Three-dimensional structure of a genetically engineered variant of porcine growth hormone

Study of goldfish (Carassius auratus) growth hormone structure–function relationship by domain swapping

Using goldfish as a model, the structure-function relationship of goldfish growth hormone was studied using the strategy of homologous domain swapping. Chimeric mutants were constructed by exchanging homologous regions between goldfish growth hormone (gfGH II) and goldfish prolactin (gfPRL) with their cloned complementary DNAs. Six mutants, with their domain-swapped, were generated to have different combinations of three target regions, including the helix a, helix d and the large section in between these helices (possess the helices b, c and other random coiled regions). After expression in E. coli and refolding, these mutants were characterized by using competitive receptor binding assay (RRA) and growth hormone responding promoter activation assay. The different activity profiles of mutants in Spi 2.1 gene promoter assays from that in RRA shows that, for gfGH, receptor binding dose not confer receptor signal activations. When either helices a or d of gfGH was maintained with other helices replaced by their gfPRL counterparts, both receptor binding and hence gene activation activities are reduced. In mutants with helices b and c in gfGH maintained, containing the gfGH middle section, and helices a and d swapped with gfPRL, the had reduced RRA activities but the promoter activation activities retained. In conclusion, as in the case of human GH, the gfGH molecule possesses two functional sites: one of them is composed of discontinuous epitopes located on the target regions of this study and is for receptor binding; another site is located on the middle section of the molecule that helices a and d are not involved, and it is for activation of GH receptor and intracellular signals.

Pegvisomant therapy for acromegaly

Despite traditional, multimodality therapy that consisted of surgery, radiotherapy and medical therapies, many patients with acromegaly could not be adequately treated. Pegvisomant is a novel growth hormone receptor antagonist that became available for the treatment of acromegaly in 2003. This drug is a growth hormone variant that has nine mutations to human growth hormone. These give it high affinity for the growth hormone receptor as well as disrupting growth hormone receptor dimerization, with the net effect being antagonism of growth hormone at its receptor. Traditional methods of therapy for acromegaly treat the disease by reducing pituitary tumor secretion of growth hormone and, thus, lowering serum insulin-like growth factor-I levels. Pegvisomant, by contrast, blocks the actions of circulating growth hormone excess, but does not lower serum growth hormone levels. Its efficacy, therefore, is assessed by monitoring serum insulin-like growth factor-I levels. In clinical trials, pegvisomant has been shown to effectively normalize insulin-like growth factor-I levels in up to 97% of patients and to improve acromegaly-related signs and symptoms, and morbidities such as insulin resistance. As the action of pegvisomant does not rely on the tumor's receptor profile, it can be effective even in patients resistant to somatostatin analog therapy. Individually tailored therapy guided by serum insulin-like growth factor-I normalization goals and improvement in clinical signs and symptoms should be undertaken while growth hormone deficiency should be avoided. Pegvisomant is very well tolerated, but liver transaminase levels need to be monitored during therapy. As pegvisomant does not shrink pituitary tumors, the underlying rate of tumor growth may continue on this therapy and periodic pituitary imaging needs to be conducted during therapy.

Crystal Structure and Site 1 Binding Energetics of Human Placental Lactogen

In primates, placental lactogen (PL) is a pituitary hormone with fundamental roles during pregnancy involving fetal growth, metabolism, and stimulating lactation in the mother. Human placental lactogen (hPL) is highly conserved with human growth hormone (hGH) and both hormones bind to the hPRLR extracellular domain (ECD), the first step in receptor homodimerization, in a Zn2+-dependent manner. A modified surface plasmon resonance method was developed to measure the kinetics for hPL and hGH binding to the hPRLR ECD, with and without Zn2+ and showed that hPL has about a tenfold higher affinity for the hPRLR ECD1 than hGH. The crystal structure of the free state of hPL has been determined to 2.0 A resolution showing the molecule possesses an overall structure similar to other long chain four-helix bundle cytokines. Comparison of the free hPL structure with the 1:1 complex structure of hGH bound to the hPRLR ECD1 suggests that two surface loops undergo conformational changes >10 A upon binding. An 18 residue Ala-scan was used to characterize the binding energy epitope for the site 1 interface of hPL. Individual alanine substitutions at five positions reduced binding affinity by a DeltaDeltaG > or = 3 kcal mol(-1). A comparison of the hPL site 1 epitope with that previously determined for hGH indicates contributions of individual residues track reasonably well between hPL and hGH. In particular, residues involved in the zinc-binding site and Lys172 constitute the principal binding determinants for both hormones. However, several residues that are identical between hPL and hGH contribute quite differently to the binding of the hPRLR ECD1. Additionally, the overall magnitudes of the DeltaDeltaG changes observed from the Ala-scan of hPL were markedly larger than those determined in the comparative scan of hGH to the hPRLR ECD1. The structural and biophysical data presented here show that subtle changes in the structural context of an interaction can lead to significantly different effects at the individual residue level.

Growth hormone receptor antagonists

The currently available long-acting somatostatin analogs normalize serum growth hormone (GH) levels and insulin-like growth factor-I levels in approximately 60% of patients with acromegaly. The recently introduced GH receptor antagonist, pegvisomant, is able to normalize insulin-like growth factor-I levels in virtually all acromegalic subjects. Although no correlation between increased GH concentrations and tumor size has been found, long-term safety studies are still in progress. Also, pegvisomant monotherapy is administered once daily and is very costly. Combined treatment of a somatostatin analog with pegvisomant appears to be an effective and rational approach.

