Secretion of authentic 20-kDa human growth hormone (20K hGH) in Escherichia coli and properties of the purified product

Growth hormone receptor agonists and antagonists: From protein expression and purification to long-acting formulations

Recombinant human growth hormone (rhGH) and GH receptor antagonists (GHAs) are used clinically to treat a range of disorders associated with GH deficiency or hypersecretion, respectively. However, these biotherapeutics can be difficult and expensive to manufacture with multiple challenges from recombinant protein generation through to the development of long-acting formulations required to improve the circulating half-life of the drug. In this review, we summarize methodologies and approaches used for making and purifying recombinant GH and GHA proteins, and strategies to improve pharmacokinetic and pharmacodynamic properties, including PEGylation and fusion proteins. Therapeutics that are in clinical use or are currently under development are also discussed.

Biosynthesis and Secretion of Human Tissue Kallikrein in Transgenic Chlamydomonas reinhardtii

The green alga Chlamydomonas reinhardtii was recently been shown to be an effective bio-manufacturing platform for the production of recombinant proteins. The advantage of using C. reinhardtii is that it is fast to grow, inexpensive to culture, and relatively safe. However, the expression of foreign proteins is always low and difficult to purify in C. reinhardtii. Human kallikrein has the potential to be developed into certain drugs, like insulin. Therefore, its biosynthesis is important to drug development. In this study, we synthesized the sg gene, a signal peptide sequence of alkaline phosphatase, and inserted it into a pH124 plasmid, which contains a HSP70A-RBCS2 promoter and a RBCS2 terminator. Then, we inserted the human kallikrein gene klk1 behind the sg sequence to make a pHsgk124 vector. The pHsgk124 were transferred into a cell-wall deficient strain of C. reinhardtii, cc-503, by using the glass bead method. Southern blot analysis showed that sg and klk1 were incorporated into genes of the transgenic C. reinhardtii. RT-PCR analysis showed that it had an active transcription and its expression increased three times under heat stress. Western blot analyses of proteins inside and outside cells (in the culture medium) showed that klk1 was expressed in the cell and the resulting protein was secreted into medium. An enzyme activity assay showed that the recombinant protein had the ability to hydrolyze the specific substrate H-D-Val-Leu-Arg-Pna. In conclusion, we successfully bioengineered C. reinhardtii to produce and secrete human kallikrein protein, which has important biomedical implications.

Growth hormone variants: a potential avenue for a better diagnostic characterization of growth hormone deficiency in children

Human GH (hGH) is a heterogeneous protein hormone consisting of several isoforms. This heterogeneity is the consequence of multiple hGH genes, mRNA splicing, post-translational modifications, and peripheral metabolism, and it represents one important reason for the disparity among GH assay results from different laboratories. However, other factors are involved: a) interference from endogenous GH binding proteins; b) different specificities of anti- GH (monoclonal and polyclonal) antibodies; c) different matrix effects among the calibrators; d) the use of different calibrators. The measurement of GH levels in response to provocative testing is an essential part of the diagnosis of GH deficiency. For this purpose, an accurate, reproducible and universally valid GH measurement would be highly desirable, but, despite a huge number of efforts in clinical biochemistry, this goal remains elusive.

Growth hormone doping in sports: a critical review of use and detection strategies

GH is believed to be widely employed in sports as a performance-enhancing substance. Its use in athletic competition is banned by the World Anti-Doping Agency, and athletes are required to submit to testing for GH exposure. Detection of GH doping is challenging for several reasons including identity/similarity of exogenous to endogenous GH, short half-life, complex and fluctuating secretory dynamics of GH, and a very low urinary excretion rate. The detection test currently in use (GH isoform test) exploits the difference between recombinant GH (pure 22K-GH) and the heterogeneous nature of endogenous GH (several isoforms). Its main limitation is the short window of opportunity for detection (~12-24 h after the last GH dose). A second test to be implemented soon (the biomarker test) is based on stimulation of IGF-I and collagen III synthesis by GH. It has a longer window of opportunity (1-2 wk) but is less specific and presents a variety of technical challenges. GH doping in a larger sense also includes doping with GH secretagogues and IGF-I and its analogs. The scientific evidence for the ergogenicity of GH is weak, a fact that is not widely appreciated in athletic circles or by the general public. Also insufficiently appreciated is the risk of serious health consequences associated with high-dose, prolonged GH use. This review discusses the GH biology relevant to GH doping; the virtues and limitations of detection tests in blood, urine, and saliva; secretagogue efficacy; IGF-I doping; and information about the effectiveness of GH as a performance-enhancing agent.

