Stimulation of mitogen-activated protein kinase pathway in rat somatotrophs by growth hormone-releasing hormone

Prolactin and Growth Hormone Signaling and Interlink Focused on the Mammosomatotroph Paradigm: A Comprehensive Review of the Literature

Prolactin (PRL) and growth hormone (GH) are peptide hormones that bind to the class 1 cytokine receptor superfamily, a highly conserved cell surface class of receptors. Both hormones control their own secretion via a negative autocrine loop in their own mammosomatotroph, lactotroph or somatotroph. In this regard, GH and PRL are regulated by similar signaling pathways involving cell growth and hormone secretion. Thus, GH and PRL dysregulation and pituitary neuroendocrine tumor (PitNET) development may have common pathogenic pathways. Based on cell linage, lactotroph and somatotroph PitNETs come from pituitary-specific POU-class homeodomain transcription factor (Pit-1). Mammosomatotroph and plurihormonal PitNETs are a unique subtype of PitNETs that arise from a single-cell population of Pit-1 lineage. In contrast, mixed somatotroph-lactotroph PitNETs are composed of two distinct cell populations: somatotrophs and lactotrophs. Morphologic features that distinguish indolent PitNETs from locally aggressive ones are still unidentified, and no single prognostic parameter can predict tumor aggressiveness or treatment response. In this review, we aim to explore the latest research on lactotroph and somatotroph PitNETs, the molecular mechanisms involved in PRL and GH axis regulation and the signaling pathways involved in their aggressiveness, particularly focused on mammosomatotroph and mixed subtypes. Finally, we summarize epidemiological, clinical, and radiological features of these exceptional tumors. We aim to shed light, from basic to clinical settings, on new perspectives and scientific gaps in this field.

Proteomic analysis of hypothalamus in prepubertal and pubertal female goat

The functions of proteins at the onset of puberty in goats remain largely unexplored. To identify the proteins regulating puberty in goats, we analysed protein abundance and pathways in the hypothalamus of female goats. We applied tandem mass tag (TMT) labelling, liquid chromatography-tandem mass spectrometry (LC-MS/MS), and parallel reaction monitoring (PRM) to examine hypothalamus of pubertal (cases; n = 3) and prepubertal (controls; n = 3) goats. We identified 5119 proteins, including 69 differentially abundant proteins (DAPs), of which 35 were upregulated and 34 were downregulated. Fourteen DAPs were randomly selected to verify these results using PRM, and the results were consistent with the TMT quantitative results. DAPs were enriched in MAPK signalling pathway, Ras signalling pathway, Autophagy-animal, Endocytosis, and PI3K/Akt/mTOR signalling pathway categories. These pathways are related to embryogenesis, cell proliferation, cell differentiation, and promoting the release of gonadotropin-releasing hormone (GnRH) in the hypothalamus. In particular, PDGFRβ and MAP3K7 occupied important locations in the protein-protein interaction network. The results demonstrate that DAPs and their related signalling pathways are crucial in regulating puberty in goats. However, further research is needed to explore the functions of DAPs and their pathways to provide new insights into the mechanism of puberty onset. SIGNIFICANCE: In domestic animals, reaching the age of puberty is an event that contributes significantly to lifetime reproductive potential. And the hypothalamus functions directly in the complex systemic changes that control puberty. Our study was the first TMT proteomics analysis on hypothalamus tissues of pubertal goats, which revealed the changes of protein and pathways that are related to the onset of puberty. We identified 69 DAPs, which were enriched in the MAPK signaling pathway, the Ras signaling pathway, and the IGF-1/PI3K/Akt/mTOR pathway, suggesting that these processes were probably involved in the onset of puberty.

