Differential intracellular signalling properties of the growth hormone receptor induced by the activation of an anti-GHR antibody

Short stature related to Growth Hormone Insensitivity (GHI) in childhood

Linear growth during childhood is the result of the synergic contribution of different factors. The best growth determinant system during each period of life is represented by the growth hormone-insulin-like growth factor axis (GH-IGF), even if several other factors are involved in normal growth. Within the broad spectrum of growth disorders, an increased importance has been placed on growth hormone insensitivity (GHI). GHI was reported for the first time by Laron as a syndrome characterized by short stature due to GH receptor (GHR) mutation. To date, it is recognized that GHI represents a wide diagnostic category, including a broad spectrum of defects. The peculiar characteristic of GHI is the low IGF-1 levels associated with normal or elevated GH levels and the lack of IGF-1 response after GH administration. Recombinant IGF-1 preparations may be used in the treatment of these patients.

Zinc ions increase GH signaling ability through regulation of available plasma membrane-localized GHR

It is well known that zinc ion (Zn²⁺ ) can regulate the biological activity of growth hormone (GH). However, until now, the mechanism by which Zn²⁺ regulates GH biological activity remains unclear. In the current study, we first performed molecular docking between Zn²⁺ and porcine GH (pGH) using computational biology. We then explored the effect of Zn²⁺ on the GH signaling ability in the cell model expressing porcine growth hormone receptor (GHR). It was found that the phosphorylation levels of Janus kinase 2, signal transducers and activators of transcription 5/3/1, and GHR increased significantly under Zn²⁺ treatment, indicating that Zn²⁺ can enhance the signaling ability of GH/GHR. On this basis, we further explored how Zn²⁺ regulates the biological activity of GH/GHR. The results showed that downregulation and turnover of GHR changed under Zn²⁺ /pGH treatment. Zn²⁺ enhanced the membrane residence time of pGH/GHR and delayed GHR downregulation. Further investigation showed that the internalization dynamic of pGH/GHR was changed by Zn²⁺ , which prolonged the residence time of pGH/GHR in the cell membrane. These factors acted together to upregulate the signaling of GH/GHR. This study lays a foundation for further exploration of the biological effects of Zn²⁺ on GH.

Endocytosis and Degradation of Pegvisomant and a Potential New Mechanism That Inhibits the Nuclear Translocation of GHR

CONTEXT

Pegvisomant, a growth hormone receptor (GHR) antagonist, is a well-known drug that was designed to treat acromegaly. However, recent studies have indicated that the GHR is a "moonlighting" protein that may exhibit dual functions based on its localization in the plasma membrane and nucleus. In light of this finding, we explored whether pegvisomant is a potential "moonlighting" GHR antagonist. In addition, the mechanisms of the endocytosis, postendocytic sorting, and degradation of pegvisomant are not fully understood.

OBJECTIVE

This study investigated whether pegvisomant is a "moonlighting" antagonist and explored the mechanisms of the endocytosis, postendocytic sorting, and degradation of pegvisomant.

METHODS

Indirect immunofluorescence and Western blot coupled with pharmacological inhibitors and gene silencing (small interfering RNA) were used to explore the mechanisms of the endocytosis, postendocytic sorting, and degradation of pegvisomant. Western blot, immunohistochemistry, and indirect immunofluorescence coupled with subcellular fractionation analysis were used to determine the effect of pegvisomant on GHR's nuclear localization in vitro and in vivo.

RESULTS

Here, we show that the endocytosis of pegvisomant is mainly mediated though the clathrin pathway. Further study of the postendocytic sorting of pegvisomant shows that pegvisomant enters into different types of endosomes under GHR mediation. In addition, GHR is slightly downregulated by pegvisomant; further study indicates that proteasomes and lysosomes may cooperate to regulate pegvisomant/GHR degradation. Most importantly, we show that pegvisomant inhibits the nuclear localization of GHR.

CONCLUSION

Our study showed that pegvisomant is a "moonlighting" antagonist. In addition, we revealed the mechanisms of the endocytosis, postendocytic sorting, and degradation of pegvisomant.

Growth hormone during in vitro fertilization in older women modulates the density of receptors in granulosa cells, with improved pregnancy outcomes

OBJECTIVE

To study the effect of aging and granulosa cell growth hormone receptor (GHR) expression, and the effect of growth hormone (GH) co-treatment during IVF on receptor expression.

DESIGN

Laboratory study.

SETTING

University.

