Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P31749 (AKT)
 22,954 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In order to better define the role of HIV-related chemokines in human erythropoiesis we studied: A) the expression of chemokine receptors, both on human CD34(+) cells which include erythroid progenitors and on more mature erythroid cells; B) the functionality of these receptors by calcium flux, chemotaxis assay and phosphorylation of mitogen-activated protein kinases (MAPK) p42/44 (ERK1/ERK2) and AKT, and finally C) the influence of chemokines on BFU-E formation. We found that HIV-related chemokine receptor CXCR4, but not CCR5, is detectable on human CD34(+) BFU-E cells. CXCR4 surface expression decreased during erythroid maturation, although CXCR4 mRNA was still present in cells isolated from differentiated erythroid colonies. SDF-1, a CXCR4 ligand, induced calcium flux and phosphorylation of MAPK (p42/44) and AKT in CD34(+)KIT(+) bone marrow mononuclear cells which contain BFU-E, as well as chemotactic activity of both human CD34(+) BFU-E progenitors and erythroid cells isolated from day 2-6 BFU-E colonies. Responsiveness to SDF-1 decreased when the cells differentiated to the point of surface expression of the erythroid-specific marker Glycophorin-A. In contrast, the CCR5 ligands (macrophage inflammatory protein-1alpha [MIP-1alpha], MIP-1beta, and RANTES) did not activate calcium flux, MAPK and AKT phosphorylation or chemotaxis of CD34(+)KIT(+) cells or cells isolated from the BFU-E colonies. Interestingly, none of the chemokines tested in this study had any effect on BFU-E colony formation. In conclusion, only CXCR4 is functional, and its specific ligand SDF-1 may therefore play an important role in the homing and/or retention of early erythroid precursors in the bone marrow environment.
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PMID:The role of HIV-related chemokine receptors and chemokines in human erythropoiesis in vitro. 1074 85

The role of the chemokine binding stromal-derived factor 1 (SDF-1) in normal human megakaryopoiesis at the cellular and molecular levels and its comparison with that of thrombopoietin (TPO) have not been determined. In this study it was found that SDF-1, unlike TPO, does not stimulate alpha(IIb)beta(3)(+) cell proliferation or differentiation or have an antiapoptotic effect. However, it does induce chemotaxis, trans-Matrigel migration, and secretion of matrix metalloproteinase 9 (MMP-9) and vascular endothelial growth factor (VEGF) by these cells, and both SDF-1 and TPO increase the adhesion of alpha(IIb)beta(3)(+) cells to fibrinogen and vitronectin. Investigating the intracellular signaling pathways induced by SDF-1 and TPO revealed some overlapping patterns of protein phosphorylation/activation (mitogen-activated protein kinase [MAPK] p42/44, MAPK p38, and AKT [protein kinase B]) and some that were distinct for TPO (eg, JAK-STAT) and for SDF-1 (eg, NF-kappa B). It was also found that though inhibition of phosphatidyl-inositol 3-kinase (PI-3K) by LY294002 in alpha(IIb)beta(3)(+) cells induced apoptosis and inhibited chemotaxis adhesion and the secretion of MMP-9 and VEGF, the inhibition of MAPK p42/44 (by the MEK inhibitor U0126) had no effect on the survival, proliferation, and migration of these cells. Hence, it is suggested that the proliferative effect of TPO is more related to activation of the JAK-STAT pathway (unique to TPO), and the PI-3K-AKT axis is differentially involved in TPO- and SDF-1-dependent signaling. Accordingly, PI-3K is involved in TPO-mediated inhibition of apoptosis, TPO- and SDF-1-regulated adhesion to fibrinogen and vitronectin, and SDF-1-mediated migration. This study expands the understanding of the role of SDF-1 and TPO in normal human megakaryopoiesis and indicates the molecular basis of the observed differences in cellular responses. (Blood. 2000;96:4142-4151)
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PMID:Stromal-derived factor 1 and thrombopoietin regulate distinct aspects of human megakaryopoiesis. 1111 Jun 85

