Signaling mechanisms of cytokine receptors and their perturbances in disease

Characterization and functional analysis of SOCS9 from orange-spotted grouper (Epinephelus coioides) during virus infection

The suppressor of cytokine signaling (SOCS) proteins family have twelve members including eight known mammalian SOCS members (CISH, SOCS1-7) and four new discovery members (SOCS3b, SOCS5b, SOCS8 and SOCS9) that is regarded as a classic feedback inhibitor of cytokine signaling. Although the function of the mammalian SOCS proteins have been well studied, little is known about the roles of SOCS in fish during viral infection. In this study, the molecular characteristics of SOCS9 from orange-spotted grouper (Epinephelus coioides, EcSOCS9) is investigated. The EcSOCS9 protein encoded 543 amino acids with typical SH2 (389-475aa) and SOCS_box (491-527aa), sharing high identities with reported fish SOCS9. EcSOCS9 was expressed in all detected tissues and highly expressed in kidney. After red-spotted grouper nervous necrosis virus (RGNNV) infection, the expression of EcSOCS9 was significantly induced in vitro. Furthermore, EcSOCS9 overexpression enhanced RGNNV replication, promoted virus-induced mitophagy that evidenced by the increased level of LC3-Ⅱ, BCL2, PGAM5 and decreased level of BNIP3 and FUNDC1. Besides, EcSOCS9 overexpression suppressed the expression levels of ATP6, CYB, ND4, ATP level and induced ROS level. The expression levels of interferon (IFN) related factors (IRF1, IRF3, IRF7, P53), inflammatory factors (IL1-β, IL8, TLR2, TNF-α) and IFN-3, ISRE, NF-κB, AP1 activities were also reduced by overexpressing EcSOCS9. These date suggests that EcSOCS9 impacts RGNNV infection through modulating mitophagy, regulating the expression levels of IFN- related and inflammatory factors, which will expand our understanding of fish immune responses during viral infection.

Molecular biology and functional genomics of immune-endocrine interactions in the Japanese eel, Anguilla japonica

Immune-endocrine interactions are an important pathogen resistance mechanism in fish. We review the immune-endocrine interactions in the Japanese eel, Anguilla japonica, with special reference to high throughput gene sequencing. These data may be relevant to the significant decrease in the eel harvest in recent years and will aid in the selection of appropriate disease-resistant strains for aquaculture. More than 1000 sequences that whose expression in elvers responded to air exposure were identified through comprehensive gene expression analysis using next-generation sequencing. These included transcription factors within the MAPK pathway. Significant changes in expression after air exposure were detected by quantitative polymerase chain reaction analysis in many genes related to disease resistance. These factors include innate immune system factors and cytokines that interact with the endocrine system during the stress response. Other applications of immune-endocrine interactions in eel culture are discussed.

Protected amine labels: a versatile molecular scaffold for multiplexed nominal mass and sub-Da isotopologue quantitative proteomic reagents

We assemble a versatile molecular scaffold from simple building blocks to create binary and multiplexed stable isotope reagents for quantitative mass spectrometry. Termed Protected Amine Labels (PAL), these reagents offer multiple analytical figures of merit including, (1) robust targeting of peptide N-termini and lysyl side chains, (2) optimal mass spectrometry ionization efficiency through regeneration of primary amines on labeled peptides, (3) an amino acid-based mass tag that incorporates heavy isotopes of carbon, nitrogen, and oxygen to ensure matched physicochemical and MS/MS fragmentation behavior among labeled peptides, and (4) a molecularly efficient architecture, in which the majority of hetero-atom centers can be used to synthesize a variety of nominal mass and sub-Da isotopologue stable isotope reagents. We demonstrate the performance of these reagents in well-established strategies whereby up to four channels of peptide isotopomers, each separated by 4 Da, are quantified in MS-level scans with accuracies comparable to current commercial reagents. In addition, we utilize the PAL scaffold to create isotopologue reagents in which labeled peptide analogs differ in mass based on the binding energy in carbon and nitrogen nuclei, thereby allowing quantification based on MS or MS/MS spectra. We demonstrate accurate quantification for reagents that support 6-plex labeling and propose extension of this scheme to 9-channels based on a similar PAL scaffold. Finally, we provide exemplar data that extend the application of isotopologe-based quantification reagents to medium resolution, quadrupole time-of-flight mass spectrometers.

Notch in the vertebrate nervous system: an old dog with new tricks

The Notch pathway is prominent among those known to regulate neural development in vertebrates. Notch receptor activation can inhibit neurogenesis, maintain neural progenitor character, and in some contexts promote gliogenesis and drive binary fate choices. Recently, a wave of exciting studies has emerged, which has both solidified previously held assertions and expanded our understanding of Notch function during neurogenesis and in the adult brain. These studies have examined pathway regulators and interactions, as well as pathway dynamics, with respect to both gene expression and cell-cell signaling. Here, focusing primarily on vertebrates, we review the current literature on Notch signaling in the nervous system, and highlight numerous recent studies that have generated interesting and unexpected advances.

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.

Beyond dimerization: a membrane-dependent activation model for interleukin-4 receptor-mediated signalling

Class I cytokine receptors efficiently transfer activation signals from the extracellular space to the cytoplasm and play a dominant role in growth control and differentiation of human tissues. Although a significant body of literature is devoted to this topic, a consistent mechanistic picture for receptor activation in the membrane environment is still missing. Using the interleukin-4 receptor (IL-4R) as an example, we propose that the membrane-proximal stem-loop of the extracellular domains contains pivotal elements of a rotational switch. Interfacial energies of amino acid side-chains contained in the highly conserved WSXWS at the surface of the lipid bilayer suggest a new functional role for this motif. A generic activation mechanism for this receptor class is presented, which may impact the design of a new generation of biophysical assay systems.

