Phylogeny and evolution of class-I helical cytokines

Sortilin facilitates signaling of ciliary neurotrophic factor and related helical type 1 cytokines targeting the gp130/leukemia inhibitory factor receptor beta heterodimer

Sortilin is a member of the Vps10p domain family of neuropeptide and neurotrophin binding neuronal receptors. The family members interact with and partly share a variety of ligands and partake in intracellular sorting and protein transport as well as in transmembrane signal transduction. Thus, sortilin mediates the transport of both neurotensin and nerve growth factor and interacts with their respective receptors to facilitate ligand-induced signaling. Here we report that ciliary neurotrophic factor (CNTF), and related ligands targeting the established CNTF receptor alpha, binds to sortilin with high affinity. We find that sortilin may have at least two functions: one is to provide rapid endocytosis and the removal of CNTF, something which is not provided by CNTF receptor alpha, and the other is to facilitate CNTF signaling through the gp130/leukemia inhibitory factor (LIF) receptor beta heterodimeric complex. Interestingly, the latter function is independent of both the CNTF receptor alpha and ligand binding to sortilin but appears to implicate a direct interaction with LIF receptor beta. Thus, sortilin facilitates the signaling of all helical type 1 cytokines, which engage the gp130/LIF receptor beta complex.

The second prolactin receptor in Nile tilapia (Oreochromis niloticus): molecular characterization, tissue distribution and gene expression

Prolactin (PRL) is one of the most versatile hormones found in the pituitary of vertebrates and exerts its actions through binding to a specific PRL receptor (PRLR). Here we describe the cloning and characterization of a second prolactin receptor (ntPRLR2), isolated from the ovary of Nile tilapia (Oreochromis niloticus). The newly identified PRLR cDNA was 2011 bp in length and encoded 529 amino acids. It shared 31.6% identity in nucleotide sequence and 29.2% in deduced amino acid sequence with the first PRLR identified in Nile tilapia (ntPRLR1). Both of these ntPRLRs resemble the long form mammalian PRLRs. The nominated ntPRLR2 was further confirmed as a real prolactin receptor based on its competence to transactivate the beta-casein and c-fos promoters in the transiently ntPRLR2-transfected HEK293 cells. The ntPRLR2 gene also found to encode a 864-bp short form transcript in the ovary, which was confirmed by Northern blot analysis. A tissue distribution study by real-time PCR revealed that the mRNA of both receptors (ntPRLR1 and ntPRLR2) was widely expressed in different tissues, with an extremely high abundance in the osmoregulatory organs, including the gills, intestine and kidney. ntPRLR1 mRNA was more abundant than ntPRLR2 in the testis, while the reverse expression pattern was found in the ovary. In the ovary, ntPRLR2 mRNA demonstrated a distinct gonadal development-dependent expression profile, with significantly higher levels at a sexual mature stage than at sexual recrudescent and sexual regressed stages. When challenged with estradiol, ntPRLR2 mRNA expression was up-regulated by E2, whereas E2 had no significant effect on ntPRLR1.

Obligate ordered binding of human lactogenic cytokines

Class 1 cytokines bind two receptors to create an active heterotrimeric complex. It has been argued that ligand binding to their receptors is an ordered process, but a structural mechanism describing this process has not been determined. We have previously described an obligate ordered binding mechanism for the human prolactin/prolactin receptor heterotrimeric complex. In this work we expand this conceptual understanding of ordered binding to include three human lactogenic hormones: prolactin, growth hormone, and placental lactogen. We independently blocked either of the two receptor binding sites of each hormone and used surface plasmon resonance to measure human prolactin receptor binding kinetics and stoichiometries to the remaining binding surface. When site 1 of any of the three hormones was blocked, site 2 could not bind the receptor. But blocking site 2 did not affect receptor binding at site 1, indicating a requirement for receptor binding to site 1 before site 2 binding. In addition we noted variable responses to the presence of zinc in hormone-receptor interaction. Finally, we performed Förster resonance energy transfer (FRET) analyses where receptor binding at subsaturating stoichiometries induced changes in FRET signaling, indicative of binding-induced changes in hormone conformation, whereas at receptor:hormone ratios in excess of 2:1 no additional changes in FRET signaling were observed. These results strongly support a conformationally mediated obligate-ordered receptor binding for each of the three lactogenic hormones.

Insufficiency of Janus kinase 2-autonomous leptin receptor signals for most physiologic leptin actions

OBJECTIVE

Leptin acts via its receptor (LepRb) to signal the status of body energy stores. Leptin binding to LepRb initiates signaling by activating the associated Janus kinase 2 (Jak2) tyrosine kinase, which promotes the phosphorylation of tyrosine residues on the intracellular tail of LepRb. Two previously examined LepRb phosphorylation sites mediate several, but not all, aspects of leptin action, leading us to hypothesize that Jak2 signaling might contribute to leptin action independently of LepRb phosphorylation sites. We therefore determined the potential role in leptin action for signals that are activated by Jak2 independently of LepRb phosphorylation (Jak2-autonomous signals).

