The interleukin-4-related lymphokines and their binding to hematopoietin receptors

Prolactin receptor regulates the seasonal reproduction of striped hamsters

In this study, differential mRNA expression patterns of prolactin receptor (PRLR) in the hypothalamus and gonads, and the correlation with follicle stimulating hormone (FSH) and luteinizing hormone (LH) in striped hamster serum from spring, summer, autumn and winter were analyzed. Mature female and male striped hamsters in oestrus were used. Expression levels of PRLR in the hypothalamus, ovaries and testis from the summer and winter individuals were significantly higher compared with levels from the spring and autumn, whereas FSH and LH serum concentrations from summer and winter individuals were significantly lower compared with that from the spring and autumn. PRLR expression levels in hypothalamus, ovaries and testis were negatively correlated with FSH and LH serum concentrations, illustrating that PRLR might negatively regulate seasonal reproductive activity. PRLR expression levels in ovaries and testes were significantly higher compared with levels in the hypothalamus, suggesting that the regulative effects of PRLR in gonads might be significantly higher compared with that in the hypothalamus. Furthermore, PRLR expression levels from the spring, summer, autumn and winter seasons in the hypothalamus and gonads were significantly higher in females compared with levels in males, indicating that the regulative effect of PRLR might be sex dependent. Taken together, this study helps to understand in depth the seasonal regulative reproduction mechanism of striped hamsters to reasonably control population abundance.

Cytokine therapy

Cytokines are a heterogeneous group of soluble small polypeptides or glycoproteins, which exert pleiotropic and redundant effects that promote growth, differentiation and activation of normal cells. Cytokines can have either pro- or anti-inflammatory activity and immunosuppressive activity, depending on the microenvironments. The tumor microenvironment consists of a variable combination of tumor cells, endothelial cells and infiltrating leukocytes, such as macrophages, T-lymphocytes, natural killer (NK) cells, B cells and antigen-presenting cells (APCs). Cytokine production acts as a means of communication in the tumor microenvironment. In this article, we review the cross-talk between cytokines in the tumor environment and the cytokine therapies that have been used till date for glioma treatment.

Consequences of regulated pre-mRNA splicing in the immune system

Alternative splicing is widely recognized to be a ubiquitous and crucial mechanism for generating protein diversity and regulating protein expression. Numerous immunologically relevant genes have been found to undergo alternative splicing; however, there has been little effort to develop a coherent picture of how alternative splicing might be used as a general mechanism to regulate the function of the immune system. In this review, I summarize the mechanisms by which splicing is controlled in T cells, and discuss the role of alternative splicing and alternative isoform expression in the regulation of T-cell activation and function.

Enhanced interleukin-4 production in CD4+ T cells and elevated immunoglobulin E levels in antigen-primed mice by bisphenol A and nonylphenol, endocrine disruptors: involvement of nuclear factor-AT and Ca2+

Bisphenol A (BPA) and p-nonylphenol (NP) are representative endocrine disruptors (EDs) that may have adverse effects on human health. The influence of these compounds on allergic immune responses remains unclear. In this study, we have examined the effects of BPA and NP on production of interleukin-4 (IL-4), a pro-inflammatory cytokine closely associated with allergic immune responses. Both BPA and NP significantly enhanced IL-4 production in keyhole limpet haemocyanin (KLH)-primed CD4+ T cells in a concentration-dependent manner. Treatment with BPA or NP in vivo resulted in significant increase of IL-4 production in CD4+ T cells and of antigen-specific immunoglobulin E (IgE) levels in the sera of KLH-primed mice. Furthermore, BPA and NP enhanced the activation of IL-4 gene promoter in EL4 T cells transiently transfected with IL-4 promoter/reporter constructs, and the enhancing effect mapped to a region in the IL-4 promoter containing binding sites for nuclear factor (NF)-AT. Activation of T lymphocytes by phorbol 12-myristate 13-acetate/ionomycin resulted in markedly enhanced binding activities to the NF-AT site, which significantly increased upon addition of BPA or NP, as demonstrated by the electrophoretic mobility shift assay, indicating that the transcription factor NF-AT was involved in the enhancing effect of BPA and NP on IL-4 production. The enhancement of IL-4 production by BPA or NP was significantly reduced by nitrendipine, a blocker of Ca2+ influx, and by FK506, a calcineurin inhibitor. FK506 inhibited the NF-AT-DNA binding activity and IL-4 gene promoter activity enhanced by BPA or NP. These results represent the first report describing possible enhancement of allergic response by EDs through increasing IL-4 production in CD4+ T cells and antigen-specific IgE levels in the sera via the stimulation of Ca2+/calcineurin-dependent NF-AT activation.

