Modulation of hepatic acute phase gene expression by epidermal growth factor and Src protein tyrosine kinases in murine and human hepatic cells

As part of systemic inflammatory reactions, interleukin 6 (IL-6) induces acute phase protein (APP) genes through the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway. Epidermal growth factor (EGF), which contributes to the regenerative process after liver injury and also activates STATs, does not induce but attenuates IL-6-stimulated expression of several APP genes in primary mouse hepatocytes. The APP-modifying action of EGF receptor (EGFR) was characterized in HepG2 cells. Although EGF less effectively engages STAT proteins in these cells, it reduces expression of fibrinogen and haptoglobin, but stimulates production of alpha(1)-antichymotrypsin and induces transcription through the alpha(1)-antichymotrypsin and C-reactive protein promoter. The stimulatory EGFR signal is insensitive to inhibition of JAKs and appears to involve Src kinases and STAT proteins as shown by inhibition through overexpression of C-terminal Src kinase (Csk) and transdominant negative STAT3, respectively. A mediator role of Src is supported by the ability of c-Src and v-Src to activate STATs and induce transcription through APP promoters. Src kinases have been observed in association with the IL-6 receptor; however, inhibition of Src kinases by Csk enhances IL-6-induced transcription. The Csk effect is attributed to prevention of Src kinases from phosphorylating gp130 at the docking site for the signal-moderating protein tyrosine phosphatase SHP-2. The inhibitory EGFR signal on APP expression correlates with the activation of Erk1 and Erk2. The study shows a dual signaling function for EGFR and suggests that the ratio of receptor-activated STATs and Erks influence the level of stimulated or inhibited expression of individual APPs.

Dual signaling role of the protein tyrosine phosphatase SHP-2 in regulating expression of acute-phase plasma proteins by interleukin-6 cytokine receptors in hepatic cells

One of the major actions of interleukin-6 (IL-6) is the transcriptional activation of acute-phase plasma proteins (APP) genes in liver cells. Signaling by the IL-6 receptor is mediated through the signal transducing subunit gp130 and involves the activation of Janus-associated kinases (JAKs), signal transducer and activator of transcription 3 (STAT3), and mitogen-activated protein (MAP) kinase. Functional analysis of gp130 in rat hepatoma cells by using transduced chimeric G-CSFR-gp130 receptor constructs demonstrates that SHP-2, the Src homology 2 (SH2) domain-containing protein tyrosine phosphatase, acts as a negative regulator of the JAK/STAT signaling in part by downregulating JAK activity, thereby indirectly moderating the induction of STAT3-dependent APP genes. This study shows that in hepatoma cells, the recruitment and tyrosine phosphorylation of SHP-2, but not SHC, is the primary signaling event associated with the activation of MAP kinases (ERK1/2) by gp130. Overexpression of truncated SHP-2 that lacks Grb2-interacting sites, but not the full-length catalytically inactive SHP-2, reduces ERK activation by IL-6, confirming the signal-mediating role of SHP-2. Activation of ERK1/2 is correlated with induction of the immediate-early response genes. Stimulation of the c-fos, c-jun, and egr-1 genes is essentially absent in cells expressing gp130 with a Y759F mutation, which is unable to recruit SHP-2. Interestingly, both JAK/STAT and SHP-2 pathways regulate the induction of the junB gene. Moreover, disengagement of SHP-2 from gp130 signaling not only enhances APP gene induction but also further reduces cell proliferation, in part correlated with the attenuated expression of immediate-early response genes. These results suggest that IL-6 regulation of APP genes is affected by SHP-2 in two ways: SHP-2 acts as a phosphatase on the JAK/STAT pathway and serves as linker to the MAP kinase pathway, which in turn moderates APP production.

Identification of c-myc promoter-binding protein and X-box binding protein 1 as interleukin-6 target genes in human multiple myeloma cells

Interleukin-6 (IL-6) is implicated in the in vivo proliferation of malignant plasma cells in multiple myeloma. To define the molecular basis of the IL-6-induced mitogenic response in myeloma cells, we applied STAR (subtractive transcriptional amplification of mRNA), a new differential expression analysis technology, to isolate mRNAs preferentially expressed in IL-6-treated versus untreated cultures of the factor-responsive myeloma cell line U266. From the resulting collection of STAR clones, sequence information was obtained for a total of 72 distinct transcripts. Of these, 29 were found to correspond to known genes, 22 matched expressed sequence tags in public databases and 21 showed no sequence similarity to any existing entries. Among the known genes uncovered in the screen were those encoding proteins that function in cell division, cell signalling and gene/protein expression. Northern blot analysis documented that two transcription factor genes chosen for further study, c-myc promoter-binding protein (MBP-1) and X-box binding protein 1 (XBP-1), were up-regulated in U266 cells about 3-fold relative to the cell cycle-dependent beta-actin gene 12 h after IL-6 treatment. Both genes were also similarly up-regulated by IL-6 in factor-dependent ANBL-6 myeloma cells. These results indicate that MBP-1 and XBP-1 are IL-6 genes in myeloma cells; as such, they may play a role in IL-6-mediated growth control in multiple myeloma.