Surface plasmon resonance in doping analysis

Doping analysis relies on the determination of prohibited substances that should not be present in the body of an athlete or that should be below a threshold value. In the case of xenobiotics their mere presence is sufficient to establish a doping offence. However, in the case of human biotics the analytical method faces the difficulty of distinguishing between endogenous and exogenous origin. For this purpose ingenious strategies have been implemented, often aided by state-of-the-art technological advancements such as mass spectrometry in all its possible forms. For larger molecules, i.e. protein hormones, the innate structural complexity, the heterogeneous nature, and the extremely low levels in biological fluids have rendered the analytical procedures heavily dependent of immunological approaches. Although approaches these confer specificity and sensitivity to the applications, most rely on the use of two, or even three, antibody incubations with the consequent increment in assay variability. Moreover, the requirement for different antibodies that separately recognise different epitopes in screening and confirmation assays further contributes to differences encountered in either measurement. The development of analytical techniques to measure interactions directly, such as atomic force microscopy, quartz crystal microbalance or surface plasmon resonance, have greatly contributed to the accurate evaluation of molecular interactions in all fields of biology, and expectations are that this will only increase. Here, an overview is provided of surface plasmon resonance, and its particular value in application to the field of doping analysis.

Specific monoclonal antibodies and ultrasensitive immunoassays for 20K and 22K human growth hormone

OBJECTIVE

Generation of specific monoclonal antibodies (mAbs) against 20K and 22K human growth hormone (hGH) and development of ultrasensitive immunoassays to quantify 20K and 22K hGH.

DESIGN

Mice were immunized with recombinant 20K or 22K hGH. Hybridoma cells were screened with biotinylated 20K and 22K hGH simultaneously. The specific mAbs were further characterized and used for construction of isoform specific assays. The ultrasensitive chemiluminescent assays were developed with AMDEX streptavidin-HRP and a sensitive substrate.

RESULTS

The 20K hGH specific mAb 1G12 and the 22K hGH specific mAb 5E1 showed less than 0.1% cross-reactivity to 22K or 20K hGH by competitive binding assay, respectively. Western blot analysis also confirmed the specificity of mAb 1G12 and mAb 5E1. Using mAb 1G12 and mAb 5E1, 20K and 22K specific assays with working range of 2-2000 pg/mL were constructed. The 22K hGH concentrations in 103 serum samples from different healthy subjects in the basal GH state were 343.7+/-421.5 pg/mL (18.6-1820 pg/mL). The 20K hGH concentrations were 30.7+/-37.5 pg/mL (2.4-205pg/mL). The ratios of 20K to 20K plus 22K hGH were 9.8+/-4.4% (3.3-28.3%). Both 22K hGH and 20K hGH concentrations in women (465.9+/-476.3 pg/mL and 43.7+/-46.1 pg/mL, n=47) were significantly higher than those (241.1+/-337.0 pg/mL and 20K hGH 19.8+/-23.0 pg/mL, n=56, P<0.01) in men. However, there was no difference in the proportion of 20K to 20K plus 22K between men and women (P>0.05). The strong correlation between 20K and 22K hGH (R=0.914, P<0.01) indicated the constant proportion between 20K and 22K hGH in the basal GH state of healthy subjects.

CONCLUSIONS

Specific monoclonal antibodies and ultrasensitive chemiluminescent immunoassays for 20K and 22K hGH were generated. The ultrasensitive immunoassays are essential for the determination of 20K and 22K hGH in the basal GH state. This universal ultrasensitive immunoassay form can be adapted to other immunoassays for broad application.

20-kDa placental hGH-V has diminished diabetogenic and lactogenic activities compared with 22-kDa hGH-N while retaining antilipogenic activity

Placental human growth hormone-variant (hGH-V) and pituitary human growth hormone-N (hGH-N) are of identical size (22 kDa) but differ in 13 residues scattered throughout the protein. Several isoforms of GH are produced by the hGH-N and hGH-V genes including a 20-kDa hGH-V resulting from a 45-bp deletion caused by the use of an alternative acceptor site within exon 3. To date, the biological properties of the 20-kDa GH-V have not been characterized in vivo. Using young male Wistar rats fed either chow or a high-fat (HF) diet for 4 wk postweaning, we investigated the effect of 7 days treatment with either 22-kDa hGH-N, 20-kDa hGH-V (5 ug x g(-1) x day(-1) sc), or vehicle on body composition and endocrine and metabolic profiles. Total body growth (absolute weight gain and linear growth trajectory) in the 20-kDa hGH-V-treated animals was intermediary between that of control and hGH-N-treated animals. Both 22-kDa hGH-N and 20-kDa hGH-V significantly reduced total body fat mass compared with control animals, and there were no differences between the GH isoforms in anti-lipogenic activity in animals fed the HF diet. Fasting plasma insulin and C peptide were significantly increased in animals on the HF diet and further increased by hGH-N but were unchanged in 20-kDa hGH-V-treated animals compared with saline-treated controls. Plasma volume as assessed by hematocrit was increased in hGH-N-treated animals but was unchanged in 20-kDa hGH-V-treated animals compared with controls. Furthermore, 20-kDa hGH-V had reduced lactogenic (prolactin receptor mediated) activity characteristic of hGH-N as tested in vitro compared with the 20-kDa hGH-N and 22-kDa hGH-N variants. In summary, placental 20-kDa hGH-V retains some of the growth-promoting and all antilipogenic activities of pituitary 22-kDa hGH-N but has diminished diabetogenic and lactogenic properties compared with the native 22-kDa hGH-N.

