Src kinase, but not the src kinase family member p56lck, mediates stromal cell-derived factor 1alpha/CXCL12-induced chemotaxis of a T cell line

Syndecan-1 increases B-lymphoid cell extravasation in response to HIV-1 Tat via αvβ3/pp60src/pp125FAK pathway

Syndecan-1 is a heparan sulfate proteoglycan (HSPG) commonly upregulated in AIDS-related B lymphoid malignancies. Tat is the main HIV-1 transactivating factor that has a major role in the pathogenesis of AIDS-related lymphomas (ARL) by engaging heparan sulfate proteoglycans (HSPGs), chemokine receptors and integrins at the lymphoid cell (LC) surface. Here B-lymphoid Namalwa cell clones that do not express or overexpress syndecan-1 (EV-Ncs and SYN-Ncs, respectively) were compared for their responsiveness with Tat: in the absence of syndecan-1, Tat induces a limited EV-Nc migration via C-X-C motif chemokine receptor 4 (CXCR4), G-proteins and Rac. Syndecan-1 overexpression increases SYN-Nc responsiveness to Tat and makes this response independent from CXCR4 and G-protein and dependent instead on pp60src phosphorylation. Tat-induced SYN-Nc migration and pp60src phosphorylation require the engagement of α_vβ₃ integrin and consequent pp125FAK phosphorylation. This complex set of Tat-driven activations is orchestrated by the direct interaction of syndecan-1 with pp60src and its simultaneous coupling with α_vβ₃. The Tat/syndecan-1/α_vβ₃ interplay is retained in vivo and is shared also by other syndecan-1⁺ B-LCs, including BJAB cells, whose responsiveness to Tat is inhibited by syndecan-1 knockdown. In conclusion, overexpression of syndecan-1 confers to B-LCs an increased capacity to migrate in response to Tat, owing to a switch from a CXCR4/G-protein/Rac to a syndecan-1/α_vβ₃/pp60src/pp125FAK signal transduction pathway that depends on the formation of a complex in which syndecan-1 interacts with Tat via its HS-chains, with α_vβ₃ via its core protein ectodomain and with pp60src via its intracellular tail. These findings have implications in ARL progression and may help in identifying new therapeutical targets for the treatment of AIDS-associated neoplasia.

Inhibition of CXCL12-mediated chemotaxis of Jurkat cells by direct immunotoxicants

Directional migration of cells to specific locations is required in tissue development, wound healing, and immune responses. Immune cell migration plays a crucial role in both innate and adaptive immunity. Chemokines are small pro-inflammatory chemoattractants that control the migration of leukocytes. In addition, they are also involved in other immune processes such as lymphocyte development and immune pathology. In a previous toxicogenomics study using the Jurkat T cell line, we have shown that the model immunotoxicant TBTO inhibited chemotaxis toward the chemokine CXCL12. In the present work, we aimed at assessing a novel approach to detecting chemicals that affect the process of cell migration. For this, we first evaluated the effects of 31 chemicals on mRNA expression of genes that are known to be related to cell migration. With this analysis, seven immunotoxicants were identified as potential chemotaxis modulators, of which five (CoCl2 80 µM, MeHg 1 µM, ochratoxin A 10 µM, S9-treated ochratoxin A 10 µM, and TBTO 100 nM) were confirmed as chemotaxis inhibitor in an in vitro trans-well chemotaxis assay using the chemokine CXCL12. The transcriptome data of the five compounds together with previously obtained protein phosphorylation profiles for two out of five compounds (i.e., ochratoxin A and TBTO) revealed that the mechanisms behind the chemotaxis inhibition are different for these immunotoxicants. Moreover, the mTOR inhibitor rapamycin had no effect on the chemotaxis of Jurkat cells, indicating that the mTOR pathway is not involved in CXCL12-mediated chemotaxis of Jurkat cells, which is opposite to the findings on human primary T cells (Munk et al. in PLoS One 6(9):e24667, 2011). Thus, the results obtained from the chemotaxis assay conducted with Jurkat cells might not fully represent the results obtained with human primary T cells. Despite this difference, the present study indicated that some compounds may exert their immunotoxic effects through inhibition of CXCL12-mediated chemotaxis.