Case report: The cardio-facio-cutaneous syndrome due to a novel germline mutation in MAP2K1: A multifaceted disease with immunodeficiency and short stature

Cardio-facio-cutaneous syndrome (CFCS) belongs to the group of RASopathies, clinical disorders defined by disruptions in the RAS/MAPK signaling pathway. It is caused by heterozygous gain-of-function germline mutations in genes encoding protein kinases: BRAF, MAP2K1 (MEK1), MAP2K2 (MEK2), and in the GTPase-encoding gene KRAS. CFCS is characterized by craniofacial dysmorphic features, congenital heart defects, severe malnutrition, proportionate short stature, anomalies within the structure of skin and hair, and psychomotor disability. The pathophysiology of growth impairment is multifactorial with feeding difficulties, growth hormone deficiency, and insensitivity. Immunodeficiency has not been hitherto reported as an integral part of CFCS yet an increased activation of the RAS/MAPK signaling pathway may contribute to explaining the causal relationship between RASopathy and the dysfunctions within the B and T lymph cell compartments resulting in a deficiency in T cell costimulation and B cell maturation with impaired class switch recombination, somatic hypermutation, and high-affinity antibody production. We report on a boy born prematurely at 32 WGA, with the perinatal period complicated by pneumonia, respiratory distress syndrome, and valvular pulmonary stenosis. The boy suffered from recurrent pneumonia, obstructive bronchitis, sepsis, urinary tract infection, and recurrent fevers. He presented with severe hypotrophy, psychomotor disability, short stature, craniofacial dysmorphism, dental hypoplasia, sparse hair, and cryptorchidism. Whole genome sequencing showed a novel heterozygous pathogenic germline missense variant: c.364A > G; p.Asn122Asp in the MAP2K1 gene, supporting the diagnosis of CFCS. The immunological workup revealed hypogammaglobulinemia, IgG subclass, and specific antibody deficiency accompanied by decreased numbers of T helper cells and naive and memory B cells. Replacement immunoglobulin therapy with timely antibiotic prophylaxis were instituted. At the age of six years, growth hormone deficiency was diagnosed and the rGH therapy was started. The ever-increasing progress in genetic studies contributes to establishing the definitive CFCS diagnosis and sheds the light on the interrelated genotype-phenotype heterogeneity of RASopathies. Herein, we add new phenotypic features of predominating humoral immunodeficiency to the symptomatology of CFCS with a novel mutation in MAP2K1. While CFCS is a multifaceted disease, increased pediatricians' awareness is needed to prevent the delay in diagnostics and therapeutic interventions.

Clinical and molecular spectra of BRAF-associated RASopathy

Noonan syndrome (NS) and cardio-facio-cutaneous (CFC) syndrome are the most common subtypes of RASopathy. As an effector of Ras, BRAF is one of the molecules responsible for RASopathy. We investigated the phenotypic and genotypic features of 26 patients with BRAF-associated RASopathy. The clinical diagnoses were CFC (n = 21, 80.8%), NS (n = 3, 11.5%), NS/CFC (n = 1, 3.8%), and undefined syndromic intellectual disability (ID) (n = 1, 3.8%). The mostly shared phenotypes were ID (90.5%), cutaneous manifestations (84.6%), congenital heart defects (76.9%), short stature (76.9%), and dysmorphic features such as short neck (65.4%) and low-set ears (65.4%). Importantly, moderate to severe ID (57.1%) and epilepsy (26.9%) were noted. Eighteen different missense mutations were found, including a novel mutation, p.Phe498Tyr. p.Gln257Arg (n = 9, 34.6%) was the most common mutation, and the mutations were clustered in the cysteine-rich domain or protein kinase domain. A review of previously reported cases along with our findings revealed the existence of multiple sub-phenotypes of RASopathy within a single genotype, indicating that BRAF-associated RASopathy is not variant-specific. Our study further delineated the diverse and expanded clinical phenotypes of BRAF-associated RASopathy with their molecular genetic characteristics.

RASopathies Are Associated With Delayed Puberty; Are They Associated With Precocious Puberty Too?