Identification of biological/biochemical marker(s) for preterm delivery

Fetal and neonatal mortality and morbidity rates are strongly associated with gestational age for delivery: the risk for poor outcome increases as gestational age decreases. Attempts to predict preterm delivery (PTD, spontaneous delivery before 37 weeks' gestation) have been largely unsuccessful, and rates of PTD have not improved in recent decades. More recently, the reported associations between infections in pregnancy and PTD suggest preventive initiatives that could be taken. The overall objective of the current study is to assess whether specific markers of infection (primarily interleukin (IL) 1beta, tumour necrosis factor (TNF) alpha, IL-6, and IL-10) obtained from maternal blood during pregnancy, alone or in combination with other risk factors for PTD, permit identification of women at risk for spontaneous PTD. To achieve this objective, data are obtained from two Danish prospective cohort studies involving serial collection of maternal blood samples, newborn cord blood samples, and relevant confounders and other risk factors for PTD. The first study consists of a completed Danish regional cohort of 3000 pregnant women enrolled in a study of microbiological causes of PTD, upon which a nested case-control study of PTD in 84 cases and 400 controls has been performed. The second study is a nested case-control study of 675 PTD cases (equally divided into three gestational age categories of 24-29 weeks' gestation, 30-33 weeks' gestation, and 34-36 weeks' gestation) and 675 controls drawn from the ongoing Danish National Birth Cohort study of 100 000 pregnant women enrolled during 1997-2001. The second study will provide the opportunity to refine and retest hypotheses from the first study, as well as to explore new hypotheses. Our preliminary work suggests that a single predictive marker effectively accounting for a large proportion of PTD is unlikely to be found. Rather, a search for multiple markers indicative of the multifactorial aetiology of PTD is likely to be more successful. Knowledge gained from the proposed studies will be implemented in a third, clinical intervention study against PTD. The first phase of the clinical intervention study will be to establish a risk-assessment model based on the "best" combination of biological/biochemical measures and other factors associated with PTD in order to identify pregnant women at very high risk of PTD. The second phase will be to apply an intervention model of tailored obstetric care to the very high-risk pregnant women for PTD identified in phase one. The intervention will be carried out against each specific risk factor associated with PTD identified for the individual. The aim is to reduce the risk for PTD attributed to the combination of risk factors included in the clinical intervention study.

Characterization of a powerful high affinity antagonist that inhibits biological activities of human interleukin-13

Interleukin-13 (IL-13), a predominantly Th2-derived cytokine, appears to play a central pathological role in asthma, atopic dermatitis, allergic rhinitis, some parasitic infections, and cancer. We hypothesized that an IL-13 antagonist may have profound therapeutic utility in these conditions. We, therefore, mutagenized human IL-13 in which Glu at position 13 was substituted by a Lys residue. This highly purified recombinant IL-13 variant, IL-13E13K, bound with 4-fold higher affinity to the IL-13 receptor than wild-type IL-13 but retained no detectable proliferative activity on the TF-1 hematopoietic cell line. IL-13E13K competitively inhibited IL-13- and IL-4-dependent TF-1 proliferation. It also inhibited IL-13-induced STAT-6 (signal transduction and activator of transducer-6) activation in immune cells and cancer cells and reversed IL-13-induced inhibition of CD14 expression on human primary monocytes. These results demonstrate that high affinity binding and signal generation can be uncoupled efficiently in a ligand receptor interaction. These results also suggest that IL-13E13K may be a useful antagonist for the treatment of allergic, inflammatory, and parasitic diseases or even malignancies in which IL-13 plays a central role.

Identification and characterization of a critical CP2-binding element in the human interleukin-4 promoter

Expression of cytokine genes in T cells is thought to result from a complex network of antigen- and mitogen-activated transcriptional regulators. CP2, a factor homologous to Drosophila Elf-1 and previously found to be a critical regulator of several viral and cellular genes in response to developmental signals, is rapidly activated in T helper (Th) cells in response to mitogenic stimulation. Here we show that overexpression of CP2 enhances interleukin (IL)-4 promoter-driven chloramphenicol acetyltransferase expression, while repressing IL-2 promoter activity, in transiently transfected Jurkat cells. A CP2-protected element, partially overlapping the nuclear factor of activated T cell-binding P2 sequence, was required for IL-4 promoter activation in CP2-overexpressing Jurkat cells. This CP2-response element is the site of a cooperative interaction between CP2 and an inducible heteromeric co-factor(s). Mutation of conserved nucleotide contacts within the CP2-response element prevented CP2 binding and significantly reduced constitutive and induced IL-4 promoter activity. Expression of a CP2 mutant lacking the Elf-1-homology region of the DNA-binding domain inhibited IL-4 promoter activity in a dominant negative fashion in transiently transfected Jurkat cells. Moreover, overexpressed CP2 markedly enhanced, while its dominant negative mutant consistently suppressed, expression of the endogenous IL-4 gene in the murine Th2 cell line D10. Taken together, these findings point to CP2 as a critical IL-4 transactivator in Th cells.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Identification of 40 genes on a 1-Mb contig around the IL-4 cytokine family gene cluster on mouse chromosome 11

Five related cytokine genes, interleukin 3 (Il3), interleukin 4 (Il4), interleukin 5 (Il5), interleukin 13 (Il13), and granulocyte-macrophage colony-stimulating factor (Csfgm or Csf2), are tightly linked on mouse chromosome 11. We now describe a 1-Mb transcript map of this cytokine cluster. Genomic clones obtained by screening mouse bacterial artificial chromosome (BAC) and P1-derived artificial chromosome (PAC) libraries were subcloned into the pSPL3 expression vector and transfected into COS7 cells for exon trapping. In total, 118 distinct, putative exons were sequenced and characterized, mapping up to 29 distinct genes to the mouse cluster, including Il4 and Csf2. Northern blot and RT-PCR analyses indicate that all of these genes are expressed. Analysis of 1 Mb of published sequence from the region of conserved synteny on human chromosome 5q31-q33 identified 45 gene candidates, including 35 expressed genes in the human IL-4 cytokine gene cluster. Probes for 20 human genes were tested for cross-hybridization to murine BAC and PAC clones, thereby mapping 11 additional genes to the mouse complex. Thus, a total of 40 genes including 6 cytokine genes have been physically mapped within 1 Mb of mouse chromosome 11. Gene order in this complex is similar, but not identical, between human and mouse. The integrated physical and transcript maps should prove valuable as a complement to genomic sequencing and expression-dependent transcript maps of this segment of the genome.