RESEARCH DESIGN AND METHODS

We inserted sequences encoding a truncated LepRb mutant (LepRb(Delta65c), which activates Jak2 normally, but is devoid of other LepRb intracellular sequences) into the mouse Lepr locus. We examined the leptin-regulated physiology of the resulting Delta/Delta mice relative to LepRb-deficient db/db animals.

RESULTS

The Delta/Delta animals were similar to db/db animals in terms of energy homeostasis, neuroendocrine and immune function, and regulation of the hypothalamic arcuate nucleus, but demonstrated modest improvements in glucose homeostasis.

CONCLUSIONS

The ability of Jak2-autonomous LepRb signals to modulate glucose homeostasis in Delta/Delta animals suggests a role for these signals in leptin action. Because Jak2-autonomous LepRb signals fail to mediate most leptin action, however, signals from other LepRb intracellular sequences predominate.

Phylogenetic and functional analysis identifies Ets-1 as a novel regulator of the Th2 cytokine gene locus

The Th2 cytokine gene locus has emerged as a remarkable example of coordinated gene expression, the regulation of which seems to be rooted in an extensive array of cis-regulatory regions. Using a hypothesis-generating computational approach that integrated multispecies (n = 11) sequence comparisons with algorithm-based transcription factor binding-site predictions, we sought to identify evolutionarily conserved noncoding regions (ECRs) and motifs shared among them, which may underlie coregulation. Twenty-two transcription factor families were predicted to have binding sites in at least two Th2 ECRs. The ranking of these shared motifs according to their distribution and relative frequency pointed to a regulatory hierarchy among the transcription factor families. GATA sites were the most prevalent and widely distributed, consistent with the known role of GATA3 as a Th2 master switch. Unexpectedly, sites for ETS-domain proteins were also predicted within several Th2 ECRs and the majority of these sites were found to support Ets-1 binding in vitro and in vivo. Of note, the expression of all three Th2 cytokines (IL-5, -13, and -4) was significantly and selectively decreased in Th2 cells generated from Ets-1-deficient mice. Collectively, these data suggest that Ets-1 contributes to Th2 cytokine gene regulation by interacting with multiple cis-regulatory regions throughout the Th2 locus.

Peptide hormone regulation of angiogenesis

It is now apparent that regulation of blood vessel growth contributes to the classical actions of hormones on development, growth, and reproduction. Endothelial cells are ideally positioned to respond to hormones, which act in concert with locally produced chemical mediators to regulate their growth, motility, function, and survival. Hormones affect angiogenesis either directly through actions on endothelial cells or indirectly by regulating proangiogenic factors like vascular endothelial growth factor. Importantly, the local microenvironment of endothelial cells can determine the outcome of hormone action on angiogenesis. Members of the growth hormone/prolactin/placental lactogen, the renin-angiotensin, and the kallikrein-kinin systems that exert stimulatory effects on angiogenesis can acquire antiangiogenic properties after undergoing proteolytic cleavage. In view of the opposing effects of hormonal fragments and precursor molecules, the regulation of the proteases responsible for specific protein cleavage represents an efficient mechanism for balancing angiogenesis. This review presents an overview of the actions on angiogenesis of the above-mentioned peptide hormonal families and addresses how specific proteolysis alters the final outcome of these actions in the context of health and disease.

Identification of a putative invertebrate helical cytokine similar to the ciliary neurotrophic factor/leukemia inhibitory factor family by PSI-BLAST-based approach

Most of our knowledge of helical cytokine-like molecules in invertebrates relies on functional assays and similarities at the physicochemical level. It is hard to predict helical cytokines in invertebrates based on sequences from mammals and vertebrates, because of their long evolutionary divergence. In this article, we collected 12 kinds of fish cytokines and constructed their respective consensus sequences using hidden Markov models; then, the conserved domains region of each consensus sequence were further extracted by the SMART tool, and used as the query sequence for PSI-BLAST analysis in Drosophila melanogaster. After two filtering processes based on the properties of helical cytokines, we obtained one protein named CG14629, which shares 25% identities/46% positives to fish M17 cytokine in the half length of the N-terminus. Considering the homology between M17 and LIF/CNTF (leukemia inhibitory factor/ciliary neurotrophic factor), and the close relationship between Dome, the putative cytokine receptor in Drosophila cells, and LIFR/CNTFR (LIF receptor/CNTF receptor), the results suggest that CG14629 is a good candidate for the helical cytokine ortholog in D. melanogaster.

