRL forms were isolated together in high yield by the isolation procedure used for glycosylated porcine PRL/(G-pPRL) and pPRL, involving acetone extraction/precipitation, NaCl and isoelectric precipitation, and gel filtration. Purification of G-ePRL required additional Con A chromatography. The N-terminal amino acid sequencing for 32 cycles of G-ePRL and ePRL resulted in sequences identical to the known primary structure of ePRL. Based on MALDI mass spectrometry analysis and SDS-PAGE mobilities, G-ePRL and ePRL had estimated molecular weights of 25,000 and 23,000 Da, respectively. G-ePRL displayed only 60% of the immunoreactivity of ePRL in homologous radioimmunoassay. Using the Nb2 lymphoma cell bioassay, ePRL was found to have about 1/30th the mitogenic activity of bovine PRL; G-ePRL was approximately 1/10th as active as ePRL. Glycosylation of G-ePRL at Asn31 was confirmed by isolation and sequence analysis of an enzymatically derived G-ePRL glycopeptide spanning residues 29-37. Monosaccharide compositions of intact G-ePRL and this glycopeptide were very similar (Man3, GlcNAc2, GalNAc1, Fuc0.6, Gal0.2, NeuAc0.15) and resembled that of G-pPRL. The glycopeptide contained one sulfate residue as determined by ion chromatography after acid hydrolysis, indicating the presence of a sulfated monosaccharide. Comparative carbohydrate analysis of G-ePRL and other G-PRL preparations suggests that the functionally significant Asn31 carbohydrate unit is a fucosylated complex mono- and /or biantennary oligosaccharide terminating with a sulfated GalNAc residue and two or three Man residues.

Human dermal fibroblast cells express prolactin in vitro

This study demonstrates the synthesis and release of prolactin (PRL) from dermal fibroblasts (>98%) in vitro, suggesting a potential local source of PRL in skin. PRL release was first detected in confluent cultures (0.25 x 10(6) plated cells) on or before day 18 and increased to a maximal level of 2 ng/72 h by day 30. Medroxyprogesterone acetate and estradiol (E2) had no effect on PRL release, but prostaglandin E2 (PGE2) reduced the time required for PRL induction to 6-9 days. The steroids and PGE2 together were synergistic, reaching maximal values of approximately 10 ng/72 h after 2 or more weeks of treatment. Dibutyryl-cyclic AMP, a second messenger in prostaglandin signal transduction, was also synergistic with medroxyprogesterone acetate and E2, but induced significant PRL expression in the absence of the steroids (28 and 12 ng/72 h, respectively). The increase in PRL release was not a result of increased cell proliferation, because the PRL-secreting cultures had 32.2 +/- 8.8% less DNA (N = 3 individuals, 93% confidence limit) than control cultures after 3 weeks of treatment with dibutyryl-cyclic AMP, medroxyprogesterone acetate, and E2. Dermal fibroblast PRL was immunologically and electrophoretically identical to decidual and pituitary PR-Ls, and Northern blot analysis demonstrated a PRL mRNA size of 1.15 kb. Maximal PRL release from fibroblast cells was 32.0 +/- 6.1 ng/72 h (mean +/- SD at 95% confidence limit) for a donor population representing both males (n = 15) and females (n = 7) between the ages of 20-week gestation to 52 years. In contrast to term decidual fibroblast cells that also express PRL, dermal fibroblasts did not co-express insulin-like growth factor-binding protein-1.

Identification of the major site of rat prolactin phosphorylation as serine 177

Phosphorylation of prolactin by endogenous protein kinases within isolated secretory granules was shown to result in the production of both phosphoserine and phosphothreonine residues. The majority of the radiolabel was determined to be present in the C terminus of the molecule after specific cleavage with glandular kallikrein. Glandular kallikrein cleaves in three places at the C terminus, liberating three small peptides, only one of which contains a phosphorylatable residue. Sequencing of this phosphopeptide showed it to be Arg175-Lys185. Thus the major site of prolactin phosphorylation was determined to be serine 177. Using a synthetic peptide equivalent to this region of the molecule (Ser161-Val180), serine 177 was demonstrated to be a substrate for protein kinase A as well as for one of the endogenous granule kinases. Inclusion of the synthetic peptide in an endogenous granule phosphorylation reaction resulted in competition for the kinase and reduced phosphorylation of prolactin. Protein kinase A phosphorylation of purified prolactin resulted in the production of only phosphoserine and primarily the most abundant (monophosphorylated) variant. We conclude that serine 177 is the major in vivo phosphorylation site of rat prolactin and that phosphorylation of this site can be reproduced by protein kinase A in vitro. The minor threonine phosphorylation site was demonstrated by two-dimensional tryptic peptide mapping and mass analysis to be either threonine 58 or 63, both of which are contained within a single peptide.