The aim of this study was to learn more on the role of chemokines in the regulation of human megakryopoiesis. Normal human megakaryoblasts were expanded in serum-free liquid cultures and subsequently (1) phenotyped for expression of various chemokine receptors, (2) evaluated if chemokine receptors which they express are functional after stimulation by chemokines (calcium flux assay, chemotaxis, phosphorylation of MAPK-p42/44 and AKT proteins), and (3) investigated for expression and secretion of selected chemokines by employing RT-PCR and ELISA assays, respectively. In addition we also phenotyped peripheral blood platelets for expression of chemokine receptors and chemokines. We found that while human megakaryoblasts express several chemokine receptors (CXCR4, CCR6, CCR8, CCR5, CCR2 and CXCR3), CXCR4 was the only receptor detectable by FACS on human platelets. Moreover, among various chemokines tested, only SDF-1 (CXCR4 ligand) stimulated calcium flux and chemotaxis in normal human megakaryoblasts and phosphorylated MAPK-p42/44 and AKT in these cells. Although mRNAs for several chemokines were detectable by RT-PCR in normal human megakaryoblasts, only RANTES, IL-8, MCP-1 and PF-4 were found to be secreted by these cells. Finally we noticed that no chemokine tested in this study affected CFU-Meg colony formation by human CD34+ cells in serum-free cultures. We conclude that from all the chemokine receptor-chemokine axes tested, only SDF-1-CXCR4 axis was functional in assays employed in our studies, which further support the view that this axis plays a privileged role in regulating normal human megakaryopoiesis.
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PMID:Biological significance of chemokine receptor expression by normal human megakaryoblasts. 1153 79

To better define the role HIV-related chemokine receptor-chemokine axes play in human hematopoiesis, we investigated the function of the CXCR4 and CCR5 receptors in human myeloid, T- and B-lymphoid cell lines selected for the expression of these receptors (CXCR4(+), CXCR4(+) CCR5(+), and CCR5(+) cell lines). We evaluated the phosphorylation of MAPK p42/44, AKT, and STAT proteins and examined the ability of the ligands for these receptors (stromal-derived factor-1 [SDF-1] and macrophage inflammatory protein-1beta [MIP-1beta]) to influence cell growth, apoptosis, adhesion, and production of vascular endothelial growth factors (VEGF), matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in these cell lines. We found that A) SDF-1, after binding to CXCR4, activates multiple signaling pathways and that in comparison with the MIP-1beta-CCR5 axis, plays a privileged role in hematopoiesis; B) SDF-1 activation of the MAPK p42/44 pathway and the PI-3K-AKT axis does not affect proliferation and apoptosis but modulates integrin-mediated adhesion to fibronectin, and C) SDF-1 induces secretion of VEGF, but not of MMPs or TIMPs. Thus the role of SDF-1 relates primarily to the interaction of lymphohematopoietic cells with their microenvironment and does not directly influence their proliferation or survival. We conclude that perturbation of the SDF-1-CXCR4 axis during HIV infection may affect interactions of hematopoietic cells with the hematopoietic microenvironment.
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PMID:The SDF-1-CXCR4 axis stimulates VEGF secretion and activates integrins but does not affect proliferation and survival in lymphohematopoietic cells. 1155 54

We identified five human T-lymphoid cell lines (PB-1, Sez-4, C19PL, HUT 102B and ATL-2) which highly express CD4 in addition to CXCR4 and CCR5. In order to evaluate if these cells are infectabile by human immunodeficiency virus (HIV) and could be employed as a model in HIV research we exposed these cell lines to X4 (T-cell tropic) and R5 (macrophage tropic) and subsequently tried to correlate their infectability with (i) level of chemokine coreceptor (CXCR4 and CCR5) expression, (ii) coreceptor functionality (calcium flux, chemotaxis and phosphorylation of MAPK p42/44 and AKT) and (iii) endogenous expression and secretion of HIV-related chemokines which compete with the virus for binding to CXCR4 (SDF-1/CXCL12) or CCR5 (MIP-1beta/CCL4, MIP-1alpha/CCL3, RANTES/CCL5, MCP-2/CCL8, MCP-3/CCL7 and MCP-4/CCL13). We demonstrated that while PB-1 cells are infectable by both X4 and R5 HIV, Sez-4, C91PL, HUT 102B and ATL-2 cells were infected by X4 HIV only. Moreover, we noticed that the susceptibility of these cells to HIV did not correspond either with the level of surface expression or with the functionality of CXCR4 or CCR5; however, it was modulated to some degree by the endogenously secreted HIV-related chemokines. Thus all five mature T-cell lines described here may provide useful new models for studying various aspects of HIV infection. In addition we demonstrate that the infectability of cells by HIV is modulated by so far unidentified intrinsic factors as well as some already known endogenously secreted chemokines. The identification of these factors may be important for developing new strategies to protect cells from HIV infection.
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PMID:New T-lymphocytic cell lines for studying cell infectability by human immunodeficiency virus. 1173 46

