Published papers

To prepare reagents for a study of the interactions of prolactin (PRL) and growth hormone (GH) receptors (Rs) with suppressor of cytokine signaling (SOCS) proteins in living cells by fluorescence resonance energy transfer methodology, the respective proteins were tagged with cyan (CFP) or yellow (YFP) fluorescent protein. Constructs encoding ovine (o)PRLR-YFP, oPRLR-CFP, oGHR-YFP, and oGHR-CFP tagged downstream of the receptor DNA were prepared in the plasmid pcDNA plasmid and tested for biological activity in HEK 293T cells transiently cotransfected with those constructs and the reporter gene encoding luciferase. All four constructs were biologically active and as potent as their untagged counterparts. Cells transfected with those proteins exhibited fluorescence in the cytoplasm and the membrane. Constructs encoding DNA tagged with YFP or CFP upstream of SOCS1, SOCS2, SOCS3, and SOCS6 were prepared in pECFP-C1 and pEYFP-C1 plasmids. The biological activities of SOCS1 and SOCS3 tagged at their amino termini were assayed by their ability to inhibit placental lactogen (PL)- or GH-induced activation of JAK2/STAT5-mediated luciferase transcription in HEK 293T cells; the activity of SOCS2 was assayed by its ability to abolish SOCS1-induced inhibition. The tagged proteins exhibited biological activity that was equal to or even more potent than their untagged counterparts. The biological activities of CFP-SOCS2 and YFP-SOCS2 were also assayed using GST-GHR binding assay. Their interaction with the cytosolic domain of GHR was equivalent to their respective untagged counterparts. The biological activity of the construct encoding SOCS6 was not tested because of lack of a suitable assay. Cells transfected with eight of these tagged constructs expressed the fluorescent proteins in both the nucleus and cytosol; the tagged SOCS2 was localized mostly in the latter compartment. © 2002 Elsevier Science (USA). All rights reserved.

The mechanisms that regulate susceptibility to virus-induced autoimmunity remain undefined. We establish here a fundamental link between the responsiveness of target pancreatic β cells to interferons (IFNs) and prevention of coxsackievirus B4 (CVB4)-induced diabetes. We found that an intact β cell response to IFNs was critical in preventing disease in infected hosts. The antiviral defense, raised by β cells in response to IFNs, resulted in a reduced permissiveness to infection and subsequent natural killer (NK) cell-dependent death. These results show that β cell defenses are critical for β cell survival during CVB4 infection and suggest an important role for IFNs in preserving NK cell tolerance to β cells during viral infection. Thus, alterations in target cell defenses can critically influence susceptibility to disease.

Many growth factors and hormones modulate the reproductive status in mammals. Among these, insulin and insulin-like growth factor I (IGF-I) regulate the development of gonadal tissues. SH2-B has been shown to interact with insulin and IGF-I receptors, although the role of SH2-B in these signals has not been clarified. To investigate the role of SH2-B, we generated mice with a targeted disruption of the SH2-B gene. Both male and female SH2-B-/- mice showed slight retardation in growth and impaired fertility. Female knockout mice possess small, anovulatory ovaries with reduced numbers of follicles and male SH2-B-/- mice have small testes with a reduced number of sperm. SH2-B-/-cumulus cells do not respond to either follicle-stimulating hormone or IGF-I. These data suggest that SH2-B plays a critical role in the IGF-I-mediated reproductive pathway in mice.

We previously demonstrated using restriction landmark genomic scanning-based 2-dimensional genome electrophoresis method decreased results of 16 primary hepatocellular carcinomas (HCCs) revealed reduction of intensity of 60 NotI-landmark spots, and increase in five spots that were frequently observed in HCCs. Most frequently decreased spot (14/16 HCCs) was identified to it corresponds to a gene encoding SSI-1, a JAK-binding protein (SSI-1/SOCS-1/JAB) that regulated the JAK/STAT signal transduction pathway. This signaling pathway is important for relaying signals from various cytokines outside the cell to the inside. Expression level of SOCS-1 messenger RNA was markedly suppressed in 50% of HCCs (4/8). Loss of heterozygosity at the SSI-1 gene, was found in all cases with aberrant expression. Methylation analysis of the CpG-rich regions of SSI-1 gene revealed hypermethylation of these regions. In an additional series of methylation analysis using 30 HCCs, 16 (53%) showed hypermethylation of the gene. These results indicate that the SSI-1 gene is silenced in a substantial portion of HCC though the combined mechanisms of methylation of either 5′ or exon CpG rich regions and by a chromosomal loss of the remaining allele. © 2002 Elsevier Science Ireland Ltd. All rights reserved.