Regulated secretion of prolactin by the mouse insulinoma cell line beta TC-3

Our aim is to use cultured cells capable of regulated protein secretion for the production of recombinant proteins that require particular types of post-translational modifications. Here we have generated a stable transfected beta TC-3 cell line, beta TC-IPR9, that secretes high levels of recombinant prolactin. Transfected cells synthesize both the 27 kDa glycosylated and a 23 kDa nonglycosylated prolactin; the 23 kDa nonglycosylated species was secreted preferentially when cells were placed in secretion medium containing isobutylmethylxanthine (IBMX) and high concentrations of glucose, K+, and Ca2+. When the cells were cultured in medium containing low concentrations of glucose, K+, and Ca2+, most of the prolactin and insulin were not secreted; much of the prolactin was proteolytically converted to a 16 kDa form. Within the first 30 minutes after transferring the cells to medium containing secretagogues there was a 20-fold increase in the rate of secretion of prolactin; all of the 16 kDa species was secreted. The recombinant cells could be cycled several times between medium in which prolactin was biosynthesized and medium in which it was secreted. Preferential secretion of proteolytically processed prolactin in a medium without contaminating proteins offers an example of the advantage of this technology for production of other recombinant proteins.

Characterization of a transcriptional attenuator within the 5' R region of the human T cell leukemia virus type 1

Several regulatory sequences have been characterized in the HTLV-I promoter. We report here identification of a sequence element downstream of the transcriptional start site within the first 52 nucleotides of the 5' R region, which acts negatively on the activity of the HTLV-I promoter. Determination of the half-lives of the RNAs either including or lacking this sequence element showed that the observed effect intervenes at the transcriptional level. This negative element does not affect basal activity of the HTLV-I TATA box, but down-regulates transcription induced by strong activators. Thus, we propose that this so-called negative regulatory sequence functions as an attenuator of transcription.

The effect of protein synthesis inhibitors on the glycosylation site occupancy of recombinant human prolactin

The relationship between synthesis and N-linked glycosylation site occupancy of recombinant human prolactin produced from C127 cells was studied with the aid of a battery of protein synthesis inhibitors. Non-lethal concentrations of sodium fluoride, gougerotin, puromycin, anisomycin, and emetine did not alter site occupancy, but low concentrations (< 10 micrograms ml-1) of cycloheximide increased the fraction of secreted prolactin bearing oligosaccharide from 20% to 80% of the total. Cycloheximide is an inhibitor of the elongation step of protein synthesis. The observed increase in glycosylation site occupancy upon addition of cycloheximide is consistent with the current opinion that the initial glycosylation event occurs cotranslationally during a limited time period. Cycloheximide may extend this time period by reducing elongation rate. However, the absence of any effect from treatment with other inhibitors of elongation suggests that cycloheximide is unique in its behavior on this system.

Isolation and characterization of phosphorylated bovine prolactin

Quantitative isolation of bovine prolactin was accomplished by immunoaffinity chromatography using clonal antibody as the stationary ligand. The phosphorylated and non-phosphorylated (native) prolactins contained in the immunopurified preparations were separated by chromatofocusing. Isolates from individual pituitaries revealed that phosphorylated prolactin represented between 20 and 80% of the total prolactin. The stoichiometry of phosphate in phosphorylated prolactin was 1.4:1 when determined by amino acid analysis after preparation of the S-ethylcysteine derivative. One major phosphorylation site, serine-90, and two minor sites, serine-26 and -34, were determined by mapping and sequencing studies. Serine-90 was conserved in prolactins, growth hormones and placental lactogens. Serine-26 and -34 were conserved in prolactins, but were not found in growth hormones or placental lactogens. Absorption spectroscopy of the aromatic amino acid residues indicated that phosphorylation of prolactin was associated with a unique structural conformation.