Crystal structure of the C-terminal SH3 domain of the adaptor protein GADS in complex with SLP-76 motif peptide reveals a unique SH3-SH3 interaction

The Grb2-like adaptor protein GADS is essential for tyrosine kinase-dependent signaling in T lymphocytes. Following T cell receptor ligation, GADS interacts through its C-terminal SH3 domain with the adaptors SLP-76 and LAT, to form a multiprotein signaling complex that is crucial for T cell activation. To understand the structural basis for the selective recognition of GADS by SLP-76, herein is reported the crystal structure at 1.54 Angstrom of the C-terminal SH3 domain of GADS bound to the SLP-76 motif 233-PSIDRSTKP-241, which represents the minimal binding site. In addition to the unique structural features adopted by the bound SLP-76 peptide, the complex structure reveals a unique SH3-SH3 interaction. This homophilic interaction, which is observed in presence of the SLP-76 peptide and is present in solution, extends our understanding of the molecular mechanisms that could be employed by modular proteins to increase their signaling transduction specificity.

Neurotensin enhances nitric oxide generation via the JAK2-STAT1 pathway in murine macrophage Raw264.7 cells during costimulation with LPS and IFNgamma

Neurotensin has been known to be implicated in immune function, but its molecular mechanisms remain largely unclear. In this study, we report that neurotensin increased the intracellular calcium levels of murine macrophage Raw264.7 cells, and that this calcium increase disappeared in the presence of either U73122, a PLC inhibitor, or SR48692, a neurotensin receptor antagonist. Also, the production of nitric oxide (NO) during costimulation with lipopolysaccharide (LPS) and interferon gamma (IFNgamma) was potentiated by exposure to neurotensin, whereas neurotensin itself had no ability to induce NO generation. The up-regulation of NO generation was correlated with the induction of inducible NO synthase (iNOS). In addition, the activities of janus activated kinase 2 (JAK2)-signal transducer and activated transcription 1 (STAT1) and the migration capacity of macrophage were increased as the result of costimulation of neurotensin with LPS and IFNgamma, and pretreatment of either U73122 or SR48692 attenuated these phenomenon. Moreover, the neurotensin-mediated enhancement of NO generation and migration were observed in the wild-type JAK2 transfected cells, but not in the dominant negative JAK2 transfected cells. Together, these results demonstrate that neurotensin can effect enhancement in LPS/IFNgamma-induced NO generation and migration capacity, via the JAK2-STAT1 pathway.

The Inhibitory Effects of Interleukin‐1 on Growth Hormone Action During Catabolic Illness

Growth hormone (GH) induces the expression of the anabolic genes responsible for growth, metabolism, and differentiation. Normally, GH stimulates the synthesis of circulating insulin-like growth factor-I (IGF-I) by liver, which upregulates protein synthesis in many tissues. The development of GH resistance during catabolic illness or inflammation contributes to loss of body protein, resulting in multiple complications that prolong recovery and cause death. In septic patients, increased levels of proinflammatory cytokines and GH resistance are commonly observed together. Numerous studies have provided evidence that the inhibitory effects of cytokines on skeletal muscle protein synthesis during sepsis and inflammation are mediated indirectly by changes in the GH/IGF-I system. Interleukin (IL)-1, a member of the family of proinflammatory cytokines, interacts with most cell types and is an important mediator of the inflammatory response. Infusion of a specific IL-1 receptor antagonist (IL-1Ra) ameliorates protein catabolism and GH resistance during systemic infection. This suggests that IL-1 is an important mediator of GH resistance during systemic infection or inflammation. Consequently, a better understanding of the interaction between GH, IL-1, and the regulation of protein metabolism is of great importance for the care of the patient.

The molecular pathogenesis of acute myeloid leukemia

The description of the molecular pathogenesis of acute myeloid leukemias (AML) has seen dramatic progress over the last years. Two major types of genetic events have been described that are crucial for leukemic transformation: alterations in myeloid transcription factors governing hematopoietic differentiation and activating mutations of signal transduction intermediates. These processes are highly interdependent, since the molecular events changing the transcriptional control in hematopoietic progenitor cells modify the composition of signal transduction molecules available for growth factor receptors, while the activating mutations in signal transduction molecules induce alterations in the activity and expression of several transcription factors that are crucial for normal myeloid differentiation. The purpose of this article is to review the current literature describing these genetic events, their biological consequences and their clinical implications. As the article will show, the recent description of several critical transforming mutations in AML may soon give rise to more efficient and less toxic molecularly targeted therapies of this deadly disease.

TGF-beta signaling in T cells: roles in lymphoid and epithelial neoplasia

Transforming growth factor-beta (TGF-beta) plays an essential role in regulating the homeostasis of cells in the lymphoid lineage. TGF-beta signaling is not required for normal thymopoiesis, but is essential for regulating the expansion, activation, and effector function of the mature CD4+ and CD8+ T cells in the peripheral lymphoid organs and target tissues. Recent studies in both mice and humans have elucidated an important and complex role for TGF-beta in regulatory T-cell biology. Disruption of TGF-beta signaling in T cells impairs the maintenance of regulatory T cells, results in the expansion of activated effector T cells, and is associated with the production of cytokines that have major effects on cells in their environment. While autoimmunity and inflammation are the principal phenotypes associated with the abrogation of TGF-beta signaling in T cells in mice, emerging evidence now also directly links Smad-dependent TGF-beta signaling in T cells to the suppression of epithelial neoplasia. The TGF-beta receptor-activated Smad3 plays a critical role in mediating many of the inhibitory effects of TGF-beta signaling in T cells, and has now been established as an important suppressor of leukemogenesis. These studies are increasing our awareness of the many complex mechanisms through which TGF-beta signaling controls the pathogenesis of cancer.