A fatal cytokine-induced systemic inflammatory response reveals a critical role for NK cells

The mechanism of cytokine-induced shock remains poorly understood. The combination of IL-2 and IL-12 has synergistic antitumor activity in vivo, yet has been associated with significant toxicity. We examined the effects of IL-2 plus IL-12 in a murine model and found that the daily, simultaneous administration of IL-2 and IL-12 resulted in shock and 100% mortality within 4 to 12 days depending on the strain employed. Mice treated with IL-2 plus IL-12 exhibited NK cell apoptosis, pulmonary edema, degenerative lesions of the gastrointestinal tract, and elevated serum levels of proinflammatory cytokines and acute phase reactants. The actions of TNF-alpha, IFN-gamma, macrophage-inflammatory protein-1alpha, IL-1, IL-1-converting enzyme, Fas, perforin, inducible nitric oxide synthase, and STAT1 did not contribute to the observed toxicity, nor did B or T cells. However, toxicity and death from treatment with IL-2 plus IL-12 could be completely abrogated by elimination of NK cells. These results suggest that the fatal systemic inflammatory response induced by this cytokine treatment is critically dependent upon NK cells, but does not appear to be mediated by the known effector molecules of this cellular compartment. These data may provide insight into the pathogenesis of cytokine-induced shock in humans.

The STAT3-independent signaling pathway by glycoprotein 130 in hepatic cells

Interleukin (IL)-6 is a major regulator of hepatic acute-phase plasma protein (APP) genes. The membrane-proximal 133-amino acid cytoplasmic domain of glycoprotein (gp) 130, containing one copy of the Box3 motif, is sufficient to transmit a productive signal to endogenous APP genes in rat hepatoma H-35 cells. In contrast, a mutant gp130 domain lacking the Box3 motif activates Janus kinases to a normal level but fails to activate signal transducer and activator of transcription 3 and to up-regulate a number of APP genes, including thiostatin, fibrinogen, hemopexin, and haptoglobin. However, in the absence of Box3, gp130 still stimulates the expression of alpha2-macroglobulin and synergizes with IL-1 to up-regulate alpha1-acid glycoprotein. The Box3 motif is not required for activation of the SH2-containing protein tyrosine phosphatase 2 or the mitogen-activated protein kinase (MAPK), nor is the immediate induction of egr-1 and junB significantly altered. Surprisingly, gp130 without any functional Box3 stimulates prolonged activation of MAPK, leading to an extended period of up-regulation of egr-1 and to an extracellularly regulated kinase-mediated reduction in the IL-6-stimulated production of thiostatin. IL-6 reduces proliferation of H-35 cells through signaling by the Box3. In addition, cells expressing Box3-deficient gp130 showed distinct morphologic changes upon receptor activation. Taken together, these results indicate that Box3-derived and Box3-independent signals cooperate in the control of hepatic APP genes and that Box3 may be involved in the modulation of MAPK activity in gp130 signaling.

A novel mutant gammac chain from a patient with typical phenotype of X-linked severe combined immunodeficiency (SCID) has partial signalling function for mediating IL-2 and IL-4 receptor action

Mutations of the common gamma (gammac) chain result in X-linked SCID (X-SCID), which is characterized by the reduction in number or absence of peripheral blood T cells and natural killer (NK) cells, with retention of normal numbers of B cells. In the present study we describe a novel mutant gammac chain of an X-SCID patient with a typical X-SCID phenotype. This mutant receptor subunit is able to associate with Jak3 to transduce a weak signal. The Jak3-specific action is demonstrated by the induction of gene expression through the haematopoietin receptor response element (HRRE) by IL-2 and IL-4 in the experimental model of transiently transfected hepatoma cells over-expressing Jak3. This result suggests that a threshold in the gammac-Jak3 interaction determines the X-SCID phenotype.

