Distribution and abundance of messenger ribonucleic acid for growth hormone receptor isoforms in human tissues

Tmem263 deletion disrupts the GH/IGF-1 axis and causes dwarfism and impairs skeletal acquisition

Genome-wide association studies (GWAS) have identified a large number of candidate genes believed to affect longitudinal bone growth and bone mass. One of these candidate genes, TMEM263, encodes a poorly characterized plasma membrane protein. Single nucleotide polymorphisms in TMEM263 are associated with bone mineral density in humans and mutations are associated with dwarfism in chicken and severe skeletal dysplasia in at least one human fetus. Whether this genotype-phenotype relationship is causal, however, remains unclear. Here, we determine whether and how TMEM263 is required for postnatal growth. Deletion of the Tmem263 gene in mice causes severe postnatal growth failure, proportional dwarfism, and impaired skeletal acquisition. Mice lacking Tmem263 show no differences in body weight within the first 2 weeks of postnatal life. However, by P21 there is a dramatic growth deficit due to a disrupted growth hormone (GH)/insulin-like growth factor 1 (IGF-1) axis, which is critical for longitudinal bone growth. Tmem263-null mice have low circulating IGF-1 levels and pronounced reductions in bone mass and growth plate length. The low serum IGF-1 in Tmem263-null mice is associated with reduced hepatic GH receptor (GHR) expression and GH-induced JAK2/STAT5 signaling. A deficit in GH signaling dramatically alters GH-regulated genes and feminizes the liver transcriptome of Tmem263-null male mice, with their expression profile resembling wild-type female, hypophysectomized male, and Stat5b-null male mice. Collectively, our data validates the causal role for Tmem263 in regulating postnatal growth and raises the possibility that rare mutations or variants of TMEM263 may potentially cause GH insensitivity and impair linear growth.

Reduced high-intensity training distance in growing horses had no effect on IGF-1 concentrations, but training onset interrupted time-dependent IGF-1 decline

This study investigated plasma insulin like growth factor (IGF)-1 concentrations in 16 young Standardbred horses introduced to systematic high-intensity training at two different levels of intensity. Growth and locomotion asymmetry and correlations between these and plasma IGF-1 concentrations were also examined. From September as 1-year olds to March as 2-year olds (Period 1), all horses were subjected to the same submaximal training program. In March (start of Period 2), the horses were divided into two groups (n=8) and one group was introduced to regular high-intensity training. The other group was introduced to a program where the high-intensity exercise distances were reduced by 30%. These two training programs were maintained for the remaining 21 months of the study (Periods 2, 3, and 4). There was no effect of training group on plasma IGF-1 concentrations. A continuous decline in IGF-1 levels was observed throughout the study (P<0.0001), with one notable interruption in Period 2 when the IGF-1 concentration remained at the level seen at the start of Period 1. Growth rate of body length was equally high in Periods 1 and 2 (P>0.05). Front and hind limb asymmetry was elevated in Period 2 compared with Period 1. There were positive correlations between IGF-1 concentrations and changes in body condition score, and a negative correlation between IGF-1 concentration and weight. These results indicate that introduction to high-intensity training induces IGF-1 release in horses, but that a 30% difference in the distances used in high-intensity training does not affect IGF-1 levels. The temporary interruption in decline in IGF-1 release with the onset of high-intensity training may influence growth pattern and locomotion asymmetry, but further studies are needed to assess causality.

