Role of the cytokine-inducible SH2 protein CIS in desensitization of STAT5b signaling by continuous growth hormone

Role of SOCS and VHL Proteins in Neuronal Differentiation and Development

The basic helix-loop-helix factors play a central role in neuronal differentiation and nervous system development, which involve the Notch and signal transducer and activator of transcription (STAT)/small mother against decapentaplegic signaling pathways. Neural stem cells differentiate into three nervous system lineages, and the suppressor of cytokine signaling (SOCS) and von Hippel-Lindau (VHL) proteins are involved in this neuronal differentiation. The SOCS and VHL proteins both contain homologous structures comprising the BC-box motif. SOCSs recruit Elongin C, Elongin B, Cullin5(Cul5), and Rbx2, whereas VHL recruits Elongin C, Elongin B, Cul2, and Rbx1. SOCSs form SBC-Cul5/E3 complexes, and VHL forms a VBC-Cul2/E3 complex. These complexes degrade the target protein and suppress its downstream transduction pathway by acting as E3 ligases via the ubiquitin-proteasome system. The Janus kinase (JAK) is the main target protein of the E3 ligase SBC-Cul5, whereas hypoxia-inducible factor is the primary target protein of the E3 ligase VBC-Cul2; nonetheless, VBC-Cul2 also targets the JAK. SOCSs not only act on the ubiquitin-proteasome system but also act directly on JAKs to suppress the Janus kinase-signal transduction and activator of transcription (JAK-STAT) pathway. Both SOCS and VHL are expressed in the nervous system, predominantly in brain neurons in the embryonic stage. Both SOCS and VHL induce neuronal differentiation. SOCS is involved in differentiation into neurons, whereas VHL is involved in differentiation into neurons and oligodendrocytes; both proteins promote neurite outgrowth. It has also been suggested that the inactivation of these proteins may lead to the development of nervous system malignancies and that these proteins may function as tumor suppressors. The mechanism of action of SOCS and VHL involved in neuronal differentiation and nervous system development is thought to be mediated through the inhibition of downstream signaling pathways, JAK-STAT, and hypoxia-inducible factor-vascular endothelial growth factor pathways. In addition, because SOCS and VHL promote nerve regeneration, they are expected to be applied in neuronal regenerative medicine for traumatic brain injury and stroke.

SOCS-2 gene expression at diagnosis does not predict for outcome of chronic myeloid leukemia patients on imatinib treatment

SOCS-2 gene expression at diagnosis has been suggested as a predictor of clinical outcome in chronic myeloid leukemia (CML). In this study SOCS-2 and GUS expression levels were determined by real-time PCR in pretherapeutic samples at diagnosis. First, three patient groups were compared after assessment at 48 months: optimal molecular responders (n = 35), patients with resistance to imatinib (n = 28), and blast crisis patients (n = 27). A significant difference in SOCS-2 gene expression at diagnosis was observed comparing blast crisis vs. resistant patients (p = 0.042) and optimal responders (p = 0.010). Second, a validation sample of consecutively randomized patients (n = 123) was investigated. No discriminative SOCS-2 gene expression cutoff could be derived to predict molecular or cytogenetic response, progression-free or overall survival. Although SOCS-2 gene was differentially expressed at the time of diagnosis in blast crisis patients when compared to other groups, a prognostic impact in consecutively randomized patients was not observed.

Global analysis of expression, maturation and subcellular localization of mouse liver transcriptome identifies novel sex-biased and TCPOBOP-responsive long non-coding RNAs

BACKGROUND

While nuclear transcription and RNA processing and localization are well established for protein coding genes (PCGs), these processes are poorly understood for long non-coding (lnc)RNAs. Here, we characterize global patterns of transcript expression, maturation and localization for mouse liver RNA, including more than 15,000 lncRNAs. PolyA-selected liver RNA was isolated and sequenced from four subcellular fractions (chromatin, nucleoplasm, total nucleus, and cytoplasm), and from the chromatin-bound fraction without polyA selection.

RESULTS

Transcript processing, determined from normalized intronic to exonic sequence read density ratios, progressively increased for PCG transcripts in going from the chromatin-bound fraction to the nucleoplasm and then on to the cytoplasm. Transcript maturation was similar for lncRNAs in the chromatin fraction, but was significantly lower in the nucleoplasm and cytoplasm. LncRNA transcripts were 11-fold more likely to be significantly enriched in the nucleus than cytoplasm, and 100-fold more likely to be significantly chromatin-bound than nucleoplasmic. Sequencing chromatin-bound RNA greatly increased the sensitivity for detecting lowly expressed lncRNAs and enabled us to discover and localize hundreds of novel regulated liver lncRNAs, including lncRNAs showing sex-biased expression or responsiveness to TCPOBOP a xenobiotic agonist ligand of constitutive androstane receptor (Nr1i3).

CONCLUSIONS

Integration of our findings with prior studies and lncRNA annotations identified candidate regulatory lncRNAs for a variety of hepatic functions based on gene co-localization within topologically associating domains or transcription divergent or antisense to PCGs associated with pathways linked to hepatic physiology and disease.

Investigation of the role of β-TrCP in growth hormone transduction defect (GHTD)

Background Growth hormone(GH) and epidermal growth factor (EGF) stimulate cell growth and differentiation, and crosstalking between their signaling pathways is important for normal cellular development. Growth hormone transduction defect (GHTD) is characterized by excessive GH receptor (GHR) degradation, due to over-expression of the E3 ubiquitin ligase, cytokine inducible SH2-containing protein (CIS). GH induction of GHTD fibroblasts after silencing of messenger RNA (mRNA) CIS (siCIS) or with higher doses of GH restores normal GH signaling. β-Transducing-repeat-containing protein (β-TrCP), another E3 ubiquitin ligase, also plays a role in GHR endocytosis. We studied the role of β-TrCP in the regulation of the GH/GHR and EGF/EGF receptor (EGFR) pathways in normal and GHTD fibroblasts. Materials and methods Fibroblast cultures were developed from gingival biopsies of a GHTD (P) and a control child (C). Protein expression and cellular localization of β-TrCP were studied by Western immunoblotting and immunofluorescence, respectively, after: (1) GH 200 μg/L human GH (hGH) induction, either with or without silence CIS (siCIS), and (2) inductions with 200 μg/L GH or 1000 μg/L GH or 50 ng/mL EGF. Results After induction with: (1) GH200/siCIS, the protein expression and cytoplasmic-membrane localization of β-TrCP were increased in the patient, (2) GH200 in the control and GH1000 in the patient, the protein and cytoplasmic-membrane localization of β-TrCP were increased and (3) EGF, the protein expression and cytoplasmic-membrane localization of β-TrCP were increased in both the control and the patient. Conclusions (1) β-TrCP appears to be part of the negative regulatory mechanism of the GH/GHR and EGF/EGFR pathways. (2) There appears to be a negative correlation between β-TrCP and CIS. (3) In the control and GHTD patient, β-TrCP increases when CIS is suppressed, possibly as a compensatory inhibitor of the GH/GHR pathway.

Body height in paediatric inflammatory bowel diseases: A structural equation model analysis

BACKGROUND

Linear growth restriction is a unique feature of paediatric inflammatory bowel diseases (IBD), and reduced insulin-like growth factor (IGF-1) is a major determinant of short stature. We aimed to assess factors influencing somatic height in children suffering from IBD.

MATERIALS AND METHODS

This was a retrospective, cross-sectional study conducted after approval by Institutional authorities. Anthropometric data, disease-related factors, biochemical and clinical indices of inflammation and endocrine parameters were recorded and considered as explanatory covariates. A structural equation model analysis was utilized. Somatic height was the outcome of interest, and possible associations of explanatory covariates directly or through the mediation effect of IGF-1 were assessed.

RESULTS

Systemic inflammation, as expressed by high-sensitivity intereukin-6 (IL-6), and nutritional status described by body mass index (BMI) were the pathways that significantly affected stature through the mediation effect of IGF-1. Cortisol showed a direct, positive and independent of IGF-1 association with height.

CONCLUSIONS

Insulin-like growth factor-1 is a key player in the process that results in impaired linear growth. Malnutrition and systemic inflammation have a restrictive action on growth by reducing circulating IGF-1. The positive relation of serum cortisol to height could correspond to suppressed pituitary-adrenal axis due to long-term use of glucocorticoids.