Development of immunotherapeutic strategies for the treatment of malignant neoplasms

Focused preclinical studies have been used to gain insight into the mechanism of therapeutic activity of cytokines, growth factors and biological response modifiers (BRMs). These data can then be used to develop a clinical hypothesis to facilitate the development of these new biological drugs. In this manuscript, we discuss a number of preclinical and clinical studies using interferon-gamma, IL-2, and the colony stimulating factors. The importance of the systematic profiling of the biological activity of such biological drugs is emphasized and we discuss the utility of the mechanistic data in their clinical development. The overall preclinical approach identifies the cellular, biochemical or gene regulatory event that is associated with the therapeutic activity of a biologic and this surrogate (be it biological, chemical, or quality of life) is then used to optimize the clinical protocol in a phase 1b trial. This, in theory, results in the rapid identification of the optimal dose, schedule and route of administration for subsequent testing in a phase II/III clinical trial.

Isolation and characterization of glycosylated and non-glycosylated prolactins from alligator and crocodile

Two molecular forms of prolactin (PRL), glycosylated and non-glycosylated, were isolated from pituitary glands of two reptiles, alligator and crocodile. The reptilian PRLs were extracted under alkaline conditions from the precipitate obtained after pituitaries were first extracted with 0.25 M sucrose, 1 mM NH4HCO3, pH 6.3. Purification was performed by ion exchange chromatography on DE-52, gel filtration on Sephadex G-75 superfine, and reversed phase high performance liquid chromatography. Two forms of both alligator and crocodile PRL, designated PRLI and PRLII, with molecular weights of 26,000 and 24,000 were isolated. Alligator and crocodile PRLI and PRLII were stained specifically in immunoblots with anti-sea turtle PRL and anti-ostrich PRL. Sequence analysis revealed that both forms of alligator and crocodile PRLs consisted of 199 amino acid residues with a glycosylation consensus sequence (Asn-Ala-Ser) at position 60 in alligator and crocodile PRLs with a molecular weight of 26,000 (PRLI). In contrast, Thr was substituted for Asn at position 60 in the PRLs with a molecular weight of 24,000 (PRLII). The sequences of alligator PRLs differed from crocodile PRLs only in position 134: Val for alligator PRLs and Ile for crocodile PRLs. There is a high degree of structural conservation between the reptilian PRLs isolated in this study and avian PRL; each showed 92% sequence identity with chicken PRL and 89% with turkey PRL.

Purification to homogeneity of bovine prolactin by high-performance ion-exchange chromatography

Homogeneous bovine prolactin (bPRL) has been obtained using a procedure based on high-performance anion-exchange chromatography. The procedure enables up to 6 mg of 99.4% pure bPRL to be obtained per hour, with a recovery of 32.4%. The purity of the protein was checked by N-terminal sequencing and sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The highly purified bPRL obtained with this method is suitable for complete structural and immunochemical studies.

Comparisons of glycosylated and nonglycosylated amniotic fluid prolactins in normal second- and third-trimester pregnancies

Prolactins in glycosylated and nonglycosylated form were isolated from 218 second- and third-trimester amniotic fluid samples by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, electrotransferred to nitrocellulose paper, and probed with anti-human prolactin serum and protein A labeled with iodine 125. The glycosylated and nonglycosylated prolactin bands were exposed by autoradiography. The bands were analyzed by densitometry, and the ratio of glycosylated to total (glycosylated + nonglycosylated) prolactin was calculated (glycosylated/total ratio) and compared with matched prolactin radioimmunoassay measurements. Both radioimmunoassay-measured and nonglycosylated prolactin decreased from the second to the third trimester whereas glycosylated prolactin concentrations remained unchanged. Concomitantly, glycosylated/total prolactin ratios increased significantly (p less than 0.001). The correlation of radioimmunoassay-measured prolactin was closer to nonglycosylated prolactin (r2 = 0.32, p = 0.00001) than to glycosylated prolactin (r2 = 0.02, p = 0.06). We suggest that the proportion of amniotic fluid glycosylated prolactin increases with length of gestation and that glycosylation of prolactin is inversely related to total prolactin secretion. Furthermore, prolactin's immunoreactivity correlated more closely to the nonglycosylated-prolactin variant, suggesting that radioimmunoassay of prolactin poorly recognizes the glycosylated prolactin form.

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.

