GH Activity Research Articles

Abstract 584: Identification of mutations in HSV-1 envelope glycoprotein B that enhance retargeted infection

Abstract Conditionally-replicating herpes simplex virus type 1 (HSV-1) vectors, including mutants deleted for the neurovirulence factor ICP34.5 currently in clinical trials, are promising agents for oncolytic virotherapy. As an alternative strategy to accomplish cytocidal HSV replication exclusively in cancer cells, we have designed modified viral envelope glycoproteins to limit virus entry uniquely to EGF receptor (EGFR)-bearing cells. HSV-1 entry is initiated by the interaction of glycoprotein D (gD) with one of its receptors, herpesvirus entry mediator (HVEM) or nectin-1. Receptor binding results in a conformational change in gD triggering activation of gB and gH as the effectors of fusion between the viral envelope and cell membranes. To target virus entry solely to EGFR-expressing cells, we mutated or deleted gD residues essential for binding to the natural entry receptors and inserted an EGFR-specific single-chain antibody (scFv). Although ablation of virus entry through HVEM and nectin-1 was successful, entry through the EGFR was detectable but inefficient. To address this flaw, we carried out in vitro evolution experiments to isolate gain-of-function mutations that could compensate for defective gD-receptor interactions. We passaged a nectin-1-binding impaired HSV-1 mutant repeatedly through cells expressing a gD-binding impaired nectin-1 until visible plaques appeared. Plaque purification and sequence analysis revealed that each isolate contained the same double mutation in gB. We transferred the gB double mutation into wild-type virus and observed entry into cells that are normally resistant to HSV infection due to the absence of authentic gD receptors. In addition, we found that the mutant-gB virus was capable of entering cells through nectins other than nectin-1, and that entry into nectin-1-bearing cells was markedly accelerated compared to wild-type virus. We combined the gB double mutation with the EGFR-retargeted gD allele and found that this combination yielded increased entry into target cells without raising off-target infection. We are currently expanding this strategy to target other cancer-specific cell-surface markers. By enhancing the efficiency of retargeted infection, the gB double mutation is likely to reduce the need for strong mutations in current oncolytic vectors that not only prevent virus replication in normal cells, but also diminish replication in tumor cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 584.

Tyrosines 868, 966, and 972 in the Kinase Domain of JAK2 Are Autophosphorylated and Required for Maximal JAK2 Kinase Activity

Janus kinase 2 (JAK2) is activated by a majority of cytokine family receptors including receptors for GH, leptin, and erythropoietin. To identify novel JAK2-regulatory and/or -binding sites, we set out to identify autophosphorylation sites in the kinase domain of JAK2. Two-dimensional phosphopeptide mapping of in vitro autophosphorylated JAK2 identified tyrosines 868, 966, and 972 as sites of autophosphorylation. Phosphorylated tyrosines 868 and 972 were also identified by mass spectrometry analysis of JAK2 activated by an erythropoietin-bound chimeric erythropoietin receptor/leptin receptor. Phosphospecific antibodies suggest that the phosphorylation of all three tyrosines increases in response to GH. Compared with wild-type JAK2, which is constitutively active when overexpressed, JAK2 lacking tyrosine 868, 966, or 972 has substantially reduced activity. Coexpression with GH receptor and protein tyrosine phosphatase1B allowed us to investigate GH-dependent activation of these mutated JAK2s in human embryonic kidney 293T cells. All three mutated JAK2s are activated by GH, although to a lesser extent than wild-type JAK2. The three mutated JAK2s also mediate GH activation of signal transducer and activator of transcription 3 (Stat3), signal transducer and activator of transcription 5b (Stat5b) and ERK1, but at reduced levels. Coexpression with Src-homology 2B1beta (SH2B1beta), like coexpression with GH-bound GH receptor, partially restores the activity of all three JAK2 mutants. Based on these results and the crystal structure of the JAK2 kinase domain, we hypothesize that small changes in the conformation of the regions of JAK2 surrounding tyrosines 868, 966, and 972 due to e.g. phosphorylation, binding to a ligand-bound cytokine receptor, and/or binding to Src-homology 2B1, may be essential for JAK2 to assume a maximally active conformation.