PATIENT(S)

A total of 445 follicles were collected from 62 women undergoing standard infertility treatment.

INTERVENTION(S)

Preovulatory ovarian follicle biopsies of granulosa cells and follicular fluid.

MAIN OUTCOME MEASURE(S)

Older women with a poor ovarian reserve were co-treated with GH to determine the effect of the adjuvant during IVF on the granulosal expression density of FSH receptor (FSHR), LH receptor (LHR), bone morphogenetic hormone receptor (BMPR1B), and GHR. Ovarian reserve, granulosa cell receptor density, oocyte quality, and pregnancy and live birth rates were determined.

RESULT(S)

Growth hormone co-treatment increased the receptor density for granulosal FSHR, BMPR1B, LHR, and GHR compared with the non-GH-treated patients of the same age and ovarian reserve. Growth hormone co-treatment increased GHR density, which may increase GHR activity. The GH co-treatment was associated with a significant increase in pregnancy rate.

CONCLUSION(S)

Growth hormone co-treatment restored the preovulatory down-regulation of FSHR, BMPR1B, and LHR density of the largest follicles, which may improve the maturation process of luteinization in older patients with reduced ovarian reserve. The fertility of the GH-treated patients improved.

Cellular internalization and trafficking of 20 KDa human growth hormone

Twenty kilodalton human growth hormone (20K-GH) is the second most abundant GH isoform after the twenty-two kilodalton human growth hormone (22 K-GH) isoform. 20K-GH exhibits similar but not identical physiological activities as that of 22K-GH. The cell behaviour of 22K-GH has been extensively studied, but little or no information has been reported regarding 20K-GH. Here, we focussed on the internalization of 20K-GH. We found that the internalization of 20K-GH is rapid and occurs in a time- and dose-dependent manner. 20K-GH internalization is mediated by GHR. It appears that the internalization of 20K-GH and GHR into the cytoplasm is mediated by clathrin and/or caveolin. The current study indicates that 20K-GH can internalize into the cytoplasm and suggests that the internalized 20K-GH may exhibit different functions from those of 22K-GH.

Growth Hormone and Insulin-Like Growth Factor Action in Reproductive Tissues

The role of growth hormone (GH) in human fertility is widely debated with some studies demonstrating improvements in oocyte yield, enhanced embryo quality, and in some cases increased live births with concomitant decreases in miscarriage rates. However, the basic biological mechanisms leading to these clinical differences are not well-understood. GH and the closely-related insulin-like growth factor (IGF) promote body growth and development via action on key metabolic organs including the liver, skeletal muscle, and bone. In addition, their expression and that of their complementary receptors have also been detected in various reproductive tissues including the oocyte, granulosa, and testicular cells. Therefore, the GH/IGF axis may directly regulate female and male gamete development, their quality, and ultimately competence for implantation. The ability of GH and IGF to modulate key signal transduction pathways such as the MAP kinase/ERK, Jak/STAT, and the PI3K/Akt pathway along with the subsequent effects on cell division and steroidogenesis indicates that these growth factors are centrally located to alter cell fate during proliferation and survival. In this review, we will explore the function of GH and IGF in regulating normal ovarian and testicular physiology, while also investigating the effects on cell signal transduction pathways with subsequent changes in cell proliferation and steroidogenesis. The aim is to clarify the role of GH in human fertility from a molecular and biochemical point of view.

Growth Hormone Did Not Activate Its Intracellular Signaling Molecules in Rats' Liver Hepatocytes During Early Life Period

BACKGROUND

Although growth hormone (GH) has essential roles in the growth of animals, it has no growth-promoting effect during infancy period. The molecular mechanism underlying lack of growth-promoting effect of GH during infancy period remains unclear. Important signaling pathways are mediated by GH, including Janus kinase 2 (JAK2), extracellular signal-regulated kinase 1/2 (ERK1/2), signal transducers, and activators of transcription 5, 3, and 1 (STATs 5, 3 and 1).

OBJECTIVES

This study explored the underlying molecular mechanisms driving to the lack of growth-promoting effect of GH in the early stage of life by in vivo assessment of intracellular signal response (STAT5/ 3/ 1, JAK2 and ERK1/ 2) to GH at different physiological stages.

METHODS

In this study, five age groups of rats (1-, 4-day-old, and 1-, 2-, 3-week-old) were selected. The rats were anesthetized using pentobarbital (100 mg/kg) and then received the rat GH (2mg/kg) via inferior vena cava injection. The control rats were injected with normal saline during the same period. The intracellular signal response to GH was assessed by Western blot analysis.