20K-GH and its use in detecting GH abuse

Following the successful production of recombinant 20K-GH, several studies investigating the physiology of this GH isoform have been undertaken. In this report, we review studies of its biological effect, measurement and secretion. To use serum 20K-GH level in detecting GH abuse, new method has been established and serum 22K-GH, 20K-GH were measured in normal subjects and athletes, and no abnormal results were found among athletes. Another study confirmed that serum 22K-GH increased remarkably and 20K-GH decreased following the exogenous administration of 22K-GH. The duration was relatively short, approximately 24-36h in our and other studies. The increase of the ratio, 22K-GH/20K-GH was the most suitable indicator of GH abuse. Studies supported by the WADA were undertaken in collaboration with an Australian Group. A new approach for the GH isoform assay by beads assay platform is being developed. It is concluded that the direct measurement of 20K-GH is a valid scientific approach, for detecting GH abuse, although the duration of the positive results is short. Our method will be useful in combination with the marker method, an out-of-competition test or test for target cases. Furthermore, its application for the doping test passport is considered to be a possible future strategy.

Growth hormone isoforms

Human growth hormone (GH) is a heterogeneous protein hormone consisting of several isoforms. The sources of this heterogeneity reside at the level of the genome, mRNA splicing, post-translational modification and metabolism. The GH gene cluster on chromosome 17q contains 2 GH genes (GH1 or GH-N and GH2 or GH-V) in addition to 2(-3) genes encoding the related chorionic somatomammotropin. Alternative mRNA splicing of the GH1 transcript yields two products: 22K-GH (the principal pituitary GH form) and 20K-GH. Post-translationally modified GH forms include N(alpha)-acylated, deamidated and glycosylated monomeric GH forms, as well as both non-covalent and disulfide-linked oligomers up to at least pentameric GH. GH fragments generated in the course of peripheral metabolism may be measured in immunoassays for GH. The GH-N gene is expressed in the pituitary, the GH-V gene in the placenta. Secretion of pituitary GH forms is pulsatile under control from the hypothalamus, whereas secretion of placental GH-V is tonic and rises progressively in maternal blood during the 2nd and 3rd trimester. Pituitary GH forms are co-secreted during a secretory pulse; no isoform-specific stimuli have been identified. There are minor differences in somatogenic and metabolic bioactivity among the GH isoforms, depending on species and assay system used. Both 20K-GH and GH-V have poor lactogenic activity. Oligomeric GH forms have variably diminished bioactivity compared to monomeric forms. GH isoforms cross-react in most immunoassays, but assays specific for 22K-GH, 20K-GH and GH-V have been developed. The metabolic clearance of 20K-GH and GH oligomers is delayed compared to that of 22K-GH. The heterogeneous mixture of GH isoforms in blood is further complicated by the presence of two GH-binding proteins, which form complexes with GH; isoform proportions also vary depending on the lag time from a secretory pulse because of different half-lives. GH forms excreted in the urine reflect monomeric GH isoforms in blood, but constitute only a minute fraction of the GH production rate. The heterogeneity of GH is one important reason for the notorious disparity among assay results. It also presents an opportunity for distinguishing endogenous from exogenous GH.

Growth hormone isoforms release in response to physiological and pharmacological stimuli

Ten healthy subjects used to performing regular physical activity and eight subjects affected by idiopathic isolated GH deficiency (GHD) were enrolled; 22- and 20-kDa GH secretion and its biological activity were evaluated in response to pharmacological stimuli such as arginine, L-dopa or glucagon in GHD children, while the hormonal response to exercise was studied according to Bruce protocol in healthy subjects. We found a significant increase in 22- and 20-kDa GH level in healthy subjects after monitored physical exercise (MPE; basal 0.28+/-0.12 vs 7.37+/-2.08 ng/ml and basal 0.076+/-0.04 vs 0.18+/-0.05 ng/ml, respectively). Furthermore, the 22-kDa/20-kDa ratio significantly increased in children who had undergone MPE and the GH bioactivity basal mean value also increased significantly after exercise (basal 2.86+/-0.76 vs 7.64+/-1.9 ng/ml). The mean value of 22-kDa GH in GHD patients increased significantly following GH pharmacological stimulation (2.78+/-0.63 ng/ml) when compared with mean basal (0.20+/-0.11 ng/ml) value. In the GHD group the basal concentration of 20-kDa GH significantly increased following GH pharmacological stimulation (0.34+/-0.11 vs 0.72+/-0.2 ng/ml); the 22-kDa/20-kDa ratio significantly increased too. Likewise, GH bioactivity in children with GHD increased significantly after pharmacological stimulation test (basal 2.53+/-0.56 vs 7.33+/-1.26 ng/ml). Both GH isoform concentrations and their biological activity are significantly increased in healthy subjects after submaximal exercise protocol and in GHD children after pharmacological stimuli.