IL-3, IL-5, and GM-CSF signaling: crystal structure of the human beta-common receptor

The cytokines, interleukin-3 (IL-3), interleukin-5 (IL-5), and granulocyte-macrophage colony stimulating factor (GM-CSF), are polypeptide growth factors that exhibit overlapping activities in the regulation of hematopoietic cells. They appear to be primarily involved in inducible hematopoiesis in response to infections and are involved in the pathogenesis of allergic and inflammatory diseases and possibly in leukemia. The X-ray structure of the beta common (betac) receptor ectodomain has given new insights into the structural biology of signaling by IL-3, IL-5, and GM-CSF. This receptor is shared between the three ligands and functions together with three ligand-specific alpha-subunits. The structure shows betac is an intertwined homodimer in which each chain contains four domains with approximate fibronectin type-III topology. The two betac-subunits that compose the homodimer are interlocked by virtue of the swapping of beta-strands between domain 1 of one subunit and domain 3 of the other subunit. Site-directed mutagenesis has shown that the interface between domains 1 and 4 in this unique structure forms the functional epitope. This epitope is similar to those of other members of the cytokine class I receptor family but is novel in that it is formed by two different receptor chains. The chapter also reviews knowledge on the closely related mouse beta(IL-3) receptor and on the alpha-subunit-ligand interactions. The knowledge on the two beta receptors is placed in context with advances in understanding of the structural biology of other members of the cytokine class I receptor family.

Tissue-specific and glucose-responsive expression of the pancreatic derived factor (PANDER) promoter

Pancreatic derived factor (PANDER) is a recently identified cytokine-like protein that is dominantly expressed in the islets of Langerhans of the pancreas. To investigate the mechanism of tissue-specific regulation of PANDER, we identified and characterized the promoter region. The transcriptional start site was identified 520 bp upstream of the translational start codon by 5'-RLM-RACE. Computer algorithms identified several islet-associated and glucose-responsive binding motifs that included A and E boxes, hepatocyte nuclear factors 1 and 4, Oct-1, and signal transducer and activator of transcription 3, and 5. Reporter gene analysis revealed cell type-specific PANDER promoter expression in islet and liver-derived cell lines. Levels of PANDER mRNA were directly concordant to the observed cell type-specific PANDER promoter gene expression. The minimal element was mapped to the 5'-UTR and located between +200 and +491 relative to the transcriptional start site and imparted maximal gene expression. In addition, several putative glucose-responsive binding sites were further functionally characterized to reveal critical regulatory elements of PANDER. The PANDER promoter was demonstrated to be glucose-responsive in a dose-dependent manner in murine insulinoma beta-TC3 cells and primary murine islets, but unresponsive in glucagon-secreting alpha-TC3 cells. Our findings revealed that the 5'-UTR of PANDER contains the minimal element for gene expression and imparts both tissue-specificity and glucose-responsiveness. The regulation of PANDER gene expression mimics that of insulin and suggests a potential biological function of PANDER involved in metabolic homeostasis.

Mechanisms of glucose-induced secretion of pancreatic-derived factor (PANDER or FAM3B) in pancreatic beta-cells

Pancreatic-derived factor (PANDER) is an islet-specific cytokine present in both pancreatic alpha- and beta-cells, which, in vitro, induces beta-cell apoptosis of primary islet and cell lines. In this study, we investigated whether PANDER is secreted by pancreatic alpha- and beta-cells and whether PANDER secretion is regulated by glucose and other insulin secretagogues. In mouse-derived insulin-secreting beta-TC3 cells, PANDER secretion in the presence of stimulatory concentrations of glucose was 2.8 +/- 0.4-fold higher (P < 0.05) than without glucose. Insulin secretion was similarly increased by glucose in the same cells. The total concentration of secreted PANDER in the medium was approximately 6-10 ng/ml (0.3-0.5 nmol/l) after a 24-h culture with glucose. L-Glucose failed to stimulate PANDER secretion in beta-TC3 cells. KCl stimulated PANDER secretion 2.1 +/- 0.1-fold compared with control without glucose. An L-type Ca2+ channel inhibitor, nifedipine, completely blocked both glucose- or KCl-induced insulin and PANDER secretion. In rat-derived INS-1 cells, glucose (20 mmol/l) stimulated PANDER secretion 4.4 +/- 0.9-fold, while leucine plus glutamine stimulated 4.4 +/- 0.7-fold compared with control without glucose. In mouse islets overexpressing PANDER, glucose (20 mmol/l) stimulated PANDER secretion 3.2 +/- 0.5-fold (P < 0.05) compared with basal (3 mmol/l glucose). PANDER was also secreted by alpha-TC3 cells but was not stimulated by glucose. Mutations of cysteine 229 or of cysteines 91 and 229 to serine, which may form one disulfide bond, and truncation of the COOH-terminus or NH2-terminus of PANDER all resulted in failure of PANDER secretion, even though these mutant or truncated PANDERs were highly expressed within the cells. In conclusion, we found that 1) PANDER is secreted from both pancreatic alpha- and beta-cells, 2) glucose stimulates PANDER secretion dose dependently in beta-cell lines and primary islets but not in alpha-cells, 3) PANDER is likely cosecreted with insulin via the same regulatory mechanisms, and 4) structure and conformation is vital for PANDER secretion.

Cloning and characterization of the gene encoding growth hormone in finback whale (Balaenoptera physalus)

In mammals growth hormone (GH) is generally a strongly conserved protein, reflecting a slow rate of molecular evolution. However, during primate and artiodactyl evolution episodes of rapid change occurred, so that the GHs of higher primates and ruminants differ markedly from those of other mammals. To extend knowledge of GH evolution in Cetartiodactyla (Artiodactyla plus Cetacea) we have previously characterized GH genes from several members of this group, including the common dolphin. Surprisingly the sequence deduced for dolphin GH differed at several residues from that described previously for another cetacean, finback whale. To investigate this anomaly we have now cloned and characterized the GH gene from finback whale. The overall organization of this gene is similar to that of dolphin, and the deduced amino acid sequence of finback whale GH differs from that of dolphin GH at only residue 47, and from that of pig GH at only residue 149. Phylogenetic analysis of the data provides further support for inclusion of Cetacea within the order Cetartiodactyla, as sister group of Hippopotamidae. The results support the idea that in Cetartiodactyla a burst of rapid evolution of GH occurred after the separation of the line leading to ruminants from other cetartiodactyls. Overall, the GH gene in cetaceans appears to be evolving more slowly than in most other cetartiodactyls.