High-level constitutive expression of alpha 1-acid glycoprotein and lack of protection against tumor necrosis factor-induced lethal shock in transgenic mice

alpha 1-Acid glycoprotein (AGP) is an acute phase protein produced by hepatocytes. Although its exact biological function remains controversial, it was shown to protect galactosamine-sensitized or normal mice against hepatitis and lethal shock induced by tumor necrosis factor (TNF). Rat-AGP-transgenic mice, constitutively producing several mg AGP per ml serum were tested for their response to a combined challenge with TNF and D-(+)-galactosamine. A previously characterized, single transgenic line (9.5-5) was used. In contrast to our expectations both heterozygous or homozygous transgenic mice were not protected by the endogenously overproduced AGP. However, both transgenic and non-transgenic mice were protected by pretreatment with interleukin-1, an effect which we believe is mediated by the induction of acute phase proteins like AGP. Furthermore, both types of mice were protected by exogenous bovine AGP, suggesting that the lack of protection by endogenous AGP is not because of a repressed response to AGP. Finally, we demonstrate that purified AGP from the serum of transgenic mice is as protective as the AGP from non-transgenic mice or rats. The results suggest that AGP is protective only when its concentration is rapidly induced, perhaps because the endogenous steady state synthesis of AGP, in non-transgenic as well as transgenic mice, is coupled to the production of an AGP-binding factor. This study provides an interesting example of differences in outcome to a lethal challenge between an acute administered and a chronically produced protective protein.

Neuropilin-1 is a placenta growth factor-2 receptor

Placenta growth factor (PlGF) belongs to the family of vascular endothelial growth factors (VEGFs). It binds to the flt-1 VEGF receptor but not to the KDR/flk-1 receptor which is thought to mediate most of the angiogenic and proliferative effects of VEGF. Three PlGF isoforms are produced by alternative splicing. PlGF-1 and PlGF-3 differ from PlGF-2 since they lack the exon 6 encoded peptide which bestows upon PlGF-2 its heparin binding properties. Cross-linking experiments revealed that 125I-PlGF-2 binds to two endothelial cell surface receptors in a heparin dependent fashion. The binding of 125I-PlGF-2 to these receptors was inhibited by an excess of PlGF-2 and by the 165-amino acid form of VEGF (VEGF165), but not at all by VEGF121 and very marginally if at all by PlGF-1. The apparent molecular weight and the binding characteristics of these receptors correspond to those of the recently identified VEGF165 specific receptor neuropilin-1, and we therefore conclude that neuropilin-1 is a receptor for PlGF-2. The binding of 125I-PlGF-2 as well as the binding of 125I-VEGF165 to these receptors was inhibited by a synthetic peptide derived from exon 6 of PlGF. Furthermore, the binding of 125I-PlGF-2, but not that of 125I-VEGF165, was also inhibited by a synthetic peptide derived from exon 7 of PlGF. These observations indicate that the peptides encoded by these exons probably participate in the formation of the domain which mediates the binding of PlGF-2 to these receptors. We have also determined, using chemically modified heparin species, that the presence of sulfate moieties on the glucosamine-O-6 and on the iduronic acid-O-2 groups of heparin was required for the potentiation of 125I-PlGF-2 binding to these receptors. To determine if PlGF-2 is able to induce biological responses that are not induced by PlGF-1, we compared the effects of PlGF-1 and PlGF-2 on the migration and proliferation of endothelial cells. Both PlGF forms induced migration of endothelial cells. However, there was no quantitative difference between the response to PlGF-2 and the response to PlGF-1. Furthermore, neither PlGF-1 nor PlGF-2 had any effect upon the proliferation of the endothelial cells.

Expression and function of the megakaryocyte growth and development factor receptor in acute myeloid leukemia blasts

The receptor for megakaryocyte growth and development factor (MGDF), also known as thrombopoietin, has recently been cloned. MGDF stimulates platelet production and maturation both in vitro and in vivo. MGDF may thus have a role in attenuating the thrombocytopenia associated with acute myeloid leukemia (AML) and its therapy. However, there is concern that MGDF might induce AML blast proliferation and thereby increase the risk of treatment failure. To address this concern, we studied the expression of c-mpl mRNA and c-Mpl protein by blasts from AML patients. In addition we examined the in vitro effect of MGDF as well as the combined effect of MGDF and granulocyte colony-stimulating factor (G-CSF) or stem cell factor (SCF) on leukemic blast proliferation, recruitment into S-phase, induction of programmed cell death and activation of signal transducers and activators of transcription (STAT) proteins. Our results demonstrate that blasts from a substantial proportion of cases of AML express the receptor at either the mRNA or protein level. Moreover, the function of the MGDF receptor was demonstrated by activation of STAT proteins following exposure to MGDF. Nevertheless, blast proliferation in response to MGDF was rare, and the proliferative effect of MGDF was less than that of G-CSF or SCF. Furthermore, MGDF did not prevent programmed cell death induced by cytarabine. Finally, there appeared to be no correlation between receptor expression by AML blasts and functional response to MGDF. Based on these data, it would appear that clinical trials of MGDF may be undertaken safely in patients with AML.