Local non-pituitary growth hormone is induced with aging and facilitates epithelial damage

Microenvironmental factors modulating age-related DNA damage are unclear. Non-pituitary growth hormone (npGH) is induced in human colon, non-transformed human colon cells, and fibroblasts, and in 3-dimensional intestinal organoids with age-associated DNA damage. Autocrine/paracrine npGH suppresses p53 and attenuates DNA damage response (DDR) by inducing TRIM29 and reducing ATM phosphorylation, leading to reduced DNA repair and DNA damage accumulation. Organoids cultured up to 4 months exhibit aging markers, p16, and SA-β-galactosidase and decreased telomere length, as well as DNA damage accumulation, with increased npGH, suppressed p53, and attenuated DDR. Suppressing GH in aged organoids increases p53 and decreases DNA damage. WT mice exhibit age-dependent colon DNA damage accumulation, while in aged mice devoid of colon GH signaling, DNA damage remains low, with elevated p53. As age-associated npGH induction enables a pro-proliferative microenvironment, abrogating npGH signaling could be targeted as anti-aging therapy by impeding DNA damage and age-related pathologies.

Chesnokova et al. show that non-pituitary growth hormone (npGH) is induced in aging DNA-damaged colon epithelium and suppresses DNA damage response by attenuating the phosphorylation of DNA repair proteins. npGH induction promotes DNA damage accumulation, resulting in age-associated colon microenvironment changes. Accordingly, disrupted GH signaling in aging mice prevents accumulated DNA damage.

Growth Plate Chondrocytes: Skeletal Development, Growth and Beyond

Growth plate chondrocytes play central roles in the proper development and growth of endochondral bones. Particularly, a population of chondrocytes in the resting zone expressing parathyroid hormone-related protein (PTHrP) is now recognized as skeletal stem cells, defined by their ability to undergo self-renewal and clonally give rise to columnar chondrocytes in the postnatal growth plate. These chondrocytes also possess the ability to differentiate into a multitude of cell types including osteoblasts and bone marrow stromal cells during skeletal development. Using single-cell transcriptomic approaches and in vivo lineage tracing technology, it is now possible to further elucidate their molecular properties and cellular fate changes. By discovering the fundamental molecular characteristics of these cells, it may be possible to harness their functional characteristics for skeletal growth and regeneration. Here, we discuss our current understanding of the molecular signatures defining growth plate chondrocytes.

The Role of Growth Hormone in Mesenchymal Stem Cell Commitment

Growth hormone (GH) is best known for its prominent role in promoting prepubertal growth and in regulating body composition and metabolism during adulthood. In recent years, the possible role of GH in the modulation of mesenchymal stem cell (MSC) commitment has gained interest. MSCs, characterized by active self-renewal and differentiation potential, express GH receptors. In MSCs derived from different adult tissues, GH induces an inhibition of adipogenic differentiation and favors MSC differentiation towards osteogenesis. This activity of GH indicates that regulation of body composition by GH has already started in the tissue progenitor cells. These findings have fostered research on possible uses of MSCs treated with GH in those pathologies, where a lack of or delays in bone repair occur. After an overview of GH activities, this review will focus on the research that has characterized GH’s effects on MSCs and on preliminary studies on the possible application of GH in bone regenerative medicine.

Expression of the growth hormone receptor isoforms and its correlation with the metabolic profile in morbidly obese subjects

BACKGROUND AND AIM OF THE STUDY

Given the lipolytic effect of GH and its potential role in determining adipose tissue distribution, we evaluated the expression of the GH hormone receptor (GHR) isoforms in patients with morbid obesity seeking associations with metabolic parameters.

METHODS

262 morbidly obese subjects (mean age 42.5 ± 11 years, 75% women) underwent PCR-genotyping of the exon 3 GHR polymorphism. In 17 of these subjects, who proved to be heterozygous for the exon 3 genotype (+3/-3), subcutaneous and visceral adipose tissue was obtained during bariatric surgery; total RNA was extracted, reversely transcribed, and the different isoforms of the GHR (exon 3 containing and lacking flGHR as well as the trGHR) were PCR-amplified using specific primers.