The role of growth hormone-receptor antagonism in relation to acromegaly

Acromegaly is a rare but disabling condition associated with reduced life expectancy. It is caused almost invariably by a growth hormone-secreting pituitary adenoma. Transsphenoidal surgery and/or radiotherapy are still considered to be the treatment of choice, but despite recent advances in both these forms of treatment, the overall surgical cure rate remains approximately 60%, and radiotherapy is characterised by delayed effect and a high incidence of hypopituitarism. Medical therapy in the form of dopamine agonists and somatostatin analogues has traditionally been used as an adjunct to surgery and/or radiotherapy, but is increasingly being used as first line therapy in the treatment of acromegaly. Recently, a third form of medical therapy, the growth hormone receptor antagonist, pegvisomant, has been licensed for use in acromegaly. This article examines the design, properties, clinical efficacy and safety of pegvisomant.

Episodic molecular evolution of pituitary growth hormone in Cetartiodactyla

The sequence of growth hormone (GH) is generally strongly conserved in mammals, but episodes of rapid change occurred during the evolution of primates and artiodactyls, when the rate of GH evolution apparently increased substantially. As a result the sequences of higher primate and ruminant GHs differ markedly from sequences of other mammalian GHs. In order to increase knowledge of GH evolution in Cetartiodactyla (Artiodactyla plus Cetacea) we have cloned and characterized GH genes from camel (Camelus dromedarius), hippopotamus (Hippopotamus amphibius), and giraffe (Giraffa camelopardalis), using genomic DNA and a polymerase chain reaction technique. As in other mammals, these GH genes comprise five exons and four introns. Two very similar GH gene sequences (encoding identical proteins) were found in each of hippopotamus and giraffe. The deduced sequence for the mature hippopotamus GH is identical to that of dolphin, in accord with current ideas of a close relationship between Cetacea and Hippopotamidae. The sequence of camel GH is identical to that reported previously for alpaca GH. The sequence of giraffe GH is very similar to that of other ruminants but differs from that of nonruminant cetartiodactyls at about 18 residues. The results demonstrate that the apparent burst of rapid evolution of GH occurred largely after the separation of the line leading to ruminants from other cetartiodactyls.

Interleukin-10 and related cytokines and receptors

The Class 2 alpha-helical cytokines consist of interleukin-10 (IL-10), IL-19, IL-20, IL-22, IL-24 (Mda-7), and IL-26, interferons (IFN-alpha, -beta, -epsilon, -kappa, -omega, -delta, -tau, and -gamma) and interferon-like molecules (limitin, IL-28A, IL-28B, and IL-29). The interaction of these cytokines with their specific receptor molecules initiates a broad and varied array of signals that induce cellular antiviral states, modulate inflammatory responses, inhibit or stimulate cell growth, produce or inhibit apoptosis, and affect many immune mechanisms. The information derived from crystal structures and molecular evolution has led to progress in the analysis of the molecular mechanisms initiating their biological activities. These cytokines have significant roles in a variety of pathophysiological processes as well as in regulation of the immune system. Further investigation of these critical intercellular signaling molecules will provide important information to enable these proteins to be used more extensively in therapy for a variety of diseases.

Growth hormone and glucose metabolism: the model of the GH-receptor antagonists

Pegvisomant is a GH analogue that includes a single amino acid substitution at position 120 that generates the GHR antagonist. Additional changes include amino acid substitutions within binding site 1 and a further modification by the addition of polyethylene glycol moieties that increase the half-life and reduce the immunogenicity of the molecule. In acromegalics, pegvisomant is the most effective treatment for normalizing the IGF-I, and pegvisomant significantly improves insulin sensitivity in patients suffering from acromegaly. However, there are simply no data available that might support a role for pegvisomant treatment in disorders in which glucose metabolism is disturbed and in which reducing GH action would be theoretically beneficial.

Recombinant goldfish growth hormones (gfGH-I and -II) expressed in Escherichia coli have similar biological activities

Complementary DNA regions coding for two different mature goldfish growth hormones (gfGH-I and gfGH-II) with four and five cysteine residues were cloned into the bacterial expression vector, pRSETA. The recombinant gfGH-I (five cysteines) and -II (four cysteines) were produced in Escherichia coli as the fusion proteins carrying N-terminal 6XHis tag, which facilitates purification by using metal chelating affinity chromatography under denaturing condition with urea. The recombinant hormones were further refolded by gradually removing the urea. Native gfGH was also purified from goldfish pituitary glands and served as a positive control in the present study. The native and recombinant hormones were tested in goldfish hepatic radioreceptor assay and in vitro Spi 2.1 promoter activation assay. Our results showed that the two recombinant gfGHs are biologically active, and they have similar biological activities despite their having different cysteine contents.

Growth hormone receptor antagonists: discovery, development, and use in patients with acromegaly

An understanding of the events that occur during GH receptor (GHR) signaling has facilitated the development of a GHR antagonist (pegvisomant) for use in humans. This molecule has been designed to compete with native GH for the GHR and to prevent its proper or functional dimerization-a process that is critical for GH signal transduction and IGF-I synthesis and secretion. Clinical trials in patients with acromegaly show GHR blockade to be an exciting new mode of therapy for this condition, and pegvisomant may have a therapeutic role in diseases, such as diabetes and malignancy, in which abnormalities of the GH/IGF-I axis have been observed. This review charts the discovery and development of GHR antagonists and details the experience gained in patients with acromegaly.

Protein folding by a quasi-static-like process: a first-order state transition

In this paper we report that quasi-static-like processes, in which stable intermediates were introduced carefully and deliberately, may be used to reversibly unfold and refold purified native porcine growth hormone. Through circular dichroism (CD) and dynamic light scattering (DLS), we were able to study the secondary structure conformational changes, tertiary structure thermal stabilities, and the particle size distributions of both the intermediates and the final folded product. The CD data showed that the secondary structure was restored in the initial folding stage, whereas the tertiary structure within the protein was restored one step before the last folding stage, as elucidated by thermal stability experiments. DLS analysis suggested that the average hydrodynamic radii of the folding intermediates shrunk to nativelike size immediately after the first folding stage. Our data suggested that the denaturant-containing protein folding reaction is a first-order-like state transition process. This quasi-static-like process may be useful in the prevention of aggregate formation in protein purification and thus can be used in protein engineering to improve the overall yield from harvesting proteins.