RASopathies, such as Noonan, Costello, and cardio-facio-cutaneous syndromes, are developmental disorders caused by mutations in rat sarcoma-mitogen-activated protein kinase pathway genes. Mutations that cause Noonan syndrome have been associated with delayed puberty. Here we report 4 patients with either Costello or cardio-facio-cutaneous syndrome who developed precocious puberty, suggesting complex regulation of the hypothalamic-pituitary-gonadal axis and the timing of puberty by the rat sarcoma-mitogen-activated protein kinase pathway. Additional study of the timing of puberty among patients with RASopathies is warranted to ascertain the incidence of delayed and precocious puberty in these conditions and to examine genotype-phenotype correlations, which may provide insight into pathways that regulate the timing of puberty.

Growth Hormone-Releasing Hormone in Diabetes

Growth hormone-releasing hormone (GHRH) is produced by the hypothalamus and stimulates growth hormone synthesis and release in the anterior pituitary gland. In addition, GHRH is an important regulator of cellular functions in many cells and organs. Expression of GHRH G-Protein Coupled Receptor (GHRHR) has been demonstrated in different peripheral tissues and cell types, including pancreatic islets. Among the peripheral activities, recent studies demonstrate a novel ability of GHRH analogs to increase and preserve insulin secretion by beta-cells in isolated pancreatic islets, which makes them potentially useful for diabetes treatment. This review considers the role of GHRHR in the beta-cell and addresses the unique engineered GHRH agonists and antagonists for treatment of type 2 diabetes mellitus. We discuss the similarity of signaling pathways activated by GHRHR in pituitary somatotrophs and in pancreatic beta-cells and possible ways as to how the GHRHR pathway can interact with glucose and other secretagogues to stimulate insulin secretion. We also consider the hypothesis that novel GHRHR agonists can improve glucose metabolism in Type 2 diabetes by preserving the function and survival of pancreatic beta-cells. Wound healing and cardioprotective action with new GHRH agonists suggest that they may prove useful in ameliorating certain diabetic complications. These findings highlight the future potential therapeutic effectiveness of modulators of GHRHR activity for the development of new therapeutic approaches in diabetes and its complications.

Cardio-facio-cutaneous syndrome: clinical features, diagnosis, and management guidelines

Cardio-facio-cutaneous syndrome (CFC) is one of the RASopathies that bears many clinical features in common with the other syndromes in this group, most notably Noonan syndrome and Costello syndrome. CFC is genetically heterogeneous and caused by gene mutations in the Ras/mitogen-activated protein kinase pathway. The major features of CFC include characteristic craniofacial dysmorphology, congenital heart disease, dermatologic abnormalities, growth retardation, and intellectual disability. It is essential that this condition be differentiated from other RASopathies, as a correct diagnosis is important for appropriate medical management and determining recurrence risk. Children and adults with CFC require multidisciplinary care from specialists, and the need for comprehensive management has been apparent to families and health care professionals caring for affected individuals. To address this need, CFC International, a nonprofit family support organization that provides a forum for information, support, and facilitation of research in basic medical and social issues affecting individuals with CFC, organized a consensus conference. Experts in multiple medical specialties provided clinical management guidelines for pediatricians and other care providers. These guidelines will assist in an accurate diagnosis of individuals with CFC, provide best practice recommendations, and facilitate long-term medical care.

The absence of somatotroph proliferation during continuous stress is a result of the lack of extracellular signal-regulated kinase 1/2 activation

The integrity of homeostasis can be affected by chronic stress, and hyposomatotropism is evident in chronic stress-associated illnesses. In the present study, we demonstrated that a continuous stress (CS) severely affected somatotrophs among hormone-secreting cells in the anterior lobe (AL) of the pituitary by using a rat CS model. Among AL cells, the proliferation of somatotrophs was almost entirely suppressed in rats that had 3-5 days of CS (5dCS), although other hormone-secreting cells continued to proliferate. The cell size of somatotrophs was reduced at 5dCS (P<0.01), the number of secretory granules was increased at 3dCS (P<0.01) and serum growth hormone (GH) was on declining trend during 1 to 5dCS, suggesting that GH release was inhibited. GH-releasing hormone (GHRH) mRNA level in the arcuate nucleus was transiently decreased, whereas its receptor expression in the AL was significantly increased in CS rats. When 5dCS rats were injected with GHRH, transient GH secretion was observed, whereas proliferation of somatotrophs did not occur. The GHRH administration failed to stimulate extracellular signal-regulated kinase (ERK) 1/2 phosphorylation and the nuclear translocation of ERK in somatotrophs. These results suggest that somatotrophs of 5dCS rats expressed sufficient GHRH receptor, which could transfer a signal for GH release. However, the GHRH-induced proliferation signal was blocked somewhere between the receptor and ERK1/2. Because significant increase of corticosterone in the initial stage (the 1-3dCS) was observed in this model, the corticosterone may affect the signalling. Although the mechanism underlying the blockage of the proliferation signal in somatotrophs under CS remains unclear, these somatotrophic disorder, suggesting that the present animal model may be useful for understanding the molecular mechanisms of chronic stress-associated illnesses.