E-cadherin is critical for collective sheet migration and is regulated by the chemokine CXCL12 protein during restitution

Chemokines and other immune mediators enhance epithelial barrier repair. The intestinal barrier is established by highly regulated cell-cell contacts between epithelial cells. The goal of these studies was to define the role for the chemokine CXCL12 in regulating E-cadherin during collective sheet migration during epithelial restitution. Mechanisms regulating E-cadherin were investigated using Caco2(BBE) and IEC-6 model epithelia. Genetic knockdown confirmed a critical role for E-cadherin in in vitro restitution and in vivo wound repair. During restitution, both CXCL12 and TGF-β1 tightened the monolayer by decreasing the paracellular space between migrating epithelial cells. However, CXCL12 differed from TGF-β1 by stimulating the significant increase in E-cadherin membrane localization during restitution. Chemokine-stimulated relocalization of E-cadherin was paralleled by an increase in barrier integrity of polarized epithelium during restitution. CXCL12 activation of its cognate receptor CXCR4 stimulated E-cadherin localization and monolayer tightening through Rho-associated protein kinase activation and F-actin reorganization. These data demonstrate a key role for E-cadherin in intestinal epithelial restitution.

Dual acylation and lipid raft association of Src-family protein tyrosine kinases are required for SDF-1/CXCL12-mediated chemotaxis in the Jurkat human T cell lymphoma cell line

Chemokines play pivotal roles in regulating a wide variety of biological processes by modulating cell migration and recruitment. Deregulation of chemokine signaling can alter cell recruitment, contributing to the pathogenic states associated with autoimmune disease, inflammatory disorders, and sepsis. During chemotaxis, lipid rafts and their resident signaling molecules have been demonstrated to partition to different parts of the cell. Herein, we investigated the role of lipid raft resident Src-family kinases (SFK) in stromal cell-derived factor 1/CXCL12-mediated chemotaxis. We have shown that Lck-deficient J.CaM 1.6 cells are defective in CXCL12-mediated chemotaxis in contrast to their parental counterpart, Jurkat cells. Ectopic expression of the SFK hematopoietic cell kinase (Hck) in J.CaM 1.6 cells reconstituted CXCL12 responsiveness. The requirement of lipid raft association of SFK was assessed using both isoforms of Hck: the dually acylated p59(Hck) isoform that is targeted to lipid rafts and the monoacylated p61(Hck) isoform that is nonraft-associated. We have shown using several gain and loss of acylation alleles that dual acylation of Hck was required for CXCL12-mediated chemotaxis in J.CaM 1.6 cells. These results highlight the importance of the unique microenvironment provided by lipid rafts and their specific contribution in providing specificity to CXCL12 signaling.

Depsipeptide (FK228) preferentially induces apoptosis in BCR/ABL-expressing cell lines and cells from patients with chronic myelogenous leukemia in blast crisis