Negative Regulation of Cytokine Signaling in Immunity

Cytokines are key modulators of immunity. Most cytokines use the Janus kinase and signal transducers and activators of transcription (JAK-STAT) pathway to promote gene transcriptional regulation, but their signals must be attenuated by multiple mechanisms. These include the suppressors of cytokine signaling (SOCS) family of proteins, which represent a main negative regulation mechanism for the JAK-STAT pathway. Cytokine-inducible Src homology 2 (SH2)-containing protein (CIS), SOCS1, and SOCS3 proteins regulate cytokine signals that control the polarization of CD4+ T cells and the maturation of CD8+ T cells. SOCS proteins also regulate innate immune cells and are involved in tumorigenesis. This review summarizes recent progress on CIS, SOCS1, and SOCS3 in T cells and tumor immunity.

Post-Receptor Inhibitors of the GHR-JAK2-STAT Pathway in the Growth Hormone Signal Transduction

The growth hormone (GH) plays a key role in the regulation of metabolic processes in an organism. Determination of the correct structure and functioning of the growth hormone receptor (GHR) allowed for a more detailed research of its post-receptor regulators, which substantially influences its signal transduction. This review is focused on the description of the post-receptor inhibitors of the GHR-JAK2-STAT pathway, which is one of the most important pathways in the transduction of the somatotropic axis signal. The aim of this review is the short characterization of the main post-receptor inhibitors, such as: cytokine-inducible SH2-containing protein (CIS), Suppressors of Cytokine Signaling (SOCS) 1, 2 and 3, sirtuin 1 (SIRT1), protein inhibitors of activated STAT (PIAS) 1, 3 and PIAS4, protein tyrosine phosphatases (PTP) 1B and H1, Src homology 2 (SH2) domain containing protein tyrosine phosphatase (SHP) 1, 2 and signal regulatory protein (SIRP) α1. The equilibrium between these regulators activity and inhibition is of special concern because, as many studies showed, even slight imbalance may disrupt the GH activity causing serious diseases. The regulation of the described inhibitors expression and activity may be a point of interest for pharmaceutical industry.

Suppressors of cytokine signaling: Potential immune checkpoint molecules for cancer immunotherapy

Inhibition of immune checkpoint molecules, PD‐1 and CTLA4, has been shown to be a promising cancer treatment. PD‐1 and CTLA4 inhibit TCR and co‐stimulatory signals. The third T cell activation signal represents the signals from the cytokine receptors. The cytokine interferon‐γ (IFNγ) plays an important role in anti‐tumor immunity by activating cytotoxic T cells (CTLs). Most cytokines use the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, and the suppressors of cytokine signaling (SOCS) family of proteins are major negative regulators of the JAK/STAT pathway. Among SOCS proteins, CIS, SOCS1, and SOCS3 proteins can be considered the third immunocheckpoint molecules since they regulate cytokine signals that control the polarization of CD4⁺ T cells and the maturation of CD8⁺ T cells. This review summarizes recent progress on CIS, SOCS1, and SOCS3 in terms of their anti‐tumor immunity and potential applications.

Epidermal growth factor receptor (EGFR) involvement in successful growth hormone (GH) signaling in GH transduction defect

BACKGROUND

Growth hormone (GH) transduction defect (GHTD) is a growth disorder with impaired signal transducer and activator of transcription 3 (STAT3) phosphorylation mediated by overexpression of cytokine-inducible SH2-containing protein (CIS), which causes increased growth hormone receptor (GHR) degradation. This study investigated the role of epidermal growth factor (EGF) in the restoration of normal GH signaling in GHTD.

METHODS

Protein expression, cellular localization and physical contact of proteins of the GH and EGF signaling pathways were studied by Western immunoblotting, immunofluorescence and co-immunoprecipitation, respectively. These were performed in fibroblasts of one GHTD patient (P) and one control child (C) at the basal state and after induction with human GH (hGH) 200 μg/L (GH200), either with or without silencing of CIS mRNA, and after induction with hGH 1000 μg/L (GH1000) or 50 ng/mL EGF.

RESULTS

The membrane availability of the EGF receptor (EGFR) and the activated EGFR (pEGFR) was increased in P only after simultaneous GH200 and silencing of CIS mRNA or with GH1000, whereas this occurred in C after GH200 alone. After EGF induction, the membrane localization of GHR, STAT3 and that of EGFR were increased in P more than in C.

CONCLUSIONS

In conclusion, in GHTD, the EGFR seems to participate in successful GH signaling, but induction of GHTD fibroblasts with a higher dose of hGH is needed. The EGF/EGFR pathway, in contrast to the GH/GHR pathway, seems to function normally in P and is more primed compared to C. The involvement of the EGFR in successful GH signaling may explain the catch-up growth seen in the Ps when exogenous hGH is administered.

Deep Sequencing Analysis of miRNA Expression in Breast Muscle of Fast-Growing and Slow-Growing Broilers

Growth performance is an important economic trait in chicken. MicroRNAs (miRNAs) have been shown to play important roles in various biological processes, but their functions in chicken growth are not yet clear. To investigate the function of miRNAs in chicken growth, breast muscle tissues of the two-tail samples (highest and lowest body weight) from Recessive White Rock (WRR) and Xinghua Chickens (XH) were performed on high throughput small RNA deep sequencing. In this study, a total of 921 miRNAs were identified, including 733 known mature miRNAs and 188 novel miRNAs. There were 200, 279, 257 and 297 differentially expressed miRNAs in the comparisons of WRRh vs. WRRl, WRRh vs. XHh, WRRl vs. XHl, and XHh vs. XHl group, respectively. A total of 22 highly differentially expressed miRNAs (fold change > 2 or < 0.5; p-value < 0.05; q-value < 0.01), which also have abundant expression (read counts > 1000) were found in our comparisons. As far as two analyses (WRRh vs. WRRl, and XHh vs. XHl) are concerned, we found 80 common differentially expressed miRNAs, while 110 miRNAs were found in WRRh vs. XHh and WRRl vs. XHl. Furthermore, 26 common miRNAs were identified among all four comparisons. Four differentially expressed miRNAs (miR-223, miR-16, miR-205a and miR-222b-5p) were validated by quantitative real-time RT-PCR (qRT-PCR). Regulatory networks of interactions among miRNAs and their targets were constructed using integrative miRNA target-prediction and network-analysis. Growth hormone receptor (GHR) was confirmed as a target of miR-146b-3p by dual-luciferase assay and qPCR, indicating that miR-34c, miR-223, miR-146b-3p, miR-21 and miR-205a are key growth-related target genes in the network. These miRNAs are proposed as candidate miRNAs for future studies concerning miRNA-target function on regulation of chicken growth.

Permanent uncoupling of male-specific CYP2C11 transcription/translation by perinatal glutamate

Perinatal exposure of rats and mice to the typically reported 4mg/g bd wt dose of monosodium glutamate (MSG) results in a complete block in GH secretion as well as obesity, growth retardation and a profound suppression of several cytochrome P450s, including CYP2C11, the predominant male-specific isoform--all irreversible effects. In contrast, we have found that a lower dose of the food additive, 2mg/g bd wt on alternate days for the first 9days of life results in a transient neonatal depletion of plasma GH, a subsequent permanent overexpression of CYP2C11 as well as subnormal (mini) GH pulse amplitudes in an otherwise normal adult masculine episodic GH profile. The overexpressed CYP2C11 was characterized by a 250% increase in mRNA, but only a 40 to 50% increase in CYP2C11 protein and its catalytic activity. Using freshly isolated hepatocytes as well as primary cultures exposed to the masculine-like episodic GH profile, we observed normal induction, activation, nuclear translocation and binding to the CYP2C11 promoter of the GH-dependent signal transducers required for CYP2C11 transcription. The disproportionately lower expression levels of CYP2C11 protein were associated with dramatically high expression levels of an aberrant, presumably nontranslated CYP2C11 mRNA, a 200% increase in CYP2C11 ubiquitination and a 70-80% decline in miRNAs associated, at normal levels, with a suppression of CYP2C expression. Whereas the GH-responsiveness of CYP2C7 and CYP2C6 as well as albumin was normal in the MSG-derived hepatocytes, the abnormal expression of CYP2C11 was permanent and irreversible.