RESULTS

JAK2 and STAT5 were expressed in 1-day and 4-day-old newborn rats and their expression levels were comparable with the levels of the 1-, 2-, and 3-week-old rats; however, JAK2/STAT5 phosphorylation was not observed in 1-day-old and 4-day-old newborn rats after stimulation with GH in the liver. Similar to JAK2 and STAT5, we did not detect STAT3/1 activation during infancy stages although basic STAT3 and STAT1 were also expressed in hepatocytes from newborn rats. In addition we detected ERK1/2 activation in 4-day-old, 1-, 2-, and 3-week-old rats but not in 1-day-old rats.

CONCLUSIONS

JAK2, STAT5, STAT3, STAT1, and ERK1/2 were not simultaneously activated by GH in newborn rats; this finding may be one of the underlying mechanism of GH insensitivity in newborn rats.

Porcine growth hormone induces the nuclear localization of porcine growth hormone receptor in vivo

Objective

Recent studies have challenged the traditional paradigm that growth hormone receptor (GHR) displays physiological functions only in the cell membrane. It has been demonstrated that GHR localizes to the cell nucleus and still exhibits important physiological roles. The phenomenon of nuclear localization of growth hormone (GH)-induced GHR has previously been described in vitro. However, until recently, whether GH could induce nuclear localization of GHR in vivo was unclear.

Methods

In the present study, we used pig as an animal model, and porcine growth hormone (pGH) or saline was injected into the inferior vena cava. We subsequently observed the localization of porcine growth hormone receptor (pGHR) using multiple techniques, including, immunoprecipitation and Western-blotting, indirect immunofluorescence assay and electronmicroscopy.

Results

The results showed that pGH could induce nuclear localization of pGHR. Taken together, the results of the present study provided the first demonstration that pGHR was translocated to cell nuclei under pGH stimulation in vivo.

Conclusion

Nuclear localization of pGHR induced by the in vivo pGH treatment suggests new functions and/or novel roles of nuclear pGHR, which deserve further study.

The role of growth hormone receptor in β cell function

Growth hormone (GH) exerts numerous effects on tissues through binding to its receptor, GHR, which resides on cell membranes in many different organs and tissues. Endocrine pancreatic β cells are the only source of insulin secretion in response to metabolic demand, thereby regulating blood glucose and maintaining metabolic homeostasis. β cell dysfunction is the main composition of diabetes mellitus. Numerous studies have provided strong evidence that GHR signaling plays an independent role in β cell function. In this review, we focus on the role of GHR signaling in β cell actions and the underlying molecular mechanisms.

The 20kDa and 22kDa forms of human growth hormone (hGH) exhibit different intracellular signalling profiles and properties

Human Growth Hormone (hGH) includes two main variants. The first is 22kDa GH (22K-GH), which is predominant in the blood circulation. The second most abundant variant is 20K-GH, which makes up 5-10% of the blood circulation. Both bind and activate the same receptor, called the human growth hormone receptor (GHR). However, the reason why 22K-GH and 20K-GH exhibit similar, but not identical physiological activities remains poorly understood. In this article, the intracellular signalling profiles between these two hormones were examined. Western blot analyses were performed in 3T3-F442A and CHO cells transfected with GHR (CHO-GHR). The results revealed that both 22K-GH and 20K-GH can activate Janus kinase 2 (JAK2) and signal transducers and activators of transcription 1, 3 and 5 (STATs 1/3/5). Both induced tyrosine phosphorylation of JAK2 and STAT/1/3/5 in a time-dependent and dose-dependent manner. However, there were significant differences in the intracellular signalling properties between 22K-GH and 20K-GH. In particular, the kinetics of signalling shown by 22K-GH and 20K-GH is different. In addition, we found that the 20K-GH-induced tyrosine phosphorylation of signalling proteins was weaker than that of 22K-GH. Together, these observations indicate that the levels and kinetics of phosphorylation mediated by the main signalling proteins triggered by 22K-GH or 20K-GH were not exactly the same. This may provide a possible explanation for the different biological activities exhibited by 22K-GH and 20K-GH.

