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Results for “Signaling”

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At least 343 records · Page 19Linked to original sources

PubMed2004

Cognate B cell signaling via MHC class II: differential regulation of B cell antigen receptor and MHC class II/Ig-alpha beta signaling by CD22.

Recent studies demonstrate that MHC class II molecules can signal via associated Ig-alphabeta dimers, signal transducers previously thought to function only in B cell Ag receptor (BCR) signaling. Surprisingly, the biologic outputs of MHC class II and BCR ligation (by thymus-dependent Ags) differ, e.g., MHC class II signaling leads to robust proliferation and extension of pseudopods. It seemed possible that these differences might be due, at least in part, to differential use of inhibitory coreceptors thought to modulate membrane Ig signals. In this study, we demonstrate that CD22, an inhibitory BCR coreceptor, neither associates with nor functions in MHC class II/Ig-alphabeta signaling. Interestingly, CD22 is actively excluded from cell surface MHC class II aggregates.

Animals↗

PubMed1999

Mitogenic signaling by ATP/P2Y purinergic receptors in astrocytes: involvement of a calcium-independent protein kinase C, extracellular signal-regulated protein kinase pathway distinct from the phosphatidylinositol-specific phospholipase C/calcium pathway.

Activation of ATP/P2Y purinergic receptors stimulates proliferation of astrocytes, but the mitogenic signaling pathway linked to these G-protein-coupled receptors is unknown. We have investigated the role of extracellular signal-regulated protein kinase (ERK) in P2Y receptor-stimulated mitogenic signaling as well as the pathway that couples P2Y receptors to ERK. Downregulation of protein kinase C (PKC) in primary cultures of rat cerebral cortical astrocytes greatly reduced the ability of extracellular ATP to stimulate ERK. Because occupancy of P2Y receptors also leads to inositol phosphate formation, calcium mobilization, and PKC activation, we explored the possibility that signaling from P2Y receptors to ERK is mediated by a phosphatidylinositol-specific phospholipase C (PI-PLC)/calcium pathway. However, neither inhibition of PI-PLC nor chelation of calcium significantly reduced ATP-stimulated ERK activity. Moreover, a preferential inhibitor of calcium-dependent PKC isoforms, Gö 6976, was significantly less effective in blocking ATP-stimulated ERK activity than GF102903X, an inhibitor of both calcium-dependent and -independent PKC isoforms. Furthermore, ATP stimulated a rapid translocation of PKCdelta, a calcium-independent PKC isoform, but not PKCgamma, a calcium-dependent PKC isoform. ATP also stimulated a rapid increase in choline, and inhibition of phosphatidylcholine hydrolysis blocked ATP-evoked ERK activation. These results indicate that P2Y receptors in astrocytes are coupled independently to PI-PLC/calcium and ERK pathways and suggest that signaling from P2Y receptors to ERK involves a calcium-independent PKC isoform and hydrolysis of phosphatidylcholine by phospholipase D. In addition, we found that inhibition of ERK activation blocked extracellular ATP-stimulated DNA synthesis, thereby indicating that the ERK pathway mediates mitogenic signaling by P2Y receptors.

Animals↗

PubMed1999

CD22 cross-linking generates B-cell antigen receptor-independent signals that activate the JNK/SAPK signaling cascade.

CD22 is a B-cell-specific adhesion molecule that modulates BCR-mediated signal transduction. Ligation of human CD22 with monoclonal antibodies (MoAbs) that block the ligand binding site triggers rapid tyrosine phosphorylation of CD22 and primary B-cell proliferation. Because extracellular signal-regulated kinases (ERKs) couple upstream signaling pathways to gene activation and are activated by B-cell antigen receptor (BCR) signaling, we examined whether CD22 ligation also activated ERKs and/or modified BCR-induced ERK activation. Ligation of CD22 on either primary B cells or B-cell lines failed to significantly activate the mitogen activated protein kinase (MAPK) ERK-2, but did activate the stress-activated protein kinases (SAPKs; c-jun NH2-terminal kinases or JNKs). In contrast, BCR ligation resulted in ERK-2 activation without significant SAPK activation. Concurrent ligation of CD22 and BCR enhanced BCR-mediated ERK-2 activation without appreciably modulating CD22-induced SAPK activation. Consistent with its induction of SAPK activity, there was a marked increase in nuclear extracts of activator protein-1 (AP-1) and c-jun levels within 2 hours of exposure of primary B cells to the CD22 MoAb. Despite their differences in ERK activation, both CD22 and BCR ligation triggered several Burkitt lymphoma cell lines to undergo apoptosis, and the 2 stimuli together induced greater cell death than either signal alone. The pro-apoptotic effects were CD22-blocking MoAb-specific and dose-dependent. Examination of expression levels of Bcl-2 protoncogene family members (Bcl-2, Bcl-x(L), Mcl-1, and Bax) showed a downregulation of Bcl-x(L) and Mcl-1 after CD22 ligation. This study provides a plausible mechanism to explain how CD22 and BCR signaling can costimulate B-cell proliferation and induce apoptosis in Burkitt lymphoma cell lines.