Cloning, expression, and initial characterization of a novel cytokine-like gene family

We report the identification and characterization of a novel cytokine-like gene family using structure-based methods to search for novel four-helix-bundle cytokines in genomics databases. There are four genes in this family, FAM3A, FAM3B, FAM3C, and FAM3D, each encoding a protein (224-235 amino acids) with a hydrophobic leader sequence. Northern analysis indicates that FAM3B is highly expressed in pancreas, FAM3D in placenta, and FAM3A and FAM3C in almost all tissues. Immunohistochemistry showed that FAM3A is expressed prominently in the vascular endothelium, particularly capillaries. We found that FAM3A and FAM3B protein were both localized to the islets of Langerhans of the endocrine pancreas. Recombinant FAM3B protein has delayed effects on beta-cell function, inhibiting basal insulin secretion from a beta-cell line in a dose-dependent manner.

Cloning and characterisation of the GH gene from the common dolphin (Delphinus delphis)

The sequence of growth hormone (GH) is generally strongly conserved in mammals, but episodes of rapid change occurred during the evolution of primates and artiodactyls, when the rate of GH evolution apparently increased at least 50-fold. As a result, the sequences of human and ruminant GHs differ substantially from those of other non-primate GHs. Recent molecular studies have suggested that cetaceans are closely related to artiodactyls and may be deeply nested within the artiodactyl phylogenetic tree. To extend the knowledge of GH in Cetartiodactyla (Artiodactyla plus Cetacea), we have cloned and characterised a single GH gene from the common dolphin (Delphinus delphis), using genomic DNA and a polymerase chain reaction technique. As in other mammals, the dolphin GH gene comprises five exons and four introns. The deduced sequence for the mature dolphin GH differs from that of pig at two residues only, showing that the apparent burst of rapid evolution of GH occurred largely after the separation of cetaceans and ruminants.

Gene expression of colony-stimulating factors and stem cell factor after myocardial infarction in the mouse

Recent studies have suggested that cytokines such as macrophage colony-stimulating factor (M-CSF) might be involved in the pathogenesis of ischaemic heart disease. Macrophage colony-stimulating factor, granulocyte-colony stimulating factor (G-CSF), granulocyte-macrophage-colony stimulating factor (GM-CSF), stem cell factor (SCF), interleukin-3 (IL-3) and interleukin-7 (IL-7) are potent cytokines belonging to the same structual class that may affect function, growth and apoptosis both in the heart and other organs. The aims of the present study were to characterize a post-infarction model in the mouse and to examine mRNA expression of M-CSF, GM-CSF, SCF, IL-3 and IL-7 during the development of heart failure. Myocardial infarction (MI) was induced in mice by ligation of the left coronary artery. Average infarct size was 40% and the mice developed myocardial hypertrophy and pulmonary oedema. Ribonuclease (RNAase) protection assays showed abundant cardiac expression of M-CSF and SCF. After MI, we measured down-regulation of cytokine mRNA expression in the heart (M-CSF, SCF), lung (M-CSF), liver (M-CSF) and spleen (M-CSF) compared with sham. Cardiac G-CSF, GM-CSF and IL-7 mRNAs were not detected. In conclusion, abundant cardiac gene expression of M-CSF and SCF was found. In our mouse model of MI, M-CSF and SCF were down-regulated in the heart and several other organs suggesting specific roles for these cytokines during development of ischaemic heart failure.

Molecular cloning of growth hormone encoding cDNA of Indian major carps by a modified rapid amplification of cDNA ends strategy

A modified rapid amplification of cDNA ends (RACE) strategy has been developed for cloning highly conserved cDNA sequences. Using this modified method, the growth hormone (GH) encoding cDNA sequences of Labeo rohita, Cirrhina mrigala and Catla catla have been cloned, characterized and overexpressed in Escherichia coli. These sequences show 96-98% homology to each other and are about 85% homologous to that of common carp. Besides, an attempt has been made for the first time to describe a 3-D model of the fish GH protein.

Receptor dimerization in GH and erythropoietin action--it takes two to tango, but how?

The receptors for GH and erythropoietin are members of the cytokine receptor superfamily. They are single membrane-spanning proteins that bind ligand in the extracellular domain and couple to cytosolic JAK tyrosine kinases to initiate signaling. The ligand-engaged GH receptor (GHR) and erythropoietin receptor (EpoR) extracellular domains are believed to exist in a dimerized configuration in which a single ligand molecule engages two receptor extracellular domains. The last several years have witnessed a rapid expansion in our knowledge of the structural and functional details of this dimerization process and have forced a reexamination of how the ligand-containing complexes achieve their conformation. For EpoR, there is good evidence that the unliganded receptor is already a preformed dimer that is activated by a ligand-induced change in the receptor conformation. Owing in some measure to the unavailability of the analogous crystal structure of the unliganded GHR extracellular domain, it is still unknown whether GHR adopts a similar preformed dimer/conformational change in response to GH as is found for EpoR. This review critically examines the state of our knowledge pertaining to GHR and EpoR dimerization, noting differences and similarities between the two.

Dissolution behavior of porcine somatotropin with simultaneous gel formation and lysine Schiff-base hydrolysis

The primary goal of this work was to develop a reliable in vitro dissolution model to evaluate the effects of Schiff-base hydrolysis and gel formation on the dissolution kinetics of pellets of porcine somatotropin (pST) and pST conjugated with ortho-vanillin (ov-pST) via Schiff-base formation, in an effort to develop an extended-release pST implant. Experimentally, dissolution was investigated as a function of ov concentration in pH 7.4, phosphate buffered saline under sink conditions where steady-state (constant flux) dissolution is typically observed. However, the resulting dissolution profiles displayed variable release rates due to gel formation at the solid-liquid interface, which impeded pST release. Chemical modification of pST with ov reduced gel formation and also resulted in much lower release rates. A mathematical model was developed that quantitatively accounts for changes in dissolution rates due to transient gel formation via irreversible aggregation, along with the effects of reversible Schiff-base hydrolysis involving ov, and predicts dissolution rates in the presence of ov decrease due to the much lower solubility of ov-pST. Our results indicate that although ov-pST is less prone to aggregate, pST/ov-pST equilibration is rapid compared to dissolution and therefore aggregation remains the limiting factor, and ultimately precludes this approach as a viable extended-release delivery system.