Expression of signal transducers and activators of transcription proteins in acute myeloid leukemia blasts

Hematopoietic cytokine receptor signaling pathways involve activation of signal transducers and activators of transcription (STAT) proteins, which are postulated to be involved in cellular differentiation. Aberrant STAT isoforms (beta forms rather than the normal alpha forms) have been described and have been found to block the normal signaling pathway from the receptor. Bcr/Abl proteins have been suggested to directly activate STATs, without exposure to growth factors. We asked whether STATs play a role in leukemogenesis. We analyzed constitutive and induced patterns of STAT activity in pretreatment blasts from 36 newly diagnosed acute myeloid leukemia (AML) patients and studied protein tyrosine kinases (PTKs) that may be involved in STAT activity, using in vitro and in-gel kinase assays. The beta forms were expressed in 21 of 27 samples (78%). Constitutive STAT3 and STAT5 activity was found in samples from 28 and 22% of patients, respectively. Response to exogenous cytokines identified two groups. STAT activity in one group was modulated by exogenous cytokines: constitutive STAT activity increased in some patients but decreased or disappeared in response to cytokines in others. The second group was cytokine insensitive. Additionally, we found constitutive PTK activity in two patients whose blasts demonstrated constitutive STAT activity, suggesting that PTKs use cytokine receptor signal pathways to activate STATs in AML blasts without exposure to exogenous cytokines. Our data suggest that (a) constitutive expression of aberrant STATs may be involved in blocking differentiation of AML blasts, (b) exogenous cytokines may activate STAT-inhibitory pathways, and (c) STATs may be activated by PTKs in some AML blasts.

Architecture of nonspecific protein-DNA interactions in the Sso7d-DNA complex

Many biochemical processes, including DNA packing, maintenance and control, rely on non-sequence specific protein-DNA interactions. Nonspecific DNA-binding proteins have evolved to tolerate a wide range of DNA sequences, yet bind with a respectable affinity. The nonspecific binding requirement is in contrast to that imposed on, for example, transcription factors and implies a different structural basis for the biomolecular recognition process. To address this issue, and the mechanism for archaeal DNA packing, we determined the structure of the Sso7d protein from Sulfolobus solfataricus in complex with DNA. Sso7d binds DNA by placing a triple-stranded beta-sheet across the DNA minor groove. The protein is anchored in this position by the insertion of hydrogen bond-donating side chains into the groove and additionally stabilized by electrostatic and non-polar interactions with the DNA backbone. This structure explains how strong binding can be achieved independent of DNA sequence. Sso7d binding also distorts the DNA conformation and introduces significant unwinding of the helix. This effect suggests a mechanism for DNA packing in Sulfolobus based on negative DNA supercoiling.

Novel regio- and stereoselective O-6-desulfation of the glucosamine moiety of heparin with N-methylpyrrolidinone-water or N,N-dimethylformamide-water mixtures

The degree of completeness and selectivity of the solvolytic O-6-desulfation reactions of the glucosamine moiety adjacent to the 2-O-sulfoiduronic acid group of heparin was systematically studied. Using solutions of various ammonium salts of heparin (salts of tributylamine, quinoline and pyridine) in mixtures of 9:1 aprotic solvents and water (solvents of medium polarity, in order of decreasing polarity: Me2SO > Me2NCHO > Me2NAc > N-methylpyrrolidinone), the influence of different reaction conditions were studied. The ammonium salt of heparin with a strong base (e.g., tributylamine) in Me2SO showed almost no desulfation, while in Me2NCHO a relatively low degree of completeness of O-6-desulfation (30%) with moderate selectivity (15% [I-2(OS)]-desulfation) was observed. Weak bases like quinoline or pyridine in Me2SO-water resulted in nearly complete [A-6(OS)]-desulfation (95 and 94%, respectively) with low selectivity [I-2(OS)]-desulfation (49 and 35%, respectively). The heparin pyridinium salt in Me2NCHO-water showed both a relatively high degree of completeness and high selectivity (72% [A-6(OS)]- and 8% [I-2(OS)]-desulfation). The highest regioselectivity (i.e., a high degree of completeness accompanied by high selectivity) was achieved using an N-methylpyrrolidinone-water mixture (88% [A-6(OS)]-desulfation and 10% [I-2(OS)]-desulfation). A nearly complete O-6-desulfation (95%), accompanied by a lower selectivity (18% [I-2(OS)]-desulfation), was achieved when the reaction was carried out twice. Lower temperature improved selectivity (5% [I-2(OS)]-desulfation) but reduced the completeness of [A-6(OS)]-desulfation (72%). In comparison with the variety of O-6-desulfations reported to date, the novel reactions presented in this article led to remarkable increase in completeness and regioselectivity of the reactions that were investigated.