Regulation of cytokine-inducible SH2-containing protein (CIS) by ubiquitination and Elongin B/C interaction

Cytokine-inducible SH2-containing protein (CIS) inhibits prolactin receptor (PRLR) signaling and acts as part of an E3 ubiquitin ligase complex through interactions with Elongin B/C proteins. This study aimed to identify CIS lysine ubiquitination sites and determine roles of ubiquitination and Elongin B/C interactions on CIS protein stability and PRLR signaling inhibition. Site-directed mutations revealed that CIS can be ubiquitinated on all six lysine residues. Elongin B/C interaction box mutation had no influence on CIS ubiquitination. CIS stability was increased by mutation of lysine residues and further enhanced by co-mutation of Elongin B/C interaction domain. CIS inhibition of STAT5B phosphorylation and casein promoter activation was dependent on CIS interactions with Elongin B/C, but not on CIS ubiquitination. These data indicate CIS protein stability is regulated through multiple mechanisms, including ubiquitination and interaction with Elongin B/C proteins, whereas CIS functional inhibition of PRLR signaling is dependent on the Elongin B/C interaction.

Comprehensive analysis of the whole transcriptomes from two different pig breeds using RNA-Seq method

Next-generation sequencing RNA-Seq technology is a powerful tool that creates new possibilities for whole-transcriptome analysis. In our study, the RNA-Seq method was applied to analyze global changes in transcriptome from muscle tissue (m. semimembranosus) in two pig breeds (Pietrain and Polish Landrace, PL). The breeds differ in terms of muscularity, growth rate and reproduction traits. Using three different approaches (deseq, cufflinks and edger) and taking into account the most restrictive criteria, 35 genes differentially expressed between Pietrain and PL pigs were identified. In both breeds, the most abundant were transcripts encoding ribosomal and cytoskeletal proteins (TPM3, TCAP, TMOD4, TPM2, TNNC1) and calcium-binding proteins involved in muscle contraction, calcium-mediated signaling or cation transport (CASQ1, MLC2V, SLC25A4, MYL3). In PL pigs, we identified up-regulation of several genes that play crucial roles in reproduction: female gamete generation (BDP1, PTPN21, USP9X), fertilization (EGFR) and embryonic development (CPEB4). In the Pietrain breed, only seven genes were over-expressed (CISH, SPP1, TUBA8, ATP6V1C2, IGKC, predicted LOC100510960 and LOC100626400), and they play important roles in, for example, negative regulation of apoptosis, immune response, cell-cell signaling, cell growth and migration as well as the metabolic process. The functions of the majority of selected genes were consistent with phenotypic variation in investigated breeds; thus, we proposed a new panel of candidate genes that can be associated with economically important pig traits.

GH administration patterns differently regulate epidermal growth factor signaling

Current GH administration protocols imply frequent s.c. injections, resulting in suboptimal compliance. Therefore, there is interest in developing delivery systems for sustained release of the hormone. However, GH has different actions depending on its continuous or pulsatile plasma concentration pattern. GH levels and circulating concentration patterns could be involved in the regulation of epidermal growth factor receptor (EGFR) expression in liver. Aberrant expression of this receptor and/or its hyperactivation has been associated with the pathogenesis of different types of carcinoma. Considering that one of the adverse effects associated with GH overexpression and chronic use of GH is the increased incidence of malignancies, the aim of this study was to analyze the effects of GH plasma concentration patterns on EGFR expression and signaling in livers of mice. For this purpose, GH was administered by s.c. daily injections to produce an intermittent plasma pattern or by osmotic pumps to provoke a continuously elevated GH concentration. Intermittent injections of GH induced upregulation of liver EGFR content, augmented the response to EGF, and the induction of proteins involved in promotion of cell proliferation in female mice. In contrast, continuous GH delivery in male mice was associated with diminished EGFR in liver and decreased EGF-induced signaling and expression of early genes. The results indicate that sustained delivery systems that allow continuous GH plasma patterns would be beneficial in terms of treatment safety with regard to the actions of GH on EGFR signaling and its promitogenic activity.

The role of suppressors of cytokine signalling in human neoplasms

Suppressors of cytokine signalling 1-7 (SOCS1-7) and cytokine-inducible SH2-containing protein (CIS) are a group of intracellular proteins that are well known as JAK-STAT and several other signalling pathways negative feedback regulators. More recently several members have been identified as tumour suppressors and dysregulation of their biological roles in controlling cytokine and growth factor signalling may contribute to the development of many solid organ and haematological malignancies. This review explores their biological functions and their possible tumour suppressing role in human neoplasms.

Inhibition of IL-6 family cytokines by SOCS3

IL-6 a multi-functional cytokine with important effects in both inflammation and haematopoiesis. SOCS3 is the primary inhibitor of IL-6 signalling, interacting with gp130, the common shared chain of the IL-6 family of cytokines, and JAK1, JAK2 and TYK2 to control both the duration of signalling and the biological response. Recent biochemical and structural studies have shown SOCS3 binds to only these three JAKs, all of which are associated with IL-6 signalling, and not JAK3. This specificity is determined by a three residue "GQM" motif in the kinase domain of JAK1, JAK2 and TYK2. SOCS3 binds to JAK and gp130 simultaneously, and inhibits JAK activity in an ATP-independent manner by partially occluding the kinase's substrate binding groove with its kinase inhibitory region. We therefore propose a model in which each of gp130, JAK and SOCS3 are directly bound to the other two, allowing SOCS3 to inhibit IL6 signalling with high potency and specificity.

Suppressor of Cytokine Signaling (SOCS) 5 utilises distinct domains for regulation of JAK1 and interaction with the adaptor protein Shc-1

Suppressor of Cytokine Signaling (SOCS)5 is thought to act as a tumour suppressor through negative regulation of JAK/STAT and epidermal growth factor (EGF) signaling. However, the mechanism/s by which SOCS5 acts on these two distinct pathways is unclear. We show for the first time that SOCS5 can interact directly with JAK via a unique, conserved region in its N-terminus, which we have termed the JAK interaction region (JIR). Co-expression of SOCS5 was able to specifically reduce JAK1 and JAK2 (but not JAK3 or TYK2) autophosphorylation and this function required both the conserved JIR and additional sequences within the long SOCS5 N-terminal region. We further demonstrate that SOCS5 can directly inhibit JAK1 kinase activity, although its mechanism of action appears distinct from that of SOCS1 and SOCS3. In addition, we identify phosphoTyr317 in Shc-1 as a high-affinity substrate for the SOCS5-SH2 domain and suggest that SOCS5 may negatively regulate EGF and growth factor-driven Shc-1 signaling by binding to this site. These findings suggest that different domains in SOCS5 contribute to two distinct mechanisms for regulation of cytokine and growth factor signaling.

Human airway eosinophils exhibit preferential reduction in STAT signaling capacity and increased CISH expression

Allergic asthma, a chronic respiratory disorder marked by inflammation and recurrent airflow obstruction, is associated with elevated levels of IL-5 family cytokines and elevated numbers of eosinophils (EOS). IL-5 family cytokines elongate peripheral blood EOS (EOS(PB)) viability, recruit EOS(PB) to the airways, and, at higher concentrations, induce degranulation and reactive oxygen species generation. Although airway EOS (EOS(A)) remain signal ready in that GM-CSF treatment induces degranulation, treatment of EOS(A) with IL-5 family cytokines no longer confers a survival advantage. Because the IL-5 family receptors have common signaling capacity, but are uncoupled from EOS(A) survival, whereas other IL-5 family induced endpoints remain functional, we tested the hypothesis that EOS(A) possess a JAK/STAT-specific regulatory mechanism (because JAK/STAT signaling is critical to EOS survival). We found that IL-5 family-induced STAT3 and STAT5 phosphorylation is attenuated in EOS(A) relative to blood EOS from airway allergen-challenged donors. However, IL-5 family-induced ERK1/2 phosphorylation is not altered between EOS(A) and EOS from airway allergen-challenged donors. These observations suggest EOS(A) possess a regulatory mechanism for suppressing STAT signaling distinct from ERK1/2 activation. Furthermore, we found, in EOS(PB), IL-5 family cytokines induce members of the suppressors of cytokine signaling (SOCS) genes, CISH and SOCS1. Additionally, following allergen challenge, EOS(A) express significantly more CISH and SOCS1 mRNA and CISH protein than EOS(PB) counterparts. In EOS(PB), long-term pretreatment with IL-5 family cytokines, to varying degrees, attenuates IL-5 family-induced STAT5 phosphorylation. These data support a model in which IL-5 family cytokines trigger a selective downregulation mechanism in EOS(A) for JAK/STAT pathways.