Leptin stimulates Xenopus lung development: evolution in a dish

The transition from uni- to multicellular organisms required metabolic cooperativity through cell-cell interactions mediated by soluble growth factors. We have empirically demonstrated such an integrating mechanism by which the metabolic hormone leptin stimulates lung development, causing the thinning of the gas exchange surface and the obligate increase in lung surfactant synthesis. All of these processes have occurred both phylogenetically and developmentally during the course of vertebrate lung evolution from fish to man. Here we show the integrating effects of the environmentally sensitive, pleiotropic hormone leptin on the development of the Xenopus laevis tadpole lung. The process described in this study provides a mechanistically integrated link between the metabolic regulatory hormone leptin and its manifold downstream effects on a wide variety of physiologic structures and functions, including locomotion and respiration, the cornerstones of land vertebrate evolution. It provides physiologic selection pressure at multiple levels to progressively generate Gene Regulatory Networks both within and between organs, from cells to systems. This model provides a cipher for understanding the evolution of complex physiology.

A phylogenetic approach to gene expression data: evidence for the evolutionary origin of mammalian leukocyte phenotypes

The evolution of multicellular organisms involved the evolution of specialized cell types performing distinct functions; and specialized cell types presumably arose from more generalized ancestral cell types as a result of mutational event, such as gene duplication and changes in gene expression. We used characters based on gene expression data to reconstruct evolutionary relationships among 11 types of lymphocytes by the maximum parsimony method. The resulting phylogenetic tree showed expected patterns including separation of the lymphoid and myeloid lineages; clustering together of granulocyte types; and pairing of phenotypically similar cell types such as T-helper cells type 1 and T-helper cells type 2 (Th1 and Th2). We used phylogenetic analyses of sequence data to determine the time of origin of genes showing significant expression difference between Th1 and Th2 cells. Many such genes, particularly those involved in the regulation of gene expression or activation of proteins, were of ancient origin, having arisen by gene duplication before the most recent common ancestor (MRCA) of tetrapods and teleosts. However, certain other genes with significant expression difference between Th1 and Th2 arose after the tetrapod-teleost MRCA, and some of the latter were specific to eutherian (placental) mammals. This evolutionary pattern is consistent with previous evidence that, while bony fishes possess Th1 and Th2 cells, the latter differ phenotypically in important respects from the corresponding cells of mammals. Our results support a gradualistic model of the evolution of distinctive cellular phenotypes whereby the unique characteristics of a given cell type arise as a result of numerous independent mutational changes over hundreds of millions of years.

Genes associated with an effective host response by Chinook salmon to Renibacterium salmoninarum

An effective host response to Renibacterium salmoninarum, the etiologic agent of bacterial kidney disease, is poorly characterized. Using suppression subtractive hybridization, we exploited the difference in early host response in the pronephros of fish challenged by an attenuated strain (MT239) or a virulent strain (ATCC 33209) of R. salmoninarum. Among the 132 expressed sequence tag (EST) clones that were sequenced, 20 were selected for expression analysis at 24 and 72h after challenge. ESTs matching two interferon inducible genes (IFN-inducible GBP and VLIG1), the ligand GAS6, and the kinase VRK2 were upregulated in fish exposed to MT239, but downregulated or unchanged in fish exposed to 33209. A second group of ESTs matching genes involved in apoptosis (caspase 8) and immune function (IkappaBalpha, p47(phoX), EMR/CD97) were more slowly upregulated in fish exposed to 33209 compared to fish exposed to MT239. The ESTs displaying elevated expression in MT239-exposed fish may represent important cellular processes to bacterial challenge, and may be useful indicators of an effective host response to R. salmoninarum infection.

Zebrafish granulocyte colony-stimulating factor receptor signaling promotes myelopoiesis and myeloid cell migration

Granulocyte colony-stimulating factor receptor (GCSFR) signaling participates in the production of neutrophilic granulocytes during normal hematopoietic development, with a particularly important role during emergency hematopoiesis. This study describes the characterization of the zebrafish gcsf and gcsfr genes, which showed broad conservation and similar regulation to their mammalian counterparts. Morpholino-mediated knockdown of gcsfr and overexpression of gcsf revealed the presence of an anterior population of myeloid cells during primitive hematopoiesis that was dependent on GCSF/GCSFR for development and migration. This contrasted with a posterior domain that was largely independent of this pathway. Definitive myelopoiesis was also partially dependent on a functional GCSF/GCSFR pathway. Injection of bacterial lipopolysaccharide elicited significant induction of gcsf expression and emergency production of myeloid cells, which was abrogated by gcsfr knockdown. Collectively, these data demonstrate GCSF/GCSFR to be a conserved signaling system for facilitating the production of multiple myeloid cell lineages in both homeostatic and emergency conditions, as well as for early myeloid cell migration, establishing a useful experimental platform for further dissection of this pathway.