RESULTS

27% were +3/+3 homozygous, 20% -3/-3 homozygous and 53% were +3/-3 heterozygous. Compared to subjects homozygous for the +3 genotype, homozygous and heterozygous carriers of the -3 genotype were significantly heavier and tended to have a higher HOMA 2-IR. Expression of the flGHR and trGHR mRNA was demonstrated in all evaluated samples of subcutaneous and visceral adipose tissue from the 17 patients. The exon 3+ isoform was expressed in all adipose tissue samples, whereas only six subjects expressed the 3- isoform as well. The only distinctive feature of these six patients was a higher HbA1c.

CONCLUSIONS

The heterozygous GHR +3/-3 genotype is more prevalent in subjects with morbid obesity. Patients expressing the exon +3 and exon -3 isoforms in adipose tissue had a higher HbA1c, than those expressing only the exon -3 isoform.

Abrogation of GH action in Kupffer cells results in increased hepatic CD36 expression and exaggerated nonalcoholic fatty liver disease

OBJECTIVE

To investigate the effects of GH signaling on Kupffer cells and the resulting changes in lipid homeostasis and their underlying mechanism(s) in the livers of diet-induced obese (DIO) mice.

DESIGN

Male macrophage specific-growth hormone receptor knockout mice (MacGHR KO) and their litter mate controls were fed a high fat diet containing 60% calories from fat for 26 weeks. Lipid content and lipid profiles in the liver and circulation were analyzed. Expression levels of CD36 in the liver were quantified by RT-PCR and Western Blot.

RESULTS

Increased hepatic lipid content and abundance of long-chain unsaturated fatty acids were observed in the liver of MacGHR KO mice. These findings were associated with increased steady state levels of CD36 mRNA and protein in MacGHR KO mice when compared with their litter mate controls.

CONCLUSION

GH action in Kupffer cells is required for maintaining hepatic lipid homeostasis, in part via regulation of hepatic CD36 expression.

Expression of a hindlimb-determining factor Pitx1 in the forelimb of the lizard Pogona vitticeps during morphogenesis

With over 9000 species, squamates, which include lizards and snakes, are the largest group of reptiles and second-largest order of vertebrates, spanning a vast array of appendicular skeletal morphology. As such, they provide a promising system for examining developmental and molecular processes underlying limb morphology. Using the central bearded dragon (Pogona vitticeps) as the primary study model, we examined limb morphometry throughout embryonic development and characterized the expression of three known developmental genes (GHR, Pitx1 and Shh) from early embryonic stage through to hatchling stage via reverse transcription quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry (IHC). In this study, all genes were found to be transcribed in both the forelimbs and hindlimbs of P. vitticeps. While the highest level of GHR expression occurred at the hatchling stage, Pitx1 and Shh expression was greatest earlier during embryogenesis, which coincides with the onset of the differentiation between forelimb and hindlimb length. We compared our finding of Pitx1 expression—a hindlimb-determining gene—in the forelimbs of P. vitticeps to that in a closely related Australian agamid lizard, Ctenophorus pictus, where we found Pitx1 expression to be more highly expressed in the hindlimb compared with the forelimb during early and late morphogenesis—a result consistent with that found across other tetrapods. Expression of Pitx1 in forelimbs has only rarely been documented, including via in situ hybridization in a chicken and a frog. Our findings from both RT-qPCR and IHC indicate that further research across a wider range of tetrapods is needed to more fully understand evolutionary variation in molecular processes underlying limb morphology.