Mechanisms and management of growth impairment in children affected by inflammatory bowel disease

Growth failure is a typical complication of pediatric inflammatory bowel disease. Factors responsible for stunting are multiple, and proinflammatory cytokines such as TNF-α and IL-6 play a pivotal role. Other determinants are disease severity and location, malnutrition, increased nutritional needs, genetics and drugs. The achievement of optimal linear growth and the remission of gastrointestinal symptoms are the principal targets of pediatric inflammatory bowel disease treatment. Thus, it is very important to assess and monitor linear growth at diagnosis and during follow-up of disease until final adult height achievement. The main strategies for management or prevention of growth impairment in these children are aimed to ensure optimal nutrition, obtain a rapid and complete remission of the disease avoiding or minimizing steroid usage and consider surgical resection, in particular in case of localized ileo or ileocecal disease, to achieve remission in early or mid-puberty. In the last few years, some authors have evaluated the effects of recombinant human growth hormone treatment in children and adolescents with inflammatory bowel disease. However, further studies are needed to better assess its efficacy.

Growth hormone STAT5-mediated signaling and its modulation in mice liver during the growth period

Postnatal growth exhibits two instances of rapid growth in mice: the first is perinatal and independent of growth hormone (GH), the second is peripuberal and GH-dependent. Signal transducer and activator of transcription 5b (STAT5b) is the main GH-signaling mediator and it is related to IGF1 synthesis and somatic growth. The aim of this work was to assess differential STAT5 sensitivity to GH during the growth period in mouse liver of both sexes. Three representative ages were selected: 1-week-old animals, in the GH-independent phase of growth; 2.5-week-old mice, at the onset of the GH-dependent phase of growth; and 9-week-old young adults. GH-signaling mediators were assessed by immunoblotting, quantitative RT-PCR and immunohistochemistry. GH-induced STAT5 phosphorylation is low at one-week and maximal at 2.5-weeks of age when compared to young adults, accompanied by higher protein content at the onset of growth. Suppressor CIS and phosphatase PTP1B exhibit high levels in one-week animals, which gradually decline, while SOCS2 and SOCS3 display higher levels at adulthood. Nuclear phosphorylated STAT5 is low in one-week animals while in 2.5-week animals it is similar to 9-week control; expression of SOCS3, an early response GH-target gene, mimics this pattern. STAT5 coactivators glucocorticoid receptor (GR) and hepatic nuclear factor 1 (HNF1) abundance is higher in adulthood. Therefore, GH-induced STAT5 signaling presents age-dependent activity in liver, with its maximum coinciding with the onset of GH-dependent phase of growth, accompanied by an age-dependent variation of modulating factors. This work contributes to elucidate the molecular mechanisms implicated in GH responsiveness during growth.

The biology and mechanism of action of suppressor of cytokine signaling 3

Suppressors of cytokine signaling 3 (SOCS3) has been shown to be an important and non-redundant feedback inhibitor of several cytokines including leukemia inhibitory factor, IL-6, IL-11, Ciliary neurotrophic factor (CNTF), leptin, and granulocyte colony-stimulating factor (G-CSF). Loss of SOCS3 in vivo has profound effects on placental development, inflammation, fat-induced weight gain, and insulin sensitivity. SOCS3 expression is induced by Janus kinase (JAK)/signal transducers and activators of transcription (STAT) signaling and it then binds to specific cytokine receptors (including gp130, G-CSF, and leptin receptors). SOCS3 then inhibits JAK/STAT signaling in two distinct ways. First, SOCS3 is able to directly inhibit the catalytic activity of JAK1, JAK2, or TYK2 while remaining bound to the cytokine receptor. Second, SOCS3 recruits elongins B/C and Cullin5 to generate an E3 ligase that ubiquitinates both JAK and cytokine receptor targeting them for proteasomal degradation. Detailed in vivo studies have revealed that SOCS3 action not only limits the duration of cytokine signaling to prevent overactivity but it is also important in maintaining the specificity of cytokine signaling.

A novel viral SOCS from infectious spleen and kidney necrosis virus: interacts with Jak1 and inhibits IFN-α induced Stat1/3 activation

Interferon (IFN)-induced Janus kinase (Jak)/signal transducer and activator of transcription (Stat) pathway is important in controlling immune responses and is negatively response-regulated by the suppressor of cytokine signaling (SOCS) proteins. However, several viruses have developed various strategies to inhibit this pathway to circumvent the anti-viral immunity of the host. The infectious spleen and kidney necrosis virus (ISKNV) is the type species of the genus Megalocytivirus in the family Iridoviridae and a causative agent of epizootics in fish. ISKNV ORF103R encodes a predicted viral SOCS (vSOCS) with high homology to the vertebrate SOCS1, but lacks a SOCS-box domain. Interestingly, vSOCS only exists in the genus Megalocytivirus. ISKNV-vSOCS can block the IFN-α-induced Jak/Stat pathway in HepG2 cells. Over-expression of ISKNV-vSOCS inhibited the activities of IFN-stimulated response element (ISRE) promoter; however, the inhibitions by ISKNV-vSOCS were dose-dependent. ISKNV-vSOCS interacted with Jak1 protein and inhibited its tyrosine kinase activity in vitro. ISKNV-vSOCS also impaired the phosphorylation of Stat1 and Stat3 proteins and suppressed their activations. The point mutations (F18D, S66A, S85A, and R64K) of ISKNV-vSOCS significantly impaired the inhibition of IFN-α-induced ISRE-promoter activation. In conclusion, vSOCS inhibits IFN-α-induced Stat1/Stat3 signaling, suggesting that Megalocytivirus has developed a novel strategy to evade IFN anti-viral immunity via vSOCS protein.

Biology and significance of the JAK/STAT signalling pathways

Since its discovery two decades ago, the activation of the Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway by numerous cytokines and growth factors has resulted in it becoming one of the most well-studied intracellular signalling networks. The field has progressed from the identification of the individual components to high-resolution crystal structures of both JAK and STAT, and an understanding of the complexities of the molecular activation and deactivation cycle which results in a diverse, yet highly specific and regulated pattern of transcriptional responses. While there is still more to learn, we now appreciate how disruption and deregulation of this pathway can result in clinical disease and look forward to adoption of the next generation of JAK inhibitors in routine clinical treatment.

The role of growth hormone and insulin-like growth factor-1 in Crohn's disease: implications for therapeutic use of human growth hormone in pediatric patients

PURPOSE OF REVIEW

This review evaluates the role of the growth hormone (GH) and insulin-like growth factor (IGF) in influencing linear growth in pediatric Crohn's disease. It also examines the current evidence concerning the use of recombinant human growth hormone (rhGH) as a potential therapy in achieving optimal growth and inducing mucosal healing for pediatric Crohn's disease.

RECENT FINDINGS

Current treatment strategies for Crohn's disease including antitumor necrosis factor-α (TNF-α) therapy have been demonstrated to improve growth velocity, but linear growth deficits persist despite optimization of therapy. By complex mechanisms, including the reduction of levels of IGF-1 and induction of systemic and hepatic GH resistance, cytokines such as TNF-α and interleukin-6 (IL-6), commonly elevated in active Crohn's disease, are important as mediators of linear growth delay. Recent evidence suggests that rhGH therapy is effective in improving short-term linear growth for a selected group of patients but of limited benefit as a therapy for improving mucosal disease and reducing clinical disease activity.

SUMMARY

Crohn's disease interacts with the GH-IGF-1 axis in important ways. Recent studies evaluating rhGH use in pediatric Crohn's disease have demonstrated some efficacy in reversing persistent linear growth delay but limited benefits in terms of improving mucosal disease and clinical disease activity. Larger studies of adequate power are needed to confirm a true benefit in terms of growth, to examine a potential benefit with regard to modification of disease activity, and to evaluate long-term risks.