Increased biological activity of deglycosylated recombinant human granulocyte/macrophage colony-stimulating factor produced by yeast or animal cells

Human granulocyte/macrophage colony-stimulating factor (hGM-CSF) produced by several recombinant sources including Escherichia coli, yeast, and animal cells was studied. Recombinant animal cells produced hGM-CSF in low quantities and in multiple forms of varying size. Mammalian hGM-CSF was purified 200,000-fold using immunoaffinity and lectin chromatography. Partially purified proteins produced in yeast and mammalian cells were assayed for the effects of deglycosylation. Following enzymatic deglycosylation, immunoreactivity was measured by radioimmunoassay and biological activity was measured in vitro on responsive human primary cells. Removal of N-linked oligosaccharides from both proteins increased their immunoreactivities by 4- to 8-fold. Removal of these oligosaccharides also increased their specific biological activities about 20-fold, to reach approximately the specific activity of recombinant hGM-CSF from E. coli. The E. coli produced-protein--lacking any carbohydrate--had by far the highest specific activity observed for the recombinant hGM-CSFs.

Detection of multiple PRL- and GH-like proteins in human pituitary by Western blot analysis

Surgically removed normal and tumorous pituitary tissues from a prolactinoma patient were analyzed by Western blot techniques for PRL and GH variants. Criteria for identification were the Rf of the bands within the gel, immunologic crossreactivity to specific antisera, and structural verification by tyrosine peptide-mapping of individual bands from the gel. The authors found the tumor-tissue to be characterized by the presence of a PRL band greater in concentration than in the normal tissue and the virtual absence of a GH band. Immunoblotting of the electrophoretically resolved proteins form both types of tissues revealed several new bands crossreactive with human PRL and GH antibodies. Some of the new bands were of Mr greater than the monomeric PRL and GH and others were of lower Mr. Relative of two of the low mobility Mr PRL-immunoreactive bands designated as 16K and 8K corresponded to the Rf of the two fragments of cleaved PRL, which suggested that cleaved PRL occurred naturally in the human pituitary gland. The most conspicuous of the new PRL-immunoreactive bands, a 25,000 Mr protein migrating slightly behind PRL, displayed strong crossreactivity to hPRL antibodies and was present in greater concentration in the prolactinoma tissue than in the normal tissue. These properties suggested that it was related to hPRL and perhaps represented its glycosylated variant. However, its tyrosine peptide map did not resemble that of hPRL. Thus, it is not clear whether it represented G-hPRL or a new pituitary protein that cross-reacts with hPRL antibodies. In addition, two other bands of low Mr, designated as unknown 1 and unknown 2, reacted with hPRL antibodies. Immunostaining with hGH antibodies revealed the 20K-hGH variant, the F1 fragment of cleaved hGH, and a pair of new bands immediately behind GH that could represent glycosylated hGH--possibly a product of Seeburg's variant hGH gene. Both PRL and GH antibodies elicited numerous bands of high Mr by the technique employed, far more than ever observed by Sephadex chromatography. The nature of the high Mr bands remains unknown. Further characterization of these new PRL- and GH-immunoreactive proteins might help in the understanding of the multiple physiologic functions of PRL and GH in man.

Detection and enzymatic deglycosylation of a glycosylated variant of prolactin in human plasma

Immunoperoxidase electrophoresis was applied to the plasma of a patient showing a high level of prolactin (PRL) secreted by a pituitary adenoma. Two PRL monomers were detected with an anti-hPRL antiserum: a major 22 kDa form and a minor 25 kDa form. Concanavalin A-Sepharose 4B chromatography revealed that the 25 kDa form was a glycosylated variant of PRL. Incubation of this variant with endoglycosidase F led to its transformation into the 22 kDa form.

Multiple forms of pituitary prolactin, a glycosylated form of porcine prolactin with enhanced biological activity

Three forms of prolactin differing in molecular weight (Mr 23,000, 25,000 and 50,000, respectively) and electrophoretic mobility have been isolated and purified from fresh-frozen porcine pituitary glands. The prolactin form with Mr 25,000 is identified as a glycoprotein having an affinity to concanavalin A. The carbohydrate unit containing GlcNAc3, GalNAc1, Man3, Fuc 0.5, Gal 0.4 is linked to asparagine at the 31 position. The amino acid composition and partial primary structure of the glycosylated prolactin are identical to those of the major prolactin form (Mr 23,000). Based on isoelectric focusing and nondenaturing disc-electrophoresis, the glycosylated prolactin appears more acidic than the major form. The glycosylated form of the hormone has 140% of the activity of the non-glycosylated prolactin when measured by the pigeon crop sac assay. The new form accounts for 30-40% of the total monomeric prolactin in the porcine pituitary. The yield was 200 mg purified glycosylated prolactin from 1000 g pituitary gland. The third form of hormone (Mr 50,000) was shown to be a disulphide linked prolactin dimer.