Evidence for down-regulation of phosphoinositide 3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR)-dependent translation regulatory signaling pathways in Ames dwarf mice

How growth hormone (GH) stimulates protein synthesis is unknown. Phosphoinositide 3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathways balance anabolic and catabolic activities in response to nutrients and growth factor signaling. As a test of GH signaling, immunoassays of two downstream translation regulatory proteins were compared in ad libitum-fed 2-month-old normal and Ames (Prop1df) dwarf mice. Phosphorylation of the p70 and p85 isoforms of S6 kinase 1 in liver and the p70 isoform in gastrocnemius muscle were significantly decreased in dwarfs. Messenger RNA (mRNA) Cap-binding demonstrated significantly higher levels of translation repressor 4E-BP1/eukaryotic initiation factor 4E (eIF4E) (coprecipitates) from dwarf livers, but not muscle. Consistent with these binding data, significantly less phosphorylation of 4E-BP1 was documented in dwarf liver. These data suggest a link between GH signaling and translation control in a model of extended longevity.

Suppressors of cytokine signaling in health and disease

Cytokines consist of a large family of secreted proteins, including pro-inflammatory agents, growth hormone and erythropoietin, that utilize the Janus kinase (JAK) signal transducer and activator of transcription (STAT) signal transduction pathway to mediate many of their key physiologic and pathologic actions. These actions include cytokine-mediated inflammation, immunoregulation, hematopoiesis and growth. The JAK-STAT pathway is regulated by several processes, among which negative feedback regulation by the suppressors of cytokine signaling (SOCS), members of a family of eight proteins, is particularly important. Each cytokine induces one or more specific SOCS proteins that in turn down-regulate the signal initiated by the cytokine. Through their impact on the cytokine-activated JAK-STAT pathway, the SOCS proteins are involved in many diseases that come to the attention of the pediatric nephrologist. For example, an increase in the expression of SOCS-2 and -3 may be a cause of growth hormone resistance and thus may contribute to the growth retardation that affects children with chronic renal failure. Because of their obvious biologic importance, the SOCS proteins have been the subject of intense research that includes the development of strategies to utilize these proteins to control cytokine-induced JAK/STAT signal transduction for therapeutic purposes.

Inducers of oxidative stress block ciliary neurotrophic factor activation of Jak/STAT signaling in neurons

Generation of reactive oxygen species (ROS) with the accumulation of oxidative damage has been implicated in neurodegenerative disease and in the degradation of nervous system function with age. Here we report that ROS inhibit the activity of ciliary neurotrophic factor (CNTF) in nerve cells. Treatment with hydrogen peroxide (H(2)O(2)) as a generator of ROS inhibited CNTF-mediated Jak/STAT signaling in all cultured nerve cells tested, including chick ciliary ganglion neurons, chick neural retina, HMN-1 motor neuron hybrid cells, and SH-SY5Y and BE(2)-C human neuroblastoma cells. H(2)O(2) treatment of non-neuronal cells, chick skeletal muscle and HepG2 hepatoma cells, did not inhibit Jak/STAT signaling. The H(2)O(2) block of CNTF activity was seen at concentrations as low as 0.1 mm and within 15 min, and was reversible upon removal of H(2)O(2) from the medium. Also, two other mediators of oxidative stress, nitric oxide and rotenone, inhibited CNTF signaling. Treatment of neurons with H(2)O(2) and rotenone also inhibited interferon-gamma-mediated activation of Jak/STAT1. Depleting the intracellular stores of reduced glutathione by treatment of BE(2)-C cells with nitrofurantoin inhibited CNTF activity, whereas addition of reduced glutathione protected cells from the effects of H(2)O(2). These results suggest that disruption of neurotrophic factor signaling by mediators of oxidative stress may contribute to the neuronal damage observed in neurodegenerative diseases and significantly affect the utility of CNTF-like factors as therapeutic agents in preventing nerve cell death.

Beryllium-specific immune response in primary cells from healthy individuals

The effect of beryllium (Be) exposure has been extensively studied in patients with chronic beryllium disease (CBD). CBD patients carry mutated MHC class II alleles and show a hyperproliferation of T cells upon Be exposure. The exact mechanism of Be-induced T-cell proliferation in these patients is not clearly understood. It is also not known how the inflammatory and suppressive cytokines maintain a balance in healthy individuals and how this balance is lost in CBD patients. To address these issues, we have initiated cellular and biochemical studies to identify Be-responsive cytokines and other cellular markers that help maintain a balance in healthy individuals. We have established an immune cell model derived from a mixture of peripheral blood mononuclear cells (PBMCs) and dendritic cells (DCs). In this article, we demonstrate that pro-inflammatory cytokine IL6 shows decreased release whereas suppressive cytokine IL10 shows enhanced release after 5-10 h of Be treatment. Furthermore, the Be-specific pattern of IL6 and IL10 release is dependent upon induction of threonine phosphorylation of a 45 kDa cytosolic protein (p45), as early as 90 min after Be treatment. Pharmacological inhibition of phosphatidylinositol 3' kinase (PI3'K) by wortmannin and p38 mitogen-activated protein kinase (MAPK) by SB203580 reveal that PI3'K mediates Be-specific p45 phosphorylation and IL6 release, whereas p38 MAPK regulates the release of IL6 and IL10 and the phosphorylation of p45 independent of metal-salt treatment. While the IL10 and IL6 release pathways are uncoupled in these cells, they are linked to phosphorylation of p45. These findings suggest that the balance between IL10 and IL6 release and the correlated p45 phosphorylation are important components of the Be-mediated immune response in healthy individuals.