Dissecting interferon-induced transcriptional programs in human peripheral blood cells

Interferons are key modulators of the immune system, and are central to the control of many diseases. The response of immune cells to stimuli in complex populations is the product of direct and indirect effects, and of homotypic and heterotypic cell interactions. Dissecting the global transcriptional profiles of immune cell populations may provide insights into this regulatory interplay. The host transcriptional response may also be useful in discriminating between disease states, and in understanding pathophysiology. The transcriptional programs of cell populations in health therefore provide a paradigm for deconvoluting disease-associated gene expression profiles.We used human cDNA microarrays to (1) compare the gene expression programs in human peripheral blood mononuclear cells (PBMCs) elicited by 6 major mediators of the immune response: interferons alpha, beta, omega and gamma, IL12 and TNFalpha; and (2) characterize the transcriptional responses of purified immune cell populations (CD4+ and CD8+ T cells, B cells, NK cells and monocytes) to IFNgamma stimulation. We defined a highly stereotyped response to type I interferons, while responses to IFNgamma and IL12 were largely restricted to a subset of type I interferon-inducible genes. TNFalpha stimulation resulted in a distinct pattern of gene expression. Cell type-specific transcriptional programs were identified, highlighting the pronounced response of monocytes to IFNgamma, and emergent properties associated with IFN-mediated activation of mixed cell populations. This information provides a detailed view of cellular activation by immune mediators, and contributes an interpretive framework for the definition of host immune responses in a variety of disease settings.

Suppressors of cytokine signaling (SOCS) in T cell differentiation, maturation, and function

Cytokines are key modulators of T cell biology, but their influence can be attenuated by suppressors of cytokine signaling (SOCS), a family of proteins consisting of eight members, SOCS1-7 and CIS. SOCS proteins regulate cytokine signals that control the polarization of CD4(+) T cells into Th1, Th2, Th17, and T regulatory cell lineages, the maturation of CD8(+) T cells from naïve to "stem-cell memory" (Tscm), central memory (Tcm), and effector memory (Tem) states, and the activation of these lymphocytes. Understanding how SOCS family members regulate T cell maturation, differentiation, and function might prove critical in improving adoptive immunotherapy for cancer and therapies aimed at treating autoimmune and infectious diseases.

Mechanisms of growth impairment in pediatric Crohn's disease

Crohn's disease manifests during childhood or adolescence in up to 25% of patients. The potential for linear growth impairment as a complication of chronic intestinal inflammation is unique to pediatric patient populations. Insulin-like growth factor I (IGF-I), produced by the liver in response to growth hormone (GH) stimulation, is the key mediator of GH effects at the growth plate of bones. An association between impaired growth in children with Crohn's disease and low IGF-I levels is well recognized. Early studies emphasized the role of malnutrition in suppression of IGF-I production. However, a simple nutritional hypothesis fails to explain all the observations related to growth in children with Crohn's disease. The direct, growth-inhibitory effects of proinflammatory cytokines are increasingly recognized and explored. The potential role of noncytokine factors, such as lipopolysaccharides, and their potential to negatively influence the growth axis have recently been investigated with intriguing results. There is now reason for optimism that the modern anticytokine therapeutic agents available for treating children and adolescents with Crohn's disease will reduce the prevalence of this otherwise common complication. As our understanding of the mechanisms that underlie growth impairment advance, so too should the opportunity for developing further novel and targeted therapies.

Sex differences in the expression of hepatic drug metabolizing enzymes

Sex differences in pharmacokinetics and pharmacodynamics characterize many drugs and contribute to individual differences in drug efficacy and toxicity. Sex-based differences in drug metabolism are the primary cause of sex-dependent pharmacokinetics and reflect underlying sex differences in the expression of hepatic enzymes active in the metabolism of drugs, steroids, fatty acids and environmental chemicals, including cytochromes P450 (P450s), sulfotransferases, glutathione transferases, and UDP-glucuronosyltransferases. Studies in the rat and mouse liver models have identified more than 1000 genes whose expression is sex-dependent; together, these genes impart substantial sexual dimorphism to liver metabolic function and pathophysiology. Sex differences in drug metabolism and pharmacokinetics also occur in humans and are due in part to the female-predominant expression of CYP3A4, the most important P450 catalyst of drug metabolism in human liver. The sexually dimorphic expression of P450s and other liver-expressed genes is regulated by the temporal pattern of plasma growth hormone (GH) release by the pituitary gland, which shows significant sex differences. These differences are most pronounced in rats and mice, where plasma GH profiles are highly pulsatile (intermittent) in male animals versus more frequent (nearly continuous) in female animals. This review discusses key features of the cell signaling and molecular regulatory mechanisms by which these sex-dependent plasma GH patterns impart sex specificity to the liver. Moreover, the essential role proposed for the GH-activated transcription factor signal transducer and activator of transcription (STAT) 5b, and for hepatic nuclear factor (HNF) 4alpha, as mediators of the sex-dependent effects of GH on the liver, is evaluated. Together, these studies of the cellular, molecular, and gene regulatory mechanisms that underlie sex-based differences in liver gene expression have provided novel insights into the physiological regulation of both xenobiotic and endobiotic metabolism.

The SOCS box encodes a hierarchy of affinities for Cullin5: implications for ubiquitin ligase formation and cytokine signalling suppression

The SOCS (suppressors of cytokine signalling) family of proteins inhibits the cytokine-induced signalling cascade in part by promoting the ubiquitination of signalling intermediates that are then targeted for proteasomal degradation. This activity relies upon an interaction between the SOCS box domain, the adapter complex elonginBC and a member of the Cullin family, the scaffold protein of an E3 ubiquitin ligase. In this study, we dissected this interaction in vitro using purified components.We found that all eight SOCS proteins bound Cullin5 but required prior recruitment of elonginBC. Neither SOCS nor elonginBC bound Cullin5 when in isolation. Interestingly, the affinity of each SOCS-elonginBC complex for Cullin5 varied by 2 orders of magnitude across the SOCS family. Unexpectedly, the most potent suppressors of signalling, SOCS-1 and SOCS-3, bound most weakly to the E3 ligase scaffold, with affinities 100- and 10-fold lower, respectively, than the rest of the family. The remaining six SOCS proteins all bound Cullin5 with high affinity (K(d) of ~10 nM) due to a slower off-rate and hence a longer halflife of the complex. This difference in affinity may reflect a difference in mode of action as only SOCS-1 and SOCS-3 have been shown to suppress signalling using both SOCS box-dependent and SOCS box-independent mechanisms. This is not the case with the other six SOCS proteins, and our data imply the existence of two distinct subclasses of SOCS proteins with a high affinity for Cullin5, the E3 ligase scaffold, possibly reflecting complete dependence upon ubiquitination for suppression of cytokine signalling.

The many faces of the SOCS box

The suppressors of cytokine signalling (SOCS) box is a structural domain found at the C-terminus of over 70 human proteins. It is usually coupled to a protein interaction module such as an SH2 domain in case of SOCS proteins, a family of modulators of cytokine signaling. The SOCS box participates in the formation of E3 ligase complexes, marking activated cytokine receptor complexes for proteasomal degradation. A similar mechanism was recently uncovered for controlling SOCS activity itself, since SOCS2 was found to enhance the turnover of other SOCS proteins. The SOCS box can also add unique features to individual SOCS proteins: it can function as an adaptor domain as was demonstrated for SOCS3, or as a modulator of substrate binding in case of CIS. In this review we discuss these multiple roles of the SOCS box, which emerges as a versatile module controlling cytokine signaling via multiple mechanisms.

STAT5 activity in pancreatic β-cells

Signal transducer and activator of transcription (STAT)5A and -5B are latent transcription factors activated by cytokines and hormones of the cytokine family. In pancreatic insulin-secreting β-cells, STAT5A and -5B are activated primarily by prolactin and growth hormone stimulation and are important mediators of the potent stimulation of proliferation and insulin production caused by these hormones. STAT5A and -5B are both expressed in β-cells and control the expression of a number of mRNAs implicated in cell replication control, insulin biosynthesis and secretion. In addition to STAT5A and -5B being transcriptional activators, they may also repress gene transcription. By these means, STAT5 proteins increase the levels of anti-apoptotic transcripts in β-cells and repress expression of pro-apoptotic genes. This review focuses on the anti-apoptotic role of STAT5 signaling, providing a mechanism for β-cell resistance to pro-apoptotic cytokines, Type 1 diabetes mellitus and obesity-associated β-cell stress. It is clear from studies of STAT5 signaling in pancreatic β-cells that STAT5 is important for postnatal β-cell compensatory growth (as in pregnancy or obesity) and in the defense against β-cell stress factors.