The effect of GHRH antagonists on human glioblastomas and their mechanism of action

The effects of new growth hormone-releasing hormone (GHRH) antagonists JMR-132 and MIA-602 and their mechanism of action were investigated on 2 human glioblastoma cell lines, DBTRG-05 and U-87MG, in vitro and in vivo. GHRH receptors and their main splice variant, SV1 were found on both cell lines. After treatment with JMR-132 or MIA-602, the cell viability decreased significantly. A major decrease in the levels of phospho-Akt, phospho-GSK3β and phosho-ERK 1/2 was detected at 5 and 10 min following treatment with the GHRH antagonists, whereas elevated levels of phospho-p38 were observed at 24 hr. The expression of caspase-3 and poly(ADP-ribose) (PARP), as the downstream executioners of apoptosis were found to be significantly elevated after treatment. Following treatment of the glioblastoma cells with GHRH antagonists, nuclear translocation of apoptosis inducing factor (AIF) and Endonuclease G (Endo G) and the mitochondrial release of cytochrome c (cyt c) were detected, indicating that the cells were undergoing apoptosis. In cells treated with GHRH antagonists, the collapse of the mitochondrial membrane potential was shown with fluorescence microscopy and JC-1 membrane potential sensitive dye. There were no significant differences between results obtained in DBTRG-05 or U-87MG cell lines. After treatment with MIA-602 and JMR-132, the reduction rate in the growth of DBTRG-05 glioblastoma, xenografted into nude mice, was significant and tumor doubling time was also significantly extended when compared with controls. Our study demonstrates that GHRH antagonists induce apoptosis through key proapoptotic pathways and shows the efficacy of MIA-602 for experimental treatment of glioblastoma.

Antagonists of growth hormone-releasing hormone inhibit the proliferation of human benign prostatic hyperplasia cells

BACKGROUND

Growth hormone-releasing hormone (GHRH), besides stimulating the secretion of GH from the pituitary gland, acts as an autocrine/paracrine growth factor in many cancers. Antagonists of GHRH inhibit growth of experimental human tumors, but their effects on benign prostatic hyperplasia (BPH) have not been studied.

MATERIALS AND METHODS

We evaluated the effects of GHRH and GHRH antagonists JMR-132, MZ-5-156, MIA-601, and MIA-479 on the proliferation rate of human BPH-1 cells. We also measured by Western blot the influence of GHRH and GHRH antagonist JMR-132 on the expression of the PCNA and the activation of ERK1/2 and JAK/STAT3.

RESULTS

BPH-1 cells express GHRH and GHRH-receptor proteins. The proliferation rate of BPH-1 cells is increased by GHRH and inhibited by all the GHRH antagonists, the latest analogs MIA-601 and MIA-479 being the most potent. The stimulatory effect of GHRH is nullified by GHRH antagonists. GHRH strongly activates and GHRH antagonists significantly suppress the expression of the PCNA and the phosphorylation of ERK1/2 and JAK2/STAT3 pathways in these cells. Treatment with JAK2 inhibitor (AG490) decreases the proliferation rate of BPH-1 cells, and AG490 does nullify the effect of GHRH.