Growth Hormone (GH) Deficiency Type II: A Novel GH-1 Gene Mutation (GH-R178H) Affecting Secretion and Action

ABSTRACT Context and Objective Main features of the autosomal dominant form of GH deficiency (IGHD II) include markedly reduced secretion of GH combined with low concentrations of IGF-I leading to short stature. Design, Setting, and Patients A female patient presented with short stature (height −6.0 sd score) and a delayed bone age of 2 yr at the chronological age of 5 yr. Later, at the age of 9 yr, GHD was confirmed by standard GH provocation test, which revealed subnormal concentrations of GH and a very low IGF-I. Genetic analysis of the GH-1 gene revealed the presence of a heterozygous R178H mutation. Interventions and Results AtT-20 cells coexpressing both wt-GH and GH-R178H showed a reduced GH secretion after forskolin stimulation compared with the cells expressing only wt-GH, supporting the diagnosis of IGHD II. Because reduced GH concentrations found in the circulation of our untreated patient could not totally explain her severe short stature, functional characterization of the GH-R178H performed by studies of GH receptor binding and activation of the Janus kinase-2/signal transducer and activator of transcription-5 pathway revealed a reduced binding affinity of GH-R178H for GH receptor and signaling compared with the wt-GH. Conclusion This is the first report of a patient suffering from short stature caused by a GH-1 gene alteration affecting not only GH secretion (IGHD II) but also GH binding and signaling, highlighting the necessity of functional analysis of any GH variant, even in the alleged situation of IGHD II.

Growth Hormone (GH) Deficiency Type II: A Novel GH-1 Gene Mutation (GH-R178H) Affecting Secretion and Action

Main features of the autosomal dominant form of GH deficiency (IGHD II) include markedly reduced secretion of GH combined with low concentrations of IGF-I leading to short stature. A female patient presented with short stature (height -6.0 sd score) and a delayed bone age of 2 yr at the chronological age of 5 yr. Later, at the age of 9 yr, GHD was confirmed by standard GH provocation test, which revealed subnormal concentrations of GH and a very low IGF-I. Genetic analysis of the GH-1 gene revealed the presence of a heterozygous R178H mutation. AtT-20 cells coexpressing both wt-GH and GH-R178H showed a reduced GH secretion after forskolin stimulation compared with the cells expressing only wt-GH, supporting the diagnosis of IGHD II. Because reduced GH concentrations found in the circulation of our untreated patient could not totally explain her severe short stature, functional characterization of the GH-R178H performed by studies of GH receptor binding and activation of the Janus kinase-2/signal transducer and activator of transcription-5 pathway revealed a reduced binding affinity of GH-R178H for GH receptor and signaling compared with the wt-GH. This is the first report of a patient suffering from short stature caused by a GH-1 gene alteration affecting not only GH secretion (IGHD II) but also GH binding and signaling, highlighting the necessity of functional analysis of any GH variant, even in the alleged situation of IGHD II.

Total and high molecular weight adiponectin are elevated in patients with Laron syndrome despite marked obesity

Patients with Laron syndrome (LS; primary GH insensitivity) caused by molecular defects of the GH receptor gene, are characterized by dwarfism, profound obesity, and hyperlipidemia. The aim of the current study was to evaluate adiponectin levels in LS, as obesity is known to be associated with low adiponectin. We studied nine untreated LS adult patients (5 males, 4 females) and six girls with LS receiving once-daily treatment by IGF1. Total and high molecular weight (HMW) adiponectin levels, adiponectin multimers distribution, and metabolic indices were analyzed in serum samples obtained during several years of follow-up. Adiponectin levels in the severely obese adult LS patients (percent body fat; females 61.0+/-2.5%, males 40.6+/-8.1%) were two- to three-fold higher than those reported for subjects of corresponding age, gender and degree of adiposity. Total adiponectin was significantly higher in females compared with males (21.4+/-3.5 vs 10.2+/-4.6 microg/ml, P<0.001). The elevated adiponectin in LS subjects was associated with an increased abundance of the HMW isoform, and positively correlated with body fat percentage (r=0.65, P=0.017) and leptin (r=0.65, P=0.012). There was no correlation between adiponectin levels (total and HMW) and the degree of insulin resistance in LS subjects or their blood lipids levels. Adiponectin was also high in young girls with LS (22.9+/-7.4 microg/ml) and did not change during long-term IGF1 replacement therapy. Adiponectin hypersecretion in LS, despite profound obesity, suggests that GH activity may negatively impact adiponectin secretion from adipocytes.