Bacterial lipopolysaccharide (LPS) triggers innate immune responses through Toll-like receptor (TLR) 4. We show here that the suppressor of cytokine-signaling-1 (SOCS1/JAB) is rapidly induced by LPS and negatively regulates LPS signaling. SOCS1+/- mice or SOCS1-/- mice with interferon-γ (IFNγ)-deficient background were more sensitive to LPS-induced lethal effects than were wild-type littermates. LPS-induced NO2- synthesis and TNFα production were augmented in SOCS1-/- macrophages. Furthermore, LPS tolerance, a protection mechanism against endotoxin shock, was also strikingly reduced in SOCS1-/- cells. LPS-induced I-κB and p38 phosphorylation was upregulated in SOCS1-/- macrophages, and forced expression of SOCS1 suppressed LPS-induced NF-κB activation. Thus, SOCS1 directly suppresses TLR4 signaling and modulates innate immunity.

The development of helper T (Th) cell subsets, which secrete distinct cytokines, plays an important role in determining the type of immune response. The IL-4-mediated Janus kinase-signal transducer and activator of transcription signaling pathway is crucial for mediating Th2 cell development. Notably, this pathway is selectively impaired in Th1 cells, although the molecular basis of this impairment remains unclear. We show here that during Th1 differentiation a reduction in the association of Janus kinase 1 with the IL-4 receptor (IL-4R) correlated with the appearance of the suppressor of cytokine signaling-5 (SOCS5). SOCS5 protein was preferentially expressed in committed Th1 cells and interacted with the cytoplasmic region of the IL-4Rα chain irrespective of receptor tyrosine phosphorylation. This unconventional interaction of SOCS5 protein with the IL-4R resulted in the inhibition of IL-4-mediated signal transducer and activator of transcription-6 activation. T cells from transgenic mice constitutively expressing SOCS5 exhibited a significant reduction of IL-4-mediated Th2 development. Therefore, the induced SOCS5 protein in Th1 differentiation environment may play an important role by regulating Th1 and Th2 balance.

The signal transducer and activator of transcription (STAT) family proteins are transcription factors critical in mediating cytokine signaling. Among them, STAT3 is often constitutively phosphorylated and activated in human cancers and in transformed cell lines and is implicated in tumorigenesis. However, cause of the persistent activation of STAT3 in human tumor cells is largely unknown. The hepatitis C virus (HCV) is a major etiological agent of non-A and non-B hepatitis, and chronic infection by HCV is associated with development of liver cirrhosis and hepatocellular carcinoma. HCV core protein is proposed to be responsible for the virus-induced transformation. We now report that HCV core protein directly interacts with and activates STAT3 through phosphorylation of the critical tyrosine residue. Activation of STAT3 by the HCV core in NIH-3T3 cells resulted in rapid proliferation and up-regulation of Bcl-XL and cyclin-D1. Additional expression of STAT3 in HCV core-expressing cells resulted in anchorage-independent growth and tumorigenesis. We propose that the HCV core protein cooperates with STAT3, which leads to cellular transformation.

Inflammation progresses by the action of pro-inflammatory cytokines, including interleukin-1 (IL-1), the tumor necrosis factor (TNF), gamma-interferon (IFNγ), IL-12, IL-18, and the granulocyte-macrophage colony-stimulating factor, and is resolved by anti-inflammatory cytokines such as IL-4, IL-10, IL-13, IFNα, and the transforming growth factor (TGF)β. The intracellular signal transduction pathways of these cytokines have been studied extensively, and these pathways ultimately activate transcription factors, such as NF-κB, Smad, and STATs. Recently, the negative -feedback regulation of these pathways has been identified. In this review, we provide examples of the relationship between cytokine signal transduction, negative-signal regulation, and inflammatory disease models. Furthermore, we illustrate several approaches for treating inflammatory diseases by modulating extracellular and intracellular signaling pathways. © 2002 Elsevier Science Ltd. All rights reserved.