Oversecretion of interleukin-15 from skeletal muscle reduces adiposity

Obesity is a risk factor for development of insulin resistance, type 2 diabetes, cardiovascular disease, osteoarthritis, and some forms of cancer. Many of the adverse health consequences of excess fat deposition are caused by increased secretion of proinflammatory adipokines by adipose tissue. Reciprocal muscle-to-fat signaling factors, or myokines, are starting to be identified. Interleukin-15 (IL-15) is a cytokine that is highly expressed in muscle tissue and that, on the basis of cell culture experiments, has been proposed to act as a circulating myokine that inhibits adipose tissue deposition. To test this hypothesis in vivo, two lines of transgenic mice that overexpressed IL-15 mRNA and protein in skeletal muscle tissue were constructed. By substitution of the inefficient native IL-15 signal peptide with a more efficient signal peptide, one of the transgenic mouse lines also exhibited elevated secretion of IL-15 in the circulation. Overexpression of IL-15 in muscle tissue without secretion in the bloodstream resulted in no differences in body composition. Elevated circulating levels of IL-15 resulted in significant reductions in body fat and increased bone mineral content, without appreciably affecting lean body mass or levels of other cytokines. Elevated circulating levels of IL-15 also inhibited adiposity induced by consumption of a high-fat/high-energy diet in male, but not female, transgenic mice. Female mice with elevated serum IL-15 exhibited increased deposition of lean body mass on a low-fat/low-energy diet and a high-fat/high-energy diet. These findings indicate that muscle-derived circulating IL-15 can modulate adipose tissue deposition and support addition of IL-15 to the growing list of potential myokines that are increasingly being implicated in regulation of body composition.

Analysis of genes isolated from plated hemocytes of the Pacific oyster, Crassostreas gigas

A complementary deoxyribonucleic acid library was constructed from hemocytes of Crassostrea gigas that had been plated on poly-lysine plates for 24 h. From this library, 2,198 expressed sequence tags (ESTs) of greater than or equal to 100 bp were generated and analyzed. A large number of genes that potentially could be involved in the physiology of the oyster hemocyte were uncovered. They included proteins involved in cytoskeleton rearrangement, proteases and antiproteases, regulators of transcription and translation, cell death regulators, receptors and their associated protein factors, lectins, signal transduction proteins, and enzymes involved in eicosanoid and steroid synthesis and xenobiotic metabolism. Based on their relationship with innate immunity, the expression of selected genes was analyzed by quantitative polymerase chain reaction in gills from bacterial-challenged oysters. Several genes observed in the library were significantly upregulated by bacterial challenge including interleukin 17, astacin, cystatin B, the EP4 receptor for prostaglandin E, the ectodysplasin receptor, c-jun, and the p100 subunit of nuclear factor-kB. Using a similar approach, we have been analyzing the genes expressed in trout macrophages. While there are significant differences between the types of genes present in vertebrate macrophages compared with oyster hemocytes, there are some striking similarities including proteins involved in cytoskeletal rearrangement, proteases and antiproteases, and genes involved in certain signal transduction pathways underlying immune processes such as phagocytosis. Finally, C. virginica homologs of some of the C. gigas genes uncovered in the ESTs were obtained by aligning the ESTs reported here, against the assembled C. virginica ESTs at the National Center for Biotechnology Information.

Insulin stimulates interleukin-6 expression and release in LS14 human adipocytes through multiple signaling pathways

IL-6 is an important cytokine that regulates both immune and metabolic functions. Within adipose tissue, preadipocytes produce significant amounts of IL-6, but little is known about the factors or mechanisms that regulate IL-6 production in these cells. Using LS14, a newly developed human adipocyte cell line, our objective was to determine the mechanisms by which insulin stimulates IL-6 production and release in preadipocytes. Insulin increased IL-6 gene expression and secretion in a time- and dose-dependent manner. Insulin decreased cyclic AMP (cAMP) but increased cyclic GMP (cGMP) levels, and IL-6 expression/release was stimulated by a cGMP analog. The stimulatory effect of insulin and cGMP was abrogated by a specific inhibitor of protein kinase G (cyclic GMP-dependent protein kinase). Both insulin and cGMP rapidly induced phosphorylation of cAMP response element binding protein. Insulin also activated the MAPK signaling pathway, and its blockade prevented the insulin-stimulated increases in IL-6 cell content and release, but not IL-6 gene expression. Although inhibition of the proteosome increased IL-6 cell content and release, proteosome activity was unaffected by insulin. These data suggest that the stimulatory effects of insulin on IL-6 release involve several interrelated components: transcription, intracellular releasable pool, and secretion, which are differentially regulated and, thus, determine the size of the releasable pool of IL-6. Insulin-induced IL-6 gene expression is mediated by cGMP/cyclic GMP-dependent protein kinase/cAMP response element binding protein, whereas MAPK is involved in the insulin-stimulated IL-6 synthesis/release.