CONCLUSION

This study demonstrates for the first time that GHRH can act as a growth factor in BPH-1 cells and that GHRH antagonists can reverse its stimulatory effect. New observations are provided on the mechanism of action of GHRH antagonists in BPH. Our findings support the merit of further work on the development of GHRH antagonists for therapy of BPH.

Activation of Janus kinase/signal transducer and activator of transcription 3 pathway by growth hormone-releasing hormone

Growth hormone-releasing hormone (GHRH) can act as a potent growth factor in various cancers. The mitogenic activity of this neuropeptide is exerted through binding to the pituitary type receptors (GHRH-R) or their splice variants (SV). In the present work, we studied whether this hormone can activate the JAK2/STAT3 pathway which plays a crucial role in cancer cell proliferation and is also linked to carcinogenesis. We transfected HeLa human cervical cancer cells, which are not sensitive to GHRH analogs with the pGHRH-R. Transfected cells responded to the GHRH or its antagonist with an increase or a decrease in proliferation, respectively. These results were confirmed by the expression of proliferating cell nuclear antigen. We then showed that these effects are linked to the activation of the JAK2/STAT3 pathway. Our work demonstrates the activation of JAK/STAT3 pathway by GHRH and sheds further light to the mechanisms of the antitumorogenic action of GHRH antagonists.

Stimulatory effect of growth hormone-releasing hormone (GHRH(1-29)NH2) on the proliferation, VEGF and chromogranin A secretion by human neuroendocrine tumor cell line NCI-H727 in vitro

Growth hormone-releasing hormone (GHRH) and its receptors have been implicated in a variety of cellular processes like cell survival, proliferation, apoptosis, angiogenesis and neoplastic transformation of various non-pituitary tissues. Here, we investigated for the first time the in vitro effect of GHRH(1-29)NH2 on the proliferation and the secretion of vascular endothelial growth factor (VEGF) and chromogranin A by the human bronchial neuroendocrine tumor cells NCI-H727. GHRH(1-29)NH2 at the concentrations of 10(-8)-10(-6)M increased the proliferation of these cells and this effect was associated with a statistically significant increase in VEGF and chromogranin A secretion into the supernatants of the tested cells. Our findings indicate that GHRH functions as a trophic hormone for bronchial neuroendocrine (NET) tumors.

Antioxidant activity of growth hormone-releasing hormone antagonists in LNCaP human prostate cancer line

Hypothalamic growth hormone-releasing hormone (GHRH) controls the release of growth hormone and acts as a growth factor in various tumors. Potent antagonistic analogues of GHRH have been synthesized that strongly suppress the growth of diverse cancers through several mechanisms. However, the influence of GHRH antagonists on the redox (reduction/oxidation) status of cancers has not been investigated. Cellular generation of reactive oxygen species (ROS) is central to redox signaling and is implicated in the initiation, development, and progression of cancer. In this study, we evaluated by Western blot the effects in vitro of GHRH and its antagonist JMR-132 on proliferating cell nuclear antigen, tumor suppressor protein p53, transcription factor NF-kappaB p50 and its phosphorylated form, caspase 3, and cleaved caspase 3 in the LNCaP human prostate cancer cell line. GHRH stimulated and GHRH antagonist inhibited the expression of the major antioxidant enzymes, as well as the expression of COX 2 and cytochrome c oxidase IV, which are enzymes involved in the generation of ROS. GHRH augmented and GHRH antagonist suppressed lipid and protein oxidative stress markers, as well as the intracellular generation of ROS. In all these tests, GHRH antagonists exerted strong antioxidant activity. Because the metabolism of ROS and oxidative stress have been associated with initiation and progression of not only prostate tumors but also other malignancies, our findings reinforce previous experimental evidence that GHRH antagonists could be useful for cancer therapy.