Regulation of Cytokine Receptor Signaling by Nuclear Hormone Receptors: A New Paradigm for Receptor Interaction

Cytokine receptors act through a complex signaling network involving Janus kinases (JAKs) and the signal transducers and activators of transcription (STATs) to regulate diverse biological processes controlling growth, development, homeostasis, and immune function. JAK/STAT signaling is terminated by negative regulators including the suppressors of cytokine signaling (SOCSs), protein tyrosine phosphatases, and protein inhibitors of activated STAT. There is a wealth of evidence that nuclear hormone receptors (NHRs) are important regulators of cytokine action. The molecular mechanisms underlying NHR regulation are incompletely understood, but may include control of cytokine production and modulation of the expression and signaling of cytokine receptors. NHRs regulate cytokine receptor signaling by affecting STAT expression and by acting as coregulators of STAT transcriptional action. More recently, NHRs have been shown to exert regulatory effects indirectly through SOCSs, which is a novel mechanism for receptor crosstalk. Better understanding of the regulatory interaction between these two classes of receptors potentially leads to new drug design and/or therapeutic strategies for treatment of cytokine-related diseases.

Growth hormone (GH) receptors in prostate cancer: gene expression in human tissues and cell lines and characterization, GH signaling and androgen receptor regulation in LNCaP cells

Various hormones and growth factors have been implicated in progression of prostate cancer, but their role and the underlying molecular mechanism(s) involved remain poorly understood. In this study, we investigated the role of human growth hormone (GH) and its receptor (GHR) in human prostate cancer. We first demonstrated mRNA expression of GHR and of its exon 9-truncated isoform (GHR(tr)) in benign prostate hyperplasia (BPH) and prostate adenocarcinoma patient tissues, as well as in LNCaP, PC3 and DU145 human prostate cancer cell lines. GHR mRNA levels were 80% higher and GHR(tr) only 25% higher, in the carcinoma tissues than in BPH. Both isoforms were also expressed in LNCaP and PC3 cell lines and somewhat less so in DU145 cells. The LNCaP cell GHR protein was further characterized, on the basis of its M(r) of 120kDa, its binding to two different GHR monoclonal antibodies, its high affinity and purely somatogenic binding to (125)I-hGH and its ability to secrete GH binding protein, all characteristic of a functional GHR. Furthermore, GH induced rapid, time- and dose-dependent signaling events in LNCaP cells, including phosphorylation of JAK2 tyrosine kinase, of GHR itself and of STAT5A (JAK2-STAT5A pathway), of p42/p44 MAPK and of Akt/PKB. No effect of GH (72h) could be shown on basal or androgen-induced LNCaP cell proliferation nor on PSA secretion. Interestingly, however, GH caused a rapid (2-12h) though transient striking increase in immunoreactive androgen receptor (AR) levels (< or =5-fold), followed by a slower (24-48h) reduction (< or = 80%), with only modest parallel changes in serine-phosphorylated AR. In conclusion, the GH-induced activation of signaling pathways, its effects on AR protein in LNCaP cells and the isoform-specific regulation of GHR in prostate cancer patient tissues, suggest that GH, most likely in concert with other hormones and growth factors, may play an important role in progression of human prostate cancer.

JAK2 contributes to the intrinsic capacity of primary hematopoietic cells to respond to stem cell factor

OBJECTIVE

Stem cell factor (SCF) is the ligand for the receptor tyrosine kinase (RTK) Kit. The literature contains conflicting reports regarding the capacity of SCF to activate JAK2. Previous work has addressed this controversial issue using biochemical approaches. Here we use a genetic approach to determine the direct role of JAK2 in SCF-mediated growth and differentiation of primary hematopoietic cells.

MATERIALS AND METHODS

Fetal liver cells were isolated from JAK2-deficient murine embryos at day 12 of development. SCF-induced growth and differentiation of this unfractionated population of cells were determined by 3H-thymidine incorporation in bulk cultures, single-cell colony assays, and cytochemistry. In addition, Kit+ cells were isolated from fetal liver by fluorescence-activated cell sorting (FACS) and assessed for growth using 3H-thymidine and colony assays.

RESULTS

SCF-induced growth of unfractionated JAK2-deficient fetal liver cells was reduced by 70% compared to cells from wild-type fetal liver in single-cell assays. This was of particular note because there were three-fold more Kit+ cells in JAK2-deficient fetal liver. Reductions in SCF-induced growth were not observed in bulk cultures of JAK2-deficient fetal liver, suggesting that additional factors cooperate with SCF to overcome the absence of JAK2 in this heterogeneous population of cells. SCF-induced 3H-thymidine incorporation of FACS-purified Kit+ fetal liver deficient for JAK2 was impaired by approximately 50%, whereas colony formation in methylcellulose was reduced 95%. JAK2 also was required for differentiation of this purified population of progenitors into mast cells.

CONCLUSION

JAK2 contributes to the intrinsic capacity of fetal liver hematopoietic progenitor cells to proliferate and differentiate in response to SCF.

Perturbed signal transduction in neurodegenerative disorders involving aberrant protein aggregation

Aggregation of abnormal proteins, both inside and outside of cells, is a prominent feature of major neurodegenerative disorders, including Alzheimer's, Parkinson's, polyglutamine expansion, and prion diseases. Other articles in this special issue of NeuroMolecular Medicine describe the genetic and molecular factors that promote aberrant protein aggregation. In the present article, we consider how it is that pathogenic aggregation-prone proteins compromise signal transduction pathways that regulate neuronal plasticity and survival. In some cases the protein in question may have widespread and relatively nonspecific effects on signaling. For example, amyloid beta-peptide induces membrane-associated oxidative stress, which impairs the function of various receptors, ion channels and transporters, as well as downstream kinases and transcription factors. Other proteins, such as polyglutamine repeat proteins, may affect specific protein -protein interactions, including those involved in signaling pathways activated by neurotransmitters, neurotrophins, and steroid hormones. Synapses are particularly sensitive to abnormal protein aggregation and impaired synaptic signaling may trigger apoptosis and related cell death cascades. Impairment of signal transduction in protein aggregation disorders may be amenable to therapy as demonstrated by a recent study showing that dietary restriction can preserve synaptic function and protect neurons in a mouse model of Huntington's disease. Finally, emerging findings are revealing how activation of certain signaling pathways can suppress protein aggregation and/or the cytotoxicity resulting from the abnormal protein aggregation. A better understanding of how abnormal protein aggregation occurs and how it affects and is affected by specific signal transduction pathways, is leading to novel approaches for preventing and treating neurodegenerative disorders.