Grass carp somatolactin: I. Evidence for PACAP induction of somatolactin-alpha and -beta gene expression via activation of pituitary PAC-I receptors

Somatolactin (SL), the latest member of the growth hormone/prolactin family, is a novel pituitary hormone with diverse functions. At present, SL can be identified only in fish but not in tetrapods and its regulation at the pituitary level has not been fully characterized. Using grass carp as a model, we examined the direct effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on SL secretion and synthesis at the pituitary cell level. As a first step, the structural identity of grass carp SL, SLalpha and SLbeta, was established by 5'/3'-rapid amplification of cDNA ends. These two SL isoforms are single-copy genes and are expressed in two separate populations of pituitary cells located in the pars intermedia. In the carp pituitary, PACAP nerve fibers were detected in the nerve tracts of the neurohypophysis and extended into the vicinity of pituitary cells forming the pars intermedia. In primary cultures of grass carp pituitary cells, PACAP was effective in stimulating SL release, cellular SL content, and total SL production. The increase in SL production also occurred with parallel rises in SLalpha and SLbeta mRNA levels. With the use of a combination of molecular and pharmacological approaches, PACAP-induced SL release and SL gene expression were shown to be mediated by pituitary PAC-I receptors. These findings, as a whole, suggest that PACAP may serve as a hypophysiotropic factor in fish stimulating SL secretion and synthesis at the pituitary level. Apparently, PACAP-induced SL production is mediated by upregulation of SLalpha and SLbeta gene expression through activation of PAC-I receptors.

Teleostean IL11b exhibits complementing function to IL11a and expansive involvement in antibacterial and antiviral responses

Interleukin 11 is a class-1 helical cytokine, having the four-helix bundle structure, possessing pleiotropic characteristics involved in physiological processes including blood production, bone formation and placentation. The interleukin 11 paralogues (IL11a and IL11b) have been identified in fish with only IL11a from carp and trout have been characterized and analyzed for its expression thus far. Here, we cloned and studied the structure and expression of IL11b in Japanese flounder (Paralichthys olivaceus), and compared this with the existing information on fish IL11 paralogues. Japanese flounder IL11b (poIL11b) cDNA is composed of 1536 bp encoding for 201 aa residues with a 23 aa leader peptide, three cysteine residues (C12, C183 and C198) and four potential N-linked glycosylation sites. poIL11b does not show constitutive expression in tissues of adult fish except for the very slight expression in kidney and spleen, and the very high expression in peripheral blood leukocytes (PBLs). poIL11b is transiently up-regulated by bacterial lipopolysaccharide (LPS) and increasingly stimulated by the IFN inducer poly I:C in kidney, spleen and peripheral blood leukocytes of adult fish in vitro. It is likewise slightly stimulated by Edwardsiella tarda infection but is highly expressed after hirame rhabdovirus (HIRRV) infection in kidney of juvenile fish. The stimulation studies suggest that poIL11b, aside from its role in bacterial infection, is well involved in antiviral responses. Moreover, poIL11b structure and expression pattern appears to be slightly distinct and opposite to IL11a, respectively, suggesting a complementation of function of the duplicate fish IL11 genes.

Production of recombinant leptin and its effects on food intake in rainbow trout (Oncorhynchus mykiss)

Leptin is a key factor for the regulation of food intake and energy homeostasis in mammals, but information regarding its role in teleosts is still limited. There are large differences between mammalian and teleost leptin at both gene and protein levels, and in order to characterize the function of leptin in fish, preparation of species-specific leptin is therefore a key step. In this study, full-length cDNA coding for rainbow trout leptin was identified. In spite of low amino acid sequence similarity with other animals, leptin is highly conserved between trout and salmon (98.7%). Based on the cDNA, we produced pure recombinant trout leptin (rt-leptin) in E. coli, with a final yield of 20 mg/L culture medium. We then examined the effects of intraperitoneal (IP) injection of rt-leptin on feeding behavior and gene expression of hypothalamic NPY and POMCs (POMC A1, A2 and B) in a short-term (8 h) experiment. The rt-leptin suppressed food intake and led to transient reduction of NPY mRNA levels, while the expression of POMCs A1 and A2, was elevated compared with vehicle-injected controls. These results for rainbow trout are the first that describe a physiological role of leptin using a species-specific orthologue in teleosts, and they suggest that leptin suppresses food intake mediated by hypothalamic regulation. This anorexic effect is similar to that observed in mammals and frogs and supports that the neuroendocrine pathways that control feeding by leptin are ancient and have been conserved through evolution.