Resistance to imatinib can occur in patients with chronic myelogenous leukemia (CML). In this study, we report mechanisms of action of histone deacetylase (HDAC) inhibitor, depsipeptide (FK228) in BCR/ABL-expressing cell lines and its effectiveness in imatinib-resistant cells from patients with blast crisis of CML. FK228 potently induced apoptosis of TF-1 BCR/ABL, K562, and H7 BCR/ABL cells. We found that histone H4, BCR/ABL, heat shock protein 90 (HSP-90), p53, focal adhesion kinase (FAK), paxillin, and retinoblastoma protein (Rb) were acetylated in the treated cells. Cells were also blocked in G(2)/M phase of the cell cycle and activity of mitogen-activated protein kinase (MAPK) was blocked, but p38MAPK (p38) was activated. Inhibitor of apoptosis proteins (IAPs) were suppressed, and common results of apoptotic induction were observed, such as caspase-3, caspase-9, and poly(ADP-ribose) polymerase (PARP) activation. Although p38 was phosphorylated after FK228 treatment, histone H4 acetylation, caspase-3 activation, and apoptosis were not inhibited by treatment with the p38 inhibitor SB203580. We also found that human telomerase reverse transcriptase (hTERT) ShRNA-transfected cells demonstrated decreased FK228-induced apoptosis. Of clinical relevance, FK228-induced apoptosis of imatinib-resistant primary cells from patients with CML, who had progressed to blast crisis (BC) while receiving therapy with imatinib. In conclusion, FK228 potently induces apoptosis of CML cells by acetylation and degradation of BCR/ABL protein. Our study suggests how FK228 may mediate its effects on imatinib-resistant CML cells.

SDF-1/CXCL12 enhances in vitro replating capacity of murine and human multipotential and macrophage progenitor cells

Hematopoietic progenitor cells (HPCs) manifest a limited self-renewal capacity, as determined by a surrogate assay involving replating capacity of single colonies in vitro with generation of secondary colonies. Stromal cell-derived factor-1 (SDF-1/CXCL12), has been implicated in regulation of hematopoiesis through its modulation of hematopoietic stem cell (HSC) and HPC migration, homing, mobilization, and survival. We used bone marrow cells from SDF-1/CXCL12 transgenic and littermate control mice, and culture of normal mouse bone marrow and human cord blood cells plated in the presence or absence of recombinant SDF-1/CXCL12 to evaluate a role for SDF-1/CXCL12 in the replating capability in vitro of multipotential [colony-forming units (CFU)-GEMM] and macrophage (CFU-M) progenitor cells. Competitive repopulating capacity of mouse HSCs was assessed in lethally irradiated mice. Transgenic or exogenous SDF-1/CXCL12 significantly enhanced numbers of secondary colonies formed from primary CFU-GEMM or CFU-M colonies. In the limited setting of our in vivo studies, the SDF-1/CXCL12 transgene did not influence HSC competitive repopulation. However, the results suggest that SDF-1/CXCL12 enhances in vitro replating/self-renewal of HPCs, which may contribute to myelopoiesis in vivo. This information may be of value to ex vivo expansion of HPCs/HSCs.

Intracellular mediators of CXCR4-dependent signaling in T cells

The signaling pathways induced in T lymphocytes by CXCR4-CXCL12 interaction, which lead to the cytoskeletal macro-rearrangements observable in migrating cells, are as yet largely uncharacterized. The aim of this review is to briefly summarize the current knowledge of the signaling machinery which controls the process of chemotaxis in CXCL12-stimulated T lymphocytes.

Progesterone reduces the migration of mast cells toward the chemokine stromal cell-derived factor-1/CXCL12 with an accompanying decrease in CXCR4 receptors

Mast cell recruitment is implicated in many physiological functions and several diseases. It depends on microenvironmental factors, including hormones. We have investigated the effect of progesterone on the migration of HMC-1(560) mast cells toward CXCL12, a chemokine that controls the migration of mast cells into tissues. HMC-1(560) mast cells were incubated with 1 nM to 1 microM progesterone for 24 h. Controls were run without progesterone. Cell migration toward CXCL12 was monitored with an in vitro assay, and statistical analysis of repeated experiments revealed that progesterone significantly reduced cell migration without increasing the number of apoptotic cells (P = 0.0084, n = 7). Differences between progesterone-treated and untreated cells were significant at 1 microM (P < 0.01, n = 7). Cells incubated with 1 microM progesterone showed no rearrangment of actin filaments in response to CXCL12. Progesterone also reduced the calcium response to CXCL12 and Akt phosphorylation. Cells incubated with progesterone had one-half the control concentrations of CXCR4 (mRNA, total protein, and membrane-bound protein). Progesterone also inhibited the migration of HMC-1(560) cells transfected with hPR-B-pSG5 plasmid, which contained 2.5 times as much PR-B as the control. These transfected cells responded differently (P < 0.05, n = 5) from untreated cells to 1 nM progesterone. We conclude that progesterone reduces mast cell migration toward CXCL12 and that CXCR4 may be a progesterone target in mast cells.