Large-scale preparation and in vitro characterization of biologically active human placental (20 and 22K) and pituitary (20K) growth hormones: placental growth hormones have no lactogenic activity in humans

Expression plasmids containing DNA sequences optimized for expression in Escherichia coli were prepared encoding human pituitary (hGH-N 20K) and placental (hGH-V 20 and 22K) growth hormones. The proteins were expressed in bacteria, refolded and purified to homogeneity by anion-exchange chromatography on Q-Sepharose according to a unique protocol developed for each protein. The yields from 5l of fermentation culture varied between 400 and 700mg of electrophoretically pure, over 95% monomeric protein. Circular dichroism (CD) analysis revealed similarity of the purified hGHs' secondary structure to that of the pituitary hGH-N 22K, except for hGH-V 20K, in which the alpha-helix content was lower. The purified proteins were stable as a 0.1% sterile solution held at pH 10-11 at 4 degrees C for at least one month. All three purified hGH molecules formed a 1:2 complex with hGH receptor extracellular domain (hGHR-ECD), similar to hGH-N 22K. Binding experiments using hGHR-ECD revealed that the differences between the two 22K variants or between the two 20K variants were not significant, except that hGH-V 20K exhibited slightly lower affinity. Somatogenic activity was tested in vitro using FDC-P1 cell lines. Whereas the bioactivity of 22K hGHs and hGH-N 20K in FDC-P1-9D11 cells stably transfected with hGHR was almost equal and two to threefold higher than that of hGH-V 20K, in FDC-P1 3B9 cells stably transfected with rabbit (rb) GHR, the bioactivity of both 20K analogues was significantly (five to ninefold) lower than that of the 22K hormones. The lactogenic activity measured in heterologous assays (Nb2-11C cells and Baf/3 cells stably transfected with the long form of rabbit prolactin receptor) revealed that the activity of hGH-N 20K was close to that of hGH-N 22K in the Baf/3 cells, but 4.5-fold lower in the Nb2 cells. The activity of hGH-V 22K was ninefold less in Nb2 cells and 55-fold less in Baf/3 cells, whereas hGH-V 20K had no lactogenic activity in either bioassay. In contrast, in a homologous lactogenic assay using Baf/3 LP cells stably transfected with hPRLR, the activity of both placental hGHs was nil and the activity of hGH-N 20K was 4.3-fold lower than that of hGH-N 22K. The latter finding raises the question of whether the lack of intrinsic lactogenic activity in the placental hGHs that dominate during pregnancy has any physiological relevance.

Expression and purification of thioredoxin (TrxA) and thioredoxin reductase (TrxB) from Brevibacillus choshinensis

Brevibacillus choshinensis (formerly Bacillus brevis) is a protein-hyperproducing bacterium and has been used for commercial protein production. Here, we cloned thioredoxin (trxA) and thioredoxin reductase (trxB) genes from B. choshinensis, and expressed the gene products in Escherichia coli with an amino-terminal hexa-His-tag for purification and characterization. His-TrxA and His-TrxB were purified to homogeneity with one-step Ni-NTA affinity column chromatography, and the two recombinant proteins showed identical specific activity with or without removal of the amino-terminal His-tag, indicating that the extrasequence containing the hexa-His-tag did not affect their enzymatic activities. The E. coli expression system used here resulted in a 40-fold increase in production of His-TrxB protein compared to the level of native TrxB produced in non-recombinant B. choshinensis cells. TrxA and TrxB proteins with carboxy-terminal His-tag (TrxA-His and TrxB-His) were successfully expressed in B. choshinensis and were purified by Ni-NTA column chromatography. Co-expression of TrxA-His with recombinant human epidermal growth factor (hEGF) in B. choshinensis promoted the extracellular production of hEGF by up to about 200%.

Synthesis and chromatographic purification of recombinant human pituitary hormones

Recombinant DNA-derived proteins and, in particular, human pituitary hormones, are increasingly used for research, diagnostic and therapeutic purposes. This trend has demanded new synthetic approaches and improved purification techniques. The type and sequence of the purification steps have to be selected in accordance with the cloning and protein expression strategy, the host organism and cellular localization of the protein of interest, with a view to producing the desired product at a required purity, biological activity and acceptable cost. This review article describes and analyzes the main synthetic and purification strategies that have been used for the production of recombinant human growth hormone, prolactin, thyrotropin, luteinizing hormone and follicle-stimulating hormone, giving special consideration to the few published downstream processes utilized by the biotechnology industry. Practically all types of prokaryotic and eukaryotic organisms utilized for this purpose are also reviewed.

The effect of treatment with the oral growth hormone (GH) secretagogue MK-677 on GH isoforms

Growth hormone (GH) consists of several isoforms. We have studied the proportion, expressed as percentage of total GH concentration, of non-22kDa (non-22K) GH isoforms and 20K GH during 8-week oral treatment with MK-677 25mg daily in 12 obese males. The proportion of non-22K GH isoforms in peak total GH samples after the initial MK-677 administration was higher than that after 2 and 8 weeks (p<0.01 and p<0.05, respectively). In selected non-peak total GH samples after the initial MK-677 administration, however, the proportion of non-22K GH isoforms was similar to that in the peak total GH samples after 2 and 8 weeks. The proportion of 20K GH in 2-h samples after the initial MK-677 administration was lower than that after 2 and 8 weeks (p<0.01 and p<0.05, respectively). We concluded that the proportion of non-22K GH isoforms was higher in peak, but not in non-peak, total GH samples after the initial MK-677 administration than that observed after multiple doses. The proportion of 20K GH in 2-h samples after the initial MK-677 administration was lower than that after 2 and 8 weeks. These moderate changes in the proportion non-22K GH isoforms are likely of small importance for the clinical response to MK-677 treatment.