Retention of genes involved in the adenohypophysis-mediated endocrine system in early vertebrates

The adenohypophysis of vertebrates receives peptide hormones from the hypothalamus and secretes hormones that regulate diverse physiologic processes in peripheral organs. The adenohypophysis-mediated endocrine system is widely conserved across vertebrates but not invertebrates. Phylogenetic analysis indicates that the emergence of this system coincided with two rounds of whole-genome duplication (2R-WGD) in early vertebrates, but direct evidence linking these events has been unavailable. We detected all human paralogons (series of paralogous regions) formed in early vertebrates as traces of 2R-WGD, and examined the relationship between 2R-WGD and the evolution of genes essential to the adenohypophysis-mediated endocrine system. Regarding genes encoding transcription factors (TFs) involved in the terminal differentiation into hormone-secreting cells in adenohypophyseal development, we showed that most pairs of these genes and their paralogs were part of paralogons. In addition, our analysis also indicated that most of the paralog pairs in families of adenohypophyseal hormones and their receptors were part of paralogons. These results suggest that 2R-WGD played an important role in generating genes encoding adenohypophyseal TFs, hormones, and their receptors for increasing the diversification of hormone repertoire in the adenohypophysis-mediated endocrine system of vertebrates.

Granulocyte colony-stimulating factor: molecular mechanisms of action during steady state and 'emergency' hematopoiesis

Neutrophils are phagocytes whose principal function is to maintain anti-bacterial immunity. Neutrophils ingest and kill invading bacteria, releasing cytotoxic, chemotactic and inflammatory mediators at sites of infection. This serves to control the immediate host immune response and attract other cells, such as macrophages and dendritic cells, which are important for establishing long-term adaptive immunity. Neutrophils thus contribute to both the initiation and the maintenance of inflammation at sites of infection. Aberrant neutrophil activity is deleterious; suppressed responses can cause extreme susceptibility to infection while overactivation can lead to excessive inflammation and tissue damage. This review will focus on neutrophil regulation by granulocyte colony-stimulating factor (G-CSF), the principal cytokine controlling neutrophil development and function. The review will emphasize the molecular aspects of G-CSF-driven granulopoiesis in steady state (healthy) conditions and during demand-driven or 'emergency' conditions elicited by infection or clinical administration of G-CSF. Understanding the molecular control of granulopoiesis will aid in the development of new approaches designed to treat disorders of neutrophil production and function.

Rapid accumulation of an interleukin 17 homolog transcript in Crassostrea gigas hemocytes following bacterial exposure

Interleukin-17 (IL-17) gene models have been found in the sequenced genomes of Strongylocentrotus purpuratus and Caenorhabditis elegans. However, there have been no published reports on the empirical cloning and characterization of any interleukin cDNAs in invertebrates. From a Pacific oyster (Crassostrea gigas) hemocyte cDNA library, two clones were obtained that encoded a protein similar to vertebrate IL-17s. The putative oyster IL-17 homolog (CgIL-17) was 27% identical to rainbow trout IL-17D, 21% to human IL-17D and 24% to an IL-17D-like gene model obtained from the annotation of the sea urchin genome. IL-17s from the oyster, sea urchin, trout and human, contained conserved cysteine residues found in all forms of IL-17 in mammals. Injection of bacteria into C. gigas oysters produced a large and rapid elevation in CgIL-17 transcript abundance in hemocytes, suggesting that this is a very early response gene to pathogens that may be responsible for the stimulation of other immune genes in the oyster.

Analysis of structure, function, and evolutionary origin of the ob gene product--leptin

Leptin, the ob gene product, is a 167 amino acid polypeptide known to play a key role in regulating the fat stores of the body and is found in all eukaryotes, including mammals, aves, and also in invertebrates. To gain insight into the structure-function relation and origin of leptin, we have analyzed the amino acid sequence of leptin from 23 species by computing the frequency of occurrence of amino acids, their secondary structure, sequence homology, et cetera. Extensive conservation is observed within the leptin sequences of all the species, suggesting an evolutionary relatedness among them. It is interesting to note that human leptin shares a very high degree of homology with gorilla, chimpanzee, and orangutan indicative of a common function of leptin in them. Analysis of the codon bias in leptin from 11 species reveals that sminthopsis shows highest variation compared to human while less variation is observed in chimpanzee and orangutan, possibly reflecting the closeness in their evolution. Thus, understanding leptin's three-dimensional structure along with primary and secondary structure might enable us to understand the functional role played by this multifaceted adipocyte derived protein.