Protein tyrosine phosphatase 2 (SHP-2) moderates signaling by gp130 but is not required for the induction of acute-phase plasma protein genes in hepatic cells

Signals propagated via the gp130 subunit of the interleukin-6 (IL-6)-type cytokine receptors mediate, among various cellular responses, proliferation of hematopoietic cells and induction of acute-phase plasma protein (APP) genes in hepatic cells. Hematopoietic growth control by gp130 is critically dependent on activation of both STAT3 and protein tyrosine phosphatase 2 (SHP-2). To investigate whether induction of APP genes has a similar requirement for SHP-2, we constructed two chimeric receptors, G-gp130 and G-gp130(Y2F), consisting of the transmembrane and cytoplasmic domains of gp130 harboring either a wild-type or a mutated SHP-2 binding site, respectively, fused to the extracellular domain of the granulocyte colony-stimulating factor (G-CSF) receptor. Rat hepatoma H-35 cells stably expressing the chimeric receptors were generated by retroviral transduction. Both chimeric receptors transmitted a G-CSF-induced signal characteristic of that triggered by IL-6 through the endogenous gp130 receptor; i.e., both activated the appropriate JAK, induced DNA binding activity by STAT1 and STAT3, and up-regulated expression of the target APP genes, those for alpha-fibrinogen and haptoglobin. Notwithstanding these similarities in the patterns of signaling responses elicited, mutation of the SHP-2 interaction site in G-gp130(Y2F) abrogated ligand-activated receptor recruitment of SHP-2 as expected. Moreover, the tyrosine phosphorylation state of the chimeric receptor, the associated JAK activity, and the induced DNA binding activity of STAT1 and STAT3 were maintained at elevated levels and for an extended period of time in G-gp130(Y2F)-expressing cells following G-CSF treatment compared to that in cells displaying the G-gp130 receptor. H-35 cells ectopically expressing G-gp130(Y2F) were also found to display an enhanced sensitivity to G-CSF and a higher level of induction of APP genes. Overexpression of the enzymatically inactive SHP-2 enhanced the signaling by the wild-type but not by the Y2F mutant G-gp130 receptor. These results indicate that gp130 signaling for APP gene induction in hepatic cells differs qualitatively from that controlling the proliferative response in hematopoietic cells in not being strictly dependent on SHP-2. The data further suggest that SHP-2 functions normally to attenuate gp130-mediated signaling in hepatic (and, perhaps, other) cells by moderating JAK action.

IL-6 is an antiinflammatory cytokine required for controlling local or systemic acute inflammatory responses

IL-6 is induced often together with the proinflammatory cytokines TNFalpha and IL-1 in many alarm conditions, and circulating IL-6 plays an important role in the induction of acute phase reactions. However, whether this endogenous IL-6 plays any additional pro- or antiinflammatory roles in local or systemic responses remains unclear. In this study, the role of IL-6 in acute inflammatory responses was investigated in animal models of endotoxic lung or endotoxemia by using IL-6+/+ and IL-6-/- mice. Aerosol exposure of endotoxin induced increased IL-6 and proinflammatory cytokines TNFalpha and MIP-2 and a neutrophilic response in the lung of IL-6+/+ mice. However, the levels of TNFalpha and MIP-2 and neutrophilia were significantly higher in the lung of IL-6-/- mice. The rate of neutrophil apoptosis in these mice was similar to that in IL-6+/+ mice. A low constitutive level of antiinflammatory cytokine IL-10 was not enhanced by endotoxin and remained similar in the lung in both IL-6+/+ and IL-6-/- mice. Systemically, intraperitoneal delivery of endotoxin resulted in much more pronounced circulating levels of TNFalpha, MIP-2, GM-CSF, and IFNgamma in IL-6-/- mice than in IL-6+/+ mice, and administration of recombinant IL-6 to IL-6-/- mice abolished these differences. In contrast, circulating IL-10 levels were induced to a similar degree in both IL-6+/+ and IL-6-/- mice. Thus, our studies reveal that endogenous IL-6 plays a crucial antiinflammatory role in both local and systemic acute inflammatory responses by controlling the level of proinflammatory, but not antiinflammatory, cytokines, and that these antiinflammatory activities by IL-6 cannot be compensated for by IL-10 or other IL-6 family members.