Effects of a high-glucose environment on the pituitary growth hormone-releasing hormone receptor: type 1 diabetes compared with in vitro glucotoxicity

The present study investigated the effects of diabetes and high glucose on GHRH receptor (GHRH-R) mRNA and protein levels in the pituitary of diabetic rats 2, 21, and 60 days post-streptozotocin (post-STZ) administration. Two days post-STZ, the 2.5-kb GHRH-R mRNA transcript was increased. Twenty-one days post-STZ, both the 2.5- and 4-kb transcripts and a 72-kDa (125)I-GHRH-GHRH-R complex were elevated. Sixty days post-STZ, the 4-kb transcript remained increased and the 45-kDa (125)I-GHRH-GHRH-R complex (functional receptor) was decreased. Hypothalamic GHRH mRNA and serum total IGF-I levels were reduced at all three time points. To better understand the role of high glucose on GHRH-R regulation, time-course effects of 33 compared with 6 mM d-glucose (DG) were examined in cultured anterior pituitary cells from 2-mo-old healthy rats. Membrane lipoperoxidation was present in 33 mM DG, and GHRH-R mRNA levels were diminished after 24 h, Fluo-GHRH internalization was marginal after 16-24 h, and GHRH-induced cAMP levels were decreased after 24 and 48 h. Altogether, these results indicate that the increase of the 2.5-kb GHRH-R mRNA transcript in vivo could be a consequence of a decrease of hypothalamic GHRH mRNA levels in STZ rats. Since it does not affect primarily functional GHRH-R levels, the initial diminution of circulating IGF-I levels could result from a decreased GHRH-R stimulation by GHRH. Thus, the effect of glucotoxicity would be related to a decrease of functional GHRH-R protein, as observed in rats 60 days post-STZ and in cultured pituitary cells from healthy rats exposed to a high-glucose environment.

GHRH proliferative action on somatotrophs is cell-type specific and dependent on Pit-1/GHF-1 expression

To investigate the mechanisms by which the hypothalamic peptide GHRH influences cell division, we analyzed its effects on the proliferation of two different cell lines: CHO-4, an ovary-derived cell line, and GH3, a pituitary-derived cell line. We found that GHRH induces the proliferation of pituitary-derived cells but inhibits the proliferation of ovary-derived cells. We further characterized this dual effect of GHRH to find that the cytoplasmic signals induced by this hormone are similar in both cell lines. Moreover, in CHO-4 cells GHRH stimulates two well-known positive cell cycle regulators, c-myc and cyclin D1, but is unable to induce the degradation of the negative cell cycle regulator p27(Kip1). Significantly, when the Pit-1/GHF-1 gene is exogenously expressed in CHO-4 cells, the negative effect of GHRH on the proliferation of these cells is attenuated. Furthermore, when the levels of Pit-1 are downregulated by siRNA in GH3-GHRHR cells, the positive effects of GHRH on the proliferation of these cells are diminished. These findings add to our understanding of the molecules involved in the regulation of cell proliferation by GHRH, as we demonstrate for the first time that Pit-1 is not only required to drive the expression of the GHRH receptor, as previously described, but is also needed for the downstream effects that occur after its activation to modulate cell proliferation. These data suggest that the regulation of cell proliferation in response to a specific growth factor depends in certain cell populations on the presence of a tissue-specific transcription factor.

Class II G protein-coupled receptors and their ligands in neuronal function and protection

G protein-coupled receptors (GPCRs) play pivotal roles in regulating the function and plasticity of neuronal circuits in the nervous system. Among the myriad of GPCRs expressed in neural cells, class II GPCRs which couples predominantly to the Gs-adenylate cyclase-cAMP signaling pathway, have recently received considerable attention for their involvement in regulating neuronal survival. Neuropeptides that activate class II GPCRs include secretin, glucagon-like peptides (GLP-1 and GLP-2), growth hormone-releasing hormone (GHRH), pituitary adenylate cyclase activating peptide (PACAP), corticotropin-releasing hormone (CRH), vasoactive intestinal peptide (VIP), parathyroid hormone (PTH), and calcitonin-related peptides. Studies of patients and animal and cell culture models, have revealed possible roles for class II GPCRs signaling in the pathogenesis of several prominent neurodegenerative conditions including stroke, Alzheimer's, Parkinson's, and Huntington's diseases. Many of the peptides that activate class II GPCRs promote neuron survival by increasing the resistance of the cells to oxidative, metabolic, and excitotoxic injury. A better understanding of the cellular and molecular mechanisms by which class II GPCRs signaling modulates neuronal survival and plasticity will likely lead to novel therapeutic interventions for neurodegenerative disorders.