Desempenho profissional ou doméstico das pacientes em quimioterapia para câncer de mama

Evaluate patients with breast cancer undergoing chemotherapy with respect to their epidemiologic and clinical variables as well as performance at work or at home. this was a cross-sectional study including 52 women interviewed during breast cancer chemotherapy, stratified in two groups: those who continued to work and do household tasks, and did not continue to work or do household tasks. Patients were from two public hospitals in the State of São Paulo, one in Santo Andre and the other in São Bernardo do Campo. The WPAI - GH (Work Productivity and Activity Impairment) questionnaire was used to evaluate work and household performance of professionals or housewives, respectively. Mean age of the patients was 55.7 (SD=13.8), most were Caucasian (88.5%), married (55.8%), employed (65.3%) and the majority had to stop working because of treatment (51.0%), at more advanced stage (p<0.05), fatigue and nausea (p<0.05). Mean WPAI - GH was 67.04 (|SD = 5.62) for patients who stopped working and 49.17 (SD = 6.89) for those who continued to work (Mann-Whitney U test: p = 0.04). Chemotherapy leads to a decrease in performance of a sizable fraction of women with breast cancer undergoing chemotherapy. A more advanced stage of neoplasia was positively associated with withdrawal from these activities probably due to side effects such as fatigue and nausea.

Stimulation of the rat medullary raphe nuclei induces differential responses in respiratory muscle activity

Neural control circuits that coordinate the motor activity of the diaphragm (DIA) and the geniohyoid muscle (GH) are potentially involved in pathological conditions such as various forms of sleep apnea. Here we investigated a differential role of the raphe magnus (RMg), pallidus (RPa) and the obscurus (ROb) nuclei in the neural control of DIA and GH muscle activity in rats under volatile anesthesia. In order to characterize a topographical organization of the raphe nuclei we analyzed changes in DIA and GH during high-frequency stimulation (HFS, 10-130 Hz, 60 micros pulse width, 40-160 microA, 30s). HFS of the RMg and the ROb induced apnea, in the latter case apnea was associated with massive tonic discharge in the GH. By contrast, HFS of the RPa induced tachypnea. At caudal stimulation sites the tachypnea was accompanied by tonic DIA activity and cessation of GH. These data suggest a differential distribution of inhibitory and excitatory drives of DIA and GH muscles within distinct raphe nuclei.

P-33 ACTH releasing activity of GH releasing peptide-2 in patients with hypothalamo-pituitary diseases

P-33 ACTH releasing activity of GH releasing peptide-2 in patients with hypothalamo-pituitary diseases

JAK2, But Not Src Family Kinases, Is Required for STAT, ERK, and Akt Signaling in Response to Growth Hormone in Preadipocytes and Hepatoma Cells

Janus kinase 2 (JAK2), a tyrosine kinase that associates with the GH receptor and is activated by GH, has been implicated as a key mediator of GH signaling. Several published reports suggest that members of the Src family of tyrosine kinases may also participate in GH signaling. We therefore investigated the extent to which JAK2 and Src family kinases mediate GH activation of signal transducers and activators of transcription (STATs) 1, 3, and 5a/b, ERKs 1 and 2, and Akt, in the highly GH-responsive cell lines 3T3-F442A preadipocytes and H4IIE hepatoma cells. GH activation of Src family kinases was not detected in either cell line. Further, blocking basal activity of Src kinases with the Src inhibitors PP1 and PP2 did not inhibit GH activation of STATs 1, 3, or 5a/b, or ERKs 1 and 2. When levels of JAK2 were depressed by short hairpin RNA in 3T3-F442A and H4IIE cells, GH-stimulated activation of STATs 1, 3, and 5a/b, ERKs 1 and 2, and Akt were significantly reduced; however, basal activity of Src family kinases was unaffected. These results were supported genetically by experiments showing that GH robustly activates JAK2, STATs 3 and 5a/b, ERKs 1 and 2, and Akt in murine embryonic fibroblasts derived from Src/Yes/ Fyn triple-knockout embryos that lack known Src kinases. These results strongly suggest that JAK2, but not Src family kinases, is critical for transducing these GH signals in 3T3-F442A and H4IIE cells.