Relative localization of the prolactin receptor binding sites for lactogenic hormones

A monoclonal antibody termed MAb R7B4, directed to an epitope present in prolactin receptors (PRLRs), was used as a tool to map the receptor binding sites for human growth hormone (hGH), ovine prolactin (oPRL) and human placental lactogen (hPL). Although the three hormones completely inhibited the binding of each other to Nb2 cells or rat liver receptors, MAb R7B4 behaviour was different depending on the hormone tested and the receptor source. According to the MAb effects, PRLR from Nb2 cells would locate both hGH and oPRL close to R7B4 epitope, whereas hPL would bind far from the MAb binding site. On the other hand, PRLR from rat liver should bind hGH close to the R7B4 epitope but oPRL and hPL would be recognized by a separate region of the same receptor. Thus, results presented in this paper suggest that PRLR binding sites for hGH, oPRL and hPL do not exactly overlap in spite of full competition between ligands.

The place of pegvisomant in the management of acromegaly

Conventional treatments for acromegaly include surgery, radiotherapy, dopamine agonists and somatostatin (SMS) analogues, which effect disease control by lowering circulating growth hormone (GH). Due to variability in tumour characteristics, combinations of these treatment modalities leave a significant number of patients with sub-optimal serum GH and insulin-like growth factor-I (IGF-I) levels, which have been linked to increased morbidity and mortality. The GH receptor antagonist pegvisomant is a genetically engineered analogue of GH that prevents functional dimerisation of the growth hormone receptor (GHR); a process that is critical to GH action at the cellular level. A crucial amino acid substitution at Gly(120) to Arg(120) within the third alpha helix of the antagonist prevents functional GHR dimerisation. Pegvisomant represents a novel treatment for acromegaly as, unlike existing treatment modalities, the effectiveness of pegvisomant is independent of pituitary tumour characteristics. Initial clinical studies in patients with active acromegaly have demonstrated serum IGF-I normalisation in over 90% of patients receiving 20 mg per day, such that, in terms of serum IGF-I normalisation, pegvisomant now represents the most effective medical treatment for acromegaly. Although there are limited long-term data on the use of pegvisomant and questions regarding pituitary tumour growth and altered liver function remain, this therapy offers the prospect of serum IGF-I normalisation in the vast majority of patients with active acromegaly.

Molecular evolution of growth hormone (GH) in Cetartiodactyla: cloning and characterization of the gene encoding GH from a primitive ruminant, the chevrotain (Tragulus javanicus)

In mammals the sequence of pituitary growth hormone (GH) is generally strongly conserved, indicating a slow basal rate of molecular evolution. However, on two occasions, during the evolution of primates and that of cetartiodactyls, the rate of evolution has increased dramatically (25 to 50-fold) so that the sequences of human and ruminant GHs differ markedly from those of other mammalian GHs. To define further the burst of GH evolution that occurred in cetartiodactyls, the GH gene of the chevrotain (Tragulus javanicus) has been cloned and characterized by use of genomic DNA and a polymerase chain reaction technique. Two very similar gene sequences, which probably reflect allelic variation, were isolated. The deduced sequence for the mature chevrotain GH differs from that of the bovine or red deer GH at only two to three residues, and phylogenetic analysis shows that the burst of rapid evolution of GH that occurred in the Cetartiodactyla must have been completed before the divergence of the Tragulidae and the advanced ruminants (Pecora). The rate of evolution during this burst must therefore have been greater than previously estimated. In other aspects (including signal sequence, 5' upstream sequence, and synonymous substitutions in the coding sequence), the chevrotain GH gene differs considerably from the GH genes of other ruminants and here there is no evidence for the period of accelerated evolution that is seen for GH itself.

Instability studies of porcine somatotropin in aqueous solutions and the possible reagents for its stabilization

The instability of porcine somatotropin (pST) in various solutions and possible stabilization of the hormone by sugars and mild detergents were studied. Aggregation and decomposition of the hormone molecules in various pH solutions and under presence of sugar or detergent were monitored by gel permeation chromatography (GPC) or ultraviolet spectroscopy (UV). The pST is a very unstable hormone in an aqueous environment. It was found in this project that the peptide hormone underwent aggregation or decomposition quickly in acidic and alkaline solutions but slowly in neutral pH solutions. High losses of pST monomers were seen in concentrated solutions of the hormone. On the other hand, pST monomers were stabilized to a certain degree in glucose solutions and at a low concentration of urea. These results should facilitate the development of efficient controlled-release systems which are essential for commercializing porcine somatotropin.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Ovine placental lactogen and ovine prolactin: partial proteolysis and conformational stability

The high-resolution structure of ovine placental lactogen (oPL) and ovine prolactin (oPRL), not yet established in detail, was probed by limited proteolysis with the Glu-specific protease from Staphylococcus aureus V8. While in hGH there were no cleavage sites inside of any of the four alpha-helices, the analysis of the fragments obtained after partial proteolysis of oPL showed a site of cleavage at the putative third helix, suggesting that this helix is partially unwound at this point. The partial proteolysis of the rest of the molecule was compatible with a similar folding pattern for oPL, hGH and pGH, on the basis of the crystal structure of these last hormones. In the case of oPRL, proteolytic cleavage occurred at Glu residues which would be located at the end of the first helix and the beginning of the second in the hGH folding model, suggesting that these helices are shorter in oPRL than in hGH. In order to gain further insight on the folding of these molecules, circular dichroism and intrinsic fluorescence measurements were used to examine the effect of denaturing conditions on oPL and oPRL. After exposure to 6 M guanidine the unfolding of both proteins was completely reversed upon elimination of the denaturing agent. In contrast, exposure to pH 3.0 caused an irreversible decrease in the alpha-helical content in both hormones, most striking for oPL, indicating that this hormone is less stable than oPRL or hGH.