Elongin B/C recruitment regulates substrate binding by CIS

SOCS proteins play a major role in the regulation of cytokine signaling. They are recruited to activated receptors and can suppress signaling by different mechanisms including targeting of the receptor complex for proteasomal degradation. The activity of SOCS proteins is regulated at different levels including transcriptional control and posttranslational modification. We describe here a novel regulatory mechanism for CIS, one of the members of this protein family. A CIS mutant deficient in recruitment of the Elongin B/C complex completely failed to suppress STAT5 activation. This deficiency was not caused by altered turnover of CIS but by loss of cytokine receptor interaction. Intriguingly, no such effect was seen for binding to MyD88. The interaction between CIS and the Elongin B/C complex, which depends on the levels of uncomplexed Elongin B/C, was easily disrupted. This regulatory mechanism may be unique for CIS, as similar mutations in SOCS1, -2, -3, -6, and -7 had no functional impact. Our findings indicate that the SOCS box not only plays a role in the formation of E3 ligase complexes but, at least for CIS, can also regulate the binding modus of SOCS box-containing proteins.

Vitamin D3 cannot revert desensitization of growth hormone (GH)-induced STAT5-signaling in GH-overexpressing mice non-calcemic tissues

Growth hormone (GH) binding to a membrane receptor dimer triggers multiple intracellular signaling pathways. Signal transducers and activators of transcription are the most relevant of these pathways for GH action. GH also activates several inhibitory mechanisms, particularly suppressors of cytokine signaling (SOCS/CIS) proteins. GH-overexpressing mice exhibit hepatic desensitization of the JAK2/STAT5 GH-signaling pathway, associated with an increased abundance of CIS. Vitamin D3 has been shown to inhibit GH-induced expression of CIS and SOCS-3 and therefore prolong GH signaling in osteoblast-like cells. The purpose of the present study is to determine if vitamin D3 could attenuate CIS expression in GH-overexpressing mice, and consequently allow GH JAK2/STAT5 signaling in GH-responsive tissues in these animals. The abundance of CIS, SOCS-2, SOCS-3, STAT5b and GHR, as well as STAT5b tyrosine phosphorylation after a GH stimulus, were measured in liver and muscle of GHRH-transgenic mice treated with 1alpha,25-dihydroxyvitamin D3 for 7 days. This treatment did not diminish CIS expression in GH-overexpressing mice tissues, nor did the content of SOCS-2 and SOCS-3 significantly vary. GH-induced STAT5b phosphorylation levels were similar to basal values in transgenic mice liver treated with or without vitamin D; the refractoriness to GH was also present in muscle. Therefore, treatment with vitamin D was not sufficient to revert STAT5 GH signaling desensitization in non-calcemic tissues in GH-overexpressing mice.

Involvement of a JAK/STAT pathway inhibitor: cytokine inducible SH2 containing protein in breast cancer

Cytokines and growth factors are responsible for inducing the expression of suppressor of cytokine signaling (SOCS) and cytokine-inducible SH2 containing (CIS) proteins. SOCS and CIS proteins are negative regulators of the JAK/STAT pathway, and exert their physiological effects by suppressing the tyrosine kinase activity of cytokine receptors and inhibiting STAT activation. Growth hormone (GH) is considered as a true cytokine and its local production directly contributes to tumor progression. In an initial study, we have found that CIS expression is increased in human breast cancer in proliferative areas corresponding to high level of GH synthesis. The results of the study presented here confirm the presence of a negative feed back loop in MCF7 cells stably transfected with the hGH gene (MCF-hGH). Real-time PCR analysis showed that gene expression levels of CIS were increased by 80% in MCF-hGH cells as compared to control cell line. Similarly, we have found that the level of CIS gene expression is increased by 50% in primary cultures of human breast cancer, reinforcing the pathophysiological impact of CIS. We previously demonstrated that increasing levels of transfected CIS resulted in strong activation of the mitogen-activated protein (MAP) kinase pathway. Thus, CIS protein has been hypothesized as acting like an activator of the MAPK pathway and an inhibitor of the differentiated cells functions mediated through the JAK/STAT pathway. In the present study, we demonstrate the role of CIS protein in tumor progression in particular its positive effects on cell proliferation and colony formation.

Mammalian protein-protein interaction trap (MAPPIT) analysis of STAT5, CIS, and SOCS2 interactions with the growth hormone receptor

Binding of GH to its receptor induces rapid phosphorylation of conserved tyrosine motifs that function as recruitment sites for downstream signaling molecules. Using mammalian protein-protein interaction trap (MAPPIT), a mammalian two-hybrid method, we mapped the binding sites in the GH receptor for signal transducer and activator of transcription 5 (STAT5) a and b and for the negative regulators of cytokine signaling cytokine-inducible Src-homology 2 (SH2)-containing protein (CIS) and suppressor of cytokine signaling 2 (SOCS2). Y534, Y566, and Y627 are the major recruitment sites for STAT5. A non-overlapping recruitment pattern is observed for SOCS2 and CIS with positions Y487 and Y595 as major binding sites, ruling out SOCS-mediated inhibition of STAT5 activation by competition for shared binding sites. More detailed analysis revealed that CIS binding to the Y595, but not to the Y487 motif, depends on both its SH2 domain and the C-terminal part of its SOCS box, with a critical role for the CIS Y253 residue. This functional divergence of the two CIS/SOCS2 recruitment sites is also observed upon substitution of the Y+1 residue by leucine, turning the Y487, but not the Y595 motif into a functional STAT5 recruitment site.

A molecular basis for the sexually dimorphic response to growth hormone

Once reserved solely for the treatment of short stature, the now readily available recombinant GH has expanded the use of the hormone to include the treatment of cardiovascular, renal, muscular, skeletal, immunological, psychosocial, and metabolic abnormalities associated with GH deficiency. There are also proposals for the widespread use of the hormone to ameliorate or reverse aging. However, this extensive use of GH has revealed intrinsic sexual dimorphisms in which females are considerably less responsive to the therapeutic regimen than are males. Dynamic changes in the Janus kinase-2 (Jak2)/signal transducers and activators of transcription (Stat5B) signaling pathway [as determined by transducer activation, Stat5B binding to the GH-responsive promoter of the CYP2C11 gene, and expression levels of the suppressors of cytokine signaling family (Socs2, Socs3, and Cis)] were examined in male and female rat-derived primary hepatocyte cultures exposed to the masculine-like episodic GH profile. We report that the cellular actions of GH normally mediated by activation of the Jak2/Stat5B pathway are suppressed in female cells possibly due to an inherent overexpression of Cis, a member of the suppressors of cytokine signaling family that normally down-regulates the Jak2/Stat5B pathway.

Functional Cross-modulation between SOCS Proteins Can Stimulate Cytokine Signaling

SOCS (suppressors of cytokine signaling) proteins are negative regulators of cytokine signaling that function primarily at the receptor level. Remarkably, in vitro and in vivo observations revealed both inhibitory and stimulatory effects of SOCS2 on growth hormone signaling, suggesting an additional regulatory level. In this study, we examined the possibility of direct cross-modulation between SOCS proteins and found that SOCS2 could interfere with the inhibitory actions of other SOCS proteins in growth hormone, interferon, and leptin signaling. This SOCS2 effect was SOCS box-dependent, required recruitment of the elongin BC complex, and coincided with degradation of target SOCS proteins. Detailed mammalian protein-protein interaction trap (MAPPIT) analysis indicated that SOCS2 can interact with all members of the SOCS family. SOCS2 may thus function as a molecular bridge between a ubiquitin-protein isopeptide ligase complex and SOCS proteins, targeting them for proteasomal turnover. We furthermore extended these observations to SOCS6 and SOCS7. Our findings point to a unique regulatory role for SOCS2, SOCS6, and SOCS7 within the SOCS family and provide an explanation for the unexpected phenotypes observed in SOCS2 and SOCS6 transgenic mice.