Immunoendocrinology of preterm labor: the link between corticotropin-releasing hormone and inflammation

Preterm labor is the final common pathway after several potential insults to the uterus or fetus. The preterm labor syndrome may be precipitated by several different pathophysiologic events, including intrauterine infection, uterine ischemia, uterine overdistention, hormonal disturbances, and other problems. Intrauterine infections (both clinically evident and subclinical) are associated with increased amniotic fluid concentrations of proinflammatory cytokines, and gestational tissues and the fetus are potential sources of these cytokines. In addition to culture-proven intrauterine infection, there may be an "intrauterine inflammatory response syndrome" that could account for cases of preterm labor in which no infectious organism can be identified. Because the immunologic and endocrinologic systems regulate each other extensively, there is potential for corticotropin-releasing hormone to regulate inflammatory responses and vice versa. The cytokine interleukin 1 stimulates production of corticotropin-releasing hormone, and corticotropin-releasing hormone in turn regulates cytokine production by immune effector cells. Because maternal stress is associated with preterm birth, abnormalities in the regulation of corticotropin-releasing hormone and the production of inflammatory cytokines may be a mechanism that could form the pathophysiologic basis for this association.

Interleukin-4 down-regulates both forms of tumor necrosis factor receptor and receptor-mediated apoptosis, NF-kappaB, AP-1, and c-Jun N-terminal kinase. Comparison with interleukin-13

The activity of tumor necrosis factor (TNF), a proinflammatory cytokine, is regulated by a number of other cytokines, including interleukin (IL)-4. How IL-4 regulates various activities of TNF is not fully understood. In the present report, we investigated the effect of IL-4 on the cell surface TNF receptors in human histiocytic lymphoma U-937 cells. Pretreatment of cells with IL-4 down-regulated TNF receptors in a dose- and time-dependent manner; an almost 90% decrease occurred with 10 ng/ml IL-4 treatment for 24 h. Scatchard analysis revealed that the decrease was due to receptor number and not affinity. IL-13, which shares a common receptor subunit and various biological activities with IL-4, had no effect on TNF receptors. IL-4's effect on TNF receptors was not cell type-specific, since decreases also occurred on various epithelial and T cells. Both the p60 and p80 forms of the TNF receptor were down-regulated to the same extent. Western blot showed that IL-4 induced shedding of the TNF receptors. The decrease of TNF receptors by IL-4 was accompanied by down-regulation of TNF-induced activities, including cytotoxicity, caspase-3 activation, NF-kappaB and AP-1 activation, and c-Jun N-terminal kinase induction. Wortmannin reversed the IL-4-induced TNF receptor down-regulation and all other measured cellular responses, indicating a critical role of phosphatidylinositol 3-kinase. Rapamycin also blocked the effect of IL-4-induced regulation, thus suggesting the role of p70 S6 kinase. Overall, our results suggest that TNF receptor down-regulation by IL-4 plays a critical role in the antagonistic effects of IL-4 on TNF-induced cellular responses and that this mechanism differs from that of IL-13.