Solution structure and backbone dynamics of long-[Arg(3)]insulin-like growth factor-I

Long-[Arg(3)]insulin-like growth factor-I (IGF-I) is a potent analog of insulin-like growth factor-I that has been modified by a Glu(3) --> Arg mutation and a 13-amino acid extension appended to the N terminus. We have determined the solution structure of (15)N-labeled Long-[Arg(3)]-IGF-I using high resolution NMR and restrained molecular dynamics techniques to a precision of 0.82 +/- 0.28 A root mean square deviation for the backbone heavy atoms in the three alpha-helices and 3.5 +/- 0.9 A root mean square deviation for all backbone heavy atoms excluding the 8 N-terminal residues and the 8 C-terminal eight residues. Overall, the structure of the IGF-I domain is consistent with earlier studies of IGF-I with some minor changes remote from the N terminus. The major variations in the structure, compared with IGF-I, occur at the N terminus with a substantial reorientation of the N-terminal three residues of the IGF-I domain. These results are interpreted in terms of the lower binding affinity for insulin-like growth factor-binding proteins. The backbone dynamics of Long-[Arg(3)]IGF-I were investigated using (15)N nuclear spin relaxation and the heteronuclear nuclear Overhauser enhancement (NOE). There is a considerable degree of flexibility in Long-[Arg(3)]IGF-I, even in the alpha-helices, as indicated by an average ((1)H)(15)N NOE of 0.55 for the regions. The largest heteronuclear NOEs are observed in the helical regions, lower heteronuclear NOEs are observed in the C-domain loop separating helix 1 from helix 2, and negative heteronuclear NOEs are observed in the N-terminal extension and at the C terminus. Despite these data indicating conformational flexibility for the N-terminal extension, slow amide proton exchange was observed for some residues in this region, suggesting some transitory structure does exist, possibly a molten helix. A certain degree of flexibility may be necessary in all insulin-like growth factors to enable association with various receptors and binding proteins.

Epitope randomization redefines the functional role of glutamic acid 110 in interleukin-5 receptor activation

Sequence randomization through functional phage display of single chain human interleukin (IL)-5 was used to investigate the limits of replaceability of the Glu(110) residues that form a part of the receptor-binding epitope. Mutational analysis revealed unexpected affinity for IL-5 receptor alpha chain with variants containing E110W or E110Y. Escherichia coli-expressed Glu(110) variants containing E110W in the otherwise sequence-intact N-terminal half, including a variant with an E110A replacement in the sequence-disabled C-terminal half, were shown by their CD spectra to be folded into secondary structures similar to that of single chain human IL-5 (scIL-5). Biosensor kinetics analysis revealed that (E110W/A5)scIL-5 and (E110W/A6)scIL-5 had receptor alpha chain binding affinities similar to that of (wt/A5)scIL-5. However, (E110W/A6)scIL-5 had a significantly reduced bioactivity in TF-1 cell proliferation compared with both (wt/A5)scIL-5 and (E110W/A5)scIL-5, and this activity reduction was disproportionately greater than the much smaller effect of Glu(110) mutation on receptor binding affinity. The marked and disproportionate decrease in TF-1 proliferation observed with (E110W/A6)scIL-5 suggests a role for Glu(110) in the biological activity mediated by the signal transducing receptor betac subunit of the IL-5 receptor. This is also consistent with the lack of stimulation of JAK2 phosphorylation by the (E110W/A6)scIL-5 mutant in recombinant 293T cells, as compared with the concentration-dependent stimulation seen for scIL-5. The results reveal the dispensability of charge in the Glu(110) locus of IL-5 for receptor alpha chain binding and, in contrast, its heretofore underappreciated importance for receptor activation.

Molecular recognition events involved in the activation of the growth hormone receptor by growth hormone

Binding of growth hormone (GH) to its receptor (GHR) is a well-studied example of molecular recognition between a cytokine and its receptor. Extensive mutagenesis studies and several crystal structures have defined the key interactive amino acid residues that are involved in binding and subsequent receptor dimerization. This review encompasses each of the three molecular recognition events involved in GHR activation, namely binding of GH to its two receptors and the interactions that occur between these receptors. Particular attention is given to species and ligand specificity of hormone binding and to the molecular recognition events involved in receptor activation, including the possibility that a conformational change in the receptor is required.

Biological properties of human prolactin analogs depend not only on global hormone affinity, but also on the relative affinities of both receptor binding sites

Zinc increases the affinity of human growth hormone (hGH) for the human prolactin receptor (hPRLR) due to the coordination of one zinc ion involving Glu-174(hGH) and His-18(hGH). In contrast, binding of hPRL to the hPRLR is zinc-independent. We engineered in binding site 1 of hPRL a hGH-like zinc coordination site, by mutating Asp-183(hPRL) (homologous to Glu-174(hGH)) into Glu (D183E mutation). This mutation was also introduced into G129R hPRL, a binding site 2 mutant (Goffin, V., Kinet, S., Ferrag, F., Binart, N., Martial, J. A. , and Kelly, P. A. (1996) J. Biol. Chem. 271, 16573-16579). These analogs were characterized using a stable clone expressing both the hPRLR and a PRLR-responsive reporter gene. The D183E mutation per se decreases the binding affinity and transcriptional activity of hPRL. However, this loss is partially rescued by the addition of zinc and the effect is much more marked on bioactivity than on binding affinity. These data indicate that the D183E mutation confers zinc sensitivity to hPRL biological properties. Due to an impaired site 2, the agonistic activity of G129R analog is almost nil. Although the double mutant D183E/G129R displays lower affinity ( approximately 1 log) compared with G129R hPRL, it unexpectedly recovers partial agonistic activity in the absence of zinc. Moreover, whereas zinc increases the affinity of D183E/G129R, it paradoxically abolishes its agonistic activity. Our results demonstrate that the biological properties of hPRL analogs do not necessarily parallel their overall affinity. Rather, the relative affinities of the individual binding sites 1 and 2 may play an even more important role.