Antigens, CD↗

PubMed2000

Function- and agonist-specific Ca2+ signalling: the requirement for and mechanism of spatial and temporal complexity in Ca2+ signals.

Calcium signals have been implicated in the regulation of many diverse cellular processes. The problem of how information from extracellular signals is delivered with specificity and fidelity using fluctuations in cytosolic Ca2+ concentration remains unresolved. The capacity of cells to generate Ca2+ signals of sufficient spatial and temporal complexity is the primary constraint on their ability to effectively encode information through Ca2+. Over the past decade, a large body of literature has dealt with some basic features of Ca2+-handling in cells, as well as the multiplicity and functional diversity of intracellular Ca2+ stores and extracellular Ca2+ influx pathways. In principle, physiologists now have the necessary information to attack the problem of function- and agonist-specificity in Ca2+ signal transduction. This review explores the data indicating that Ca2+ release from diverse sources, including many types of intracellular stores, generates Ca2+ signals with sufficient complexity to regulate the vast number of cellular functions that have been reported as Ca2+-dependent. Some examples where such complexity may relate to neuroendocrine regulation of hormone secretion/synthesis are discussed. We show that the functional and spatial heterogeneity of Ca2+ stores generates Ca2+ signals with sufficient spatiotemporal complexity to simultaneously control multiple Ca2+-dependent cellular functions in neuroendocrine systems.

Animals↗

PubMed2003

Lipid peroxidation and cell cycle signaling: 4-hydroxynonenal, a key molecule in stress mediated signaling.

Role of lipid peroxidation products, particularly 4-hydroxynonenal (4-HNE) in cell cycle signaling is becoming increasingly clear. In this article, recent studies suggesting an important role of 4-HNE in stress mediated signaling for apoptosis are critically evaluated. Evidence demonstrating the modulation of UV, oxidative stress, and chemical stress mediated apoptosis by blocking lipid peroxidation by the alpha-class glutathione S-transferases (GSTs) is presented which suggest an important role of these enzymes in protection against oxidative stress and a role of lipid peroxidation products in stress mediated signaling. Overexpression of 4-HNE metabolizing GSTs (mGSTA4-4, hGSTA4-4, or hGST5.8) protects cells against 4-HNE, oxidative stress (H(2)O(2) or xanthine/xanthine oxidase), and UV-A mediated apoptosis by blocking JNK and caspase activation suggesting a role of 4-HNE in the mechanisms of apoptosis caused by these stress factors. The intracellular concentration of 4-HNE appears to be crucial for the nature of cell cycle signaling and may be a determinant for the signaling for differentiation, proliferation, transformation, or apoptosis. The intracellular concentrations of 4-HNE are regulated through a coordinated action of GSTs (GSTA4-4 and hGST5.8) which conjugate 4-HNE to GSH to form the conjugate (GS-HNE) and the transporter 76 kDa Ral-binding GTPase activating protein (RLIP76), which catalyze ATP-dependent transport of GS-HNE. A mild stress caused by heat, UV-A, or H(2)O(2)with no apparent effect on the cells in culture causes a rapid, transient induction of hGST5.8 and RLIP76. These stress preconditioned cells acquire ability to metabolize and exclude 4-HNE at an accelerated pace and acquire relative resistance to apoptosis by UV and oxidative stress as compared to unconditioned control cells. This resistance of stress preconditioned cells can be abrogated by coating the cells with anti-RLIP76 antibodies which block the transport of GS-HNE. These studies and previous reports discussed in this article strongly suggest a key role of 4-HNE in stress mediated signaling.