T cells migrate into inflamed sites through the extracellular matrix (ECM) in response to chemotactic areas and are then simultaneously or sequentially exposed to multiple chemotactic ligands. We examined the responses of human peripheral blood T cells, present in an ECM-like context, to combinatorial signaling transduced by SDF-1alpha (CXCL12), and two CCR5 ligands, RANTES (CCL5) and MIP-1beta (CCL4). Separately, these chemokines, at G protein-coupled receptor (GPCR)-stimulating concentrations, induced T cell adhesion to fibronectin (FN) and T cell chemotaxis. However, the pro-adhesive and pro-migratory capacities of SDF-1alpha and RANTES or MIP-1beta were mutually suppressed by the simultaneous or sequential exposure of the cells to these CCR5 or CXCR4 ligands. This cross-talk did not involve the internalization of the SDF-1alpha receptor, CXCR4, but rather, a decrease in phosphorylation of ERK and Pyk-2, as well as inhibition of Ca(2+) mobilization. Strikingly, early CXCR4 signaling of phosphatidylinositol-3-kinase, detected by SDF-1alpha-induced AKT phosphorylation, was insensitive to RANTES-CCR5 signals. Accordingly, early chemotaxis to SDF-1alpha was not susceptible to CCR5 occupancy, whereas late stages of T cell chemotaxis were markedly down-regulated. This is an example of a specialized functional desensitization of heterologous chemokine receptors that induces GPCR interference with T cell adhesion to ECM ligands and chemotaxis within chemokine-rich extravascular contexts.
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PMID:Heterologous desensitization of T cell functions by CCR5 and CXCR4 ligands: inhibition of cellular signaling, adhesion and chemotaxis. 1250 23

The trans-differentiation hypothesis of adult tissue-specific stem cells has been recently questioned because of insufficient proof that the so-called plasticity experiments were performed on pure populations of tissue-specific stem cells. It was shown recently, for example, that the formation of haematopoietic colonies by muscle cells depended on the presence of haematopoietic stem/progenitor cells residing within the muscle tissue and hence was not related to the plasticity of the muscle stem cells. The explanation for the presence in, or homing into, muscles of haematopoietic stem cells is, however, not clear. In our study, we hypothesised that muscle tissues secrete stromal-derived factor (SDF)- 1, an alpha-chemokine for haematopoietic stem cells (HSC), which could attract HSC circulating in peripheral blood into muscle tissue. We found, using RT-PCR and immunocytochemistry, that SDF-1 was expressed in human heart and skeletal muscles. Moreover, muscle satellite cells, which are pivotal for regeneration of muscle, highly expressed on their surface CXCR4, a G-protein-coupled receptor that binds SDF-1. To determine whether the CXCR4 receptor is functional on muscle satellite/progenitor cells, we stimulated murine satellite cells (the C2C12 cell line) with SDF-1 and demonstrated the phosphorylation of p42/44 MAPK and AKT serine-threonine kinase in these cells. Moreover, we showed that SDF-1 gradient chemoattracts these cells. We postulate that the CXCR4-positive muscle satellite and CXCR4-positive HSC circulating in the peripheral blood compete for occupancy of SDF-1-positive stem cell niches that are present in bone marrow and muscle tissues. Thus, we suggest that competition for common niches by various circulating CXCR4-positive stem cells and their ability to home to the SDF-1-positive niches in various organs, is a better explanation than stem cell plasticity of why (i) haematopoietic colonies can be cultured from muscles and (ii) early muscle progenitors could be cultured from bone marrow.
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PMID:Circulating CXCR4-positive stem/progenitor cells compete for SDF-1-positive niches in bone marrow, muscle and neural tissues: an alternative hypothesis to stem cell plasticity. 1270 74

