Biomedical subjects

Akihiko Yoshimura

Publications and source records attributed to Akihiko Yoshimura.

At least 109 records · Page 6Linked to original sources

PubMed2003

Negative regulation of cytokine signaling and inflammatory diseases.

Immune and inflammatory systems are controlled by multiple cytokines, including interleukins and interferons. These cytokines exert their biological functions through Janus tyrosine kinases and signal transducer and activators of transcription (STATs). The cytokine-inducible SH2 proteins (CIS) and suppressors of cytokine signaling (SOCS) are a family of intracellular proteins, several of which have emerged as key physiological regulators of cytokine responses, including those that regulate the inflammatory system. Several recent advances have been made in this field, including treatment of inflammatory diseases by modulating extracellular and intracellular signaling pathways.

Animals↗

PubMed2003

Mammalian Sprouty4 suppresses Ras-independent ERK activation by binding to Raf1.

The signalling cascade including Raf, mitogen-activated protein kinase (MAPK) kinase and extracellular-signal-regulated kinase (ERK) is important in many facets of cellular regulation. Raf is activated through both Ras-dependent and Ras-independent mechanisms, but the regulatory mechanisms of Raf activation remain unclear. Two families of membrane-bound molecules, Sprouty and Sprouty-related EVH1-domain-containing protein (Spred) have been identified and characterized as negative regulators of growth-factor-induced ERK activation. But the molecular functions of mammalian Sproutys have not been clarified. Here we show that mammalian Sprouty4 suppresses vascular epithelial growth factor (VEGF)-induced, Ras-independent activation of Raf1 but does not affect epidermal growth factor (EGF)-induced, Ras-dependent activation of Raf1. Sprouty4 binds to Raf1 through its carboxy-terminal cysteine-rich domain, and this binding is necessary for the inhibitory activity of Sprouty4. In addition, Sprouty4 mutants of the amino-terminal region containing the conserved tyrosine residue, which is necessary for suppressing fibroblast growth factor signalling, still inhibit the VEGF-induced ERK pathway. Our results show that receptor tyrosine kinases use distinct pathways for Raf and ERK activation and that Sprouty4 differentially regulates these pathways.

Animals↗

PubMed2003

Suppressors of cytokine signaling and immunity.

The suppressors of cytokine signaling (SOCS) and cytokine-inducible SH2 protein are key physiological regulators of the immune system. Principally, SOCS1 and SOCS3 regulate T cells as well as antigen-presenting cells, including macrophages and dendritic cells. Here we review the function of SOCS1 and SOCS3 in innate and adaptive immunity, with particular emphasis on the relationship between immune regulation and SOCS.

Animals↗

PubMed2003

Suppressor of cytokine signaling 1/JAB and suppressor of cytokine signaling 3/cytokine-inducible SH2 containing protein 3 negatively regulate the signal transducers and activators of transcription signaling pathway in normal human epidermal keratinocytes.

The suppressor of cytokine signaling/cytokine-inducible SH2 containing proteins are cytokine inducible and are negative regulators of the signal transducers and activators of the transcription signaling pathway. We investigated the mechanism regulating signal transducers and activators of transcription and the suppressor of cytokine signaling/cytokine-inducible SH2 containing protein family in keratinocytes, one of the major target cells for cytokines. Suppressor of cytokine signaling 1 mRNA was upregulated 3 h post-interferon gamma, and a 8.1-fold increase in the suppressor of cytokine signaling 1 mRNA occurred 48 h post-interferon gamma. The suppressor of cytokine signaling 3 mRNA was also upregulated from 1 h post-interferon gamma, and a 6.7-fold increase in the suppressor of cytokine signaling 3/cytokine-inducible SH2 containing protein 3 mRNA occurred between 6 and 12 h post-interferon gamma. Interleukin-6 exposure for 1 h enhanced the expression of the suppressor of cytokine signaling 3/cytokine-inducible SH2 containing protein 3 mRNA, but the suppressor of cytokine signaling 1/JAB mRNA was not induced by interleukin-6. Interleukin-4 upregulated the suppressor of cytokine signaling 1/JAB and cytokine-inducible SH2 containing protein 1 mRNA, with 3.4-fold and 5.1-fold increases in mRNA observed at 1 h post-interleukin-4, respectively. In contrast, epidermal growth factor, which phosphorylates signal transducers and activators of transcription 3, did not influence the level of the suppressor of cytokine signaling/cytokine-inducible SH2 containing protein family mRNA expression. Transfection of an adenovirus vector expressing the suppressor of cytokine signaling 1/JAB completely inhibited interferon gamma-dependent signal transducers and activators of transcription 1 phosphorylation and interleukin-4-dependent signal transducers and activators of transcription 6 phosphorylation. Transfection of adenovirus vector expressing the suppressor of cytokine signaling 1/JAB did not inhibit interleukin-6-dependent signal transducers and activators of transcription 3 phosphorylation-several reports show that the suppressor of cytokine signaling 1/JAB is a potent inhibitor of signal transducers and activators of transcription 3 signaling in the myeloid leukemia M1 cell. Transfection of the adenovirus vector expressing suppressor of cytokine signaling 3/cytokine-inducible SH2 containing protein 3 completely inhibited interleukin-6-dependent signal transducers and activators of transcription 3 phosphorylation and partially inhibited interferon gamma-dependent signal transducers and activators of transcription 1 phosphorylation. Transfection of the adenovirus vector expressing suppressor of cytokine signaling 3/cytokine-inducible SH2 containing protein 3, however, did not inhibit interleukin-4-dependent signal transducers and activators of transcription 6 phosphorylation. Transfection of the adenovirus vector expressing cytokine-inducible SH2 containing protein 1 had no effect on signal transducers and activators of transcription 1, 3, and 6 signaling in normal keratinocytes. Therefore, the relationship between signal transducers and activators of transcription and suppressor of cytokine signaling is unique in the keratinocytes, and the suppressor of cytokine signaling regulates cytokine signals in these cells.