Stromal-cell-derived factor-1/CXCL12-induced chemotaxis of a T cell line involves intracellular signaling through Cbl and Cbl-b and their regulation by Src kinases and CD45

Stromal-cell-derived factor-1alpha (SDF-1alpha/CXCL12) is a potent chemoattractant for T cells. We report that Cbl family members, Cbl and Cbl-b, are tyrosine-phosphorylated after SDF-1alpha/CXCL12 stimulation of Jurkat T cells. Enhanced phosphorylation of Cbl and Cbl-b was regulated by src family kinases, and perhaps Fyn. Activated Cbl and Cbl-b interacted with Crk-L, Zap-70, Nck, PLC-gamma and Fyb after SDF-1alpha/CXCL12 stimulation, implicating association of these proteins in SDF-1alpha/CXCL12 actions. SDF-1alpha/CXCL12 did not induce tyrosine phosphorylation of Cbl or Cbl-b in Lck-deficient T cell line J.CaM1.6 or CD45-deficient T cell line J45.01. Thus, Lck Src kinase and tyrosine phosphatase CD45 are likely involved in regulating activation of Cbl family members. A functional role for Cbl and Cbl-b in migration was demonstrated by the decrease in SDF-1/CXCL12-induced migration in a T cell line in which transfected small interfering RNA for Cbl and Cbl-b decreased expression of Cbl and Cbl-b, but not MAPK activity. SDF-1alpha/CXCL12-induced chemotaxis was greatly reduced in the CD45-deficient T cell line. Our results implicate CD45, Cbl, Cbl-b, src kinases and potentially other associated proteins as mediators of SDF-1alpha/CXCL12-induced cell migration of Jurkat T cells.

Ephrin-A1 binding to CD4+ T lymphocytes stimulates migration and induces tyrosine phosphorylation of PYK2

Eph receptors, the largest subfamily of receptor tyrosine kinases, and their ephrin ligands are important mediators of cell-cell communication regulating cell attachment, shape, and mobility. Here we demonstrate that CD4+ T lymphocytes express the EphA1 and EphA4 receptors and that these cells bind the ligand ephrin-A1. Further we show ephrin-A1 expression in vivo on high endothelial venule (HEV) endothelial cells. Ephrin-A1 binding to CD4+ T cells stimulates both stromal cell-derived factor 1α (SDF-1α)- and macrophage inflammatory protein 3β (MIP3β)-mediated chemotaxis. In line with the increased chemotactic response, increased actin polymerization is observed in particular with the combination of ephrin-A1 and SDF-1α. Signaling through EphA receptors induces intracellular tyrosine phosphorylation. In particular, proline-rich tyrosine kinase 2 (PYK2) is phosphorylated on tyrosine residues 402 and 580. Ephrin-A1-induced chemotaxis and intracellular tyrosine phosphorylation, including EphA1 and Pyk2, was inhibited by Tyrphostin-A9. In conclusion, ligand engagement of EphA receptors on CD4+ T cells stimulates chemotaxis, induces intracellular tyrosine phosphorylation, and affects actin polymerization. This, together with our finding that ephrin-A1 is expressed by HEV endothelial cells, suggests a role for Eph receptors in transendothelial migration.