Previous studies have shown that IL-10 can induce the expression of the suppressor of cytokine signaling 3 (SOCS-3) mRNA in human monocytes and neutrophils, suggesting that the capacity of IL-10 to inhibit the expression of LPS-inducible proinflammatory genes may depend on SOCS-3 induction. However, no direct experimental evidence has been provided to support such hypothesis. Herein, we show that stable transfection of SOCS-3 into the mouse macrophage cell line J774 resulted in an inhibition of NO, TNF-α, IL-6, and GM-CSF secretion in response to LPS at levels similar to those exerted by IL-10 in LPS-stimulated wild-type J774. Constitutive SOCS-3 expression also down-regulated the mRNA expression of inducible NO synthase and IL-6 and impaired the production of TNF-α, mainly at a post-transcriptional level. In addition, SOCS-3-transfected cells displayed a constitutive expression of the IL-1R antagonist gene, consistent with the observation that IL-10 enhances IL-1R antagonist mRNA in LPS-stimulated wild-type cells. Furthermore, in peritoneal macrophages harvested from mice carrying heterozygous disruption of the SOCS-3 gene, IL-10 was less effective in repressing LPS-stimulated TNF-α and NO production. Taken together, our data show that SOCS-3 inhibits LPS-induced macrophage activation, strongly supporting the idea that it plays a role in the molecular mechanism by which IL-10 down-modulates the effector functions of LPS-activated macrophages. Finally, we show that forced expression of SOCS-3 significantly suppresses the ability of IL-10 to trigger tyrosine phosphorylation of STAT3. Therefore, SOCS-3 functions both as an LPS signal inhibitor and as a negative feedback regulator of IL-10/STAT3 signaling.

We demonstrated previously γ-globin gene inhibition in K562 cells and primary erythroid progenitors treated with interleukin-6. Although several cis-acting elements have been identified in the globin promoters, the precise mechanism for cytokine-mediated globin gene regulation remains to be elucidated. In this report we demonstrate inhibitors of Stat3 phosphorylation abrogate interleukin-6-mediated γ gene silencing in erythroid cells. DNA-protein binding studies established Stat3 interaction in the 5′-untranslated γ-globin promoter region. Furthermore, co-transfection experiments with Stat3β demonstrate γ promoter inhibition in a concentration-dependent manner, which was significantly reversed when the cognate Stat3-binding site in the 5′-untranslated region was mutated. These studies establish a novel mechanism for γ gene silencing through the STAT signal transduction pathway.

Negative selection is a process to delete potentially autoreactive clones in developing thymocytes. Programmed cell death or apoptosis is thought to play an important role in this selection process. In this study, we investigated the role of apoptotic protease-activating factor 1 (Apaf1), a mammalian homologue of CED-4, in programmed cell death during the negative selection in thymus. There was no developmental abnormality in thymocytes from newborn Apaf1-/- mice in terms of CD4 and CD8 expression pattern and thymocyte number. Clonal deletion by endogenous male H-Y Ag of Apaf1-deficient thymocytes with transgenic expression of H-Y Ag-specific TCRs (H-Y Tg/Apaf1-/- thymocytes) was normally observed in lethally irradiated wild-type mice reconstituted with fetal liver-derived hemopoietic stem cells. Clonal deletion induced in vitro by a bacterial superantigen was also normal in fetal thymic organ culture. Thus, Apaf1-mediated pathway of apoptosis is dispensable for the negative selection of thymocytes. However, H-Y Tg/Apaf1-/- thymocytes showed partial resistance to H-Y peptide-induced deletion in vitro as compared with H-Y Tg/Apaf1+/- thymocytes, implicating the Apaf1-mediated apoptotic pathway in the negative selection in a certain situation. In addition, the peptide-induced deletion was still observed in H-Y Tg/Apaf1-/- thymocytes in the presence of a broad spectrum caspase inhibitor, z-VAD-fmk, suggesting the presence of caspase-independent cell death pathway playing roles during the negative selection. We assume that mechanisms for the negative selection are composed of several cell death pathways to avoid failure of elimination of autoreactive clones.