IL-5 and IL-5 receptor in asthma

Eosinophils, along with mast cells are key cells involved in the innate immune response against parasitic infection whereas the adaptive immune response is largely dependent on lymphocytes. In chronic parasitic disease and in chronic allergic disease, IL-5 is predominantly a T cell derived cytokine which is particularly important for the terminal differentiation, activation and survival of committed eosinophil precursors. The human IL-5 gene is located on chromosome 5 in a gene cluster that contains the evolutionary related IL-4 family of cytokine genes. The human IL-5 receptor complex is a heterodimer consisting of a unique alpha subunit (predominantly expressed on eosinophils) and a beta subunit which is shared between the receptors for IL-3 & GM-CSF (more widely expressed). The alpha subunit is required for ligand-specific binding whereas association with the beta subunit results in increased binding affinity. The alternative splicing of the alpha IL-5R gene which contains 14 exons can yield several alpha-IL-5R isoforms including a membrane-anchored isoform (alpha IL-5Rm) and a soluble isoform (alpha IL-5Rs). Cytokines such as IL-5 produce specific and non-specific cellular responses through specific cell membrane receptor mediated activation of intracellular signal transduction pathways which, to a large part, regulate gene expression. The major intracellular signal transduction mechanism is activation of non-receptor associated tyrosine kinases including JAK and MAP kinases which can then transduce signals via a novel family of transcriptional factors named signal transducers and activators of transcription (STATS). JAK2, STAT1, and STAT5 appear to be particularly important in IL-5 mediated eosinophil responses. Asthma is characterized by episodic airways obstruction, increased bronchial responsiveness, and airway inflammation. Several studies have shown an association between the number of activated T cells and eosinophils in the airways and abnormalities in FEV1, airway reactivity and clinical severity in asthma. It has now been well documented that IL-5 is highly expressed in the bronchial mucosa of atopic and intrinsic asthmatics and that the increased IL-5 mRNA present in airway tissues is predominantly T cell derived. Immunocytochemical staining of bronchial biopsy sections has confirmed that IL-5 mRNA transcripts are translated into protein in asthmatic subjects. Furthermore, the number of activated CD4 + T cells and IL-5 mRNA positive cells are increased in asthmatic airways following antigen challenge and studies that have examined IL-5 expression in asthmatic subjects before and after steroids have shown significantly decreased expression following oral corticosteroid treatment in steroid-sensitive asthma but not in steroid resistant and chronic severe steroid dependent asthma. The link between T cell derived IL-5 and eosinophil activation in asthmatic airways is further strengthened by the demonstration that there is an increased number of alpha IL-5R mRNA positive cells in the bronchial biopsies of atopic and non-atopic asthmatic subjects and that the eosinophil is the predominant site of this increased alpha IL-5R mRNA expression. We have also shown that the subset of activated eosinophils that expressed mRNA for membrane bound alpha IL-5r inversely correlated with FEV1, whereas the subset of activated eosinophils that expressed mRNA for soluble alpha IL-5r directly correlated with FEV1. Hence, not only does this data suggest that the presence of eosinophils expressing alpha IL-5R mRNA contribute towards the pathogenesis of bronchial asthma, but also that the eosinophil phenotype with respect to alpha IL-5R isoform expression is of central importance. Finally, there are several animal, and more recently in vitro lung explant, models of allergen induced eosinophilia, late airway responses (LARS), and bronchial hyperresponsiveness (BHR)--all of which support a link between IL-5 and airway eosinophilia and bronc

Homology model for oncostatin M based on NMR structural data

Oncostatin M (OM) is a member of the cytokine family which regulates the proliferation and differentiation of a variety of cell types and includes interleukin-6 (IL-6), leukemia inhibitory factor (LIF), and granulocyte-colony stimulating factor (G-CSF). This family of proteins adopts a four-helix bundle fold with up-up-down-down topology and contains intramolecular disulfide bonds. Since an X-ray or NMR structure for OM is not currently available, a homology model for OM was determined from the X-ray structures of human growth hormone (hGH), LIF, and G-CSF where the alignment was based on secondary structure instead of sequence. The OM secondary structure was determined from NMR structural data, and the secondary structures for hGH, LIF, and G-CSF were obtained from the reported X-ray structures. The resulting homology model was refined using sequential NOE distance 13C restraints, chemical shift information, and a conformational database.

Identification and characterization of two alternative splice variants of human interleukin-2

Our previous work showed that alternative splicing is used to make an inhibitory variant of human interleukin (IL)-4. Because of homology between IL-4 and IL-2 proteins and receptors, we tested whether alternative splicing is used to generate similar inhibitory variants of human IL-2. Messenger RNA from peripheral blood mononuclear cells was subjected to reverse transcription-polymerase chain reaction using IL-2 exon 1- and exon 4-specific primers. Two amplification products, named IL-2delta2 and IL-2delta3, were found in addition to the native IL-2 product. The IL-2delta2 cDNA sequence was identical to IL-2 cDNA throughout the entire coding region, except exon 2 was omitted by alternative splicing. In IL-2delta3 cDNA, the third exon of IL-2 was omitted by alternative splicing. Unlike IL-2, IL-2delta2 and IL-2delta3 did not stimulate T cell proliferation. However, both inhibited IL-2 costimulation of T cell proliferation, and both inhibited cellular binding of rhIL-2 to high affinity IL-2 receptors. Thus, IL-2 is the second cytokine that uses alternative splicing to generate variants that are competitive inhibitors.

Generation of a variant of human interleukin-4 by alternative splicing

A second species of interleukin-4 (IL-4) mRNA was identified using both a reverse transcription-polymerase chain reaction and an RNase protection assay. This novel IL-4 mRNA was 48 base pairs smaller than IL-4 mRNA, which is the size of IL-4 exon 2. Sequence data of cloned cDNA demonstrated that this variant contained IL-4 exons 1,3 and 4, with exon 1 spliced directly to exon 3 in an open reading frame. The entire protein encoding region of this variant, named IL-4 delta 2, was identical to IL-4 except for the omission of exon 2. IL-4 delta 2 mRNA was detected in all human peripheral blood mononuclear cells tested and in purified CD3+ T cells. Amounts of both IL-4 and IL-4 delta 2 mRNAs increased upon T cell activation, although IL-4 mRNA increased to a greater extent than IL-4 delta 2 mRNA did. Human IL-3, IL-5, IL-13, and granulocyte macrophage-colony stimulating factor did not use alternative splicing to delete exon 2. We speculate that IL-4 delta 2 may regulate IL-4 function.