ATP-Binding Cassette Transporters↗

PubMed1992

Single amino acid substitutions can convert the uncleaved signal-anchor of sucrase-isomaltase to a cleaved signal sequence.

A hydrophobic segment near the amino terminus (positions 12-32) of rabbit sucrase-isomaltase functions both as a membrane anchor and as a signal sequence for translocation into the endoplasmic reticulum. Unlike most signal sequences, that of sucrase-isomaltase is not cleaved by signal peptidase. Using in vitro transcription and translation systems, we have found that substitution of a single proline, at position 28 or 29, converted the signal-anchor to a cleaved signal sequence, with cleavage occurring after alanine 26 and the introduced proline thereby occupying position +2 or +3 relative to the cleavage site. Two deletions that shorten the transmembrane domain by 8 amino acids were also effective, whereas various other changes upstream and downstream of this domain were without effect. We conclude that susceptibility to mammalian signal peptidase is influenced both by the length of the hydrophobic region and by the secondary structure downstream of the cleavage site.

Amino Acid Sequence↗

PubMed1993

The CD19 signal transduction complex of B lymphocytes. Deletion of the CD19 cytoplasmic domain alters signal transduction but not complex formation with TAPA-1 and Leu 13.

CD19 expressed on the surface of B lymphocytes is a key member of a cell surface signal transduction complex that includes TAPA-1, Leu 13 and CD21. The human CD19 protein is composed of 540 amino acids with a cytoplasmic domain of 242 amino acids. Although the cytoplasmic domain of CD19 has no sequence homology with other proteins, the cytoplasmic domain of human, mouse, and guinea pig CD19 is highly conserved suggesting that this region of CD19 is at least partially responsible for signaling activity. In this study, the regions of CD19 required for intermolecular associations and signal transduction were determined by comparing a series of carboxyl-terminal cytoplasmic tail deletion mutants and a CD19/L-selectin chimera with native CD19. CD19 expressed in the human Rex T cell line and the K562 erythroleukemia cell line generated transmembrane signals and also associated with endogenous TAPA-1. Deletion of 95% of the CD19 cytoplasmic domain did not affect the ability of CD19 to be expressed or to associate with TAPA-1. However, replacement of the CD19 transmembrane and cytoplasmic domains with those of L-selectin (CD19-LAM) resulted in the loss of CD19 complex formation, suggesting that the membrane spanning domain is critical for this association. Similarly, the induction of homotypic adhesion through CD19 or truncated CD19 was equivalent, whereas homotypic adhesion was not induced via the CD19-LAM chimera. In addition, the cytoplasmic domain was not necessary for CD19 mAb-mediated growth inhibition or internalization. In contrast, the CD19 cytoplasmic domain was required for optimal mAb-induced increases in [Ca2+]i in CD19 cDNA-transfected Rex cells. Thus, the CD19 cytoplasmic domain is responsible for the induction of increased [Ca2+]i, and the transmembrane region is required for cell surface associations with the other members of the CD19 complex and most signaling events. Therefore, mAb binding to CD19 is likely to initiate multiple intracellular signal transduction cascades either through CD19 directly, or through other members of the CD19 complex.

Antigens, CD↗

PubMed1993

Human coagulation factor X deficiency caused by a mutant signal peptide that blocks cleavage by signal peptidase but not targeting and translocation to the endoplasmic reticulum.