Regulation of Suppressor of Cytokine Signaling 3 (SOC3) by Growth Hormone in Pro-B Cells

Suppressor of cytokine signaling 3 (SOCS3) is expressed by lymphoid cells and can modulate the sensitivity of these cells to cytokine stimulation through inhibition of Janus kinase (JAK)/signal transducers and activators of transcription (STAT) signaling pathways. This study employed a mouse pro-B cell line expressing the human GH receptor (BaF/3-GHR), to elucidate the signal transduction pathways used by GH to elicit SOCS3 expression. GH treatment of these cells caused a rapid, dose-dependent increase in SOCS3 mRNA expression, which was independent of de novo protein synthesis. As expected, GH treatment increased JAK-dependent STAT5 tyrosine phosphorylation, which bound to the proximal STAT response element (pSRE) on the SOCS3 promoter. This process appeared to involve STAT5b, rather than STAT5a. In addition, GH activation of the SOCS3 promoter required a nearby activator protein (AP) 1/cAMP response element (CRE), which bound cAMP response element binding protein, c-Fos, and c-Jun. Moreover, inhibitors of p38 MAPK and c-Jun N-terminal kinase prevented GH-stimulation of SOCS3 mRNA expression in these cells, suggesting a role for these kinases in SOCS3 transcription. Importantly, GH stimulation increased binding of FOXO3a to the SOCS3 promoter at a site overlapping the AP1/CRE response element, and overexpression of FOXO3a in these cells augmented SOCS3 promoter activation. In addition, we show a direct interaction between FOXO3a and STAT5 in these cells, which may provide a link between STAT5 and the AP1 transcription factors on the SOCS3 promoter. We conclude that regulation of SOCS3 expression by GH in a pro-B cell involves not only the pSRE, but also a transcriptionally active complex involving cAMP response element binding protein/c-Fos/c-Jun and FOXO3a. This study has implications for cytokine regulation of SOCS gene expression in lymphoid cells.

Activities of the Muscles Involved in Swallowing in Patients with Cleft Lip and Palate

This study was designed to examine the nature of the activity of swallowing muscles in patients with cleft lip and palate (CLP). The electromyographic activity of the thyrohyoid muscle (TH), the geniohyoid muscle (GH), and the myohyoid muscle (MH) of patients with CLP (CLP group) was analyzed and compared with noncleft subjects (control group) during swallowing and drinking water with and without artificial nasal obstruction. In the normal situation without nasal obstruction, a significant (p < 0.01) difference in muscle activity between the two groups was found only for TH. In the control group, the duration and magnitude of muscle activity were significantly (p < 0.01) larger in all the muscles when a nasal obstruction was applied. Meanwhile, in the CLP group these values exhibited a significant (p < 0.05) increase in GH and MH only. With nasal obstruction, the burst durations of GH and MH became significantly (p < 0.01) longer in the control group than in the CLP group. The amplitude of GH activity during swallowing was significantly (p < 0.05) larger in the control group than in the CLP group. These results suggest that in CLP patients during swallowing, TH working from the pharyngeal stage compensates for the weakness of GH and MH working in the oral phase. This may cause a premature transfer of the bolus to the pharynx before making it properly into the oral cavity.

Regulation of Growth Hormone Signaling by Selective Estrogen Receptor Modulators Occurs through Suppression of Protein Tyrosine Phosphatases