Saturation mutagenesis of human interleukin-3

A deletion variant of human interleukin-3, hIL-3(15-125), was produced in the periplasmic space of Escherichia coli and had full activity in an AML193.1.3 cell proliferation assay. Libraries of random single-amino acid substitutions were constructed at each of 105 positions in the gene for hIL-3(15-125). Approximately eight single-site substitutions at each position were produced in osmotic shock fractions and screened for activity. 15 mutants were found with bioactivity of 5-26-fold greater than that of native hIL-3. The majority of amino acids in hIL-3(15-125) could be substituted without substantial loss of activity. Substitution of residues predicted to be in the hydrophobic core of the protein often resulted in reduced activity and/or low accumulation levels. Only five residues predicted to be on the surface of the protein were intolerant of substitution and hence are candidates for sites of interaction with the receptor. We therefore propose that the majority of residues in hIL-3 serve a structural role and permit the display of a few key residues in the correct configuration for recognition by the receptor.

Genetic susceptibility to asthma--bronchial hyperresponsiveness coinherited with a major gene for atopy

BACKGROUND

Bronchial hyperresponsiveness, a risk factor for asthma, consists of a heightened bronchoconstrictor response to a variety of stimuli. The condition has a heritable component and is closely related to serum IgE levels and airway inflammation. The basis for these relations is unknown, as is the mechanism of genetic susceptibility to bronchial hyperresponsiveness. We attempted to define the interrelation between atopy and bronchial hyperresponsiveness and to investigate the chromosomal location of this component of asthma.

METHODS

We studied 303 children and grandchildren of 84 probands with asthma selected from a homogeneous population in the Netherlands. Ventilatory function, bronchial responsiveness to histamine, and serum total IgE were measured. The association between the last two variables was evaluated. Using analyses involving pairs of siblings, we tested for linkage between bronchial hyperresponsiveness and genetic markers on chromosome 5q31-q33, previously shown to be linked to a genetic locus regulating serum total IgE levels.

RESULTS

Serum total IgE levels were strongly correlated (r = 0.65, P < 0.01) in pairs of siblings concordant for bronchial hyperresponsiveness (defined as a > or = 20 percent decrease in the forced expiratory volume in one second produced by histamine [threshold dose, < or = 16 mg per milliliter]), suggesting that these traits are coinherited. However, bronchial hyperresponsiveness was not correlated with serum IgE levels (r = 0.04, P > 0.10). Analyses of pairs of siblings showed linkage of bronchial hyperresponsiveness with several genetic markers on chromosome 5q, including D5S436 (P < 0.001 for a histamine threshold value of < or = 16 mg per milliliter).

CONCLUSIONS

This study demonstrates that a trait for an elevated level of serum total IgE is coinherited with a trait for bronchial hyperresponsiveness and that a gene governing bronchial hyperresponsiveness is located near a major locus that regulates serum IgE levels on chromosome 5q. These findings are consistent with the existence of one or more genes on chromosome 5q31-q33 causing susceptibility to asthma.

Molecular modeling of the GM-CSF and IL-3 receptor complexes

A model for the structure of the cytokine interleukin-3 (IL-3) is presented based on the structural homology of the hematopoietic cytokines and utilizing the crystal structures of interleukin-5 and granulocyte macrophage colony stimulating factor (GM-CSF). In addition, models of the receptor complexes of GM-CSF and IL-3 are presented based on the structural homology of the hematopoietic receptors to growth hormone. Several key interactions between the ligands and their receptors are discovered, some in agreement with previous mutagenesis studies and others that have not yet been the subject of mutagenesis studies. The models provide insights into the binding of GM-CSF and IL-3 to their receptors.

Protein-tyrosine kinase-dependent activation of STAT transcription factors in interleukin-2- or interleukin-4-stimulated T lymphocytes

The proliferation of activated T lymphocytes is critically dependent on the binding of the T-cell growth factors, interleukin (IL)-2 and IL-4, to distinct but evolutionarily related cell surface receptors. Previous results suggest that the IL-2 receptor (IL-2R) and IL-4R are coupled to both overlapping and distinct intracellular signaling pathways in T lymphocytes. In this study, we demonstrate that activation of Janus tyrosine kinases (JAKs) and STAT transcription factors is rapidly induced by exposure of factor-dependent murine T-cell lines to IL-2 or IL-4. Both IL-2 and IL-4 stimulated the rapid activation of JAK1 and JAK3, whereas JAK2 activity was unaffected by either cytokine. These responses were accompanied by the appearance in cell nuclei of 3 DNA binding activities that recognized a high-affinity binding site for STAT factors. In transient transfection assays, this STAT factor target sequence conferred IL-2 and IL-4 inducibility on a synthetic luciferase reporter gene. Antibody supershifting experiments indicated that IL-2 induces the formation of STAT dimers containing STAT3 and STAT1 alpha. Although IL-4 also activated STAT1 alpha, the major IL4-induced STAT factor is not STAT3 and remains undefined. Pretreatment of the T-cells with the protein-tyrosine kinase inhibitor herbimycin A blocked both the nuclear translocation of STAT factors and STAT-dependent reporter gene transcription. Immunoblot analyses confirmed that cytoplasmic STAT3 was heavily phosphorylated on tyrosine in IL-2-stimulated cells, and that phosphorylated STAT3 appeared in the nuclei of these cells. These results indicate that identical JAKs and partially overlapping sets of STATs are activated by IL-2 and IL-4 in T lymphocytes.