Human factor XSanto Domingo is a form of coagulation factor X in which a mutation within the signal peptide region of the precursor protein has been correlated genetically with a severe deficiency of factor X in the affected individual. A point mutation results in substitution of Arg for Gly at the critical -3 position of the factor X signal peptide. To determine the biochemical effect of this mutation on the biosynthesis of factor X, the wild-type and mutant factor X cDNAs were subcloned into a vector for transcription and translation in vitro. Translation products of mRNAs encoding portions of both mutant and wild-type proteins were used in a systematic biochemical approach to evaluate directly the effect of the mutation on targeting, transport, and proteolytic processing in vitro. The results show that targeting and transport of factor XSanto Domingo to the endoplasmic reticulum are functionally dissociated from the removal of the signal peptide by signal peptidase. Factor XSanto Domingo is translocated into the endoplasmic reticulum but not processed by signal peptidase. Transient expression of the wild-type and mutant factor X in human embryonic kidney 293 cells revealed apparently normal secretion of the glycosylated two-chain form of factor X but no secretion of factor XSanto Domingo. Thus, the inability of signal peptidase to cleave factor XSanto Domingo is directly responsible for the absence of circulating factor X and leads to the bleeding diathesis in the affected individual.

Amino Acid Sequence↗

PubMed1998

Signal transduction pathways activated by the IL-1 receptor family: ancient signaling machinery in mammals, insects, and plants.

Interleukin-1 (IL-1) is a central regulator of the immune and inflammatory responses. Recently, significant advances have been made in the area of IL-1 receptors and IL-1 signal transduction. A family of proteins has been described that share significant homology in their signaling domains with the Type I IL-1 receptor (IL-1RI). These include the IL-1 receptor accessory protein (IL-1AcP), which does not bind IL-1 but is essential for IL-1 signaling; a Drosophila protein Toll; a number of human Toll-like receptors (hTLRs); the putative IL-18/IL-1-gamma receptor IL-1Rrp (IL-1 receptor-related protein); and a number of plant proteins. All appear to be involved in host responses to injury and infection. These homologies also extend to novel signaling proteins implicated in IL-1 action. Two IL-1 receptor-associated kinases, IRAK-1 and IRAK-2, which have homologs in Drosophila (Pelle) and plants (Pto), have been implicated in the activation of the transcription factor, nuclear factor kappaB (NF-kappaB). IRAK-1 has also been implicated in AP1 induction, Jun amino-terminal kinase (JNK) activation, and IL-2 induction. It recruits the adapter protein TRAF6 to the IL-1 receptor complex via an interaction with IL-1AcP. TRAF6 then relays the signal via NF-kappaB-inducing kinase (NIK) to two I-kappaB kinases (IKK-1 and -2), leading to NF-kappaB activation. Progress has also been made on other IL-1-responsive kinases, including JNK and p38 MAP kinase, with the latter having a role in multiple responses to IL-1. The remarkable conservation between diverse species indicates that the IL-1 system represents an ancient signaling machine critical for responses to environmental stresses and attack by pathogens.

Amino Acid Sequence↗

PubMed2006

Regulation of IL-21 signaling by suppressor of cytokine signaling-1 (SOCS1) in CD8(+) T lymphocytes.

Mice lacking the gene for suppressor of cytokine signaling 1 (SOCS1) show defective homeostasis of T lymphocytes due to accumulation of CD8(+) T cells, resulting at least partly from dysregulated IL-15 signaling. IL-15 alone does not stimulate proliferation of naïve CD8 T cells, but can synergize with IL-21 to induce proliferation, suggesting a potential role for IL-21 in the defective homeostasis of CD8(+) T lymphocytes in SOCS1(-/-) mice. Since IL-21 strongly induced SOCS1 mRNA in CD8(+) T cells, we investigated whether SOCS1 regulates their response to IL-21. CD8(+) T cells isolated from SOCS1-deficient mice proliferated vigorously in response to IL-21+IL-15. In CD8(+) T lymphocytes expressing transgenic TCR, IL-21+IL-7 provided a stronger stimulus to naïve cells whereas IL-15+IL-21 potently stimulated memory cells. Compared to truly naïve or memory cells, SOCS1(-/-) H-Y TCR(+) CD8(+) T cells displayed CD44(lo)Ly6C(hi)CD122(int)CD127(lo) partial memory phenotype and exhibited stronger response to IL-15+IL-21 than truly naïve cells. In SOCS1(-/-) CD8(+) T cells, IL-21 caused greater reduction in IL-15 threshold for activation in a dose-dependent manner. SOCS1 deficiency did not modulate IL-21Ralpha expression or sensitivity to IL-21, but delayed the loss of IL-21-induced phospho-STAT3 signal. These results show that SOCS1 is a critical regulator of IL-21 signaling in CD8(+) T cells, and support the notion that sustained IL-21 signaling might also contribute to the aberrant T cell homeostasis in SOCS1-deficient mice.