Chemokine Stromal Cell-Derived Factor 1α Induces Proliferation and Growth Hormone Release in GH4C1 Rat Pituitary Adenoma Cell Line through Multiple Intracellular Signals

We used GH4C1 cells as a model to study the effects of the chemokine stromal cell-derived factor 1 (SDF1) in pituitary functions. In these cells, SDF1alpha induced proliferation and growth hormone secretion, suggesting a possible regulatory role for this chemokine at pituitary level. We evaluated the intracellular signaling involved in these effects: SDF1alpha increased cytosolic [Ca(2+)] and activated Pyk2, extracellular signal-regulated kinases 1 and 2 (ERK1/2), and large-conductance Ca(2+)-activated K(+) channels (BK(Ca)) channels. To correlate these intracellular effectors with the proliferative and secretory effects, we inhibited their activity using BAPTA-AM (Ca(2+) chelator), 2'-amino-3'-methoxyflavone (PD98059; a mitogen-activated protein kinase kinase inhibitor), salicylate (Pyk2 inhibitor), and tetraethyl ammonium (K(+) channel blocker). All of these compounds reverted SDF1alpha-induced proliferation, suggesting the involvement of multiple intracellular pathways. Conversely, only BAPTA-AM reverted growth hormone secretion. To identify a possible cross-talk and a molecular ordering among these pathways, we tested these antagonists on SDF1alpha-dependent activation of ERK1/2, Pyk2, and BK(Ca) channels. From these experiments, we observed that the inhibition of [Ca(2+)](i) increase or BK(Ca) channel activity did not affect ERK1/2 activation by SDF1alpha; Pyk2 activation was purely Ca(2+)-dependent, not involving ERK1/2 or BK(Ca) channels; and BK(Ca) channel activity was antagonized by Pyk2 but not by ERK1/2 inhibitors. These data suggest that an SDF1alpha-dependent increase of [Ca(2+)](i) activates Pyk2, which in turn regulates BK(Ca) channel activity. Conversely, ERK1/2 activation is an independent phenomenon. In conclusion, we demonstrate that SDF1alpha causes both proliferation and growth hormone release from pituitary adenoma cells, suggesting that the activation of CXCR4 may represent a novel regulatory mechanism for growth hormone secretion and pituitary cell proliferation, which may contribute to pituitary adenoma development.

Effects of hypothalamic neuropeptides on extracellular signal-regulated kinase (ERK1 and ERK2) cascade in human tumoral pituitary cells

The G protein-coupled receptor (GPCR) activation has been demonstrated to affect the ERK1/2 cascade in different cell lines. We investigated the effects of hypothalamic neuropeptides acting via GPCR on this pathway in GH-secreting (GH-oma) and nonsecreting (NFPA) pituitary adenomas. GHRH increased ERK1/2 activity (236 +/- 80%) in both gsp- and gsp+ GH-omas, this effect being almost completely abolished by protein kinase C (PKC) blockade. Both GnRH and pituitary adenylate-activating peptide caused a similar PKC-dependent activation of ERK1/2 in most NFPA. Increasing cAMP by forskolin caused a protein kinase A-dependent increase of ERK activity (287 +/- 37%) in GH-omas and had no effect in NFPA. ERK cascade blockade in GH-omas did not affect basal and GHRH-stimulated GH release, whereas it totally prevented the 3-fold increase in cyclin D1 protein expression induced by GHRH. In conclusion, this study demonstrated that in pituitary adenomas the activation of GPCR by neurohormones caused a PKC-dependent activation of ERK1/2 cascade that, at least in GH-omas, resulted to be involved in cyclin D1 induction by GHRH. Moreover, a stimulatory effect of the protein kinase A-dependent pathway on ERK1/2 cascade occurred selectively in GH-omas, probably contributing to the mitogenic potential of the cAMP pathway in this cell type.