Binding interactions of human interleukin 5 with its receptor alpha subunit. Large scale production, structural, and functional studies of Drosophila-expressed recombinant proteins

Human interleukin 5 (hIL5) and soluble forms of its receptor alpha subunit were expressed in Drosophila cells and purified to homogeneity, allowing a detailed structural and functional analysis. B cell proliferation confirmed that the hIL5 was biologically active. Deglycosylated hIL5 remained active, while similarly deglycosylated receptor alpha subunit lost activity. The crystal structure of the deglycosylated hIL5 was determined to 2.6-A resolution and found to be similar to that of the protein produced in Escherichia coli. Human IL5 was shown by analytical ultracentrifugation to form a 1:1 complex with the soluble domain of the hIL5 receptor alpha subunit (shIL5R alpha). Additionally, the relative abundance of ligand and receptor in the hIL5.shIL5R alpha complex was determined to be 1:1 by both titration calorimetry and SDS-polyacrylamide gel electrophoresis analysis of dissolved cocrystals of the complex. Titration microcalorimetry yielded equilibrium dissociation constants of 3.1 and 2.0 nM, respectively, for the binding of hIL5 to shIL5R alpha and to a chimeric form of the receptor containing shIL5R alpha fused to the immunoglobulin Fc domain (shIL5R alpha-Fc). Analysis of the binding thermodynamics of IL5 and its soluble receptor indicates that conformational changes are coupled to the binding reaction. Kinetic analysis using surface plasmon resonance yielded data consistent with the Kd values from calorimetry and also with the possibility of conformational isomerization in the interaction of hIL5 with the receptor alpha subunit. Using a radioligand binding assay, the affinity of hIL5 with full-length hIL5R alpha in Drosophila membranes was found to be 6 nM, in accord with the affinities measured for the soluble receptor forms. Hence, most of the binding energy of the alpha receptor is supplied by the soluble domain. Taken with other aspects of hIL5 structure and biological activity, the data obtained allow a prediction for how 1:1 stoichiometry and conformational change can lead to the formation of hIL5.receptor alpha beta complex and signal transduction.

A model of the complex between interleukin-4 and its receptors

A three-dimensional model of interleukin-4 (IL-4) bound to one molecule each of the high- and low-affinity receptors (IL-4R and IL-2R gamma) was built, using the crystal structure of the complex of human growth hormone (HGH) with its receptor (HGHR) as a starting model. The modeling of IL-4 with its receptors was based on the conservation of the sequences and on the predicted structural organization for cytokine receptors, and assuming that the binding mode of the ligands would be similar. Analysis of the interface between IL-4 and both receptor molecules was carried out to reveal which residues are important for complex formation. The modeling procedures showed that there were no major problems in maintaining a reasonable fit of IL-4 with the two receptor molecules, in a manner analogous to the complex of HGH-HGHR. Many of the residues that appear by modeling to be important for binding between IL-4 and the receptors have been previously implicated in that role by different methods. A striking motif of aromatic and positively charged residues on the surface of the C-terminal domains of the receptors is highly conserved in the structure of HGH-HGHR and in the models of IL-4 complexed with its receptors.

Activation of 70-kDa S6 kinase, induced by the cytokines interleukin-3 and erythropoietin and inhibited by rapamycin, is not an absolute requirement for cell proliferation

The cytokines interleukin (IL)-3 and erythropoietin (EPO) are critical regulators of the proliferation and differentiation of cells of the hematopoietic system, but their intracellular mechanisms of action are not fully understood. Binding of IL-3 to the IL-3 receptor (IL-3R) and binding of EPO to the EPOR both induce changes in intracellular tyrosine and serine/threonine phosphorylation; the phosphorylation of a number of polypeptides appears to be a shared response upon cytokine stimulation. We have previously shown that binding of IL-2 to the IL-2R activates the 70-kDa (p70) S6 kinase, a serine/threonine kinase whose activity is regulated by serine/threonine phosphorylation; the immunosuppressant rapamycin inhibits IL-2-dependent proliferation and IL-2-triggered activation of p70 S6 kinase. We, therefore, sought to examine whether induction of p70 S6 kinase activity is a conserved response upon cytokine triggering, and whether this activity is essential for cell proliferation. Proliferation of the IL-3-dependent pro-B cell line Ba/F3 transfected with the EPOR (Ba/F3-EPOR) can be supported by either IL-3 or EPO. In this cell line, both IL-3 and EPO induced p70 S6 kinase activity; rapamycin inhibited both the IL-3 and EPO-induced activation of the 70-kDa S6 kinase as well as cellular proliferation. Thus, p70 S6 kinase activation appears to be a common intermediate triggered by the stimulation of IL-3, EPO, and IL-2 receptors. The Friend spleen focus-forming virus gp55 renders the EPOR constitutively active, and confers growth factor independence on cells expressing EPOR. Ba/F3-EPOR cotransfected with gp55 (Ba/F3-EpoRgp55) and the erythroleukemia cell line MEL, which also expresses both the EPOR and gp55, were analyzed. Rapamycin inhibited the activation of p70 S6 kinase in both cell lines. However, rapamycin inhibited proliferation of Ba/F3-EpoRgp55 but not of MEL cells despite inhibition of p70 S6 kinase activity in both cells. Thus, p70 S6 kinase activation is not an absolute requirement for cell proliferation. These results are discussed in relation to the role of the activation of the 70-kDa S6 kinase activation pathway in the regulation of cell cycle progression.