Animals↗

PubMed2006

Suppressor of cytokine signaling-1 is an IL-4-inducible gene in macrophages and feedback inhibits IL-4 signaling.

Interferon-gamma and interleukin-4 (IL-4) induce distinct gene expression profiles in macrophages by differentially activating signal transducers and activators of transcription (STAT)1 and STAT6, respectively. The role of suppressor of cytokine signaling (SOCS)-1 as a negative regulator of IFN-gamma signaling is well established. However, its potential role as a negative regulator of IL-4 signaling has not been explored. We found that IL-4, like IFN-gamma, induces rapid de novo expression of SOCS-1 in primary macrophages. Induction of SOCS-1 gene expression by IL-4 is STAT6-dependent, whereas induction of SOCS-1 by IFN-gamma is STAT1-dependent. Unlike their common ability to induce expression of SOCS-1, IL-4 also induced expression of SOCS-2 but not SOCS-3 in macrophages, whereas IFN-gamma induced expression of SOCS-3 but not SOCS-2. Forced expression of SOCS-1 or SOCS-3, but not SOCS-2, inhibited activation of STAT6 by IL-4. Moreover, SOCS-1 appears to serve as an endogenous regulator of IL-4 signaling in macrophages because the magnitude and duration of STAT6 activation as well as IL-4-mediated gene expression were much greater in SOCS-1-deficient (SOCS-1(-/-)) macrophages than in wild-type macrophages. Our findings demonstrate that, like IFN-gamma, IL-4 also induces expression of SOCS-1 in macrophages, and SOCS-1 feedback inhibits expression of STAT6-responsive genes.

Animals↗

PubMed2006

Suppressor of cytokine signaling 3 limits protection of leukemia inhibitory factor receptor signaling against central demyelination.

Enhancement of oligodendrocyte survival through activation of leukemia inhibitory factor receptor (LIFR) signaling is a candidate therapeutic strategy for demyelinating disease. However, in other cell types, LIFR signaling is under tight negative regulation by the intracellular protein suppressor of cytokine signaling 3 (SOCS3). We, therefore, postulated that deletion of the SOCS3 gene in oligodendrocytes would promote the beneficial effects of LIFR signaling in limiting demyelination. By studying wild-type and LIF-knockout mice, we established that SOCS3 expression by oligodendrocytes was induced by the demyelinative insult, that this induction depended on LIF, and that endogenously produced LIF was likely to be a key determinant of the CNS response to oligodendrocyte loss. Compared with wild-type controls, oligodendrocyte-specific SOCS3 conditional-knockout mice displayed enhanced c-fos activation and exogenous LIF-induced phosphorylation of signal transducer and activator of transcription 3. Moreover, these SOCS3-deficient mice were protected against cuprizone-induced oligodendrocyte loss relative to wild-type animals. These results indicate that modulation of SOCS3 expression could facilitate the endogenous response to CNS injury.

Animals↗

PubMed2001

Suppressor of cytokine signaling-1 attenuates the duration of interferon gamma signal transduction in vitro and in vivo.

Suppressor of cytokine signaling-1 (SOCS-1) is a cytokine-inducible intracellular protein that functions to negatively regulate cytokine signal transduction pathways. Studies in vitro have shown that constitutive overexpression of SOCS-1 inhibits signaling in response to a range of cytokines, including interferons (IFN). Mice lacking SOCS-1 die from a complex disease characterized by liver degeneration and massive inflammation. Whereas there is clear evidence of increased IFNgamma signaling in SOCS-1(-/-) mice, it is unclear to what extent this is due to increased IFNgamma levels or to increased IFNgamma sensitivity. Here we have used SOCS-1(-/-) IFNgamma(-/-) mice, which remain healthy and produce no endogenous IFNgamma, to demonstrate that in vitro and in vivo hepatocytes lacking SOCS-1 exhibit a prolonged response to IFNgamma and that this correlates with a dramatically increased sensitivity to the toxic effects of IFNgamma in vivo. Thus, SOCS-1 is required for the timely attenuation of IFNgamma signaling in vivo.