We found that the murine cell lines C2C12 and G7 derived from muscle satellite cells, which are essential for muscle regeneration, express the functional CXCR4 receptor on their surface and that the specific ligand for this receptor, alpha-chemokine stromal-derived factor 1 (SDF-1), is secreted in muscle tissue. These cell lines responded to SDF-1 stimulation by chemotaxis, phosphorylation of mitogen-activated protein kinase (MAPK) p42/44 and AKT serine-threonine kinase, and calcium flux, confirming the functionality of the CXCR4 receptor. Moreover, supernatants derived from muscle fibroblasts chemoattracted both satellite cells and human CD34(+) hematopoietic stem/progenitor cells. In a similar set of experiments, supernatants from bone marrow fibroblasts were found to chemoattract CXCR4(+) satellite cells just as they chemoattract CD34(+) cells. Moreover, preincubation of both muscle satellite cells and hematopoietic stem/progenitor CD34(+) cells before chemotaxis with T140, a specific CXCR4 inhibitor, resulted in a significantly lower chemotaxis to media conditioned by either muscle- or bone marrow-derived fibroblasts. Based on these observations, we postulate that the SDF-1-CXCR4 axis is involved in chemoattracting circulating CXCR4(+) muscle stem/progenitor and circulating CXCR4(+) hematopoietic CD34(+) cells to both muscle and bone marrow tissues. Thus, it appears that tissue-specific stem cells circulating in peripheral blood could compete for SDF-1(+) niches, and this would explain, without invoking the concept of stem cell plasticity, why hematopoietic colonies can be cultured from muscles and early muscle progenitors can be cultured from bone marrow.
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PMID:Expression of functional CXCR4 by muscle satellite cells and secretion of SDF-1 by muscle-derived fibroblasts is associated with the presence of both muscle progenitors in bone marrow and hematopoietic stem/progenitor cells in muscles. 1274 31

Among the various chemokines that are functionally active on neutrophils, platelet factor 4 (PF-4; CXCL4) appears to have a specialized role. Lacking typical chemokine activities, PF-4 stimulates neutrophils to undergo firm adhesion to endothelial cells and, in the presence of an appropriate costimulus like tumor necrosis factor (TNF), PF-4 induces exocytosis of secondary granule contents. Analyzing the individual contribution of PF-4 and its costimuli in the control of these functions at the signaling level, we demonstrate that TNF-induced activation of p38 mitogen-activated protein (MAP) kinase (but not extracellular regulated kinase [Erk] kinases) acts as general and essential costimulatory signal in PF-4-dependent neutrophil exocytosis. This was shown by the use of a specific inhibitor (SB203580), by biologic (lipopolysaccharide, N-formyl-methionyl-leucyl-phenylalanine) and pharmacologic (anisomycin) activators of p38 MAP kinase, and by phosphorylation studies. Furthermore, TNF-mediated activation of phosphatidylinositol 3-kinase (PI 3-kinase) represents an additional essential signaling component in this process as demonstrated by studies with its inhibitor wortmannin as well as by analysis of the phosphorylation of AKT kinase. PF-4, however, directly activates src-kinases and PF-4-induced adherence as well as PF-4/TNF-mediated exocytosis was inhibited by an src-kinase inhibitor PP1. Taken together, neutrophil exocytosis and adherence are regulated on p38 MAP kinase, PI 3-kinase, and src-kinase activation.
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PMID:Platelet factor 4 (PF-4)-induced neutrophil adhesion is controlled by src-kinases, whereas PF-4-mediated exocytosis requires the additional activation of p38 MAP kinase and phosphatidylinositol 3-kinase. 1459 23

Expression of the chitinase 3-like protein HC-gp39 (human cartilage glycoprotein 39) is associated with conditions of increased matrix turnover and tissue remodelling. High levels of this protein have been found in sera and synovial fluids of patients with inflammatory and degenerative arthritis. In order to assess the role of HC-gp39 in matrix degradation induced by inflammatory cytokines, we have examined its effect on the responses of connective tissue cells to TNF-alpha (tumour necrosis factor-alpha) and IL-1 (interleukin-1) with respect to activation of signalling pathways and production of MMPs (matrix metalloproteases) and chemokines. Stimulation of human skin fibroblasts or articular chondrocytes with IL-1 or TNF-alpha in the presence of HC-gp39 resulted in a marked reduction of both p38 mitogen-activated protein kinase and stress-activated protein kinase/Jun N-terminal kinase phosphorylation, whereas nuclear translocation of nuclear factor kappaB proceeded unimpeded. HC-gp39 suppressed the cytokine-induced secretion of MMP1, MMP3 and MMP13, as well as secretion of the chemokine IL-8. The suppressive effects of HC-gp39 were dependent on phosphoinositide 3-kinase activity, and treatment of cells with HC-gp39 resulted in AKT-mediated serine/threonine phosphorylation of apoptosis signal-regulating kinase 1. This process could therefore be responsible for the down-regulation of cytokine signalling by HC-gp39. These results suggest a physiological role for HC-gp39 in limiting the catabolic effects of inflammatory cytokines.
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PMID:The chitinase 3-like protein human cartilage glycoprotein 39 inhibits cellular responses to the inflammatory cytokines interleukin-1 and tumour necrosis factor-alpha. 1501 34


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