Isolation and partial characterization of a pair of prolactins released in vitro by the pituitary of a cichlid fish, Oreochromis mossambicus

The pituitary of the cichlid fish tilapia secretes two prolactins (PRLs) of molecular masses 20 kDa and 24 kDa. The 20-kDa PRL has an isoelectric point in the range of those of mammalian PRLs (pI 6.7), but the 24-kDa PRL is unusually basic (pI 8.7). Partial sequence information indicates that the PRLs are homologous but distinct proteins, differing by five amino acids within the first 29 NH2-terminal residues. Homology in the known region is higher with chum salmon PRL than with known mammalian PRLs. Reversed-phase HPLC permits isolation of these two PRLs and a single tilapia growth hormone from culture medium or from the pituitary in a single step. HPLC and radio-HPLC analysis of [3H]leucine pulse-chase experiments reveal that each PRL is secreted in vitro at remarkably high rates (21 pmol per gland per hr) and that the two PRLs are released in approximately equimolar amounts, suggesting the coordinate regulation of the secretion. Both PRLs exert characteristic PRL activity in that they prevent the loss of Na+ from the plasma of hypophysectomized tilapia in fresh water.

Automated tandem high-performance liquid chromatographic system for separation of extremely complex peptide mixtures

We have developed an automated tandem chromatography system, which consists of a combination of ion-exchange column chromatography and reversed-phase column chromatography. The system is composed of two independent high-performance liquid chromatography assemblies, in each of which programmed elution is carried out by a computer-assisted controller. A peptide mixture is applied to an ion-exchange column and is eluted in a stepwise manner. The eluent from the first column is introduced directly into the second, reversed-phase column, which is connected in tandem through a tee tube. After application of two column volumes of the eluent, reversed-phase chromatography is performed by linear gradient elution. Stepwise elution for ion-exchange chromatography and the gradient elution for reversed-phase chromatography are synchronized by a computer program. The resolving power and the reproducibility of the method were tested by using a tryptic digest of human ceruloplasmin [molecular weight 132 000 daltons (132 kDa)]. By this method, the digest was resolved reproducibly into several hundred peaks within 16 h. All of the four glycopeptides expected to be obtained by tryptic digestion were purified easily from the whole digest of the protein. Comparison of the peptide maps between a single-chain and a degraded form of ceruloplasmin facilitated the identification of two tryptic peptides, derived from the carboxyl-terminal regions of 67 kDa and 50 kDa fragments of the degraded form, which lack the carboxyl-terminal arginine and lysine residues, respectively. The method may be applicable to comparative peptide mapping of very large proteins exhibiting molecular microheterogeneity, such as carbohydrate or genetic variants; it also can be used complementarily for sequence support of DNA sequencing as well as for preparative purification of peptides as a strategy of protein sequencing of very large proteins.

Contemporary methodology for protein structure determination

The techniques used for the characterization of protein and peptide structure have undergone great changes that have improved the speed, reliability, and applicability of the process. High-performance liquid chromatography and gel electrophoresis have made the purification of proteins and peptides a routine procedure, even when the compound of interest is a minor component of a complex biological mixture. The chemistry and instrumentation used in amino acid analysis and amino acid sequencing now permit the analysis of as little as 5 to 50 picomoles of samples. This represents an increase in sensitivity of more than a thousandfold over the last 10 years and has made possible the structural analysis of a wide variety of scarce but important compounds.

Nucleotide sequence of a growth-related mRNA encoding a member of the prolactin-growth hormone family

As part of the proliferative response to serum, mouse 3T3 cells produce a set of growth-related mRNAs identified by hybridization to cloned cDNAs. One of these mRNAs, which is about 1 kilobase long, appears within a few hours after stimulation of resting cells with serum or platelet-derived growth factor and reaches a high level during the transition from the G1 to the S phase of growth. This mRNA is translated in vitro into a protein of approximately 25 kilodaltons. The corresponding cloned cDNA of 791 base pairs has been sequenced; it contains a single open reading frame that encodes a protein of 224 amino acids with extensive sequence homology to mammalian prolactins. The initial 29-amino acid segment of the encoded protein resembles the signal sequences of prehormones. That the growth-related protein is not mouse prolactin is indicated by comparison of its predicted amino acid composition with that of mouse prolactin and by the distinct fragment patterns seen when restricted mouse DNA is probed with the cloned cDNA or rat prolactin cDNA. Therefore, the growth-related protein appears to be a new member of the prolactin-growth hormone family. Because of its relationship to prolactin and growth hormone and its association with cell proliferation, the protein has been called "proliferin."