Physiological and pharmacological regulation of 20-kDa growth hormone

The 20-kDa growth hormone (GH) is generated from alternative splicing of the primary transcript of full-length 22-kDa GH. We have studied the regulation of 20-kDa GH over a range of pathophysiological conditions and in response to pharmacological stimulation using isoform-specific enzyme-linked immunosorbent assays (ELISAs). Mean 24-h levels of 20- and 22-kDa GH were higher in acromegaly and lower in GH deficiency than in normal subjects, with the 20-to-22-kDa ratio not different between the three groups. In normal subjects, 20-kDa GH was secreted in a pulsatile manner throughout the day, with peaks coinciding with those of 22-kDa GH. However, the half-life of 20-kDa GH (18.7 +/- 0.8 min) was significantly longer than that of 22-kDa GH (14.7 +/- 0.8 min; P < 0.02). Insulin-induced hypoglycemia, androgen, and oral estrogen caused a parallel and proportionate increase in both isoforms. Octreotide suppressed 20-kDa less rapidly than 22-kDa GH in blood. Administration of recombinant 22-kDa GH in normal subjects rapidly reduced the 20-kDa GH levels. In conclusion, 20-kDa GH is cosecreted with and circulates at a constant proportion of 22-kDa GH. The 20-kDa GH level is reduced by administration of exogenous 22-kDa GH, suggesting rapid negative feedback regulation on pituitary release.

Diabetogenic activity of 20 kDa human growth hormone (20K-hGH) and 22K-hGH in rats

To compare the diabetogenic activity of 20 kDa human growth hormone (20K-hGH) with that of 22K-hGH, we evaluated insulin sensitivity with a euglycaemic clamp in rats. The glucose infusion rate (GIR) in euglycaemic clamp studies was measured as an indicator of insulin sensitivity. [(14)C]glucose and 2-[(3)H] deoxy- D -glucose injection were used to calculate the rate of glucose utilization (R(d)), the hepatic glucose output (HGO), and the glucose metabolic index (R(g)'). Both 20K- and 22K-hGH were infused at equivalent rates (1.0 (mg/kg)/day). A 24 h infusion of 20K-hGH had no significant effects on the GIR, R(d), HGO and R(g)(')except for in gastrocnemius muscle. In contrast, 22K-hGH significantly lowered the GIR compared with the control (P< 0.001) and 20K-hGH groups (P< 0.01). The infusion of 22K-hGH also reduced R(d)compared with the controls and the 20K-hGH rats by 46.6% (P< 0.001) and 39.6% (P< 0.05) respectively, while no differences were observed in the HGO. Moreover, 22K-hGH inhibited glucose uptake, which was estimated from the insulin-stimulated R(g)' in some tissues. These results suggest that 22K-hGH inhibits the uptake and use of glucose in various tissues, which then leads to insulin resistance. In conclusion, the diabetogenicity of 20K-hGH is much weaker than that of 22K-hGH, and the reduced insulin-antagonizing action of 20K-hGH could have important clinical benefits.

A novel bioassay based on human growth hormone (hGH) receptor mediated cell proliferation: measurement of 20K-hGH and its modified forms

Previously we introduced the full-length hGH receptor (hGHR) into the mouse pro-B cell line, Ba/F3, and obtained stable transfectant (Ba/F3-hGHR), which could grow in response to 20K- and 22K-hGH in a dose-dependent manner(1). In the present study, we established a new bioassay system based on the proliferation of the Ba/F3-hGHR in combination with the eluted stain assay (ESTA). The Ba/F3-hGHR assay is completed in 18 h and requires only 10(-6)-fold amount of GH sample (1.8 ng) as compared with the rat weight gain assay. The validation study shows that the Ba/F3-hGHR assay is specific for hGH, precise (RSD = 1.1-19.7%) and ultrasensitive (lower limit of working range = 18.7 pg/mL). Four modified forms of recombinant 20K-hGH (oxidized, deamidated, des-Phe(1)and cleaved form) all of which are newly identified were measured by the Ba/F3-hGHR assay and the rat weight gain assay with our in-house recombinant 20K-hGH as standard. The oxidized and deamidated 20K-hGH were fully active, however the des-Phe(1)and cleaved 20K-hGH had significantly reduced activities in both assays. These findings suggest that the Ba/F3-hGHR assay is useful as an alternative to the rat weight gain assay.