Neurotrophic and Neuroregenerative Effects of GH/IGF1

Introduction. Human neurodegenerative diseases increase progressively with age and present a high social and economic burden. Growth hormone (GH) and insulin-like growth factor-1 (IGF-1) are both growth factors exerting trophic effects on neuronal regeneration in the central nervous system (CNS) and peripheral nervous system (PNS). GH and IGF-1 stimulate protein synthesis in neurons, glia, oligodendrocytes, and Schwann cells, and favor neuronal survival, inhibiting apoptosis. This study aims to evaluate the effect of GH and IGF-1 on neurons, and their possible therapeutic clinical applications on neuron regeneration in human subjects. Methods. In the literature, we searched the clinical trials and followed up studies in humans, which have evaluated the effect of GH/IGF-1 on CNS and PNS. The following keywords have been used: “GH/IGF-1” associated with “neuroregeneration”, “amyotrophic lateral sclerosis”, “Alzheimer disease”, “Parkinson’s disease”, “brain”, and “neuron”. Results. Of the retrieved articles, we found nine articles about the effect of GH in healthy patients who suffered from traumatic brain injury (TBI), and six studies (four using IGF-1 and two GH therapy) in patients with amyotrophic lateral sclerosis (ALS). The administration of GH in patients after TBI showed a significantly positive recovery of brain and mental function. Treatment with GH and IGF-1 therapy in ALS produced contradictory results. Conclusions. Although strong findings have shown the positive effects of GH/IGF-1 administration on neuroregeneration in animal models, a very limited number of clinical studies have been conducted in humans. GH/IGF-1 therapy had different effects in patients with TBI, evidencing a high recovery of neurons and clinical outcome, while in ALS patients, the results are contradictory. More complex clinical protocols are necessary to evaluate the effect of GH/IGF-1 efficacy in neurodegenerative diseases. It seems evident that GH and IGF-1 therapy favors the optimal recovery of neurons when a consistent residual activity is still present. Furthermore, the effect of GH/IGF-1 could be mediated by, or be overlapped with that of other hormones, such as estradiol and testosterone.

The impact of growth hormone on proteomic profiles: a review of mouse and adult human studies

Growth hormone (GH) is a protein that is known to stimulate postnatal growth, counter regulate insulin's action and induce expression of insulin-like growth factor-1. GH exerts anabolic or catabolic effects depending upon on the targeted tissue. For instance, GH increases skeletal muscle and decreases adipose tissue mass. Our laboratory has spent the past two decades studying these effects, including the effects of GH excess and depletion, on the proteome of several mouse and human tissues. This review first discusses proteomic techniques that are commonly used for these types of studies. We then examine the proteomic differences found in mice with excess circulating GH (bGH mice) or mice with disruption of the GH receptor gene (GHR^-/-). We also describe the effects of increased and decreased GH action on the proteome of adult patients with either acromegaly, GH deficiency or patients after short-term GH treatment. Finally, we explain how these proteomic studies resulted in the discovery of potential biomarkers for GH action, particularly those related with the effects of GH on aging, glucose metabolism and body composition.

Growth Hormone Resistance-Special Focus on Inflammatory Bowel Disease

Growth hormone (GH) plays major anabolic and catabolic roles in the body and is important for regulating several aspects of growth. During an inflammatory process, cells may develop a state of GH resistance during which their response to GH stimulation is limited. In this review, we will emphasize specific mechanisms governing the formation of GH resistance in the active phase of inflammatory bowel disease. The specific molecular effects mediated through individual inflammatory mediators and processes will be highlighted to provide an overview of the transcriptional, translational and post-translational inflammation-mediated impacts on the GH receptor (GHR) along with the impacts on GH-induced intracellular signaling. We also will review GH’s effects on mucosal healing and immune cells in the context of experimental colitis, human inflammatory bowel disease and in patients with short bowel syndrome.

Growth Hormone and Craniofacial Tissues. An update

Growth hormone is an important regulator of bone homeostasis. In childhood, it determines the longitudinal bone growth, skeletal maturation, and acquisition of bone mass. In adulthood, it is necessary to maintain bone mass throughout life. Although an association between craniofacial and somatic development has been clearly established, craniofacial growth involves complex interactions of genes, hormones and environment. Moreover, as an anabolic hormone seems to have an important role in the regulation of bone remodeling, muscle enhancement and tooth development. In this paper the influence of growth hormone on oral tissues is reviewed.