Stromal cell-derived factor-1alpha/CXCL12-induced chemotaxis of T cells involves activation of the RasGAP-associated docking protein p62Dok-1

Events mediating stromal cell-derived factor-1 (SDF-1alpha/CXCL12) chemotaxis of lymphocytes are not completely known. We evaluated intracellular signaling through RasGAP-associated protein p62Dok-1 (downstream of tyrosine kinase [Dok-1]) and associated proteins. SDF-1alpha/CXCL12 stimulated Dok-1 tyrosine phosphorylation and association with RasGAP, adaptor protein p46Nck, and Crk-L in Jurkat T cells. The phosphorylation of Dok-1 was blocked by pretreatment of cells with the src kinase inhibitor PP2. Src kinase family member Lck was implicated. SDF-1alpha/CXCL12 did not phosphorylate Dok-1 in J.CaM1.6 cells, a Jurkat derivative not expressing Lck, but did phosphorylate Dok-1 in J.CaM1.6 cells expressing Lck. SDF-1alpha/CXCL12 induced the tyrosine phosphorylation of Pyk2 and the association of Pyk2 with zeta chain-associated protein-70 kilodaltons (Zap-70) and Vav. SDF-1alpha/CXCL12 enhanced the association of RasGAP with Pyk2. CXCR4-expressing NIH3T3 and Baf3 cells transfected with full-length Dok-1 cDNA were suppressed in their responses to SDF-1alpha/CXCL12-induced chemotaxis; mitogen-activated protein (MAP) kinase activity was also decreased. Chemotaxis to SDF-1/CXCL12 was significantly enhanced in Dok-1(-/-) CD4+ and CD8+ splenic T cells. These results implicate Dok-1, Nck, Crk-L, and Src kinases-especially Lck, Pyk2, Zap-70, Vav, and Ras-GAP-in intracellular signaling by SDF-1alpha/CXCL12, and they suggest that Dok-1 plays an important role in SDF-1alpha/CXCL12-induced chemotaxis in T cells.

Inhibition of the activity of SRC and Abl tyrosine protein kinases by the binding of the Wiskott-Aldrich syndrome protein

The Wiscott-Aldrich syndrome protein, WASP, is an effector through which cdc42, a Rho family GTPase, regulates the actin cytoskeleton in hematopoietic cells. We have found that WASP binds readily to a number of tyrosine protein kinases including the Src kinases and the Abl kinase when the proteins are coexpressed during transient transfection. Binding inhibited the activity of each of these kinases strikingly, both in vitro and in vivo. Surprisingly, the binding was not due to an interaction between the proline-rich domain of WASP and the SH3 domain of these kinases. Rather, residues 83-93 in WASP were found to bind to the catalytic domains of the kinases. Binding did not decrease the affinity of Src kinases for either ATP or a peptide substrate noticeably. Rather, the V(max) of substrate phosphorylation was reduced by the binding of the peptide. This inhibition represents a novel form of regulation of protein kinase activity and suggests that that the isolation of small molecules that exploit this inhibitory mechanism may be possible.

SDF-1alpha production is negatively regulated by mouse estrogen enhanced transcript in a mouse thymus epithelial cell line

SDF-1/CXCR4 plays an important role in promoting survival, expansion, and differentiation of T cell progenitors. The present study investigates the mechanism by which estrogen inhibits SDF-1alpha expression in mouse thymus. Mouse estrogen enhanced transcript (mEET) is endogenously expressed in a mouse thymus epithelial cell line 1 (MTEC1). In MTEC1 cells that express the transfected sense mEET, the SDF-1alpha transcription and its chemotactic activity were profoundly inhibited. Conversely, in MTEC1 that express the transfected anti-sense mEET, the SDF-1alpha transcription and its chemotactic activity were substantially augmented. Moreover, we disclosed that mEET inhibited the production of SDF-1alpha by its suppression of NF-kappaB translocation into nucleus. Using a combinatorial induction of doxycycline (Dox) and 17beta-estradiol (E2) on the sense and anti-sense mEET transfectants, it was demonstrated that an increase of mEET expression enhanced E2-induced inhibition of SDF-1alpha production, while a blockade of mEET expression alleviated E2-induced inhibition of SDF-1alpha production. In conclusion, the E2-imposed suppression of SDF-1alpha production is partly mediated by mEET involved signaling pathway.