Objective. BCR/ABL is a chimeric oncoprotein that exhibits deregulated tyrosine kinase activity and is implicated in the pathogenesis of Philadelphia chromosome (Ph)-positive leukemia. A general understanding of BCR/ABL signaling events is emerging, but little is known about the endogenous inhibitors of p210 BCR/ABL. The present study focused attention on CIS1, a cytokine-inducible SH2 protein, as a potential physiologic antagonist for BCR/ABL. Materials and Methods. The murine hematopoietic cell line NSF/N1.H7 stably transfected with BCR/ABL was compared to the parental counterparts for induction of CIS1 by immunoblotting and immunoprecipitation. Cells were treated with a proteasome inhibitor to examine the effect of a proteasome inhibitor on CIS1 protein expression. To determine the effect of CIS1 on BCR/ABL-mediated transformation, we generated Rat-1 fibroblasts transfected with either a control vector, CIS1, BCR/ABL p210, or CIS1 plus BCR/ABL p210.ResultsThree forms of CIS1 with molecular masses of 32, 37, and 47 kDa were detected in BCR/ABL-transformed cells. The 47-kDa protein was a ubiquitinated protein. The proteasome inhibitor increased the formation of complexes between CIS1 and BCR/ABL. Transformation of p210 BCR/ABL was significantly suppressed in cells overexpressing CIS1. Conclusion. The results suggest that CIS1 is an endogenous inhibitor of p210 BCR/ABL and is likely to be important in the pathogenesis of Ph-positive leukemia. Copyright © 2001 International Society for Experimental Hematology.

The gp130 cytokine receptor activates a cardiomyocyte survival pathway during the transition to heart failure following the biomechanical stress of pressure overload. Although gp130 activation is observed transiently during transverse aortic constriction (TAC), its mechanism of inactivation is largely unknown in cardiomyocytes. We show here that suppressor of cytokine signaling 3 (SOCS3), an intrinsic inhibitor of JAK, shows biphasic induction in response to TAC. The induction of SOCS3 was closely correlated with STAT3 phosphorylation, as well as the activation of an embryonic gene program, suggesting that cardiac gp130-JAK signaling is precisely controlled by this endogenous suppressor. In addition to its cytoprotective action, gp130-dependent signaling induces cardiomyocyte hypertrophy. Adenovirus-mediated gene transfer of SOCS3 to ventricular cardiomyocytes completely suppressed both hypertrophy and antiapoptotic phenotypes induced by leukemia inhibitory factor (LIF). To our knowledge, this is the first clear evidence that these two separate cardiomyocyte phenotypes induced by gp130 activation lie downstream of JAK. Three independent signaling pathways, STAT3, MEK1-ERK1/2, and AKT activation, that are coinduced by LIF stimulation were completely suppressed by SOCS3 overexpression. We conclude that SOCS3 is a mechanical stress-inducible gene in cardiac muscle cells and that it directly modulates stress-induced gp130 cytokine receptor signaling as the key molecular switch for a negative feedback circuit for both myocyte hypertrophy and survival.

Immune and inflammatory systems are controlled by multiple cytokines, including ILs and INFs. These cytokines exert their biological functions through Janus tyrosine kinases and STAT transcription factors. One such cytokine, IL-6, has been proposed to contribute to the development of rheumatoid arthritis (RA). We found that STAT3 was strongly tyrosine phosphorylated in synovial tissue of RA patients, but not those with osteoarthritis. Blockade of the IL-6-gp130-JAK-STAT3-signaling pathway might therefore be beneficial in the treatment of RA. We show here that the mRNA for the endogenous cytokine signaling repressor CIS3/SOCS3 is abundantly expressed in RA patients. To determine whether CIS3 is effective in treating experimental arthritis, a recombinant adenovirus carrying the CIS3 cDNA was injected periarticularly into the ankle joints of mice with antigeninduced arthritis or collagen-induced arthritis (CIA). Periarticular injection of CIS3 adenovirus drastically reduced the severity of arthritis and joint swelling compared with control groups. CIS3 was more effective than a dominant-negative form of STAT3 in the CIA model. Thus, induction of CIS3 could represent a new approach for effective treatment of RA.