Comparison of the somatogenic action of 20 kDa- and 22 kDa-human growth hormones in spontaneous dwarf rats

The somatogenic action of the 20 kilodalton human growth hormone (20 K) was studied using the spontaneous dwarf rat (SDR), which has an isolated GH deficiency. Saline or 2.5 microg, 10 microg, or 100 microg/rat/day of recombinant 20 K or 22 K was administered to prepubertal male and female SDRs for 10 days. Their body weights, serum IGF-I, glucose and insulin were measured, and their body composition was determined. Body weights and serum IGF-I increased dose-dependently in both the 20 K- and 22 K-treated groups. There was no significant difference in body weights and serum IGF-I between the 20 K- and 22 K-treated groups except at the dose of 100 microg/rat, in which the IGF-I concentrations were higher in the 22 K-treated male SDRs (P< 0.05: 20 K vs 22 K). Blood glucose was not significantly different between the Spague-Dawley (SD) normal rats and the SDR control groups; however, serum insulin levels of the SDR were higher than those of the SD control group (P< 0.05). Additionally, there was a tendency for serum insulin and glucose levels to increase following 22 K treatment, but the differences were not significant. The percentage of body fat decreased with hGH treatment in both groups (P< 0.01: GH 10, 100 microg/rat group vs SDR control group), however, no significant differences were observed in body composition between the 20 K and 22 K treatment groups. In summary, the 20 K-hGH showed almost the same somatogenic activity as the 22 K-hGH in prepubertal male and female SDRs.

Reversible dimerization of 20 kilodalton human growth hormone (hGH)

A noncovalent dimer of the 22 kilodalton human growth hormone (22 K-hGH) is known to have diminished somatogenic activity compared with monomeric 22 K-hGH. In the present study, we examined the biological activity and physicochemical behaviour of a noncovalent dimer of the 20 kilodalton human growth hormone (20 K-hGH), an isoform of 22 K-hGH. Analysis of the equilibrium between monomeric and associated forms revealed that the associated 20 K-hGH was present in the dimeric form in aqueous solution. The kinetics of dimerization in rat plasma followed the theory of dissociation-association equilibrium, and more than 99% of 20 K-hGH molecules existed as a monomer in the equilibrium state at the physiological hGH concentration. Analysis of the pharmacokinetics showed that the ratio of the administrated dimer in rat circulation decreased from 43% to less than 4% in 2 h. A preparation of noncovalent dimeric 20 K-hGH had essentially the same degree of biological potency as that of a monomer in both in vitro and in vivo bioassays. In conclusion, dimerization of 20 K-hGH is reversible both in vitro and in vivo and a noncovalent dimer can function as a pharmaceutically active component of a 20 K-hGH preparation, in contrast to a 22 K-hGH preparation.

The binding between the stem regions of human growth hormone (GH) receptor compensates for the weaker site 1 binding of 20-kDa human GH (hGH) than that of 22-kDa hGH

Despite the lower site 1 affinity of the 20-kDa human growth hormone (20K-hGH) for the hGH receptor (hGHR), 20K-hGH has the same hGHR-mediated activity as 22-kDa human GH (22K-hGH) at low hGH concentration and even higher activity at high hGH concentration. This study was performed to elucidate the reason why 20K-hGH can activate hGHR to the same level as 22K-hGH. To answer the question, we hypothesized that the binding between the stem regions of hGHR could compensate for the weaker site 1 binding of 20K-hGH than that of 22K-hGH in the sequential binding with hGHR. To demonstrate it, we prepared 15 types of alanine-substituted hGHR gene at the stem region and stably transfected them into Ba/F3 cells. Using these cells, we measured and compared the cell proliferation activities between 20K- and 22K-hGH. As a result, the activity of 20K-hGH was markedly reduced than that of 22K-hGH in three types of mutant hGHR (T147A, H150A, and Y200A). Regarding these mutants, the dissociation constant of hGH at the first and second step (KD1 and KD2) in the sequential binding with two hGHRs was predicted based on the mathematical cell proliferation model and computational simulation. Consequently, it was revealed that the reduction of the activity in 20K-hGH was attributed to the change of not KD1 but KD2. In conclusion, these findings support our hypothesis, which can account for the same potencies for activating hGHR between 20K- and 22K-hGH, although the site 1 affinity of 20K-hGH is lower than that of 22K-hGH.

GH induced lipolysis stimulation in 3T3-L1 adipocytes stably expressing hGHR: analysis on signaling pathway and activity of 20K hGH

We have constructed a cell line of 3T3-L1 which can efficiently express human GHR (3T3-L1-hGHR) after differentiation to adipocytes. The expressed hGHR was detected as two bands with approximate molecular sizes of 120K by Western analysis using hGHR specific monoclonal antibody. Maximum lipolytic activity induced by hGH in the 3T3-L1-hGHR was enhanced 10-fold as compared to that in 3T3-L1, suggesting that expressed hGHR is functionally active. Comparative analysis using bGH and hGH revealed that 70% of lipolysis stimulation by 1-10 ng/ml hGH could be attributed to hGHR-mediated response. Analyses on inhibition and phosphorylation of signaling molecules suggested that GH-induced lipolysis stimulation is dependent on gene expression and not mediated through PKA-, PKC-, PLA-, PLC-, nor MAPK-pathway but possibly through JAK-STATs pathway. Duration of STAT5 activation by hGH continued up to 48 h. We also revealed that 22 K hGH isoform, 20K hGH which has been reported as a weaker agonist for GH-induced lipolysis stimulation, possesses equipotent activity and shows stronger action in the presence of hGHBP as compared to 22 K hGH. Taken together we conclude that the hGH-induced lipolysis was not mediated through MAP-, PKA-, PKC-, nor PLA-pathway but might be mediated through STAT pathway and that 20K hGH might show higher lipolytic activity than 22 K hGH in adipose tissue that produces a large amount of GHBP.