Activation of the Janus kinase 2 (JAK2)/signal transducer and activator of transcription 5 (STAT5) pathway by GH is terminated by the suppressors of cytokine signaling (SOCSs) and protein tyrosine phosphatases, Src homology 2 domain-containing protein tyrosine phosphatase (SHP)-1 and SHP-2. Based on our recent report that estrogen inhibits GH signaling by stimulating SOCS-2 expression, we investigated the effects of selective estrogen receptor modulators (SERMs) on GH signaling in human embryonic kidney (HEK293) and breast cancer (MDA-MB-231) cells expressing human GH receptor and estrogen receptor-alpha. 17beta-estradiol (E(2)) suppressed GH activation of a STAT5-responsive luciferase reporter and JAK2 phosphorylation in both cell models. 4-hydroxytamoxifen and raloxifene augmented these actions of GH in HEK293 cells but not breast cancer cells. SOCS-2 expression in both cell types was stimulated by E(2) but unaffected by SERMs. In HEK293 cells, SHP-1 was inhibited by raloxifene and 4-hydroxytamoxifen, whereas the latter additionally inhibited SHP-2. The phosphatases were unaffected by E(2). In breast cancer cells, phosphatase activity was not altered by SERMs or E(2). In summary, estrogen inhibited the JAK2/STAT5 signaling of GH and stimulated SOCS-2 expression in both HEK293 and breast cancer cells. By contrast, SERMs augmented GH signaling by reducing SHP activities in HEK293 cells and had no effect on both in breast cancer cells. We provide the first evidence for a novel mechanism regulating GH signaling, in which SERMs enhance GH activation of the JAK2/STAT5 pathway in a cell-type-dependent manner by attenuating protein tyrosine phosphatase activities.

Serum Growth Hormone and Glucose Levels in Acute Exercise and in the Recovery Period in Athletes

Growth hormone exerts several metabolic effects, including effects on proteins, fats and carbohydrates. Among the many metabolic activities of GH, two contradictory actions were described: acute and early insulin-like activity and chronic and late anti-insulin like activity also called diabetogenic activity. A dramatic increase in plasma concentration of GH was found during endurance exercise, but its role during exercise is not well known. According to its metabolic effects a possible role of growth hormone may be in maintenance of glucose level during exercise. The aim of this study was to analyze dynamics of changes in GH and glucose levels during acute workload and in the recovery period, in a group of well trained athletes. All the subjects exercised for 30 minutes on cycle ergometer in sitting position (work intensity 50% of VO2 max, RPM 60/min). Serum GH concentrations were measured by IRMA (immunoradiometric assays) method in blood samples obtained at rest and 6-min intervals during exercise, and 15-min intervals during recovery period. Serum glucose levels were determined by standard enzymatic method glucose oxidase (GOD PAP) at the same intervals. There were no correlations between serum GH and glucose levels either during exercise or in the recovery period. There were no differences between glucose levels during exercise, so we can not exclude possible role of GH in glucose concentration maintenance.

Diethyl pyrocarbonate, a histidine-modifying agent, directly stimulates activity of ATP-sensitive potassium channels in pituitary GH 3 cells

The ATP-sensitive K + (K ATP) channels are composed of sulfonylurea receptor and inwardly rectifying K + channel (Kir6.2) subunit. These channels are regulated by intracellular ADP/ATP ratio and play a role in cellular metabolism. Diethyl pyrocarbonate (DEPC), a histidine-specific alkylating reagent, is known to modify the histidine residues of the structure of proteins. The objective of this study was to determine whether DEPC modifies K ATP-channel activity in pituitary GH 3 cells. Steady-state fluctuation analyses of macroscopic K + current at −120 mV produced power spectra that could be fitted with a single Lorentzian curve in these cells. The time constants in the presence of DEPC were increased. Consistent with fluctuation analyses, the mean open time of K ATP-channels was significantly increased during exposure to DEPC. However, DEPC produced no change in single-channel conductance, despite the ability of this compound to enhance K ATP-channel activity in a concentration-dependent manner with an EC 50 value of 16 μM. DEPC-stimulated K ATP-channel activity was attenuated by pretreatment with glibenclamide. In current–clamp configuration, DEPC decreased the firing of action potentials in GH 3 cells. A further application of glibenclamide reversed DEPC-induced inhibition of spontaneous action potentials. Intracellullar Ca 2+ measurements revealed the ability of DEPC to decrease Ca 2+ oscillations in GH 3 cells. Simulation studies also demonstrated that the increased conductance of K ATP-channels used to mimic DEPC actions reduced the frequency of spontaneous action potentials and fluctuation of intracellular Ca 2+. The results indicate that chemical modification with DEPC enhances K ATP-channel activity and influences functional activities of pituitary GH 3 cells.