Development of a new anti-prolactin receptor (PRLR) antibody, F56, which can serve as a PRLR antagonist

In this work, we developed a new prolactin receptor (PRLR) antagonist using the hybridoma technique. A series of monoclonal antibodies against prolactin receptor (PRLR) was prepared, from which we characterized and selected one anti-PRLR antibody, F56. Epitome mapping showed that F56 and prolactin (PRL) share a common binding epitope on PRLR, and therefore, F56 could compete with prolactin (PRL) for binding to PRLR. Subsequent experiments indicated that F56 could effectively neutralize PRLR-mediated intracellular signalling molecules, such as signal transducer and activator of transcription (STAT) and extracellular signal-regulated kinase-1 and kinase 2 (ERK1/2), either by endogenously expressed PRLR or in a cell model transfected with PRLR. In addition, further experiments showed that F56 could effectively inhibit PRL-induced cell proliferation. The current study suggests that F56 has potential applications in PRLR-related studies.

Development of a Novel, Anti-idiotypic Monoclonal Anti-prolactin Antibody That Mimics the Physiological Functions of Prolactin

In this work, we prepared a panel of monoclonal anti-idiotypic antibodies to ovine prolactin (oPRL) by the hybridoma technique. Among these antibodies, one anti-idotypic antibody (designated B7) was chosen for further characterization by a series of experiments. We first demonstrated that B7 behaved as a typical Ab2β based on a series of enzyme-linked immunosorbent assays. Subsequently, the results of a competitive receptor-binding assay confirmed that B7 could specifically bind to the prolactin receptor (PRLR) expressed on target cells. Finally, we examined its biological activities in CHO-PRLR and Nb2 cells and observed that B7 could activate Janus kinase 2-signal transducer and activator of transcription signalling in CHO-PRLR and Nb2 cells and induce BaF3 proliferation. The present study suggests that i) B7 can serve as a PRLR agonist or PRL mimic and has potential applications in regulating mammary gland development, milk production and maintenance of lactation in domestic animals and ii) B7 may be a biological reagent that can be used to explore the mechanism of PRLR-mediated intracellular signalling.

Different intracellular signalling properties induced by human and porcine growth hormone

Growth hormone (GH) is reportedly species-specific. Primate growth hormone can trigger non-primate growth hormone receptor (GHR), but primates GHR cannot be activated by non-primate GH. However, it is also unclear that why primate GH and non-primate GH have different biological activities. Thus, we analysed primate growth hormone (human growth hormone (hGH)) or non-primate GH (porcine growth hormone (pGH))-induced intracellular signalling in 3T3-F442A cells and rat hepatocytes in a dose- and time-dependent manner to explore the different biological activities between them. The results revealed that both hGH and pGH can activate Janus kinase 2 (JAK2), Signal transducers and activators of transcription 1, 3 and 5 (STATs 1, 3 and 5) and extracellular signal-regulated kinase 1/2 (ERK1/2). There were no significant differences in JAK2 or ERK1/2 tyrosine phosphorylation after hGH and pGH treatment, but there were different between hGH and pGH in STAT/1/3/5 tyrosine phosphorylation, and JAK2, STAT/1/3/5 tyrosine phosphorylation was time-dependent and dose-dependent, whereas ERK1/2 was not. Both hGH and pGH demonstrated similar kinetics for STATs 1, 3 and 5 phosphorylation, but the pGH-mediated tyrosine phosphorylation was weaker than that mediated by hGH. Our observations indicated that the levels of main signalling proteins phosphorylation triggered by hGH or pGH were not exactly the same, which may explain the different biological activities showed by primate GH and non-primate GH.

Preparation and Characterization of an Antibody Antagonist That Targets the Porcine Growth Hormone Receptor

A series of antagonists specifically targeting growth hormone receptors (GHR) in different species, such as humans, rats, bovines, and mice, have been designed; however, there are currently no antagonists that target the porcine growth hormone (GH). Therefore, in this study, we developed and characterized a porcine GHR (pGHR) antibody antagonist (denoted by AN98) via the hybridoma technique. The results from enzyme-linked immunosorbent assay, fluorescence activated cell sorter, indirect immunoinfluscent assay, and competitive receptor binding analysis showed that AN98 could specifically recognize pGHR, and further experiments indicated that AN98 could effectively inhibit pGH-induced signalling in CHO-pGHR cells and porcine hepatocytes. In addition, AN98 also inhibited GH-induced insulin-like growth factor-1 (IGF-1) secretion in porcine hepatocytes. In summary, these findings indicated that AN98, as a pGHR-specific antagonist, has potential applications in pGH-pGHR-related research on domestic pigs.