Antineoplastic Agents↗

PubMed2003

CIS1 interacts with the Y532 of the prolactin receptor and suppresses prolactin-dependent STAT5 activation.

Prolactin (PRL) interacts with a single-chain prolactin-specific receptor of the cytokine receptor superfamily. PRL triggers the activation of JAK2 kinase, which phosphorylates the PRL receptor itself, and of STAT5, a member of the family of signal transducers and activators of transcription (STAT). We have shown that the STAT5-dependent immediate early gene, CIS1 (Cytokine-Inducible SH2 domain-containing protein-1), suppresses PRL-induced STAT5 activation in vitro as well as in transgenic mice. To facilitate the study of the interactions between CIS1 and the PRL receptor, we have developed the yeast tri-hybrid system, a modification of the yeast two-hybrid system. We expressed CIS1 fused to the DNA-binding domain and PRL receptor cytoplasmic domain fused to the transcription activation domain in the presence or absence of the tyrosine kinase domain of JAK2 in yeast. CIS1 bound to the PRL receptor cytoplasmic domain in a JAK2-dependent manner. Moreover, we determined that the phosphorylated Y532 of the murine PRL receptor is the binding site for CIS1. Interestingly, Y532 has been shown to be unnecessary for STAT5 activation, although CIS1 overexpression suppressed PRL-induced STAT5 activation. These data suggest that the suppression of STAT5 activation by CIS1 is not due to a simple competition with STAT5 but rather to a modification of the receptor by CIS1 binding.

Animals↗

PubMed2003

The suppressor of cytokine signaling-1 (SOCS1) is a novel therapeutic target for enterovirus-induced cardiac injury.

Enteroviral infections of the heart are among the most commonly identified causes of acute myocarditis in children and adults and have been implicated in dilated cardiomyopathy. Although there is considerable information regarding the cellular immune response in myocarditis, little is known about innate signaling mechanisms within the infected cardiac myocyte that contribute to the host defense against viral infection. Here we show the essential role of Janus kinase (JAK) signaling in cardiac myocyte antiviral defense and a negative role of an intrinsic JAK inhibitor, the suppressor of cytokine signaling (SOCS), in the early disease process. Cardiac myocyte-specific transgenic expression of SOCS1 inhibited enterovirus-induced signaling of JAK and the signal transducers and activators of transcription (STAT), with accompanying increases in viral replication, cardiomyopathy, and mortality in coxsackievirus-infected mice. Furthermore, the inhibition of SOCS in the cardiac myocyte through adeno-associated virus-mediated (AAV-mediated) expression of a dominant-negative SOCS1 increased the myocyte resistance to the acute cardiac injury caused by enteroviral infection. These results indicate that strategies directed at inhibition of SOCS in the heart and perhaps other organs can augment the host-cell antiviral system, thus preventing viral-mediated end-organ damage during the early stages of infection.

Animals↗

PubMed2003

Interaction of the growth hormone receptor with cytokine-induced Src homology domain 2 protein in rat adipocytes.