SOCS up-regulation mobilizes autologous stem cells through CXCR4 blockade

The chemokine CXCL12 influences self-renewal and differentiation of hematopoietic stem cell precursors in bone marrow by directing them toward specific stromalcell components. CXCL12 up-regulates members of the SOCS family through JAK/STAT activation, a mechanism that attenuates chemokine responses. SOCS expression may thus modulate retention of hematopoietic precursors (Sca-1(+) c-Kit(+)Lin(-) cells) in bone marrow. We show that in bovine growth hormone transgenic mice and in growth hormone-treated mice, SOCS up-regulation correlated with a large number of Sca-1(+) c-Kit(+)Lin(-) cells in blood. Retroviral transduction of SOCSs blocked in vitro migration of Sca-1(+)c-Kit(+)Lin(-) cells, as well as their capacity to reconstitute lethally irradiated mice. Furthermore, in lethally irradiated mice reconstituted with bone marrow infected by a tetracycline-regulated, SOCS-expressing lentiviral vector, doxycycline treatment promoted rapid, extensive precursor mobilization to the periphery. The results indicate that by blocking CXCR4-mediated functions, SOCSs modulate hematopoietic precursor cell retention in bone marrow, and suggest the therapeutic interest of SOCS manipulation in several pathologic situations.

Role of Ubiquitylation in Cellular Membrane Transport

Ubiquitylation of membrane proteins has gained considerable interest in recent years. It has been recognized as a signal that negatively regulates the cell surface expression of many plasma membrane proteins both in yeast and in mammalian cells. Moreover, it is also involved in endoplasmic reticulum-associated degradation of membrane proteins, and it acts as a sorting signal both in the secretory pathway and in endosomes, where it targets proteins into multivesicular bodies in the lumen of vacuoles/lysosomes. In this review we discuss the progress in understanding these processes, achieved during the past several years.

Growth hormone regulation of sex-dependent liver gene expression

The liver is a primary target for the action of GH, a pituitary protein hormone that regulates a broad range of physiological processes, including long bone growth, fatty acid oxidation, glucose uptake, and hepatic steroid and foreign compound metabolism. GH exerts sex-dependent effects on the liver in many species, with many hepatic genes, most notably genes coding for cytochrome P450 (CYP) enzymes, being transcribed in a sex-dependent manner. Sex differences in CYP expression are most striking in rats and mice (up to 500-fold male-female differences), but are also seen, albeit to a much smaller degree, in humans, where they are an important determinant of the sex dependence of hepatic drug and steroid metabolism. This article examines the mechanisms whereby GH, via its sex-dependent temporal patterns of pituitary release, activates intracellular signaling leading to the sexually dimorphic transcription of CYPs and other liver-expressed genes. Recent findings implicating the GH-regulated transcription factor STAT5b (signal transducer and activator of transcription 5b), hepatocyte nuclear factors 3beta, 4alpha and 6, and sex differences in DNA methylation and chromatin structure in the sex-dependent actions of GH are reviewed, and current mechanistic models are evaluated.

Regulation of JAK2 protein expression by chronic, pulsatile GH administration in vivo: a possible mechanism for ligand enhancement of signal transduction

Growth hormone (GH) is a key factor controlling postnatal growth and development. Despite growth-promoting effects in mammals, GH is not associated with muscle growth in the chicken. Janus kinase 2 (JAK2) has been identified as the first intracellular step in GH receptor (GHR) signaling in many species, however, there is limited knowledge regarding the GH signaling pathway in the chicken. In this study, GH-responsive, JAK2 immunoreactive proteins were first assessed in an avian hepatoma cell line (LMH). Tyrosine phosphorylation of a 120-122 kDa JAK2 immunoreactive protein was GH dose-dependent. In addition to in vitro studies, the timecourse of JAK2 activation in liver and skeletal muscle (Pectoralis superficialis) in response to a single intravenous (i.v.) injection of chicken GH (cGH), and the effect of chronic exposure to GH in a physiologically relevant pattern on JAK2 protein expression and tyrosine phosphorylation in vivo were assessed. At a dose of GH that was previously demonstrated to elicit a maximal metabolic response (6.25 microg/kg BW), maximum tyrosine phosphorylation of JAK2 appeared at 10 min post-GH administration in the pectoralis muscle, but was not detectable in liver. To assess whether chronic enhancement of GH would alter expression of JAK2, we utilized a dynamic model of pulsatile GH infusion that mimicked the early pattern of circulating GH expressed in younger, rapidly growing birds (high amplitude peaks with an inter-peak interval of 90 min). A 120-122 kDa protein in liver and muscle, and a dominant 130-136 kDa protein in the muscle, that was phosphorylated in response to GH, were specifically recognized by the JAK2 antibody. Chronic, pulsatile infusion of cGH into 8-week-old chickens was associated with increased abundance and tyrosine phosphorylation of JAK2 protein in both liver and muscle (P < 0.05), which were GH dose-dependent, and mirrored previously reported biological responses for the same birds [Vasilatos-Younken, R., Zhou, Y., Wang, X., McMurtry, J.P., Rosebrough, R.W., Decuypere, E., Buys, N., Darras, V.M., Van Der Geyten, S., Tomas, F., 2000. Altered chicken thyroid hormone metabolism with chronic GH enhancement in vivo: Consequences for skeletal muscle growth. Journal of Endocrinology 166, 609-620.]. In summary (1) JAK2 immunoreactive proteins that associate with the GHR and are tyrosine phosphorylated in response to GH were identified in an avian hepatoma cell line and expressed in both GH responsive (liver) and "non-responsive" (skeletal muscle) tissues; (2) tyrosine phosphorylation of JAK2 occurred within minutes of exposure to a single i.v. injection of GH in vivo in muscle but not liver of 8-week-old birds; and 3) there were GH dose-dependent increases in abundance of JAK2 protein and tyrosine phosphorylation in both tissues when chronically exposed to GH in a physiologically relevant pattern, that mirrored dose-dependent biological responses, including alterations in the pathway of thyroid hormone metabolism, previously reported. Enhanced JAK2 suggests one possible mechanism whereby chronic, physiologically appropriate exposure to the ligand enhances GH biological action via increased abundance of a key upstream component of the signal transduction pathway.

Janus kinase 2 enhances the stability of the mature growth hormone receptor

The abundance of surface GH receptor (GHR) is an important determinant of cellular GH sensitivity and is regulated at both transcriptional and posttranscriptional levels. In previous studies of GHR-expressing Janus kinase 2 (JAK2)-deficient human fibrosarcoma cells (gamma2A-GHR), we demonstrated that stable transfection with JAK2 resulted in increased steady-state levels of mature GHR (endoH-resistant; relative molecular mass, 115-140 kDa) relative to precursor GHR (endoH-sensitive; relative molecular mass, 100 kDa). We now examine further the effects of JAK2 on GHR trafficking by comparing gamma2A-GHR to gamma2A-GHR cells stably reconstituted with JAK2 (C14 cells). In the presence of JAK2, GHR surface expression was increased, as assessed by surface biotinylation, 125I-labeled human GH cell surface binding, and immunofluorescence microscopy assays. Although the absence of JAK2 precluded GH-stimulated signaling, GH-induced GHR disulfide linkage (a proxy for the GH-induced conformational changes in the GHR dimer) proceeded independent of JAK2 expression, indicating that the earliest steps in GH-induced GHR triggering are not prevented by the absence of JAK2. RNA interference-mediated knockdown of JAK2 in C14 cells resulted in a decreased mature to precursor ratio, supporting a primary role for JAK2 either in enhancing GHR biogenesis or dampening mature GHR degradation. To address these potential mechanisms, metabolic pulse-chase labeling experiments and experiments in which the fate of previously synthesized GHR was followed by anti-GHR immunoblotting after cycloheximide treatment (cycloheximide chase experiments) were performed. These indicated that the presence of JAK2 conferred modest enhancement (1.3- to 1.5-fold) in GHR maturation but substantially prolonged the t1/2 of the mature GHR, suggesting a predominant effect on mature GHR stability. Cycloheximide chase experiments with metalloprotease, proteasome, and lysosome inhibitors indicated that the enhanced stability of mature GHR conferred by JAK2 is not related to effects on constitutive receptor metalloproteolysis but rather is a result of reduced constitutive endosomal/lysosomal degradation of the mature GHR. These results are discussed in the context of emerging information on how JAK-family members modulate surface expression of other cytokine receptors.