Animals↗

PubMed2001

Defective gp130-mediated signal transducer and activator of transcription (STAT) signaling results in degenerative joint disease, gastrointestinal ulceration, and failure of uterine implantation.

The receptor subunit gp130 transduces multiple cell type-specific activities of the leukemia inhibitory factor (LIF)/interleukin (IL)-6 family of cytokines through the signal transducer and activator of transcription (STAT) and src homology 2 domain-bearing protein tyrosine phosphatase (SHP)-2/ras/Erk pathways. To define STAT-dependent physiological responses, we generated mice with a COOH-terminal gp130(DeltaSTAT) "knock-in" mutation which deleted all STAT-binding sites. gp130(DeltaSTAT) mice phenocopyed mice deficient for IL-6 (impaired humoral and mucosal immune and hepatic acute phase responses) and LIF (failure of blastocyst implantation). However, unlike mice with null mutations in any of the components in the gp130 signaling pathway, gp130(DeltaSTAT) mice also displayed gastrointestinal ulceration and a severe joint disease with features of chronic synovitis, cartilaginous metaplasia, and degradation of the articular cartilage. Mitogenic hyperresponsiveness of synovial cells to the LIF/IL-6 family of cyto-kines was caused by sustained gp130-mediated SHP-2/ras/Erk activation due to impaired STAT-mediated induction of suppressor of cytokine signaling (SOCS) proteins which normally limits gp130 signaling. Therefore, the joint pathology in gp130(DeltaSTAT) mice is likely to arise from the disturbance of the otherwise balanced activation of the SHP-2/ras/Erk and STAT signaling cascades emanating from gp130.

Animals↗

PubMed2005

Integration of G protein signals by extracellular signal-regulated protein kinases in SK-N-MC neuroepithelioma cells.

Mammalian cells often receive multiple extracellular stimuli under physiological conditions, and the various signaling inputs have to be integrated for the processing of complex biological responses. G protein-coupled receptors (GPCRs) are critical players in converting extracellular stimuli into intracellular signals. In this report, we examined the integration of different GPCR signals by mitogen-activated protein kinases (MAPKs) using the SK-N-MC human brain neuroepithelioma cells as a neuronal model. Stimulation of the Gi-coupled neuropeptide Y1 and Gq-coupled muscarinic M1 acetylcholine receptors, but not the Gs-coupled dopamine D1 receptor, led to the activation of extracellular signal-regulated kinase (ERK). All three receptors were also capable of stimulating c-Jun NH2-terminal kinases (JNK) and p38 MAPK. The Gi-mediated ERK activation was completely suppressed upon inhibition of Src tyrosine kinases by PP1, while the Gq-induced response was suppressed by both PP1 and the Ca2+ chelator, BAPTA-AM. In contrast, activations of JNK and p38 by Gs-, Gi-, and Gq-coupled receptors were sensitive to PP1 and BAPTA-AM pretreatments. Simultaneous stimulation of Gi- and Gq-coupled receptors resulted in the synergistic activation of ERK, but not JNK or p38 MAPK. The Gi/Gq-induced synergistic ERK activation was PTX-sensitive, and appeared to be a co-operative effect between Ca2+ and Src family tyrosine kinases. Enhanced ERK activation was associated with an increase in CREB phosphorylation, while the JNK and p38-responsive transcription factor ATF-2 was weakly enhanced upon Gi/Gq-induction. This report provides evidence that G protein signals can be integrated at the level of MAPK, resulting in differential effects on ERK, JNK and p38 MAPK in SK-N-MC cells.

Adenylyl Cyclases↗

PubMed2001

The Caenorhabditis elegans EGL-15 signaling pathway implicates a DOS-like multisubstrate adaptor protein in fibroblast growth factor signal transduction.