Leptin is an autocrine/paracrine regulator of wound healing

Leptin, a 16 kDa pleiotropic cytokine primarily expressed in adipose tissue, has been shown to cause multiple systemic biological actions. Recently, leptin has also been documented as an important component of the wound healing process and its receptor appears to be expressed in wound tissue. We have previously demonstrated that leptin is a potent angiogenic factor exerting direct effects on endothelial cells and that transcription of its encoding gene is regulated by hypoxia. Here, we hypothesize that leptin expression is acutely up-regulated in the ischemic tissue of experimental wounds. Using a combination of in situ hybridization and quantitative RT-PCR experiments, we show that leptin expression is rapidly and steadily up-regulated in skin tissue from incisional and excisional wounds. By immunohistochemistry, we demonstrate increased and sustained leptin protein levels in basal keratinocytes, blood vessel walls, and fibroblasts. To determine whether leptin is required for normal healing, excisional wounds were treated with neutralizing anti-leptin antibodies. This treatment markedly hampered healing progression and prevented wound closure and contraction. Finally, a transient rise in circulating blood leptin levels was detected within the first 24 h after inflicting the injury; we present evidence suggesting that this elevation is due to increased leptin production at the ischemic wound site. We conclude that leptin is acutely up-regulated in the injured skin and propose that this local production of leptin serves a critical functional role as an autocrine/paracrine regulator of normal wound healing.

Growth hormone reduces chloride secretion in human colonic epithelial cells via EGF receptor and extracellular regulated kinase

BACKGROUND AND AIMS

Growth hormone (GH) has been shown to alleviate symptoms in patients with Crohn's disease. Chloride secretion is important in driving intestinal fluid secretion. We examined whether GH inhibits chloride secretion induced by carbachol (CCh, a calcium-dependent pathway), and the downstream effectors responsible.

METHODS

T(84) cells were pretreated with GH at various concentrations followed by CCh (100 micromol/L). Chloride secretion was assessed as changes in short circuit current ( triangle up I(sc)) in Ussing chambers. Tyrphostins AG1478 (an epidermal growth factor receptor [EGFr] inhibitor) and AG490 (a Janus kinase 2 [JAK2] inhibitor), SB203580 (a p38 inhibitor), and PD98059 (a MEK1 inhibitor) were used.

RESULTS

GH inhibited CCh-induced chloride secretion at up to 10 nmol/L, but higher concentrations were less effective. GH caused tyrosine phosphorylation of JAK2 and EGFr. AG490 suppressed activation of JAK2 and EGFr in response to GH. AG1478 prevented GH activation of EGFr and reversed its inhibitory effect on chloride secretion. GH also induced activation of both p38 and ERK1/2. AG490 reversed GH-induced tyrosine phosphorylation of both ERK1/2 and p38, but AG1478 reversed that of ERK1/2 only. PD98059, but not SB203580, reversed the inhibitory effect of GH on chloride secretion.

CONCLUSIONS

GH inhibits CCh-induced chloride secretion via a JAK2-dependent mechanism involving transactivation of EGFr and consequent recruitment of ERK1/2. Although activated, p38 does not contribute to the inhibitory effect of GH on secretion. These data elucidate mechanisms of GH inhibition of chloride secretion in intestinal epithelia, which may be relevant to therapeutic benefits of GH in Crohn's disease or other diarrheal diseases.

Effects of leptin on endothelial function with OB-Rb gene transfer in Zucker fatty rats

The metabolic syndrome in association with obesity is a major clinical problem inducing hypertension, diabetes mellitus, and atherosclerosis. Leptin induces angiogenesis by its proliferative effects on endothelial cells (ECs) via OB receptor (OB-Rb) gene. We evaluated the growth of ECs and intracellular signalings in response to leptin in vitro and the angiogenic effects of leptin in the cornea in vivo with and without adenovirus-mediated transfer of the OB-Rb gene in Zucker fatty (ZF) rats as a model for the metabolic syndrome. Recombinant adenovirus vector encoding rat OB-Rb (Ad.OB-Rb) or Escherichia coli. LacZ (Ad.LacZ) was transfected into cultured ECs from Zucker lean (ZL) rats and ZF rats. Leptin increased DNA synthesis dose-dependently in ECs from ZL rats but not ZF rats. Infection with Ad.OB-Rb, but not with Ad.LacZ, improved the growth effects of leptin in ECs from ZF rats. Leptin induced phosphorylation of Janus kinase (JAK)2, signal transducer and activator of transcription (STAT)3, and extracellular signal-regulated kinase (ERK) in ECs from ZL rats but not ZF rats. Infection with Ad.OB-Rb restored phosphorylation of JAK2 and STAT3 in ECs from ZF rats. Leptin induced angiogenesis in cornea from ZL rats, but not from ZF rats. Coadministration of leptin and Ad.OB-Rb induced angiogenesis in cornea from ZF rats. Ad.LacZ did not influence the angiogenic effects of leptin. The impaired endothelial function with the leptin resistance may be one of causes of the atherosclerosis in the metabolic syndrome.