Desensitization of the JAK2/STAT5 GH signaling pathway associated with increased CIS protein content in liver of pregnant mice

Chronic exposure to growth hormone (GH) was related to the desensitization of the JAK2/STAT5 signaling pathway in liver, as demonstrated in cells, female rats, and transgenic mice overexpressing GH. The cytokine-induced suppressor (CIS) is considered a major mediator of this desensitization. Pregnancy is accompanied by an increment in GH circulating levels, which were reported to be associated with hepatic GH resistance, although the molecular mechanisms involved in this resistance are not clearly elucidated. We thus evaluated the JAK2/STAT5b signaling pathway and its regulation by the suppressors of cytokine signaling (SOCS)/CIS family and the JAK2-interacting protein SH2-Bbeta in pregnant mouse liver, a model with physiological prolonged exposure to high GH levels. Basal tyrosyl phosphorylation levels of JAK2 and STAT5b in pregnant mice were similar to values obtained for virgin animals, in spite of the important increment of GH they exhibit. Moreover, these signaling mediators were not phosphorylated upon GH stimulation in pregnant mice. A 3.3-fold increase of CIS protein content was found for pregnant mice, whereas the abundance of the other SOCS proteins analyzed and SH2-Bbeta did not significantly change compared with virgin animals. The desensitization of the JAK2/STAT5b GH signaling pathway observed in pregnant mice would then be mainly related to increased CIS levels rather than to the other regulatory proteins examined.

Role of the cytokine-induced SH2 domain-containing protein CIS in growth hormone receptor internalization

The cytokine-inducible SH2 domain-containing protein CIS inhibits signaling from the growth hormone (GH) receptor (GHR) to STAT5b by a proteasome-dependent mechanism. Here, we used the GH-responsive rat liver cell line CWSV-1 to investigate the role of CIS and the proteasome in GH-induced GHR internalization. Cell-surface GHR localization and internalization were monitored in GH-stimulated cells by confocal immunofluorescence microscopy using an antibody directed against the GHR extracellular domain. In GH naïve cells, GHR was detected in small, randomly distributed granules on the cell surface and in the cytoplasm, with accumulation in the perinuclear area. GH treatment induced a rapid (within 5 min) internalization of GH.GHR complexes, which coincided with the onset of GHR tyrosine phosphorylation and the appearance in the cytosol of distinct granular structures containing internalized GH. GHR signaling to STAT5b continued for approximately 30-40 min, however, indicating that GHR signaling and deactivation of the GH.GHR complex both proceed from an intracellular compartment. The internalization of GH and GHR was inhibited by CIS-R107K, a dominant-negative SH2 domain mutant of CIS, and by the proteasome inhibitors MG132 and epoxomicin, which prolong GHR signaling to STAT5b. GH pulse-chase studies established that the internalized GH.GHR complexes did not recycle back to the cell surface in significant amounts under these conditions. Given the established specificity of CIS-R107K for blocking the GHR signaling inhibitory actions of CIS, but not those of other SOCS/CIS family members, these findings implicate CIS and the proteasome in the control of GHR internalization following receptor activation and suggest that CIS-dependent receptor internalization is a prerequisite for efficient termination of GHR signaling.

Suppressor of cytokine signaling-2 modulates the fibrogenic actions of GH and IGF-I in intestinal mesenchymal cells

Growth hormone (GH) and IGF-I play important roles in wound healing during intestinal injury and inflammation, but there is also indirect evidence that locally expressed IGF-I may act to induce excessive collagen deposition, which can lead to intestinal fibrosis. Factors that dictate the balance between normal wound healing and excessive healing responses are unknown. Using RNase protection assay and in situ hybridization, we determined whether GH and/or IGF-I increase type I collagen deposition in the intestine of rats fed by total parenteral nutrition (TPN), a feeding modality used for many patients following intestinal surgery and resection. We also used an in vitro model system to confirm our in vivo effects and to directly evaluate the relative potency of GH and IGF-I on DNA synthesis and collagen deposition in intestinal myofibroblasts. Both GH and IGF-I stimulated collagen production in vivo and in vitro, and IGF-I, but not GH, stimulated DNA synthesis in vitro. In collagen production, GH was less potent than IGF-I. Suppressors of cytokine signaling (SOC) are cytokine-inducible proteins that negatively feedback to inhibit the actions of cytokines and we recently found that GH selectively upregulates SOC-2 in the intestine of TPN-fed rats. We examined whether SOC-2 may be responsible for the difference in magnitude of action of GH and IGF-I on collagen accumulation. GH, but not IGF-I, induced SOC-2 in isolated myofibroblasts, and overexpression of SOC-2 led to a suppression of GH- and IGF-I-induced collagen accumulation. SOC-2 null mice infused with IGF-I showed greater collagen gene expression compared with wild-type (WT) mice. Myofibroblasts isolated from SOC-2 null mice showed increased IGF-I-stimulated DNA synthesis compared with WT cells. Taken together, these findings suggest that SOC-2 induced by GH may play an important role in suppressing collagen accumulation and mesenchymal cell proliferation induced by GH or GH-induced IGF-I, providing a mechanism for the differing potencies of GH and IGF-I on intestinal mesenchyme and collagen synthesis.

Negative regulation of growth hormone receptor signaling

GH has been of significant scientific interest for decades because of its capacity to dramatically change physiological growth parameters. Furthermore, GH interacts with a range of other hormonal pathways and is an established pharmacological agent for which novel therapeutical applications can be foreseen. It is easy to see the requirement for a number of postreceptor mechanisms to regulate and control target tissue sensitivity to this versatile hormone. In recent years, some of the components that take part in the down-regulatory mechanism targeting the activated GH receptor (GHR) have been defined, and the physiological significance of some of these key components has begun to be characterized. Down-regulation of the GHR is achieved through a complex mechanism that involves rapid ubiquitin-dependent endocytosis of the receptor, the action of tyrosine phosphatases, and the degradation by the proteasome. The suppressors of cytokine signaling (SOCS) protein family, particularly SOCS2, plays an important role in regulating GH actions. The aim of this review is to summarize collected knowledge, including very recent findings, regarding the intracellular mechanisms responsible for the GHR signaling down-regulation. Insights into these mechanisms can be of relevance to several aspects of GH research. It can help to understand growth-related disease conditions, to explain GH resistance, and may be used to develop pharmaceuticals that enhance some the beneficial actions of endogenously secreted GH in a tissue-specific manner.

Regulation of the immune system by SOCS family adaptor proteins

Signal transduction via cytokine receptors is regulated by several mechanisms that control initiation, magnitude and duration of the signaling pathways. Cytokine-induced SOCS family adaptors function as feedback inhibitors of cytokine receptor signaling by inhibiting the JAK-STAT signal transduction pathway. Specific gene-targeted mice have unveiled critical, non-overlapping functions for SOCS1 and SOCS3 in lymphocyte development and homeostasis, and in the regulation of macrophage and dendritic cell functions. In this review, we will discuss the structure of SOCS proteins, mechanisms by which they control the JAK-STAT pathway and their role in immune regulation.

Differential hypermethylation of SOCS genes in ovarian and breast carcinomas

Suppressor of cytokine signaling (SOCS) proteins have emerged as critical attenuators of cytokine-mediated processes, suggesting a role in the suppression of tumorigenesis. In the ovary and mammary gland, cytokines such as prolactin and IL-6 are important regulators of growth and differentiation. We have investigated whether silencing or inactivation of SOCS genes occurs in ovarian and breast carcinomas. The SOCS1 and SOCS2 CpG islands were found to be hypermethylated in 23 and 14% of primary ovarian cancers, respectively, whereas only SOCS1 was methylated in breast cancers (9%). Methylation of these genes did not occur in normal tissues. No correlation was apparent between methylation and loss of heterozygosity, and no somatic mutations were found in a large panel of carcinomas. Aberrant methylation of these SOCS genes correlated with transcriptional silencing in ovarian and breast cancer cell lines, since expression was induced by the demethylating agent 5-azadeoxycytidine. SOCS3 was not hypermethylated in either cancer type. Consistent with this data, SOCS1 and SOCS2 but not SOCS3 suppressed the growth of ovarian and breast cancer cells. Hypermethylation and silencing of specific SOCS genes in the ovary, and to a lesser extent in breast, may augment cytokine responsiveness in these tissues, thereby contributing to oncogenesis.