GH stimulates the phosphorylation of tyrosine residues in the GH receptor (GHR), Janus kinase 2 (JAK2), and other signaling proteins in a transient manner that subsides within 1 h. To assess the possible roles of cytokine-induced Src homology domain 2 (SH2) (CIS/SOCS) proteins in these transient responses, we studied the expression and disposition of CIS/SOCS proteins in rat adipocytes, a physiological target of GH action. A tyrosine-phosphorylated protein that appears to be the GHR was coprecipitated from extracts of GH-treated adipocytes with alpha-CIS. In contrast, no tyrosine-phosphorylated adipocyte proteins were recovered after immunoprecipitation with alpha-SOCS3, although coprecipitation of GHR with SOCS3 was readily detected in extracts of 3T3-F442A fibroblasts. Interaction of GHR with CIS peaked between 2 and 10 min after adipocytes were treated with GH, when tyrosine phosphorylation of the GHR was maximal. By 60 min after GH, tyrosine phosphorylation of the GHR declined to very low levels, and its interaction with CIS was reduced correspondingly. Proteasome inhibitors prevented the decline in tyrosine-phosphorylated GHR and prolonged interaction of GHR and CIS for at least 1 h. These findings demonstrate the interaction of CIS with the GHR in vivo and suggest that CIS may enhance degradation of the receptor by a proteasomal pathway.

Adipocytes↗

PubMed2002

Combined hypermethylation and chromosome loss associated with inactivation of SSI-1/SOCS-1/JAB gene in human hepatocellular carcinomas.

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.

Carcinoma, Hepatocellular↗

PubMed2002

The N-terminal truncated isoform of SOCS3 translated from an alternative initiation AUG codon under stress conditions is stable due to the lack of a major ubiquitination site, Lys-6.

The suppressor of cytokine signaling-3 (SOCS3/CIS-33/SSI-3) is an important negative regulator of cytokine signaling. Here, we show that an N-terminal truncated isoform (DeltaN-SOCS3) translated from the internal AUG codon 12 was profoundly induced by endoplasmic reticulum (ER) stress- or active double-stranded RNA-activated protein kinase PKR, as a result of induction of eukaryotic initiation factor 2alpha phosphorylation. DeltaN-SOCS3 exhibited a stronger cytokine-inhibitory activity and a higher stability than WT-SOCS3 in Ba/F3 hematopoietic cells. A potential ubiquitination residue, Lys-6, at the N terminus is evolutionary conserved among SOCS3 species. The K6Q-SOCS3 mutant showed a much longer half-life than WT-SOCS3 in Ba/F3 cells. Furthermore, inhibition of the 26 S proteasome pathway increased both ubiquitination and protein levels of WT-SOCS3 but had no effect on K6Q-SOCS3. SOCS3 mutant lacking the carboxyl-terminal SOCS-box exhibited the same stability as K6Q-SOCS3. These observations suggest that the short form of SOCS3 is a naturally occurring stabilized inhibitory protein, whereas WT-SOCS3 is a short-lived protein modulated by Lys-6 ubiquitination and proteasome-dependent degradation. Our findings provide strong evidence for the first time that translational control plays an important role in stabilization and function of SOCS3.

Animals↗

PubMed2002

SHP2 and SOCS3 contribute to Tyr-759-dependent attenuation of interleukin-6 signaling through gp130.

Interleukin-6 (IL-6) activates the Jak/STAT pathway as well as the mitogen-activated protein kinase cascade. Tyrosine 759 of the IL-6 signal-transducing receptor subunit gp130 has been identified as being involved in negative regulation of IL-6-induced gene induction and activation of the Jak/STAT pathway. Because this site is known to be a recruitment motif for the protein-tyrosine phosphatase SHP2, it has been suggested that SHP2 is the mediator of tyrosine 759-dependent signal attenuation. We recently observed that the suppressor of cytokine-signaling SOCS3 also acts through the tyrosine motif 759 of gp130. However, the relative contributions of SHP2 and SOCS3 to the repression of IL-6 signaling are not understood. Therefore, we designed experiments allowing the independent recruitment of each of these proteins to the IL-6-receptor complex. We show that receptor- and membrane-targeted SHP2 counteracts IL-6 signaling independent of SOCS3 binding to gp130. On the other hand, SOCS3 inhibits signaling in cells expressing a truncated SHP2 protein, which is not recruited to gp130. These data suggest, that there are two, largely distinct modes of negative regulation of gp130 activity, despite the fact that both SOCS3 and SHP2 are recruited to the same site within gp130.