Growth hormone insensitivity: diagnostic and therapeutic approaches

INTRODUCTION

Growth hormone resistance defines several genetic (primary) and acquired (secondary) pathologies that result in completely or partially interrupted activity of growth hormone. An archetypal disease of this group is the Laron-type dwarfism caused by mutations in growth hormone receptors. The diagnosis is based on high basal levels of growth hormone, low insulin like growth factor-I (IGF-1) level, unresponsiveness to IGF generation test and genetic testing. Recombinant IGF-1 preparations are used in the treatment

CONCLUSION

In this article, clinical characteristics, diagnosis and therapeutic approaches of the genetic and other diseases leading to growth hormone insensitivity are reviewed.

Different intracellular signalling pathways triggered by an anti-prolactin receptor (PRLR) antibody: Implication for a signal-specific PRLR agonist

In this work, we prepared a panel of monoclonal antibodies directed against prolactin receptor (PRLR) using the hybridoma technique. Of these monoclonal antibodies (Mabs), the Mab designated B6 was chosen for further characterization based on its biological activity. We first demonstrated that B6 can specifically bind to the prolactin receptor (PRLR) expressed on target cells by immunoprecipitation and Western blotting analysis. Subsequently, epitope mapping studies using a competitive receptor-binding assay indicated that B6 epitopes partially overlapped with those of prolactin (PRL). We then examined the resulting signal transduction pathways activated by this antibody in T-47D and CHO-PRLR cells and found that B6 induced different intracellular signalling compared with prolactin, which activates serine-threonine kinase (AKT), extracellular signal-regulated kinase 1/2 (ERK1/2), signal transducer and activator of transcription1 (STAT1) and STAT3 but not STAT5. The present study suggests that: (a) B6 may be a signal-specific prolactin receptor (PRLR) agonist; (b) B6 may be a biological reagent that can be used to explore the mechanism of PRLR-mediated intracellular signalling. In addition, this work also implies a strategy for preparing signal-specific cytokine agonists.

Fusion Proteins for Half-Life Extension of Biologics as a Strategy to Make Biobetters

The purpose of making a "biobetter" biologic is to improve on the salient characteristics of a known biologic for which there is, minimally, clinical proof of concept or, maximally, marketed product data. There already are several examples in which second-generation or biobetter biologics have been generated by improving the pharmacokinetic properties of an innovative drug, including Neulasta(®) [a PEGylated, longer-half-life version of Neupogen(®) (filgrastim)] and Aranesp(®) [a longer-half-life version of Epogen(®) (epoetin-α)]. This review describes the use of protein fusion technologies such as Fc fusion proteins, fusion to human serum albumin, fusion to carboxy-terminal peptide, and other polypeptide fusion approaches to make biobetter drugs with more desirable pharmacokinetic profiles.

Development and characterization of a novel GHR antibody antagonist, GF185

Here, we describe the development of a panel of monoclonal antibodies targeting the growth hormone receptor (GHR). Of these monoclonal antibodies (Mabs), GF185 was selected for further characterization due to its activities. Competitive receptor-binding assays and Western blotting analyses were used to demonstrate that GF185's epitopes are localized within subdomain 1 of the growth hormone receptor extracellular domain (GHR-ECD). Subsequently, we evaluated GF185's antagonistic activities in vivo and in vitro and showed that GF185 was able to neutralize growth hormone (GH) signalling and inhibit GH-induced Ba/F3-GHR proliferation. Our findings suggest that GF185 may serve as an attractive tool for GHR-related research and has a potential future application for the treatment of GH-dependent disease.

Intracellular signaling transduction pathways triggered by a well-known anti-GHR monoclonal antibody, Mab263, in vitro and in vivo

A series of studies have reported that monoclonal antibody 263 (Mab263), a monoclonal antibody against the growth hormone receptor (GHR), acts as an agonist in vitro and in vivo. However, the intracellular signaling pathways triggered by Mab263 have not yet been delineated. Therefore, we examined the intracellular signaling pathways induced by Mab263 in vivo and in vitro in the present study. The results show that this antibody activated janus kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), STAT1 and extracellular signal-regulated kinase 1/2 (ERK1/2), but not STAT5. The phosphorylation kinetics of JAK2, STAT3/1 and ERK1/2 induced by Mab263 were subsequently analyzed in dose-response and time course experiments. Our observations indicate that Mab263 induced different intracellular signaling pathways than GH, which indicates that Mab263 is a signal-specific molecule and that Mab263 may be a valuable biological reagent to study the mechanism(s) of GHR-mediated intracellular signaling pathways.