Late gestation modulation of fetal glucocorticoid effects requires the receptor for leukemia inhibitory factor: an observational study

BACKGROUND

Ablation of the low-affinity receptor subunit for leukemia inhibitory factor (LIFR) causes multi-systemic defects in the late gestation fetus. Because corticosterone is known to have a broad range of effects and LIF function has been associated with the hypothalamo-pituitary-adrenal axis, this study was designed to determine the role for LIFR in the fetus when exposed to the elevated maternal glucocorticoid levels of late gestation. Uncovering a requirement for LIFR in appropriate glucocorticoid response will further understanding of control of glucocorticoid function.

METHODS

Maternal adrenalectomy or RU486 administration were used to determine the impact of the maternal glucocorticoid surge on fetal development in the absence of LIFR. The mice were analyzed by a variety of histological techniques including immunolabeling and staining techniques (hematoxylin and eosin, Alizarin red S and alcian blue). Plasma corticosterone was assayed using radioimmunoassay.

RESULTS

Maternal adrenalectomy does not improve the prognosis for LIFR null pups and exacerbates the effects of LIFR loss. RU486 noticeably improves many of the tissues affected by LIFR loss: bone density, skeletal muscle integrity and glial cell formation. LIFR null pups exposed during late gestation to RU486 in utero survive natural delivery, unlike LIFR null pups from untreated litters. But RU486 treated LIFR null pups succumb within the first day after birth, presumably due to neural deficit resulting in an inability to suckle.

CONCLUSION

LIFR plays an integral role in modulating the fetal response to elevated maternal glucocorticoids during late gestation. This role is likely to be mediated through the glucocorticoid receptor and has implications for adult homeostasis as a direct tie between immune, neural and hormone function.

Interaction between endocrine and immune systems in fish

Diseases in fish are serious problems for the development of aquaculture. The outbreak of fish disease is largely dependent on environmental and endogenous factors resulting in opportunistic infection. Recent studies, particularly on stress response, have revealed that bidirectional communication between the endocrine and immune systems via hormones and cytokines exists at the level of teleost fish. Recently information on such messengers and receptors has accumulated in fish research particularly at the molecular level. Furthermore, it has become apparent in fish that cells of the immune system produce or express hormones and their receptors and vice versa to exchange information between the two systems. This review summarizes and updates the knowledge on endocrine-immune interactions in fish with special emphasis on the roles of such mediators or receptors for their interactions.

Interleukins in atherosclerosis: molecular pathways and therapeutic potential

Interleukins are considered to be key players in the chronic vascular inflammatory response that is typical of atherosclerosis. Thus, the expression of proinflammatory interleukins and their receptors has been demonstrated in atheromatous tissue, and the serum levels of several of these cytokines have been found to be positively correlated with (coronary) arterial disease and its sequelae. In vitro studies have confirmed the involvement of various interleukins in pro-atherogenic processes, such as the up-regulation of adhesion molecules on endothelial cells, the activation of macrophages, and smooth muscle cell proliferation. Furthermore, studies in mice deficient or transgenic for specific interleukins have demonstrated that, whereas some interleukins are indeed intrinsically pro-atherogenic, others may have anti-atherogenic qualities. As the roles of individual interleukins in atherosclerosis are being uncovered, novel anti-atherogenic therapies, aimed at the modulation of interleukin function, are being explored. Several approaches have produced promising results in this respect, including the transfer of anti-inflammatory interleukins and the administration of decoys and antibodies directed against proinflammatory interleukins. The chronic nature of the disease and the generally pleiotropic effects of interleukins, however, will demand high specificity of action and/or effective targeting to prevent the emergence of adverse side effects with such treatments. This may prove to be the real challenge for the development of interleukin-based anti-atherosclerotic therapies, once the mediators and their targets have been delineated.

Impaired accumulation and function of memory CD4 T cells in human IL-12 receptor beta 1 deficiency

Defects in IL-12 production or IL-12 responsiveness result in a vulnerability to infection with non-viral intracellular organisms, but the immunological mechanisms responsible for this susceptibility remain poorly understood. We present an immunological analysis of a patient with disseminated Salmonella enteritidis and a homozygous splice acceptor mutation in the IL-12Rbeta1-chain gene. This mutation resulted in the absence of IL-12Rbeta1 protein on PBMC and an inability of T cells to specifically bind IL-12 or produce IFN-gamma in response to either IL-12 or IL-23. The accumulation of memory (CD45R0(high)) CD4 T cells that were CCR7(high) (putative central memory cells) was normal or increased for age. Central memory CD4 T cells of the patient and age-matched controls were similar in having a low to undetectable capacity to produce IFN-gamma after polyclonal stimulation. In contrast, the patient had a substantial decrease in the number of CCR7(neg/dull) CD45R0(high) memory CD4 T cells (putative effector memory cells), and these differed from control cells in having a minimal ability to produce IFN-gamma after polyclonal stimulation. Importantly, tetanus toxoid-specific IFN-gamma production by PBMC from the patient was also significantly reduced compared with that in age-matched controls, indicating that signaling via the IL-12Rbeta1-chain is generally necessary for the in vivo accumulation of human memory CD4 T cells with Th1 function. These results are also consistent with a model in which the IL-12Rbeta1 subunit is necessary for the conversion of central memory CD4 T cells into effector memory cells.