Amino Acid Sequence↗

PubMed2002

Angiogenesis induced by advanced glycation end products and its prevention by cerivastatin.

We previously have found that advanced glycation end products (AGE), senescent macroproteins formed at an accelerated rate in diabetes, arise in vivo not only from glucose but also from reducing sugars. Furthermore, we recently have shown that glyceraldehyde- and glycolaldehyde-derived AGE (glycer- and glycol-AGE) are mainly involved in loss of pericytes, the earliest histopathological hallmark of diabetic retinopathy. However, the effects of these AGE proteins on angiogenesis, another vascular derangement in diabetic retinopathy, remain to be elucidated. In this study, we investigated whether these AGE proteins elicit changes in cultured endothelial cells that are associated with angiogenesis. When human skin microvascular endothelial cells (EC) were cultured with glycer-AGE or glycol-AGE, growth and tube formation of EC, the key steps of angiogenesis, were significantly stimulated. The AGE-induced growth stimulation was significantly enhanced in AGE receptor (RAGE)-overexpressed EC. Furthermore, AGE increased transcriptional activity of nuclear factor-kB (NF-kB) and activator protein-1 (AP-1) and then up-regulated mRNA levels of vascular endothelial growth factor (VEGF) and angiopoietin-2 (Ang-2) in EC. Cerivastatin, a hydroxymethylglutaryl CoA reductase inhibitor; pyrrolidinedithiocarbamate; or curcumin was found to completely prevent the AGE-induced increase in NF-kB and AP-1 activity, VEGF mRNA up-regulation, and the resultant increase in DNA synthesis in microvascular EC. These results suggest that the AGE-RAGE interaction elicited angiogenesis through the transcriptional activation of the VEGF gene via NF-kB and AP-1 factors. By blocking AGE-RAGE signaling pathways, cerivastatin might be a promising remedy for treating patients with proliferative diabetic retinopathy.

Angiogenesis Inducing Agents↗

PubMed2002

Incadronate disodium inhibits advanced glycation end products-induced angiogenesis in vitro.

We have previously shown that advanced glycation end products (AGE), senescent macroprotein derivatives formed at an accelerated rate in diabetes, induced angiogenesis through overgeneration of autocrine vascular endothelial growth factor (VEGF). In the present study, effects of incadronate disodium, a nitrogen-containing bisphosphonate on AGE-elicited angiogenesis in vitro, were studied. Incadronate disodium was found to completely inhibit AGE-induced increase in DNA synthesis as well as tube formation of human microvascular endothelial cells (EC). Furthermore, incadronate disodium significantly prevented transcriptional activation of nuclear factor-kappaB and activator protein-1 and the subsequent up-regulation of VEGF mRNA levels in AGE-exposed EC. Farnesyl pyrophosphate, but not geranylgeranyl pyrophosphate, was found to completely restore the anti-angiogenic effects of incadronate disodium on EC. These results suggest that incadronate disodium could block the AGE-signaling pathway in microvascular EC through inhibition of protein farnesylation. Incadronate disodium may be a promising remedy for treatment of patients with proliferative diabetic retinopathy.

Animals↗

PubMed2002

Expression of the suppressor of cytokine signaling-5 (SOCS5) negatively regulates IL-4-dependent STAT6 activation and Th2 differentiation.

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-4Ralpha 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.

Animals↗

PubMed2002

Activation of STAT3 by the hepatitis C virus core protein leads to cellular transformation.

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.

3T3 Cells↗

PubMed2002

Involvement of suppressor of cytokine signaling-3 as a mediator of the inhibitory effects of IL-10 on lipopolysaccharide-induced macrophage activation.

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-alpha, 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-alpha, 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-alpha 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.

Animals↗

PubMed2002

Target cell defense prevents the development of diabetes after viral infection.

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

Animals↗

PubMed2002

The apoptotic protease-activating factor 1-mediated pathway of apoptosis is dispensable for negative selection of thymocytes.

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.

Animals↗

PubMed2002

Stat3 beta inhibits gamma-globin gene expression in erythroid cells.

We demonstrated previously gamma-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 gamma gene silencing in erythroid cells. DNA-protein binding studies established Stat3 interaction in the 5'-untranslated gamma-globin promoter region. Furthermore, co-transfection experiments with Stat3 beta demonstrate gamma 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 gamma gene silencing through the STAT signal transduction pathway.

5' Untranslated Regions↗