Regulation of human growth hormone receptor expression by microRNAs

Human GH binds to its receptor (GHR) on target cells and activates multiple intracellular pathways, leading to changes in gene expression, differentiation, and metabolism. GHR deficiency is associated with growth and metabolic disorders whereas increased GHR expression has been reported in certain cancers, suggesting that the GHR gene requires tight controls. Several regulatory mechanisms have been found within its 5'-untranslated region (UTR) promoter and coding regions. However, the 3'-UTR has not been previously examined. MicroRNAs (miRNAs) are small (19-22 nucleotides) noncoding RNAs that downregulate gene expression mainly through targeting the 3'-UTR of mRNAs and enhancing their degradation or inhibiting translation. In the present study, we investigated whether miRNAs regulate GHR expression. To define putative miRNA binding sites in the GHR 3'-UTR, we used multiple in silico prediction tools, analyzed conservation across species and the presence of parallel sites in GH/IGF axis-related genes, and searched for reports linking miRNAs to GHR-related physiological or pathophysiological activities. To test prioritized sites, we cotransfected a wild-type GHR 3'-UTR luciferase reporter vector as well as miRNA binding site mutants into HEK293 cells with miRNA mimics. Furthermore, we tested whether the miRNAs altered endogenous GHR mRNA and protein levels in HEK293 cells and in 2 cancer cell lines (MCF7 and LNCaP). Our experiments have identified miRNA (miR)-129-5p, miR-142-3p, miR-202, and miR-16 as potent inhibitors of human GHR expression in normal (HEK293) and cancer (MCF7 and LNCaP) cells. This study paves the way for the development of miRNA inhibitors as therapeutic agents in GH/GHR-related pathophysiologies, including cancer.

Effect of GH/IGF-1 on Bone Metabolism and Osteoporsosis

Background. Growth hormone (GH) and insulin-like growth factor (IGF-1) are fundamental in skeletal growth during puberty and bone health throughout life. GH increases tissue formation by acting directly and indirectly on target cells; IGF-1 is a critical mediator of bone growth. Clinical studies reporting the use of GH and IGF-1 in osteoporosis and fracture healing are outlined. Methods. A Pubmed search revealed 39 clinical studies reporting the effects of GH and IGF-1 administration on bone metabolism in osteopenic and osteoporotic human subjects and on bone healing in operated patients with normal GH secretion. Eighteen clinical studies considered the effect with GH treatment, fourteen studies reported the clinical effects with IGF-1 administration, and seven related to the GH/IGF-1 effect on bone healing. Results. Both GH and IGF-1 administration significantly increased bone resorption and bone formation in the most studies. GH/IGF-1 administration in patients with hip or tibial fractures resulted in increased bone healing, rapid clinical improvements. Some conflicting results were evidenced. Conclusions. GH and IGF-1 therapy has a significant anabolic effect. GH administration for the treatment of osteoporosis and bone fractures may greatly improve clinical outcome. GH interacts with sex steroids in the anabolic process. GH resistance process is considered.

Abnormal adipose tissue distribution with unfavorable metabolic profile in five children following hematopoietic stem cell transplantation: a new etiology for acquired partial lipodystrophy

We report five consecutive patients who underwent hematopoietic stem cell transplantation (HSCT) to treat leukemia or neuroblastoma early in their lives and later manifested abnormal patterns of adipose tissue distribution. Lipoatrophy was remarkable in the gluteal regions and extremities, whereas subcutaneous fat was preserved in the cheeks, neck, and abdomen. In addition, visceral fat deposition, fatty changes in the liver, and metabolic derangements such as insulin resistance and hypertriglyceridemia were evident. These features resemble Dunnigan-type familial partial lipodystrophy, which is a rare condition caused by LMNA gene mutation. These patients shared a common medical history involving HSCT, including conditioning with total body irradiation (TBI). They also received intensive chemotherapy because of multiple metastases (n = 3), relapse (n = 3), and repetitive HSCT (n = 3). We propose HSCT as a new etiology for acquired partial lipodystrophy and recommend that patients who undergo HSCT with TBI and intensive chemotherapy early in their lives must receive careful observation for the possible development of lipodystrophy and metabolic complications.