Suppressor of Cytokine Signaling-2 Deficiency Induces Molecular and Metabolic Changes that Partially Overlap with Growth Hormone-Dependent Effects

Suppressor of cytokine signaling-2 (SOCS2)-deficient (SOCS2-/-) mice grow significantly larger than their littermates, suggesting that SOCS2 is important in the negative regulation of the actions of GH and/or IGF-I. The aim of this study was to identify genes and metabolic parameters that might contribute to the SOCS2-/- phenotype. We demonstrate that although SOCS2 deficiency induces significant changes in hepatic gene expression, only a fraction of these overlap with known GH-induced effects in the liver, suggesting that SOCS2 might be an important regulator of other growth factors and cytokines acting on the liver. However, an important role of GH and IGF-I in the phenotype of these animals was demonstrated by an overexpression of IGF-binding protein-3 mRNA in the liver and increased levels of circulating IGF-binding protein-3. Other GH-like effects included diminished serum triglycerides and down-regulation of lipoprotein lipase in adipose tissue. Interestingly, SOCS2-/- mice did not differ from their wild-type littermates in glucose or insulin tolerance tests, which is in contrast with the known diabetogenic effects of GH. Furthermore, there was no evidence of impaired insulin signaling in primary hepatocytes isolated from SOCS2-/- mice. Moreover, increased expression of peroxisome proliferator-activated receptor-gamma coactivator-1alpha mRNA was detected in skeletal muscle, which might contribute to normal glycemic control despite the apparent overactivity of the GH/IGF-I axis. Our data indicate that SOCS2 deficiency partially mimics a state of increased GH activity, but also results in changes that cannot be related to known GH effects.

The ontogeny of pulsatile growth hormone secretion and its temporal relationship to the onset of puberty in the agonadal male rhesus monkey (Macaca mulatta).

The pubertal amplification of GH secretion in primates has been thought to reflect an increase in gonadal steroid hormones due to gonadotropin stimulation induced by hypothalamic GnRH release. Previous studies in agonadal, peripubertal, male rhesus monkeys have estimated the age of GnRH activation (defined as d 0) using analyses of nocturnal, pulsatile LH patterns derived from sequential blood samples. Using samples from these earlier studies, secretory patterns of GH were analyzed using Cluster at approximately 30-d intervals in the youngest prepubertal ages and at approximately 10- to 20-d intervals in the period immediately preceding and following the onset of puberty. Pulse frequency, amplitude, and mean GH increased significantly between early prepubertal ages (up to 30 d before d 0) and the late prepubertal period (between -20 d and d 0). Pulsatile GH activity increased earlier than pulsatile LH secretion in four of five animals. These findings support the conclusion that pulsatile GH secretion increases developmentally in the absence of gonadal steroids. Furthermore, the present observation that the developmental increase in GH secretion occurs earlier than previously reported is consistent with the possibility that GH itself either directly or indirectly participates in the pubertal reinitiation of GnRH pulse generator activity.

Pituitary Mapping

1662 PURPOSE: The purpose of this study was to examine the responses and adaptations of pituitary gland to produce immunoreactive growth hormone (iGH) in response to an acute resistance exercise stress before and after training in rats. METHODS: A 4-group block design: pre-training (i.e., pre-exercise group and post-exercise group) and post-training (pre-exercise group and post-exercise groups) was used. Twelvemonth old male Sprage-Dawley rats were randomly assigned to one of the 4 groups (n = 9/group). The acute exercise stress and the resistance training protocol consisted of climbing a 1-meter long ladder set at an 85o angle with a weight attached to a tail sleeve. The exercise session consisted of 10 individual repetitions of climbing with each repetition separated by a 2 min rest period. The training program was performed 3 days per week for 7 weeks. The mass lifted was gradually increased from 50 g to 535 g by the conclusion of the training program. Rats were kept on a 12: 12 h light dark cycle at 21o C and provided standard laboratory animal chow ad libitum. The Institutional Animal Care and Use Committee approved all procedures. Rats were euthanized by decapitation and immediately following death the pituitary was harvested and subsequently analyzed dividing the gland into eight distinct anatomical sections. Basal GH release was measured from sections placed in gyrotory incubation for three consecutive periods (20 min each). Tissues and cells were analyzed by light microscopy and flow cytometry. Immunoassay was used to detect iGH signals in both the peripheral blood and pituitary media with immunocytohistochemistry performed on pituitary slices to determine GH activity. RESULTS: Exercise significantly (P<0.05) increased GH concentrations and number of GH producing cells in the pituitary after exercise. With training the number of GH producing cells after exercise increased as well as [GH] in the blood and media when compared to pre-training values. No significant changes for iGH were observed pre-exercise. Surprisingly, no significant differences were observed among the different quadrants of the pituitary for the iGH signals. CONCLUSIONS: These data indicate that post-exercise increases in the concentrations of iGH with resistance exercise and training are due to an increased number of GH producing cells throughout the pituitary gland. A lack of changes at rest for iGH supports human observations of little or no changes in iGH with resistance training. How other molecular variants of the GH molecule or aggregates respond to resistance exercise and training and are anatomically located in the pituitary remains to be further characterized.