Transmembrane domain of gp130 contributes to intracellular signal transduction in hepatic cells

Interleukin-6 (IL-6) induces the expression of acute phase plasma protein genes in hepatic cells through the action of gp130, the signal-transducing subunit of the IL-6 receptor. To identify whether the transmembrane domain of gp130 is required for signaling function, cytoplasmic forms of gp130 were constructed that consisted of the tetramerizing N-terminal domain of Bcr linked to the transmembrane and cytoplasmic domains of gp130 (Bcr/gp130) or just to the cytoplasmic domain of gp130 (Bcr/gp130DeltaTM). The expression and function of both constructs were determined in transiently transfected COS-1 and HepG2 cells. Bcr/gp130 is capable of interacting with JAK1, JAK2, and TYK2; is constitutively active; and induces gene expression through IL-6-responsive elements. In contrast, Bcr/gp130DeltaTM, while expressed at a higher level than Bcr/gp130 and still able to interact with JAK1, is ineffective in recruiting the endogenous signal transduction pathways for inducing gene expression. However, Bcr/gp130DeltaTM initiates partial signaling in the presence of overexpressed JAK1 and TYK2, but not JAK2. The data suggest that the transmembrane domain of gp130 is necessary for signal transduction and determines the interaction with members of the Janus kinase family.

Constitutive and impaired signaling of leptin receptors containing the Gln --> Pro extracellular domain fatty mutation

Leptin (OB), an adipocyte-secreted circulating hormone, and its receptor (OB-R) are key components of an endocrine loop that regulates mammalian body weight. In this report we have analyzed signal transduction activities of OB-R containing the fatty mutation [OB-R(fa)], a single amino acid substitution at position 269 (Gln --> Pro) in the OB-R extracellular domain that results in the obese phenotype of the fatty rat. We find that this mutant receptor exhibits both ligand-independent transcriptional activation via interleukin 6 and hematopoietin receptor response elements and ligand-independent activation of signal transducer and activator of transcription (STAT) proteins 1 and 3. However, OB-R(fa) is unable to constitutively activate STAT5B and is highly impaired for ligand induced activation of STAT5B compared with OB-R(wt). Introduction of the fatty mutation into a OB-R/G-CSF-R chimera generates a receptor with constitutive character that is similar but distinct from that of OB-R(fa). Constitutive mutant OB-R(fa) receptor signaling is repressed by coexpression of OB-R(wt). The implications of an extracellular domain amino acid substitution generating a cytokine receptor with a partially constitutive phenotype are discussed both in terms of the mechanism of OB-R triggering and the biology of the fatty rat.

[Effect of alcohol on minimal effective nCPAP pressure]

Alcohol may have an aggravating effect on sleep disordered breathing. Aim of our study was to test the effect of alcohol on the required nCPAP pressure as determined by the self-adjusting nCPAP-system AutoSet. Ten male subjects (age 54 +/- 9 yrs, body mass index 37 +/- 5 kg/m2) with moderate to severe obstructive sleep apnoea (OSA) were investigated. Full polysomnography was performed on four consecutive days (control night with and without alcohol, nCPAP pressure determination by AutoSet with and without alcohol, in randomised order). Alcohol was given in a single dose of 80 proof vodka (1.5 ml per kg of body weight) one hour prior to bedtime. Alcohol to a deterioration of the respiratory disturbance index (RDI, 56 +/- 23 without vs. 66 +/- 19 with alcohol, p = 0.02), but no significant change was observed in mean or minimal oxygen desaturation, mean or maximal event duration. The 95th percentile of the AutoSet-pressure was not different with or without alcohol (10.7 +/- 2.5 vs. 10.6 +/- 2.5 cm H2O). Moderate alcohol intake in the evening need not be taken into account for CPAP pressure determination in moderate to severe OSA.