The effect of growth hormone on the proliferation of human Th cell clones

The effects of human growth hormone (hGH) on human Th cell clones were examined. Both 20K and 22K hGH stimulated the proliferation of Th2 and Th0 cells in the presence of mite antigen, whereas they did not stimulate the proliferation of Thl cells. Because the effect of 20K hGH was almost the same as that of 22KhGH, it was suggested that the action of hGH was not mediated through prolactin receptor but through hGH receptors. The application of growth hormone binding protein (GHBP) inhibited the cell growth of Th1 clones. In Th2 and Th0 cells GHBP inhibited the hGH-stimulated cell proliferation. However, GHBP alone did not affect the proliferation of Th2 and Th0 cells. hGH was detected in the supernatant of Th1 clones in the presence of mite antigen but it was not detected in Th2 clones. hGH was detected in one out of 4 batches of Th0 clones. These data indicated that hGH was secreted from Thl clones, and that Th0 clones possessed characteristics of both Th2 and Th0 clones.

The 20-kilodalton (kDa) human growth hormone (hGH) differs from the 22-kDa hGH in the effect on the human prolactin receptor

Previously we have demonstrated that 20-kDa human GH (20K-hGH) is a full agonist for hGH receptor (hGHR) even though its complex formation with hGHR and hGH-binding protein differs from that of 22-kDa human GH (22K-hGH). In this study, we focused on the effect of 20K-hGH on human PRL receptor (hPRLR). To elucidate the effects of 20K-hGH on hPRLR and compare them with those of 22K-hGH, we prepared two cells stably expressing full-length hPRLR, Ba/F3-hPRLR and CHO-hPRLR. In the proliferation of Ba/F3-hPRLR cells, which can grow in a dose-response to lactogenic hormones, both 20K- and 22K-hGH exhibited bell-shaped curves in the absence of exogenous zinc ion (Zn2+); however, the curve of 20K-hGH was shifted to a 10-fold higher concentration than that of 22K-hGH in view of EC50 value (the EC50 of 20K- and 22K-hGH were 15 nM and 1.5 nM, respectively). Addition of Zn2+ up to 25 microM increased the activities of both 20K- and 22K-hGH; however, the enhancement by Zn2+ was greater in 20K-hGH than in 22K-hGH, thereby the activities of both hGH isoforms reached the same level at 25 microM Zn2+. Nevertheless, in the presence of 0.25-1 microM free Zn2+, which is equal in human serum, the activity of 20K-hGH was still lower than that of 22K-hGH. The modest effect of 20K-hGH on activating hPRLR in the absence of Zn2+ was confirmed in the rat serine protease inhibitor 2.1 (Spi2.1) gene promoter activation and JAK2/Stat5 tyrosine phosphorylation in CHO-hPRLR. In addition, in human breast cancer cell T-47D, 20K-hGH was proved to stimulate Stat5 tyrosine phosphorylation to much lower degree than 22K-hGH via not hGHR but hPRLR. Taken together, our data suggest that 20K-hGH may be a weaker agonist for hPRLR than 22K-hGH in the human body; therefore 20K-hGH may alleviate the hPRLR-mediated side-effects such as breast cancer when administered to human body.

Serum levels of 20-kilodalton human growth hormone (GH) are parallel those of 22-kilodalton human GH in normal and short children

Twenty-kilodalton human GH (20K), which is one of the human GH (hGH) variants, is thought to be produced by alternative premessenger ribonucleic acid splicing. However, its physiological role is still unclear due to the lack of a specific assay. We have measured serum 20K and 22-kDa hGH (22K) by specific ELISAs to investigate the physiological role of 20K in children. The subjects were 162 normal children, aged 1 month to 20 yr; 12 patients with GH deficiency (GHD), aged 11 months to 13 yr; 57 children with non-GHD short stature, aged 2-17 yr; and 13 girls with Turner's syndrome, aged 5 months to 15 yr. Samples were collected at random from normal children and were collected after hGH provocative tests and 3-h nocturnal sleep from GHD, non-GHD short stature, and Turner's syndrome children. The mean basal serum concentrations of 22K and 20K were 2.4 +/- 2.8 ng/mL and 152.3 +/- 184.0 pg/mL in normal boys and 2.5 +/- 3.1 ng/mL and 130.6 +/- 171.5 pg/mL in normal girls, respectively. The percentages of 20K (%20K) were 5.8 +/- 2.1% and 6.0 +/- 3.2% in 83 normal boys and 79 normal girls, respectively. There was no significant difference in %20K either among ages or between the prepubertal stage and the pubertal stage in normal boys and girls. The mean %20K values in basal samples of provocative tests in 12 patients with GHD, non-GHD short stature, and Turner's syndrome were 6.5 +/- 2.4%, 6.5 +/- 3.8%, and 5.9 +/- 3.2%, respectively. There was no significant difference in %20K among normal children and these growth disorders, and there was no significant difference in %20K throughout the hGH provocative tests and 3-h nocturnal sleep in these growth disorders. There was also no significant correlation between the percentage of 20K and the height SD score or body mass index in either normal children or subjects with these growth disorders. In conclusion, the %20K is constant, regardless of age, sex, puberty, height SD score, body mass index, and GH secretion status. The regulation of serum 20K levels remains to be established.