Ghα/tissue transglutaminase 2: an emerging G protein in signal transduction

Gh protein is an heterodimer made up of two subunits α and β. Different from the traditional monomeric and heterotrimeric G proteins, Ghα subunit exhibits both GTPase and transglutaminase activities whereas Ghβ was identified as calreticulin. Activation of Gh by G protein-coupled receptors (GPCR) turns off transglutaminase activity and shifts Ghα to signal transducer. Thereafter, Ghα regulates downstream effectors. All these aspects are discussed in the present review, in order to shed new light on this atypical G protein.

Epidermal homeostasis: the role of the growth hormone and insulin-like growth factor systems.

GH and IGF-I and -II were first identified by their endocrine activity. Specifically, IGF-I was found to mediate the linear growth-promoting actions of GH. It is now evident that these two growth factor systems also exert widespread activity throughout the body and that their actions are not always interconnected. The literature highlights the importance of the GH and IGF systems in normal skin homeostasis, including dermal/epidermal cross-talk. GH activity, sometimes mediated via IGF-I, is primarily evident in the dermis, particularly affecting collagen synthesis. In contrast, IGF action is an important feature of the dermal and epidermal compartments, predominantly enhancing cell proliferation, survival, and migration. The locally expressed IGF binding proteins play significant and complex roles, primarily via modulation of IGF actions. Disturbances in GH and IGF signaling pathways are implicated in the pathophysiology of several skin perturbations, particularly those exhibiting epidermal hyperplasia (e.g., psoriasis, carcinomas). Additionally, many studies emphasize the potential use of both growth factors in the treatment of skin wounds; for example, burn patients. This overview concerns the role and mechanisms of action of the GH and IGF systems in skin and maintenance of epidermal integrity in both health and disease.

Seeking the optimal target range for insulin-like growth factor I during the treatment of adult growth hormone disorders.

Impaired GH activity at target tissues, occurring when GH action is blocked or during suboptimal GH replacement therapy, may result in a pathological state associated with lowering of IGF-I, but not GH levels. Such a state represents functional but not necessarily actual GH deficiency (GHD). The aim of this study was to identify a range of IGF-I values commensurate with GHD, which could be used to determine the risk of functional GHD during the treatment of adult GH disorders. Centrally measured baseline IGF-I data from the Kabi International Metabolic Study European GHD database were analyzed. Inclusion criteria were adult-onset GHD and two or more additional anterior pituitary hormone deficits. Adults with childhood-onset GHD and cured acromegaly were excluded. The cohort was stratified into six gender-based age ranges. Baseline IGF-I measurements from 376 females (median age, 48 yr; range, 21-77 yr) and 434 males (median age 52 yr; range 21-80 yr) were analyzed. Data were not normally distributed and are presented as medians (quartiles). The median serum IGF-I and IGF-I SDS in males were 94.0 microg/liter (64 and 141) and -1.52 (-2.53 and -0.456; n = 434). Both were significantly greater than the equivalent values of females, which were 73 microg/liter (46 and 103.5) and -2.30 (-3.28 and -1.328; n = 376; P < 0.0001 for both). Age and gender-related 90th and 95th percentiles for IGF-I SDS were determined to generate risk estimates for functional GHD, which, in conjunction with the clinical status of the patient, may be used to aid dose titration during treatment of GH disorders in adulthood.