Abnormal adipose tissue distribution with unfavorable metabolic profile in five children following hematopoietic stem cell transplantation: a new etiology for acquired partial lipodystrophy

We report five consecutive patients who underwent hematopoietic stem cell transplantation (HSCT) to treat leukemia or neuroblastoma early in their lives and later manifested abnormal patterns of adipose tissue distribution. Lipoatrophy was remarkable in the gluteal regions and extremities, whereas subcutaneous fat was preserved in the cheeks, neck, and abdomen. In addition, visceral fat deposition, fatty changes in the liver, and metabolic derangements such as insulin resistance and hypertriglyceridemia were evident. These features resemble Dunnigan-type familial partial lipodystrophy, which is a rare condition caused by LMNA gene mutation. These patients shared a common medical history involving HSCT, including conditioning with total body irradiation (TBI). They also received intensive chemotherapy because of multiple metastases (n = 3), relapse (n = 3), and repetitive HSCT (n = 3). We propose HSCT as a new etiology for acquired partial lipodystrophy and recommend that patients who undergo HSCT with TBI and intensive chemotherapy early in their lives must receive careful observation for the possible development of lipodystrophy and metabolic complications.

Green tea polyphenols reduce body weight in rats by modulating obesity-related genes

Beneficial effects of green tea polyphenols (GTP) against obesity have been reported, however, the mechanism of this protection is not clear. Therefore, the objective of this study was to identify GTP-targeted genes in obesity using the high-fat-diet-induced obese rat model. A total of three groups (n = 12/group) of Sprague Dawley (SD) female rats were tested, including the control group (rats fed with low-fat diet), the HF group (rats fed with high-fat diet), and the HF+GTP group (rats fed with high-fat diet and GTP in drinking water). The HF group increased body weight as compared to the control group. Supplementation of GTP in the drinking water in the HF+GTP group reduced body weight as compared to the HF group. RNA from liver samples was extracted for gene expression analysis. A total of eighty-four genes related to obesity were analyzed using PCR array. Compared to the rats in the control group, the rats in the HF group had the expression levels of 12 genes with significant changes, including 3 orexigenic genes (Agrp, Ghrl, and Nr3c1); 7 anorectic genes (Apoa4, Cntf, Ghr, IL-1β, Ins1, Lepr, and Sort); and 2 genes that relate to energy expenditure (Adcyap1r1 and Adrb1). Intriguingly, the HF+GTP group restored the expression levels of these genes in the high-fat-induced obese rats. The protein expression levels of IL-1β and IL-6 in the serum samples from the control, HF, and HF+GTP groups confirmed the results of gene expression. Furthermore, the protein expression levels of superoxide dismutase-1 (SOD1) and catechol-O-methyltransferase (COMT) also showed GTP-regulated protective changes in this obese rat model. Collectively, this study revealed the beneficial effects of GTP on body weight via regulating obesity-related genes, anti-inflammation, anti-oxidant capacity, and estrogen-related actions in high-fat-induced obese rats.

βTrCP controls GH receptor degradation via two different motifs

The physiological roles of GH are broad and include metabolism regulation and promotion of somatic growth. Therefore, the responsiveness of cells to GH must be tightly regulated. This is mainly achieved by a complex and well-controlled mechanism of GH receptor (GHR) endocytosis. GHR endocytosis occurs independently of GH and requires the ubiquitin ligase, SCF (βTrCP) that is recruited to the ubiquitin-dependent endocytosis (UbE) motif in the cytoplasmic tail of the GHR. In this study we report that, in addition to the UbE motif, a downstream degron, DSGRTS, binds to βTrCP. The WD40 residues on βTrCP involved in the interaction with this sequence are identical to the ones necessary for binding the classical motif, DSGxxS, in inhibitor of NFκB signalling, and β-catenin. Previously, we showed that this motif is not involved in GH-induced endocytosis. We show here that the DSGRTS sequence significantly contributes to GHR endocytosis/degradation in basal conditions, whereas the UbE motif is involved both in basal and GH-induced conditions. These findings explain the high rate of GHR degradation under basal conditions, which is important for regulating the responsiveness of cells to GH.