Identification, characterization and expression of a novel cytokine M17 homologue (MSH) in fish

Members of the interleukin 6 (IL6)-cytokine subfamily of proteins are involved in numerous physiological processes including cellular development, inflammatory function, and acute phase and immune responses. Previously, a cytokine-like gene named M17, which is closely associated with the IL6 subfamily, has been identified in fish with no apparent orthologue in higher vertebrates. Here, we cloned a novel cDNA from Japanese flounder, Paralichthys olivaceus, which had significant identity but exhibited contrasting expression with fish M17s, named here as M17 Homologue (MSH). With subsequent in silico search and full annotation of the M17 orthologue in zebrafish (Danio rerio), MSH orthologues in tiger puffer (Takifugu rubripes), green spotted pufferfish (Tetraodon nigroviridis) and stickleback (Gastorosteus aculeatus), as well as structural, synteny comparisons and phylogenetic analysis with known IL6-cytokines, we determined the novelty of the fish MSH. Japanese flounder MSH was observed to be highly expressed in immune-related tissues and are induced by immune stimulants, lipopolysaccharide (LPS), polyI:C and peptidoglycan (PG) in vitro suggesting that it is involved in fish immunity particularly against viral and bacterial agents, a functional feature exhibited by previously reported fish cytokines.

Prolactin receptor, growth hormone receptor, and putative somatolactin receptor in Mozambique tilapia: tissue specific expression and differential regulation by salinity and fasting

In fish, pituitary growth hormone family peptide hormones (growth hormone, GH; prolactin, PRL; somatolactin, SL) regulate essential physiological functions including osmoregulation, growth, and metabolism. Teleost GH family hormones have both differential and overlapping effects, which are mediated by plasma membrane receptors. A PRL receptor (PRLR) and two putative GH receptors (GHR1 and GHR2) have been identified in several teleost species. Recent phylogenetic analyses and binding studies suggest that GHR1 is a receptor for SL. However, no studies have compared the tissue distribution and physiological regulation of all three receptors. We sequenced GHR2 from the liver of the Mozambique tilapia (Oreochromis mossambicus), developed quantitative real-time PCR assays for the three receptors, and assessed their tissue distribution and regulation by salinity and fasting. PRLR was highly expressed in the gill, kidney, and intestine, consistent with the osmoregulatory functions of PRL. PRLR expression was very low in the liver. GHR2 was most highly expressed in the muscle, followed by heart, testis, and liver, consistent with this being a GH receptor with functions in growth and metabolism. GHR1 was most highly expressed in fat, liver, and muscle, suggesting a metabolic function. GHR1 expression was also high in skin, consistent with a function of SL in chromatophore regulation. These findings support the hypothesis that GHR1 is a receptor for SL. In a comparison of freshwater (FW)- and seawater (SW)-adapted tilapia, plasma PRL was strongly elevated in FW, whereas plasma GH was slightly elevated in SW. PRLR expression was reduced in the gill in SW, consistent with PRL's function in freshwater adaptation. GHR2 was elevated in the kidney in FW, and correlated negatively with plasma GH, whereas GHR1 was elevated in the gill in SW. Plasma IGF-I, but not GH, was reduced by 4 weeks of fasting. Transcript levels of GHR1 and GHR2 were elevated by fasting in the muscle. However, liver levels of GHR1 and GHR2 transcripts, and liver and muscle levels of IGF-I transcripts were unaffected by fasting. These results clearly indicate tissue specific expression and differential physiological regulation of GH family receptors in the tilapia.

Interleukin-15: a muscle-derived cytokine regulating fat-to-lean body composition

An increasing body of literature links immune and inflammatory factors to modulation of growth and control of fat:lean body composition. Recent progress in understanding the control of body composition has been made through identification of inflammatory cytokines and other factors produced by adipose tissue that affect body composition, often by direct effects on skeletal muscle tissue. Adipose-derived factors such as leptin, tumor necrosis factor-alpha, resistin, and adiponectin have been shown to affect muscle metabolism, protein dynamics, or both, by direct actions. This review summarizes recent results that support the existence of a reciprocal muscle-to-fat signaling pathway involving release of the cytokine IL-15 from muscle tissue. Cell culture studies, short-term in vivo studies, and human genotype association studies all support the model that muscle-derived IL-15 can decrease fat deposition and adipocyte metabolism via a muscle-to-fat endocrine pathway. Fat:lean body composition is an important factor determining the efficiency of meat production, as well as the fat content of meat products. Modulation of the IL-15 signaling axis may be a novel mechanism to affect body composition in meat animal production.