Optimizing the effectiveness of hematopoietic growth factors

Hematopoiesis is regulated in a very precise fashion by a balance between both positive and negative growth factor signals in the hematopoietic microenvironment. Many of these growth factor signals have been identified and are available as recombinant proteins. At the present time, the approved uses for hematopoietic growth factors involve their use to facilitate blood cell production in situations of hematopoietic suppression or in cases where endogenous growth factor production is inappropriately low. Recent studies with the hematopoietic growth factors are looking at innovative strategies for their use and new clinical situations in which to evaluate their effectiveness. This review looks at some of these new uses for hematopoietic growth factors.

Receptor binding properties of four-helix-bundle growth factors deduced from electrostatic analysis

Hormones of the hematopoietin class mediate signal transduction by binding to specific transmembrane receptors. Structural data show that the human growth hormone (hGH) forms a complex with a homodimeric receptor and that hGH is a member of a class of hematopoietins possessing an antiparallel 4-alpha-helix bundle fold. Mutagenesis experiments suggest that electrostatic interactions may have an important influence on hormone-receptor recognition. In order to examine the specificity of hormone-receptor complexation, an analysis was made of the electrostatic potentials of hGH, interleukin-2 (IL-2), interleukin-4 (IL-4), granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), and the hGH and IL-4 receptors. The binding surfaces of hGH and its receptor, and of IL-4 and its receptor, show complementary electrostatic potentials. The potentials of the hGH and its receptor display approximately 2-fold rotational symmetry because the receptor subunits are identical. In contrast, the potentials of GM-CSF and IL-2 lack such symmetry, consistent with their known high affinity for hetero-oligomeric receptors. Analysis of the electrostatic potentials supports a recently proposed hetero-oligomeric model for a high-affinity IL-4 receptor and suggests a possible new receptor binding mode for G-CSF; it also provides valuable information for guiding structural and mutagenesis studies of signal-transducing proteins and their receptors.

The molecular basis of X-linked severe combined immunodeficiency: the role of the interleukin-2 receptor gamma chain as a common gamma chain, gamma c

X-linked severe combined immunodeficiency is characterized by severe and persistent infections from early life resulting from profound impairment of both cellular and humoral immune function. XSCID is characterized by an absence or diminished number of T cells and histologic evidence of hypoplastic and abnormal differention of the thymic epithelium. The discovery that this disease results from the mutations of the IL-2R gamma chain was surprising since IL-2-deficient mice and human SCID patients had milder phenotypes. This led to the speculation that IL-2R gamma would prove to be a common gamma chain, gamma c, which would play important roles in other cytokine receptors in addition to the IL-2 receptor. There is now compelling evidence to support a role in at least two other cytokine receptors, namely the IL-4 and IL-7 receptors. Thus, with inactivation of gamma c, multiple cytokine systems are simultaneously affected, resulting in the profoundly impaired phenotype of XSCID. It is possible and even likely that gamma c will be found to be a functional component of additional receptors as well. These findings have resulted in a significant improvement in our understanding of the pathophysiologic development of the defects in XSCID and also have important ramifications for prenatal and postnatal diagnosis, carrier female identification, and gene therapy for XSCID.

Interleukin-2 receptor gamma chain: a functional component of the interleukin-4 receptor

The interleukin-2 (IL-2) receptor gamma chain (IL-2R gamma) is an essential component of high- and intermediate-affinity IL-2 receptors. IL-2R gamma was demonstrated to be a component of the IL-4 receptor on the basis of chemical cross-linking data, the ability of IL-2R gamma to augment IL-4 binding affinity, and the requirement for IL-2R gamma in IL-4-mediated phosphorylation of insulin receptor substrate-1. The observation that IL-2R gamma is a functional component of the IL-4 receptor, together with the finding that IL-2R gamma associates with the IL-7 receptor, begins to elucidate why deficiency of this common gamma chain (gamma c) has a profound effect on lymphoid function and development, as seen in X-linked severe combined immunodeficiency.

Hematopoietic cytokines: similarities and differences in the structures, with implications for receptor binding

Crystal and NMR structures of helical cytokines--interleukin-4 (IL-4), granulocyte-macrophage colony-stimulating factor (GM-CSF), and interleukin-2 (IL-2)--have been compared. Root mean square deviations in the C alpha coordinates for the conserved regions of the helices were 1-2 A between different cytokines, about twice the differences observed for independently determined crystal and solution structures of IL-4. Considerable similarity in amino acid sequence in the areas expected to interact with the receptors was detected, and the available mutagenesis data for these cytokines were correlated with structure conservation. Models of cytokine-receptor interactions were postulated for IL-4 based on its structure as well as on the published structure of human growth hormone interacting with its receptors (de Vos, A.M., Ultsch, M., & Kossiakoff, A.A., 1992, Science 255, 306-312). Patches of positively charged residues on the surfaces of helices C and D of IL-4 may be responsible for the interactions with the negatively charged residues found in the complementary parts of the IL-4 receptors.