Construction of a specific and sensitive sandwich enzyme immunoassay for 20 kDa human growth hormone

Twenty kilodalton human growth hormone (20K-hGH) is a naturally occurring isoform lacking amino acid residues 32-46 of 22K-hGH. Due to this structural similarity to 22K-hGH, no one has constructed a specific and sensitive assay system for 20K-hGH, which can be used for measuring physiological concentration of this isoform in the circulation. To construct such a specific assay system, we have generated polyclonal antibodies (pAb) and monoclonal antibodies (mAbs) against recombinant 20K-hGH. Binding characteristics to 20K-, 22K-hGH and monkey GH (mGH) of these five mAbs, designated A23, B13, C02, D05, and D14, were analyzed by enzyme immunoassays (EIAs) and surface plasmon resonance analysis. Only one of them, the mAb D05, does not crossreact with 22K-hGH. It was also observed that mAb B13 does not crossreact with mGH, although the later is 96% homologous to hGH. Using these antibodies we have established several sandwich EIA systems for circulating 20K-hGH. The combination of A23 as a solid-phase antibody and B13 as a labeled antibody permitted both high sensitivity to 20K-hGH (< 0.1 ng/ml) and low cross-reactivities with 22K-hGH (< 2%), mGH (< 0.3%) and rat GH (< 0.1%). The clearances of administered 20K-hGH were determined by this combination in both rats and monkeys. In the assay of physiologically circulating 20K-hGH in humans, the combination of D05 and affinity-purified anti-20K-hGH pAb showed the highest sensitivity to 20K-hGH (< 10 pg/ml) and substantially no cross-reactivity with 22K-hGH (< 0.1%). The plasma 20K-hGH concentration in healthy female subjects was determined by this combination. The assay systems constructed here enables us to directly measure circulating 20K-hGH in physiological condition with no interference of 22K-hGH for the first time.

The 20-kilodalton (kDa) human growth hormone (hGH) differs from the 22-kDa hGH in the complex formation with cell surface hGH receptor and hGH-binding protein circulating in human plasma

In spite of recent advance in understanding of the stoichiometry of 22-kDa human GH (22K-hGH) with cell surface hGH receptor (hGHR) and hGH-binding protein (hGH-BP) circulating in human plasma, that of 20-kDa hGH (20K-hGH) is poorly understood. To clarify this, mouse pro-B Ba/F3 cells stably expressing the full-length hGHR (Ba/F3-hGHR) and both recombinant and native hGH-BP were used in this study. Cell proliferation assay revealed that the two hGH isoforms increased Ba/F3-hGHR cells to the same extent in a dose-dependent manner at 0.1 pM-10 nM. However, the self-inhibition observed in 20K-hGH at 5 microM was significantly less than that in 22K-hGH. Furthermore, addition of 1 and 10 nM recombinant hGH-BP caused a slight inhibition in 20K-hGH, but a drastic inhibition in 22K-hGH. Gel filtration chromatography of mixtures of 20K-hGH with recombinant hGH-BP clearly demonstrated that 20K-hGH formed a 1:2 (hGH:hGH-BP) complex efficiently but no detectable 1:1 complex in any conditions. Supporting data were also obtained with native hGH-BP. Computer-aided homology modeling of 20K-hGH has provided speculative data that the conformational change caused by deletion of 15 residues may occur only in the loop between helix 1 and helix 2, resulting in the reduction of its site 1 affinity. In conclusion, 20K-hGH possesses a unique property for forming a 1:2 complex to the same extent as 22K-hGH but has difficulty in forming a 1:1 complex, which might be attributed to the conformational change restricted to its site 1 region.

The full agonistic effect of recombinant 20 kDa human growth hormone (hGH) on CHO cells stably transfected with hGH receptor cDNA

The agonistic effect of the recombinant 20 kilodalton human GH (20K-hGH) with authentic primary structure was studied using Chinese hamster ovary (CHO) cells stably transfected with hGH receptor (hGHR) cDNA and was compared with that of 22K-hGH. The binding affinities (dissociation constants) of 20K- and 22K-hGH were identical (0.41 +/- 0.11 nM and 0.41 +/- 0.04 nM, respectively). In addition, the two hGHs possessed the same potencies in activating the rat serine protease inhibitor (Spi) 2.1 gene promoter. 20K-hGH was similarly internalized as 22K-hGH but its internalization rate was a little slower than that of 22K-hGH. We also found that proliferation of CHO-hGHR cells stimulated by serum was remarkably inhibited by both hGHs to the same degree. In conclusion, both hGH isoforms exhibited the same binding affinities for hGHR and were potent enough to induce some hGHR-mediated cellular events. These suggest that 20K-hGH exerts a full agonistic activity for hGHR.