EGL-15 is a fibroblast growth factor receptor in the nematode Caenorhabditis elegans. Components that mediate EGL-15 signaling have been identified via mutations that confer a Clear (Clr) phenotype, indicative of hyperactivity of this pathway, or a suppressor-of-Clr (Soc) phenotype, indicative of reduced pathway activity. We have isolated a gain-of-function allele of let-60 ras that confers a Clr phenotype and implicated both let-60 ras and components of a mitogen-activated protein kinase cascade in EGL-15 signaling by their Soc phenotype. Epistasis analysis indicates that the gene soc-1 functions in EGL-15 signaling by acting either upstream of or independently of LET-60 RAS. soc-1 encodes a multisubstrate adaptor protein with an amino-terminal pleckstrin homology domain that is structurally similar to the DOS protein in Drosophila and mammalian GAB1. DOS is known to act with the cytoplasmic tyrosine phosphatase Corkscrew (CSW) in signaling pathways in Drosophila. Similarly, the C. elegans CSW ortholog PTP-2 was found to be involved in EGL-15 signaling. Structure-function analysis of SOC-1 and phenotypic analysis of single and double mutants are consistent with a model in which SOC-1 and PTP-2 act together in a pathway downstream of EGL-15 and the Src homology domain 2 (SH2)/SH3-adaptor protein SEM-5/GRB2 contributes to SOC-1-independent activities of EGL-15.

Animals↗

PubMed2002

The UV (Ribotoxic) stress response of human keratinocytes involves the unexpected uncoupling of the Ras-extracellular signal-regulated kinase signaling cascade from the activated epidermal growth factor receptor.

In mammals, UVB radiation is of biological relevance primarily for the cells of the epidermis. We report here the existence of a UVB response that is specific for proliferating human epidermal keratinocytes. Unlike other cell types that also display a UVB response, keratinocytes respond to UVB irradiation with a transient but potent downregulation of the Ras-extracellular signal-regulated kinase (ERK) signaling cascade. The downregulation of ERK precedes a profound decrease in the steady-state levels of cyclin D1, a mediator of the proliferative action of ERK. Keratinocytes exhibit high constitutive activity of the Ras-ERK signaling cascade even in culture medium lacking supplemental growth factors. The increased activity of Ras and phosphorylation of ERK in these cells are maintained by the autocrine production of secreted molecules that activate the epidermal growth factor receptor (EGFR). Irradiation of keratinocytes increases the phosphorylation of EGFR on tyrosine residues Y845, Y992, Y1045, Y1068, Y1086, Y1148, and Y1173 above the basal levels and leads to the increased recruitment of the adaptor proteins Grb2 and ShcA and of a p55 form of the regulatory subunit of the phosphatidylinositide 3-kinase to the UVB-activated EGFR. Paradoxically, however, UVB causes, at the same time, the inactivation of Ras and a subsequent dephosphorylation of ERK. By contrast, the signaling pathway leading from the activated EGFR to the phosphorylation of PKB/Akt1 is potentiated by UVB. The UVB response of keratinocytes appeared to be a manifestation of the more general ribotoxic stress response inasmuch as the transduction of the UVB-generated inhibitory signal to Ras and ERK required the presence of active ribosomes at the time of irradiation.

Adaptor Proteins, Signal Transducing↗

PubMed2002

The effect of suppressor of cytokine signaling 3 on GH signaling in beta-cells.

GH is an important regulator of cell growth and metabolism. In the pancreas, GH stimulates mitogenesis as well as insulin production in beta-cells. The cellular effects of GH are exerted mainly through activation of the Janus kinase-signal transducer and activator of transcription (STAT) pathway. Recently it has been found that suppressors of cytokine signaling (SOCS) proteins are able to inhibit GH-induced signal transduction. In the present study, the role of SOCS-3 in GH signaling was investigated in the pancreatic beta-cell lines RIN-5AH and INS-1 by means of inducible expression systems. Via stable transfection of the beta-cell lines with plasmids expressing SOCS-3 under the control of an inducible promoter, a time- and dose-dependent expression of SOCS-3 in the cells was obtained. EMSA showed that SOCS-3 is able to inhibit GH-induced DNA binding of both STAT3 and STAT5 in RIN-5AH cells. Furthermore, using Northern blot analysis it was shown that SOCS-3 can completely inhibit GH-induced insulin production in these cells. Finally, 5-bromodeoxyuridine incorporation followed by fluorescence-activated cell sorting analysis showed that SOCS-3 inhibits GH-induced proliferation of INS-1 cells. These findings support the hypothesis that SOCS-3 is a major regulator of GH signaling in insulin-producing cells.

Cell Division↗