Hematopoietin sub-family classification based on size, gene organization and sequence homology

The hematopoietins constitute a family of structurally related proteins that includes many cytokines, growth factors and hormones. We propose a classification for hematopoietins based on their size, gene organization and sequences; in addition, we further suggest that three cytokines, IL-11, IL-12 alpha chain and IL-13, are hematopoietins, and we place them in specific subgroups.

A computer model of the interleukin-4/receptor complex

Interleukin-4 is a member of the cytokine family, a group of related messenger proteins which collectively help to moderate and control the immune response. It is believed that the folding topology of the beta-sheets of the interleukin-4 receptor (IL4R) is the same as that seen in the crystal structure of CD4. Although the sequence identity is low, homology modeling techniques have been used to model the IL4R structure from CD4. Refinement by molecular dynamics leads to a suggested structure which has been docked to interleukin-4 (IL4). Several residues of apparent importance for binding are identified.

The high-resolution, three-dimensional solution structure of human interleukin-4 determined by multidimensional heteronuclear magnetic resonance spectroscopy

The high-resolution three-dimensional solution structure of recombinant human interleukin-4 (IL-4), a protein of approximately 15 kDa which plays a key role in the regulation of B and T lymphocytes, has been determined using three- and four-dimensional heteronuclear NMR spectroscopy. The structure is based on a total of 2973 experimental NMR restraints, comprising 2515 approximate interproton distance restraints, 102 distance restraints for 51 backbone hydrogen bonds, and 356 torsion angle restraints. A total of 30 structures was calculated by means of hybrid distance geometry-simulated annealing, and the atomic rms distribution about the mean coordinate positions for residues 8-129 is 0.44 +/- 0.03 A for the backbone atoms, 0.83 +/- 0.03 A for all atoms, and 0.51 +/- 0.04 A for all atoms excluding disordered side chains. The N- and C-terminal residues (1-7 and 130-133, respectively) appear to be disordered. The structure of IL-4 is dominated by a left-handed four-helix bundle with an unusual topology comprising two overhand connections. The linker elements between the helices are formed by either long loops, small helical turns, or short strands. The latter include a mini anti-parallel beta-sheet. A best fit superposition of the NMR structure of IL-4 with the 2.25 A resolution crystal structure [Wlodawer, A., Pavlovsky, A., & Gutschina, A. (1992) FEBS Lett. 309, 59-64] yields a backbone atomic rms difference of 1.37 A which can be mainly attributed to tighter packing of the helices in the crystal structure. This is indicated by an approximately 20% reduction in the axial separation of three pairs of helices (alpha A-alpha C, alpha A-alpha D, and alpha C-alpha D) in the crystal structure relative to the NMR structure and may reflect the greater flexibility of the molecule in solution which is reduced in the crystal due to intermolecular contacts. Comparison of the NMR structure of IL-4 with the X-ray structures of two other related proteins, granulocyte-macrophage colony stimulating factor [Diedrichs, K., Boone, T., & Karplus, P. A. (1992) Science 254, 1779-1782] and human growth hormone [de Vos, A. M., Ultsch, M., & Kossiakoff, A. A. (1992) Science 255, 306-312], that bind to the same hematopoietic superfamily of cell surface receptors reveals a remarkably similar topological fold, despite the absence of any significant overall sequence identity, and substantial differences in the relative lengths of the helices, the lengths and the nature of the various connecting elements, and the pattern and number of disulfide bridges.(ABSTRACT TRUNCATED AT 400 WORDS)

LIFR beta and gp130 as heterodimerizing signal transducers of the tripartite CNTF receptor

The ciliary neurotrophic factor (CNTF) receptor complex is shown here to include the CNTF binding protein (CNTFR alpha) as well as the components of the leukemia inhibitory factor (LIF) receptor, LIFR beta (the LIF binding protein) and gp130 [the signal transducer of interleukin-6 (IL-6)]. Thus, the conversion of a bipartite LIF receptor into a tripartite CNTF receptor apparently occurs by the addition of the specificity-conferring element CNTFR alpha. Both CNTF and LIF trigger the association of initially separate receptor components, which in turn results in tyrosine phosphorylation of receptor subunits. Unlike the IL-6 receptor complex in which homodimerization of gp130 appears to be critical for signal initiation, signaling by the CNTF and LIF receptor complexes depends on the heterodimerization of gp130 with LIFR beta. Ligand-induced dimerization of signal-transducing receptor components, also seen with receptor tyrosine kinases, may provide a general mechanism for the transmission of a signal across the cell membrane.

Biochemistry of B lymphocyte activation

The activation of B lymphocytes from resting cells proceeds from the events of early activation to clonal proliferation to final differentiation into either an antibody-secreting plasma cell or a memory B cell. This is a complex activation process marked by several alternative pathways, depending on the nature of the initial antigenic stimulus. Over the past 5-10 years, there has been an explosion of studies examining the biochemical nature of various steps in these pathways. Some of that progress is reviewed here. In particular, we have described in detail what is known about the structure and function of the AgR, as this molecule plays a pivotal role in B cell responses of various types. We have also reviewed recent progress in understanding the mechanism of action of contact-dependent T cell help and of the cytokine receptors, particularly the receptors for IL-2, IL-4, and IL-6. Clearly, all of these areas represent active areas of investigation and great progress can be anticipated in the next few years.