Exposure to octylphenol increases basal testosterone formation by cultured adult rat Leydig cells

4-Tert-octylphenol (OP) is a breakdown product of 4-tert-octylphenol ethoxylate, which is a surfactant additive widely used in the manufacture of a variety of detergents and plastic products. OP has been reported to exhibit weak estrogenic activity in many assay systems. The studies described herein examined an unusual effect of OP in increasing constitutive testosterone levels of cultured Leydig cells from young adult rats. The increase in testosterone was both dose and time sensitive, and this response was observed in medium lacking both calcium and magnesium and containing a membrane-permeable calcium chelator, suggesting that the increase in testosterone was not mediated by an increase in the permeability of extracellular calcium into cells or the redistribution/release of calcium from intracellular stores, respectively. Cellular cAMP levels also were unaffected by OP alone in cultured Leydig cells. Furthermore, initial exposure to 2000nM OP alone for 4h did not alter the subsequent conversion of endogenous cholesterol or exogenously added 22 (R)hydroxycholesterol to testosterone, suggesting that the increase in testosterone was not due to the enhanced availability of endogenous cholesterol or an increase in cholesterol side-chain cleavage activity, respectively. The increase in testosterone also was observed in the presence of the pure estrogen antagonist, ICI 182,780, or a 5alpha-reductase inhibitor, suggesting that this effect of OP was not mediated through the estrogen receptor alpha or beta pathway or by inhibition of Leydig cell testosterone metabolism, respectively. In addition, exposure of cells to comparable concentrations of two different detergents, Triton X-100 or sodium cholate, did not increase testosterone levels, suggesting that this effect of OP was not due to its potential detergent qualities. Although these studies did not identify specific mechanism(s) that increase constitutive testosterone levels by OP, they identify specific pathways that appear not to be involved. The physiological relevance of this observation is not known; nevertheless, they illustrate potential diverse actions of OP in modulating the level of androgen secreted by Leydig cells, and they emphasize that some actions of OP do not appear to be mediated through the estrogen receptor alpha or beta pathway.

Immunopathogenesis of vasculitis

Vasculitis is defined by the presence of leukocytes in the vessel wall with reactive damage to mural structures, leading to tissue ischemia and necrosis. The immunopathologic events that initiate the process of vascular inflammation and blood vessel damage are unclear. Damage of vascular endothelial cells and the recruitment and accumulation of the inflammatory infiltrate are determined by the endothelial cell and the bystanders, including the expression of adhesion molecules, the secretion of peptides and hormones, and the specific interaction with inflammatory cells. In addition to the endothelial cells, which provide costimulatory function, other cellular components and nonendothelial structures of the vessel wall are involved in controlling the inflammatory process, serve as antigen-presenting cells, and contribute with inflammatory mediators.

Erythropoietin mimetics derived from solution phase combinatorial libraries

The erythropoietin receptor (EPOr) is activated by ligand-induced homodimerization, which leads to the proliferation and differentiation of erythroid progenitors. Through the screening of combinatorial libraries of dimeric iminodiacetic acid diamides, novel small molecule binders of EPOr were identified in a protein binding assay. Evaluation of a series of analogues led to optimization of binding subunits, and these were utilized in the synthesis of higher order dimer, trimer, and tetramer libraries. Several of the most active EPOr binders were found to be partial agonists and induced concentration-dependent proliferation of an EPO-dependent cell line (UT-7/EPO) while having no effect on a cell line lacking the EPOr (FDC-P1). An additional compound library, based on a symmetrical isoindoline-5,6-dicarboxylic acid template and including the optimized binding subunits, was synthesized and screened leading to the identification of additional EPO mimetics.

Acute and chronic neutropenias. What is new?

Recently, some of the mechanisms and consequences in the severe chronic neutropenias (e.g. the neutrophil elastase gene mutations and the risk to progress to myelodysplasia and acute leukaemia) and in drug-induced agranulocytosis (e.g. the apoptosis-inducing ability of metabolites of clozapine) have been elucidated, and new aspects of autoimmune and the large granular lymphocyte syndrome were described (e.g. aberrant elaboration of Fas-ligand causing neutrophil apoptosis). Investigations of the mild to moderate chronic neutropenias have shown the significance of interactions between the myeloid development and the immune network (e.g. relations to immunoglobulin aberrations). Granulocyte-colony stimulation factor (G-CSF) is widely used in patients with severe chronic neutropenia, however, its use in other conditions is mostly based on anecdotal evidence. In addition, immune modulating regimens, such as metothrexate, ciclosporine and monoclonal antibodies, are increasingly employed for the autoimmune neutropenias.

The developmental biology of brain tumors

Tumors of the central nervous system (CNS) can be devastating because they often affect children, are difficult to treat, and frequently cause mental impairment or death. New insights into the causes and potential treatment of CNS tumors have come from discovering connections with genes that control cell growth, differentiation, and death during normal development. Links between tumorigenesis and normal development are illustrated by three common CNS tumors: retinoblastoma, glioblastoma, and medulloblastoma. For example, the retinoblastoma (Rb) tumor suppressor protein is crucial for control of normal neuronal differentiation and apoptosis. Excessive activity of the epidermal growth factor receptor and loss of the phosphatase PTEN are associated with glioblastoma, and both genes are required for normal growth and development. The membrane protein Patched1 (Ptc1), which controls cell fate in many tissues, regulates cell growth in the cerebellum, and reduced Ptc1 function contributes to medulloblastoma. Just as elucidating the mechanisms that control normal development can lead to the identification of new cancer-related genes and signaling pathways, studies of tumor biology can increase our understanding of normal development. Learning that Ptc1 is a medulloblastoma tumor suppressor led directly to the identification of the Ptc1 ligand, Sonic hedgehog, as a powerful mitogen for cerebellar granule cell precursors. Much remains to be learned about the genetic events that lead to brain tumors and how each event regulates cell cycle progression, apoptosis, and differentiation. The prospects for beneficial work at the boundary between oncology and developmental biology are great.