Evolution of Class I cytokine receptors

BACKGROUND

The Class I cytokine receptors have a wide range of actions, including a major role in the development and function of immune and blood cells. However, the evolution of the genes encoding them remains poorly understood. To address this we have used bioinformatics to analyze the Class I receptor repertoire in sea squirt (Ciona intestinalis) and zebrafish (Danio rerio).

RESULTS

Only two Class I receptors were identified in sea squirt, one with homology to the archetypal GP130 receptor, and the other with high conservation with the divergent orphan receptor CLF-3. In contrast, 36 Class I cytokine receptors were present in zebrafish, including representative members for each of the five structural groups found in mammals. This allowed the identification of 27 core receptors belonging to the last common ancestor of teleosts and mammals.

CONCLUSION

This study suggests that the majority of diversification of this receptor family occurred after the divergence of urochordates and vertebrates approximately 794 million years ago (MYA), but before the divergence of ray-finned from lobe-finned fishes around 476 MYA. Since then, only relatively limited lineage-specific diversification within the different Class I receptor structural groups has occurred.

A novel type-1 cytokine receptor from fish involved in the Janus kinase/Signal transducers and activators of transcription (Jak/STAT) signal pathway

Type I cytokine receptors mediate the action of the members of the long chain cytokines canonically involved in numerous physiological function. Here we report a novel cytokine receptor termed Japanese flounder glycoprotein 130 homologue or JfGPH, exhibiting the unique type I cytokine receptor motifs i.e. having a cytokine binding domain (CBD) containing two pairs of conserved cysteine (C) residues, a WSXWS motif, three fibronectin domains all in the extracellular region. It is also composed of the Jak binding domains Box 1 and Box 2, and a STAT 3 binding motif (Box 3) in the cytoplasmic region suggesting its mediatory role for Janus kinase/Signal transducers and activators of transcription (Jak/STAT) signal pathway. The JfGPH cDNA is about 3kb encoding 801 amino acid residues with a predicted molecular weight of 90kDa and its gene has an 11-exon/10-intron architecture. While JfGPH shows significant homology with the members of type-1 cytokine receptor family including IL6ST (or gp130), IL31alpha (or GLMR), CSF3R (or GCSFR), LIFR, OSMR, IL12Rbeta1 and LEPR, structural and phylogenetic analysis of its protein revealed that it is a novel and an ancestral cytokine receptor found in teleost. JfGPH gene is ubiquitously expressed in Japanese flounder tissues and in a natural embryo (HINAE) cell line showing its critical role in teleost physiological functions similar to gp130 in higher vertebrates. High expression of JfGPH transcripts in immune-related tissues and, in ovary and embryo-derived cell line suggest its role in immune responses, and reproduction/development, respectively. In vitro stimulation of spleen, kidney, peripheral blood leukocytes (PBLs) and HINAE revealed that JfGPH is down-regulated by polyinosinic:polycytidylic acid (poly I:C), an interferon (IFN) inducer, suggesting an apparent control of the JfGPH's expression during IFN-induced Jak/STAT signaling.

Interleukin-31 and oncostatin-M mediate distinct signaling reactions and response patterns in lung epithelial cells

Lung epithelial cells are primary targets of oncostatin M (OSM) and, to a lower degree, of interleukin (IL)-6 and IL-31, all members of the IL-6 cytokine family. The OSM receptor (OSMR) signals through activation of STAT and mitogen-activated protein kinase pathways to induce genes encoding differentiated cell functions, reduce cell-cell interaction, and suppress cell proliferation. IL-31 functions through the heteromeric IL-31 receptor, which shares with OSMR the OSMRbeta subunit, but does not engage gp130, the common subunit of all other IL-6 cytokine receptors. Because the response of epithelial cells to IL-31 is unknown, the action of IL-31 was characterized in the human alveolar epithelial cell line A549 in which the expression of the ligand-binding IL-31Ralpha subunit was increased. IL-31 initiated signaling that differed from other IL-6 cytokines by the particularly strong recruitment of the STAT3, ERK, JNK, and Akt pathways. IL-31 was highly effective in suppressing proliferation by altering expression of cell cycle proteins, including up-regulation of p27(Kip1) and down-regulation of cyclin B1, CDC2, CDK6, MCM4, and retinoblastoma. A single STAT3 recruitment site (Tyr-721) in the cytoplasmic domain of IL-31Ralpha exerts a dominant function in the entire receptor complex and is critical for gene induction, morphological changes, and growth inhibition. The data suggest that inflammatory and immune reactions involving activated T-cells regulate functions of epithelial cells by IL-6 cytokines through receptor-defined signaling reactions.