Transgenic models of growth hormone action

A growth-promoting principle of the pituitary gland was discovered in 1921, and bovine growth hormone (GH) was isolated in 1944. Since then, the structure of GH as it relates to its biological activities has been an exciting research topic. Equally fascinating is the relationship between GH structure and its metabolic activities. In attempts to define some of these activities, several investigators have used GH transgenic mice as models. In this review we summarize what is known about the molecular mechanisms of GH action. We then describe some of the GH transgenic models and point out potential targets for nutrition research.

Ovine placental lactogen and human growth hormone bind to different regions of the same receptors

Anti-human growth hormone (hGH) polyclonal and monoclonal antibodies (MAb) failed to recognize ovine placental lactogen (oPL), indicating that the antigenic topographies of both hormones are different. Binding assays showed that oPL completely inhibited hGH binding to lactogenic receptors from Nb2-cells and to somatogenic receptors from rabbit or sheep liver; in contrast, oPL only bound to a subpopulation of rat liver receptors. Zinc ion increased hGH and oPL binding to Nb2-cell receptors and slightly inhibited both hormones' recognition by somatogenic receptors. However, ZnCl(2) increased hGH binding to rat liver microsomes but prevented that of oPL. Furthermore, MAb R7B4, recognizing lactogenic as well as somatogenic receptors, entirely blocked hGH binding to the various receptor systems but not affected oPL binding. Therefore, results presented in this paper suggest that oPL and hGH bind to different regions of the same receptors.

Crystal structure of ovine interferon-tau at 2.1 A resolution

Ovine interferon-tau (ovIFN-tau) is a pregnancy recognition hormone required for normal embryonic development in sheep. In addition to its novel role in reproductive physiology, ovIFN-tau displays antiviral and antiproliferative activities similar to the IFN-alpha subtypes. To probe the structural basis for its unique activity profile, the crystal structure of ovIFN-tau has been determined at 2.1 A resolution. The fold of ovIFN-tau is similar to the previously determined crystal structures of human IFN-alpha2b and human and murine IFN-beta, which each contain five alpha-helices. Comparison of ovIFN-tau with huIFN-alpha2b, huIFN-beta, and muIFN-beta reveals unexpected structural differences that occur in regions of considerable sequence identity. Specifically, main-chain differences up to 11 A occur for residues in helix A, the AB loop, helix B, and the BC loop. Furthermore, these regions are known to be important for receptor binding and biological activity. Of particular interest, a buried ion pair is observed in ovIFN-tau between Glu71 and Arg145 which displaces a conserved tryptophan residue (Trp77) from the helical bundle core. This ion pair represents a major change in the core of ovIFN-tau compared to huIFN-alpha2b. Based on amino acid sequence comparisons, these ovIFN-tau structural features may be conserved in several human IFN-alpha subtypes and IFN-omega. The structure identifies potential problems in interpreting site-directed mutagenesis data on the human IFN-alpha family that consists of 12 proteins.

GH kinase activity in bovine anterior pituitary subcellular fractions

Growth hormone (GH) and prolactin (PRL) share significant structural homology. We have previously characterized the phosphorylation of bovine PRL and wish to determine whether a similar kinase activity phosphorylates bovine GH. Phosphorylation of bovine GH was performed using [alpha-32P]ATP labeling of subcellular fractions. Bovine GH phosphorylation was dependent on Zn2+ or Cu2+ with apparent Km's of 0.9 and 1.0 mM, respectively, and a pH maxima of 7.0. The apparent Km's of bovine GH kinase activity for exogenous bovine GH and ATP were 30 microM and 376 microM, respectively. Exogenous bovine PRL served as a competitive substrate, increasing the apparent Km for bovine GH by threefold compared to the Km determined without exogenous bovine PRL. We conclude: 1) in vitro phosphorylation of bovine GH occurs under conditions that are consistent with those found in anterior pituitary cells, and 2) a similar kinase activity phosphorylates both bovine PRL and GH.

Cloning and phylogenetic relationship of red drum somatolactin cDNA and effects of light on pituitary somatolactin mRNA expression

The nucleotide sequence for red drum somatolactin (SL) cDNA was determined and the expression of pituitary SL mRNA was examined in red drum kept under various light conditions. A full length of SL cDNA (1629 bp) was isolated and characterized from a red drum pituitary cDNA library. The SL cDNA has an open reading frame of 696 nucleotides which encodes a 24-amino-acid signal peptide and a 207-amino-acid mature peptide. Red drum SL shares 58-87% amino acid sequence identity and 56-85% nucleotide sequence identity with other teleost SLs. The characteristic seven cysteine residues and one N-glycosylation site of SL are well conserved in the red drum SL mature peptide. Phylogenetic analysis shows that red drum SL is closely related to seabream SL and is also closely related to lumpfish, flounder, halibut, and sole SLs, whereas SLs of Atlantic cod, chum salmon, rainbow trout, and eel are more distantly related to those of the more advanced teleosts. Two SL transcripts, designated as SL I at 1.8 kb and SL II at 1.3 kb, are expressed in red drum pituitaries and correspond to two polyadenylation signal sites in red drum SL cDNA at nucleotide positions 1554 and 1270. Levels of the SL I mRNA were 2- to 4-fold higher in pituitaries of blind red drum and intact fish kept under constant darkness for 1 week than those in control fish sampled during the light phase of the light-dark cycle. Similarly, pituitary levels of SL II mRNA were 9-fold higher in blind fish and 1.6- to 4-fold higher in intact fish kept under constant darkness than in the control fish. Furthermore, these changes in mRNA levels in pituitaries were accompanied by more than 10-fold increases in SL protein concentrations in plasma. The finding that the absence of light perception for extended periods leads to dramatic increases in SL mRNA expression as well as SL secretion in red drum provides further evidence that illumination levels and SL physiology are intimately related in this species.