Cytokines exert biological functions by activating Janus tyrosine kinases (JAKs), and JAK inhibitors JAB (also referred to as SOCS1 and SSI1) and CIS3 (SOCS3) play an essential role in the negative regulation of cytokine signaling. We have found that transgenic (Tg) mice expressing a mutant JAB (F59D.JAB) exhibited a more potent STAT3 activation and a more severe colitis than did wild-type littermates after treatment with dextran sulfate sodium. We now find that there is a prolonged activation of JAKs and STATs in response to a number of cytokines in T cells from Tg mice with lck promoter-driven F59D-JAB. Overexpression of F59D-JAB also sustained activation of JAK2 in Ba/F3 cells. These data suggested that F59D-JAB up-regulated STAT activity by sustaining JAK activation. To elucidate molecular mechanisms related to F59D-JAB, we analyzed the effects of F59D-JAB on the JAK/STAT pathway using the 293 cell transient expression system. We found that the C-terminal SOCS-box played an essential role in augmenting cytokine signaling by F59D-JAB. The SOCS-box interacted with the Elongin BC complex, and this interaction stabilized JAB. F59D-JAB induced destabilization of wild-type JAB, whereas overexpression of Elongin BC canceled this effect. Levels of endogenous JAB and CIS3 in T cells from F59D-JAB Tg-mouse were lower than in wild-type mice. We propose that F59D-JAB destabilizes wild-type, endogenous JAB and CIS3 by chelating the Elongin BC complex, thereby sustaining JAK activation.

Various mitogenic stimuli such as epidermal growth factor (EGF), fibroblast growth factor (FGF), and phorbol 12,13-dibutyrate (PDBu) activate the Ras-Raf-MEK-ERK pathway, but the regulatory mechanism of this pathway remains to be investigated. Here we found that in 293 cells, mammalian Sprouty2 and Sprouty4 were rapidly induced by EGF, FGF, and PDBu in an ERK pathway-dependent manner. Forced expression of Sprouty2 and Sprouty4 inhibited FGF-induced ERK activation but did not affect EGF- or PDBu-induced ERK activation. To examine whether endogenous Sproutys were also selective inhibitors, we generated a dominant negative form of Sprouty2 (Y55A) and Sprouty4 (Y53A) in which conserved tyrosine residues were mutated. These mutants reverted the suppressive effect of both Sprouty2 and Sprouty4 but not that of RasGAP or SPRED (Sprouty-related EVH1 domain-containing protein), another Sprouty-related Ras suppressor. Expression of dominant negative Sprouty2 and Sprouty4 enhanced and prolonged FGF- but not EGF-induced ERK activation in 293 cells. In PC12 cells, endogenous Sprouty4 was also induced by FGF. Overexpression of wild-type Sprouty4 blocked FGF-induced differentiation, whereas Y53A-Sprouty4 enhanced it. These observations suggest that endogenous Sprouty2 and Sprouty4 are physiological negative feedback regulators of growth factor-mediated ERK pathway and that there are Sprouty-sensitive and -insensitive ERK activation pathways. Finding a dominant negative form of Sproutys will facilitate the study of the molecular mechanism and physiological function of Sproutys.

Immune and inflammatory systems are controlled by multiple cytokines, including interleukins and interferons. Many of these cytokines exert their biological functions through JAKs (Janus tyrosine kinases) and STAT (signal transduction and activators of transcription) transcription factors. CIS (cytokine-inducible SH2 (Src homology 2) protein) and SOCS (suppressor of cytokine signaling) are a family of intracellular proteins, several of which have emerged as key physiological regulators of cytokine-mediated homeostasis, including innate and adaptive immunity. In this review we focus on the molecular mechanism of the action of CIS/SOCS family proteins and their roles in immune regulation and inflammatory diseases including rheumatoid arthritis. © 2005 BioMed Central Ltd.

It has recently been shown that small interfering RNA (siRNA)-mediated inhibition of suppressors of cytokine signalling 1 (SOCS1) function enhances the immunostimulatory capacity of dendritic cells (DCs), which leads to more effective cancer vaccination. This recent study demonstrates the importance of negative regulation of DC maturation and functions for DC-based immunotherapy. © 2005 Elsevier Ltd. All rights reserved.

The suppressor of cytokine signaling-1 (SOCS1/JAB) negatively regulates not only the cytokine-signaling pathway, but also lipopolysaccharide (LPS)-induced macrophage activation. We found that SOCS1-deficient dendritic cells (DCs) were also hyperresponsive to interferon-γ (IFNγ) and interleukin-4 (IL-4). To define the role of SOCS1-deficient DCs in vivo, we generated mice in which the SOCS1 expression was restored in T and B cells under a SOCS1 -/- background. In these mice, DCs were accumulated in the thymus and spleen and produced high levels of BAFF/BLyS, resulting in the aberrant expansion of B cells and autoreactive antibody production. SOCS1-deficient DCs efficiently stimulated B cell proliferation in vitro and auto-antibody production in vivo. These results indicate that SOCS1 plays an essential role in the normal DC functions and in the suppression of systemic autoimmunity.