Impaired JAK-STAT signal transduction contributes to growth hormone resistance in chronic uremia

Chronic renal failure (CRF) is associated with resistance to the growth-promoting and anabolic actions of growth hormone (GH). In rats with CRF induced by partial renal ablation, 7 days of GH treatment had a diminished effect on weight gain and hepatic IGF-1 and IGFBP-1 mRNA levels, compared with sham-operated pair-fed controls. To assess whether GH resistance might be due to altered signal transduction, activation of the JAK-STAT pathway was studied 10 or 15 minutes after intravenous injection of 5 mg/kg GH or vehicle. Hepatic GH receptor (GHR) mRNA levels were significantly decreased in CRF, but GHR protein abundance and GH binding to microsomal and plasma membranes was unaltered. JAK2, STAT1, STAT3, and STAT5 protein abundance was also unchanged. However, GH-induced tyrosine phosphorylation of JAK2, STAT5, and STAT3 was 75% lower in the CRF animals. Phosphorylated STAT5 and STAT3 were also diminished in nuclear extracts. The expression of the suppressor of cytokine signaling-2 (SOCS-2) was increased twofold in GH-treated CRF animals, and SOCS-3 mRNA levels were elevated by 60% in CRF, independent of GH treatment. In conclusion, CRF causes a postreceptor defect in GH signal transduction characterized by impaired phosphorylation and nuclear translocation of GH-activated STAT proteins, which is possibly mediated, at least in part, by overexpression of SOCS proteins.

CD45 tyrosine phosphatase controls common gamma-chain cytokine-mediated STAT and extracellular signal-related kinase phosphorylation in activated human lymphoblasts: inhibition of proliferation without induction of apoptosis

The objective of this study was to test whether CD45 signals can influence signaling processes in activated human lymphoblasts. To this end, we generated lymphoblasts which proliferate in response to common gamma-chain cytokines, but readily undergo apoptosis after cytokine withdrawal. In experiments with the CD45R0 mAb UCHL-1, but not control CD45 mAbs, we found significant inhibition of proliferation. Interestingly, the pan-CD45 mAb GAP8.3, which is most effective in inhibition of OKT-3-mediated proliferation in quiescent lymphocytes, was ineffective in lymphoblasts. Addition of CD3 mAb OKT-3 had no influence on IL-2-mediated proliferation (with or without UCHL-1). In contrast, after addition of OKT-3 to IL-4- and IL-7-stimulated proliferation assays, UCHL-1 signals could not significantly alter cellular proliferation. We did not find induction of apoptosis following CD45R0 signaling. In Western blots using mAbs detecting phosphorylated STAT-3, STAT-5, STAT-6, or extracellular signal-related kinase 1/2, we found that CD45R0 signaling could effectively diminish phosphorylation of these intracellular signaling components. Using RT-PCR, we found that CD45R0 signaling inhibited IL-2 mRNA production without major influence on IL-13, IL-5, or IFN-gamma mRNA levels. Costimulation with OKT-3 and IL-2 optimally induced secretion of IFN-gamma, TNF-alpha, and IL-5, which was not decreased by CD45 signals. In conclusion, we illustrate that CD45R0 signals control early cytokine receptor-associated signaling processes and mRNA and DNA synthesis in activated human lymphoblasts. Furthermore, we show the existence of CD45 epitopes (GAP8.3), which are active and critical for signaling in quiescent lymphocytes, but are nonfunctional in activated human lymphoblasts.

Cytokine receptor dimerization and activation: prospects for small molecule agonists

Ligand-induced dimerization of cell surface receptors has emerged as a general mechanism for the initiation of signal transduction. A number of therapeutically important receptor families are believed to be activated by this process. Recently available structural information, particularly for the erythropoietin receptor, has provided insight into the mechanism of receptor activation. These findings have also revealed important constraints on the nature of receptor-agonist complexes. The prospects of discovering small-molecule mimetics of such receptor agonists are discussed, including strategies which have led to the identification of a small number of peptide and non-peptide cytokine mimetics.

Molecular basis for the dephosphorylation of the activation segment of the insulin receptor by protein tyrosine phosphatase 1B

The protein tyrosine phosphatase PTP1B is responsible for negatively regulating insulin signaling by dephosphorylating the phosphotyrosine residues of the insulin receptor kinase (IRK) activation segment. Here, by integrating crystallographic, kinetic, and PTP1B peptide binding studies, we define the molecular specificity of this reaction. Extensive interactions are formed between PTP1B and the IRK sequence encompassing the tandem pTyr residues at 1162 and 1163 such that pTyr-1162 is selected at the catalytic site and pTyr-1163 is located within an adjacent pTyr recognition site. This selectivity is attributed to the 70-fold greater affinity for tandem pTyr-containing peptides relative to mono-pTyr peptides and predicts a hierarchical dephosphorylation process. Many elements of the PTP1B-IRK interaction are unique to PTP1B, indicating that it may be feasible to generate specific, small molecule inhibitors of this interaction to treat diabetes and obesity.

Leptina: o diálogo entre adipócitos e neurônios

A descoberta da leptina trouxe consigo um interesse renovado sobre o estudo do controle homeostático da energia. Sabe-se agora que o tecido adiposo branco é o maior sítio de produção da leptina. Uma vez na circulação sangüínea ela se liga a receptores específicos no cérebro, levando ao sistema nervoso central um sinal de saciedade que reflete a quantidade existente de energia em forma de gordura no organismo. Agindo por intermédio de receptores que fazem uso da via JAK/SAT de transdução do sinal intracelular, a leptina modifica a expressão e a atividade de inúmeros peptídeos hipotalâmicos que regulam o apetite e o gasto de energia. Além disso, a leptina sinaliza o estado nutricional do organismo a outros sistemas fisiológicos, modulando a função de várias glândulas alvo. Mais recentemente, a leptina recombinante foi administrada com sucesso numa paciente obesa com deficiência do hormônio devido a uma mutação do gene ob. Por outro lado, os efeitos da leptina recombinante no único estudo em pacientes com obesidade e concentrações elevadas de leptina foram menos impressionantes. Nesta revisão, discutiremos a complexidade das ações da leptina com ênfase no seu papel integrativo de sinalizadora do estado nutricional para o organismo.