International Union of Pharmacology. XXXV. The glucagon receptor family

Peptide hormones within the secretin-glucagon family are expressed in endocrine cells of the pancreas and gastrointestinal epithelium and in specialized neurons in the brain, and subserve multiple biological functions, including regulation of growth, nutrient intake, and transit within the gut, and digestion, energy absorption, and energy assimilation. Glucagon, glucagon-like peptide-1, glucagon-like peptide-2, glucose-dependent insulinotropic peptide, growth hormone-releasing hormone and secretin are structurally related peptides that exert their actions through unique members of a structurally related G protein-coupled receptor class 2 family. This review discusses advances in our understanding of how these peptides exert their biological activities, with a focus on the biological actions and structural features of the cognate receptors. The receptors have been named after their parent and only physiologically relevant ligand, in line with the recommendations of the International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR).

Antagonism of endogenous growth hormone-releasing hormone (GHRH) leads to reduced proliferation and apoptosis in MDA231 breast cancer cells

GHRH, in addition to stimulating the release of growth hormone (GH) from the pituitary, is a trophic factor for pituitary somatotrophs. Growth hormone-releasing hormone is also expressed in the gonads, gastrointestinal tract, pancreas, thymus, and lymphocytes, as well as in tumors of the pancreas, lung, central nervous system, and breast. Since GHRH has mitogenic effects, we examined the hypothesis that GHRH is an autocrine/paracrine growth factor in neoplastic breast tissue. The effect of disrupting endogenous GHRH on cell growth and apoptosis of MDA231 cells was examined through the use of a competitive GHRH antagonist, [N-acetyl-Tyr1, D-Arg2] fragment 1-29Amide (GHRHa). Cell proliferation was determined by direct cell counting and tritiated thymidine incorporation. Apoptosis was analyzed by examination of DNA laddering and nuclear condensation. GHRHa resulted in a dose-dependent, transient, and reversible decrease in cell number, proliferation rate, and tritiated thymidine uptake. Conversely, GHRHa led to a marked and dose-dependent increase in both DNA laddering and nuclear condensation. These results indicate that disruption of endogenous GHRH action in MDA231 cells results in both decreased cellular proliferation and increased apoptosis. Taken together, the findings suggest that endogenous GHRH acts as an autocrine/paracrine factor in the regulation of growth of at least some breast cancer cell types.

Peptides derived from pro-growth hormone-releasing hormone activate p38 mitogen-activated protein kinase in GH3 pituitary cells

Posttranslational processing of the pro-growth hormone-releasing hormone (proGHRH) peptide can result in the formation of at least two peptide products: GHRH and the C-terminal peptide, GHRH-related peptide (GHRH-RP). While cyclic adenosine monophosphate transduces many of the actions of GHRH, other pathways also have been implicated in its actions. The aims of this study were to examine and characterize the activation of mitogen-activated protein kinase (MAPK) pathways by GHRH, and GHRH-RP in pituitary-derived GH3 cells, as well as the activation of the transcription factors that serve as substrates for these kinases. GHRH rapidly increased p44/p42 MAPK activity in GH3 cells in a protein kinase A-dependent and a protein kinase C-independent manner and stimulated the activation of the transcription factor Elk-1. By contrast, GHRH-RP and p75-92NH2 had no effect on p44/p42 MAPK phosphorylation in these cells. Additionally, we determined that all three peptides, GHRH, GHRH-RP, and p75-92NH2, rapidly and specifically increase phosphorylation of p38 MAPK and stimulate the activation of the nuclear factor CHOP. These are the first studies to demonstrate the activation of Elk-1 by GHRH and the activation of p38 MAPK and CHOP by GHRH, GHRH-RP, and p75-92NH2. We conclude that members of the GHRH family of peptides differentially activate multiple intracellular signaling pathways and suggest that the biologic actions of GHRH may be far more diverse than previously thought.