Leptin receptor action in hepatic cells

Leptin, an adipocyte-secreted hormone, is one of the central regulators of body weight homeostasis. In humans and rodents, two major forms of leptin receptors (OB-R) are expressed. The short form (OB-RS), considered to lack signaling capability, is detected in many organs. In contrast, OB-R long form (OB-RL) predominates in the hypothalamus, but is also present at low levels in peripheral tissues. Transient transfection experiments have demonstrated that OB-RL transduces an intracellular signaling similar to interleukin (IL)-6 type-cytokine receptors. To define the specificity by which OB-R induces genes and cooperates with signal transduction pathways utilized by other hormones and cytokines, rat and human hepatoma cell lines were generated which stably express human OB-RL. Hepatoma cell lines selected for appreciable levels of OB-RL mRNA display enhanced leptin binding and responded to leptin with an IL-6 receptor-like signaling that includes the activation of STAT proteins, induction of acute-phase plasma proteins, and synergism with IL-1 and tumor necrosis factor-alpha. A leptin-mediated recruitment of phosphatidylinositol 3-kinase to insulin receptor substrate-2 was also detected. However, no significant tyrosine phosphorylation of insulin receptor substrate-2 and modulation of the immediate cell response to insulin were observed. The data suggest that OB-RL action in hepatic cells is equivalent to that of IL-6 receptor. However, leptin does not play a specific role in muting insulin action on hepatoma cells and therefore may not contribute to the diabetic symptoms associated with obesity.

Influence of subunit combinations on signaling by receptors for oncostatin M, leukemia inhibitory factor, and interleukin-6

Oncostatin M (OSM), leukemia inhibitory factor (LIF), and interleukin-6 (IL-6) induce expression of a similar set of acute phase plasma protein genes in hepatic cells. The redundant action of these cytokines has been ascribed to the involvement of the common signal-transducing receptor subunit, gp130, in combination with cytokine-specific, ligand-binding subunits. To define the specificity of the signal transduction by the LIF/OSM receptor (a heterodimer of gp130 and LIF receptor (LIFR)) and the OSM-specific receptor (a heterodimer of gp130 and OSM receptor (OSMR)), we reconstituted the receptor function by transfection into receptor-negative Hep3B hepatoma cells. Both receptors activate DNA binding activity of STAT1, -3, and -5B and induce gene transcription through IL-6-responsive elements. The signaling-competent cytoplasmic domain regions of OSMR and LIFR were defined by the analysis of progressive carboxyl-terminal deletion constructs. The 36 residue carboxyl-terminal region containing the distal box 3 sequence motif of OSMR is required for signal transduction by the OSM-specific receptor. In contrast, signaling by LIFR did not display the same requirement for receptor domains and was not strictly dependent on the box 3 elements. The signaling by endogenous LIF and OSM receptors differed from that by IL-6R by the prominent activation of STAT5 as shown in the mouse hepatoma cell line, Hepa-1. The data suggest that the signaling specificity of the receptors for the three cytokines is determined by the composition of the cytoplasmic domains associated in the signal-competent receptor complex and that the signaling is not identical among these cytokine receptors.

The carboxyl-terminal region of STAT3 controls gene induction by the mouse haptoglobin promoter

Haptoglobin (HP) is one of the major acute phase plasma proteins in the mouse, and its synthesis is additively induced by interleukin (IL)-6 and glucocorticoids. STAT3 serves as the mediator of the IL-6 receptor signal and appears to contribute to the transcriptional induction of acute phase protein genes. The carboxyl-terminal region of STAT3, consisting of an acidic domain and containing a serine phosphorylation site, has been proposed to contribute to the induction process. To assess the role of STAT3 in the transcriptional control of the HP promoter, we applied two mutant forms of STAT3: one with a deletion of the carboxyl-terminal 55 amino acid residues, STAT3Delta55C, and the other with a substitution of serine 727 to alanine, STAT3SA. Like the wild-type STAT3, both mutant STAT3 forms are activated by the signal-transducing subunit of the IL-6 receptor, gp130, or by co-transfected IL-3 receptor. Ectopic expression and activation of wild-type STAT3 or STAT3SA in HepG2 hepatoma cells similarly enhance transcription through the IL-6-response element of the HP promoter. This enhancement is specific for STAT3 and cannot be reproduced by STAT1 or STAT5. In contrast, STAT3Delta55C inhibits IL-6-induced transcriptional activation. Interestingly, whereas receptor-activated STAT3 also enhances stimulation of the haptoglobin promoter by dexamethasone through the glucocorticoid receptor, activated STAT3Delta55C reduces the regulation below the level achieved by the glucocorticoid receptor alone. This transdominant action by STAT3Delta55C is dependent on a functional IL-6-responsive element. The data suggest that the carboxyl-terminal domain, but not its serine phosphorylation site of STAT3, is required for transcription as part of the hematopoietin receptor signaling as well as for cooperation with other transcription factors such as the glucocorticoid receptor.