Tuftsin: on the 30-year anniversary of Victor Najjar's discovery

After a short description of the results of Victor Najjar's research on tuftsin and of the discoveries done by other authors in the early stage of tuftsin investigation, the current state of work on tuftsin is presented, based mainly on the literature published in the years 1984-1997. The presentation follows this order: the occurrence of tuftsin and retro-tuftsin sequences in proteins, their synthesis and biology, the antigenic properties of tuftsin, its influence on phagocytic cells, and other biologic activities of tuftsin, including antimicrobial, antiviral, antitumor and central effects, and the search for tuftsin superactive analogs.

Raman spectroscopic studies of a dimeric form of recombinant bovine growth hormone

Lyophilized dimeric recombinant bovine growth hormone (r-bGH) produced through incubation of r-bGH at 37 degrees C and 96% relative humidity for 8 days was examined by Raman spectroscopy. The secondary structure of the dimeric material is comparable to that of nonincubated r-bGH, due to the high similarity of the amide I, III, and V vibrational envelopes of the two samples. The dimeric material exhibits disulfide stretching that is indicative of the presence of only one disulfide bond (Cys53-Cys164). No sulfhydryl S-H stretching vibrations are observed, suggesting that cysteines from the cleaved disulfide bridge (Cys181-Cys189) are bound to nonsulfur atoms. Either high humidity (96%) or mild heat (37 degrees C) alone will cleave only one disulfide bond, but the final products are different. Incubation at ambient temperature and high humidity leads to a significant secondary structural change, while mild heat at very low humidity does not alter r-bGH secondary structure. Spectral data for incubations solely in mild heat are consistent with r-bGH structures that have lost the small loop (Cys181-Cys189) disulfide bridge, while incubations under only high humidity conditions are compatible with what would be expected if the large loop (Cys53-Cys164) cystine link was broken. Mild heat and high humidity are both present in dimer formation, yet only the small loop bridge is severed. The data suggest that heat may be the primary factor in determining which cystine link is broken. More severe heating (75 degrees C) cleaves both cystines and alters both secondary and tertiary structure.

Augmentation of hormonal activities with antibodies from cattle immunized with a combination of synthetic and recombinant growth hormone peptide

Antibodies generated against a synthetic growth hormone (GH) peptide in a number of animal species were shown to enhance the efficacy of GH. However, the ability to produce the effective antibodies diminished over time and repeated boosters failed to overcome the hurdle. Therefore, this study was designed to address the issue on the failed antibody responses by employing different GH peptide antigen preparations in cattle. Holstein steers were repeatedly immunized with a synthetic peptide corresponding to an amino acid sequence 54-95 of porcine GH (pGH). The peptide was conjugated to ovalbumin (OVA) as a carrier. Animals initially responded to the antigen well and elicited antibodies specific to the peptide. However, the 4th challenge with the same OVA-peptide antigen rendered animals unresponsive, resulting in a decline in antibody production. This unresponsiveness was overcome by switching the antigen at the 5th immunization from OVA-peptide to a recombinant peptide preparation which was composed of maltose binding protein (MBP) as a carrier. Antibodies generated in cattle after the 5th immunization recognized not only the pGH(54-95) peptide, but also bovine GH (bGH) and pGH. These antibodies were not immunoreactive with an unrelated control peptide. Hypophysectomized (hypox) rats were used for functional analysis and bGH was active in promoting the growth of these GH-deficient rats. The growth-promoting effect of bGH was significantly enhanced by mixing it with bovine anti-peptide antibodies prior to administration. Therefore, the present findings suggest that peptide 54-95 induces cattle to elicit antibodies capable of not only recognizing bGH but also augmenting the somatogenic effectiveness of bGH in hypox rats.

Augmentation of hormonal activities with antibodies from cattle immunized with a combination of synthetic and recombinant growth hormone peptide

Antibodies generated against a synthetic growth hormone (GH) peptide in a number of animal species were shown to enhance the efficacy of GH. However, the ability to produce the effective antibodies diminished over the time and repeated boosters failed to overcome the hurdle. Therefore, this study was designed to address the issue on the fallen antibody responses by employing different GH peptide antigen preparations in cattle. Holstein steers were repeatedly immunized with a synthetic peptide corresponding to an amino acid sequence 54-95 of porcine GH (pGH). The peptide was conjugated to ovalbumin (OVA) as a carrier. Animals initially responded to the antigen well and elicited antibodies specific to the peptide. However, the 4th challenge with the same OVA-peptide antigen rendered animals unresponsive, resulting in a decline in antibody production. This unresponsiveness was overcome by switching the antigen at the 5th immunization from OVA-peptide to a recombinant peptide preparation which was composed of maltose binding protein (MBP) as a carrier. Antibodies generated in cattle after the 5th immunization recognized not only the pGH(54-95) peptide, but also bovine GH (bGH) and pGH. These antibodies were not immunoreactive with an unrelated control peptide. Hypophysectomized (hypox) rats were used for functional analysis and bGH was active in promoting the growth of these GH-deficient rats. The growth-promoting effect of bGH was significantly enhanced by mixing with bovine anti-peptide antibodies prior to administration. Therefore, the present findings suggest that peptide 54-95 induces cattle to elicit antibodies capable of not only recognizing bGH but also augmenting the somatogenic effectiveness of bGH in hypox rats.

Biology of somatotropin in growth and lactation of domestic animals

Impressive progress has been made during the past 15 years in our understanding of the biology of somatotropin (ST) in domestic animals. In part, this progress was sparked by advances in biotechnology that made feasible the production of large quantities of recombinant bovine ST (bST) and porcine ST (pST). The availability of recombinant bST and pST resulted in an exponential increase in investigations that explored their role in growth and lactation biology, as well as evaluated their potential for commercial use. Collectively, these studies established that administration of bST to lactating dairy cows increased milk yield, and treatment of growing pigs with pST markedly stimulated muscle growth and reduced fat deposition. In addition to these "efficacy" studies, a substantial number of investigations examined the mechanisms by which ST affects lactation and growth of domestic animals. This review summarizes the diverse physiological effects ST has on growth and lactation and discusses the underlying mechanisms that mediate these effects in domestic animals.