Extrapituitary growth hormone

Pituitary somatotrophs secrete growth hormone (GH) into the bloodstream, to act as a hormone at receptor sites in most, if not all, tissues. These endocrine actions of circulating GH are abolished after pituitary ablation or hypophysectomy, indicating its pituitary source. GH gene expression is, however, not confined to the pituitary gland, as it occurs in neural, immune, reproductive, alimentary, and respiratory tissues and in the integumentary, muscular, skeletal, and cardiovascular systems, in which GH may act locally rather than as an endocrine. These actions are likely to be involved in the proliferation and differentiation of cells and tissues prior to the ontogeny of the pituitary gland. They are also likely to complement the endocrine actions of GH and are likely to maintain them after pituitary senescence and the somatopause. Autocrine or paracrine actions of GH are, however, sometimes mediated through different signaling mechanisms to those mediating its endocrine actions and these may promote oncogenesis. Extrapituitary GH may thus be of physiological and pathophysiological significance.

GH-binding protein is related to bone mineral density in non-obese androgenized women

GH and IGF system components are important regulators of bone formation and at the same time pathogenetic factors in functional hyperandrogenism (FH) in lean females. We studied the relationships between bone mineral density (BMD) and serum concentrations of GH, GH-related parameters, androgens and estrogen, in 18 non-obese women of reproductive age with functional hyperandrogenism compared to a group of 10 healthy eumenorrheic age- and weight-matched women. In androgenized women, a significant positive correlation was found between BMD and GH-binding protein (GHBP), whereas BMD did not correlate to GH or other related parameters. It is suggested that higher tissue GH receptor responsiveness in non-obese androgenized women may contribute to their higher BMD.

Estrogen inhibits GH signaling by suppressing GH-induced JAK2 phosphorylation, an effect mediated by SOCS-2

Oral estrogen administration attenuates the metabolic action of growth hormone (GH) in humans. To investigate the mechanism involved, we studied the effects of estrogen on GH signaling through Janus kinase (JAK)2 and the signal transducers and activators of transcription (STATs) in HEK293 cells stably expressing the GH receptor (293GHR), HuH7 (hepatoma) and T-47D (breast cancer) cells. 293GHR cells were transiently transfected with an estrogen receptor-alpha expression plasmid and luciferase reporters with binding elements for STAT3 and STAT5 or the beta-casein promoter. GH stimulated the reporter activities by four- to sixfold. Cotreatment with 17beta-estradiol (E(2)) resulted in a dose-dependent reduction in the response of all three reporters to GH to a maximum of 49-66% of control at 100 nM (P < 0.05). No reduction was seen when E(2) was added 1-2 h after GH treatment. Similar inhibitory effects were observed in HuH7 and T-47D cells. E(2) suppressed GH-induced JAK2 phosphorylation, an effect attenuated by actinomycin D, suggesting a requirement for gene expression. Next, we investigated the role of the suppressors of cytokine signaling (SOCS) in E(2) inhibition. E(2) increased the mRNA abundance of SOCS-2 but not SOCS-1 and SOCS-3 in HEK293 cells. The inhibitory effect of E(2) was absent in cells lacking SOCS-2 but not in those lacking SOCS-1 and SOCS-3. In conclusion, estrogen inhibits GH signaling, an action mediated by SOCS-2. This paper provides evidence for regulatory interaction between a sex steroid and the GHJAKSTAT pathway, in which SOCS-2 plays a central mechanistic role.