Characterization of interleukin-10 receptor expression on B-cell chronic lymphocytic leukemia cells

B-cell chronic lymphocytic leukemia (B-CLL) cells accumulate in vivo in the G0/G1 phase of the cell cycle, suggesting that their malignant expansion is due, at least in part, to a delay in cell death. However, the cellular or molecular factors responsible for a delay in B-CLL cell death are unknown. B-CLL cells do express receptors for interferon-alpha (IFN-alpha) and IFN-gamma, and activation of both has been shown to promote B-CLL survival in vitro by preventing apoptosis. The interleukin-10 (IL-10) receptor is another member of the IFN receptor family, but its ligand, IL-10, has been reported to induce apoptosis in B-CLL cells. In the current study, we undertook a biochemical analysis of IL-10 receptor expression on freshly isolated B-CLL cells and characterized the functional responsiveness of IL-10 binding to its constitutively expressed receptor. We show that B-CLL cells bind IL-10 with significant specificity and express between 47 and 127 IL-10 receptor sites per cell, with a dissociation constant in the range of 168 to 426 x 10(-12) mol/L. Ligand binding and activation of the IL-10 receptor expressed on B-CLL cells results in the phosphorylation of signal transducer and activator of transcription 1 (STAT1) and STAT3 proteins. This pattern of STAT protein phosphorylation is identical to IL-10 receptor activation on normal cells and similar to IFN-alpha (STAT1 and STAT3) and IFN-gamma (STAT1) receptor activation in CLL. Further, in consecutive samples of fresh blood obtained from patients with B-CLL cells, the addition of IL-10 inhibited B-CLL proliferation, enhanced B-CLL differentiation, but did not induce apoptosis. Indeed, IL-10, like IFN-gamma, was able to significantly reduce the amount of B-CLL cell death caused by hydrocortisone-induced apoptosis. We conclude that cytokines, which signal through the interferon family of receptors, have comparable functional effects on B-CLL cells.

A potential role for interleukin-15 in the regulation of human natural killer cell survival

Resting lymphocyte survival is dependent upon the expression of Bcl-2, yet the factors responsible for maintaining lymphocyte Bcl-2 protein expression in vivo are largely unknown. Natural killer (NK) cells are bone marrow-derived lymphocytes that constitutively express the beta and common gamma(c) subunits of the IL-2 receptor (R) as a heterodimer with intermediate affinity for IL-2. IL-15 also binds to IL-2Rbeta gamma(c) and is much more abundant in normal tissues than IL-2. Mice that lack the IL-2 gene have NK cells, whereas mice and humans that lack IL-2R gamma(c) do not have NK cells. Further, treatment of mice with an antibody directed against IL-2Rbeta results in a loss of the NK cell compartment. These data suggest that a cytokine other than IL-2, which binds to IL-2Rbeta gamma(c), is important for NK cell development and survival in vivo. In the current report, we show that the recently described IL-15R(alpha) subunit cooperates with IL-2Rbeta gamma(c) to transduce an intracellular signal at picomolar concentrations of IL-15. We demonstrate that resting human NK cells express IL-15R(alpha) mRNA and further, that picomolar amounts of IL-15 can sustain NK cell survival for up to 8 d in the absence of serum. NK cell survival was not sustained by other monocyte-derived factors (i.e., TNF-alpha, IL-1beta, IL-10, IL-12) nor by cytokines known to use gamma(c) for signaling (i.e., IL-4, IL-7, IL-9, IL- 13). One mechanism by which IL-15 promotes NK cell survival may involve the maintenance of Bcl-2 protein expression. Considering these functional properties of IL-15 and the fact that it is produced by bone marrow stromal cells and activated monocytes, we propose that IL-15 may function as an NK cell survival factor in vivo.

Leptin receptor (OB-R) signaling. Cytoplasmic domain mutational analysis and evidence for receptor homo-oligomerization

The leptin receptor (OB-R) mediates the weight regulatory effects of the adipocyte secreted hormone leptin (OB). Previously we have shown that the long form of OB-R, expressed predominantly in the hypothalamus, can mediate ligand-induced activation of signal transducer and activator of transcription factors 1, 3, and 5 and stimulate transcription via interleukin-6 and hematopoietin receptor responsive gene elements. Here we report that deletion and tyrosine substitution mutagenesis of OB-R identifies two distinct regions of the intracellular domain important for signaling. In addition, granulocyte-colony stimulatory factor receptor/OB-R and OB-R/granulocyte-colony stimulatory factor receptor chimeras are signaling competent and provide evidence that aggregation of two OB-R intracellular domains is sufficient for ligand-induced receptor activation. However, signaling by full-length OB-R appears to be relatively resistant to dominant negative repression by signaling-incompetent OB-R, suggesting that mechanisms exist to permit signaling by the long form of OB-R even in the presence [corrected] of excess naturally occurring short form of OB-R.