Identification of the alphavbeta3 integrin-interacting motif of betaig-h3 and its anti-angiogenic effect

betaig-h3 is an extracellular matrix protein that mediates adhesion and migration of several cell types through interaction with integrins. In the present study, we tested whether betaig-h3 mediates endothelial cell adhesion and migration, thereby regulating angiogenesis. In this study, we demonstrate that not only betaig-h3 itself but also all four fas-1 domains of betaig-h3 mediate endothelial cell adhesion and migration through interaction with the alphavbeta3 integrin. We found that the alphavbeta3 integrin-interacting motif of the four fas-1 domains of betaig-h3 is the same YH motif that we reported previously to interact with alphavbeta5 integrin. The YH peptide inhibited endothelial cell adhesion and migration in a dose-dependent manner. We demonstrate that the YH peptide has anti-angiogenic activity in vitro and in vivo using an endothelial cell tube formation assay and a Matrigel plug assay, respectively. Our results reveal that betaig-h3 bears alphavbeta3 integrin-interacting motifs that mediate endothelial cell adhesion and migration and, therefore, may regulate angiogenesis.     

Betaig-h3 supports keratinocyte adhesion,migration, and proliferation through alpha3beta1 integrin

betaig-h3 is an extracellular matrix protein and its expression is highly induced by TGF-beta and it has also been suggested to play important roles in skin wound healing. In this paper, we demonstrate that betaig-h3 is present in the papillary layer of dermis and synthesized in the basal keratinocytes in vivo and its expression is induced by TGF-beta in normal human keratinocytes (NHEK) and HaCaT cells. betaig-h3 mediates not only adhesion and spreading of keratinocytes but also supports migration and proliferation. These activities are mediated through interacting with alpha3beta1 integrin. Previously identified two alpha3beta1 integrin-interacting motifs of betaig-h3, EPDIM, and NKDIL, are responsible for these activities. The results suggest that betaig-h3 may regulate keratinocyte functions in normal skin and potentially during wound-healing process.     

TGF-beta1 enhances betaig-h3-mediated keratinocyte cell migration through the alpha3beta1 integrin and PI3K

betaig-h3 is an extracellular matrix (ECM) protein whose expression is highly induced by transforming growth factor beta1 (TGF-beta1). We previously demonstrated that betaig-h3 has two alpha3beta1 integrin-interacting motifs, which promote adhesion, migration, and proliferation of human keratinocytes. Both betaig-h3 and TGF-beta1 have been suggested to play important roles in the healing of skin wounds. In this study, we demonstrate that TGF-beta1 enhances keratinocyte adhesion and migration toward betaig-h3 through the alpha3beta1 integrin. TGF-beta1 did not increase the amount of the alpha3beta1 integrin on the cell surface, but rather increased its affinity for betaig-h3. LY294002, an inhibitor of PI3K, blocked the basal and TGF-beta1-enhanced cell migration but not adhesion to betaig-h3. A constitutively active mutant of PI3K stimulated cell migration but not adhesion to betaig-h3. The PI3K pathway is also not associated with the affinity of the alpha3beta1 integrin to betaig-h3. TGF-beta1 induced phosphorylation of AKT and FAK. Taken together, these data suggest that TGF-beta1 increases affinity of the alpha3beta1 integrin to betaig-h3, resulting in enhanced adhesion and migration of keratinocytes toward betaig-h3. TGF-beta1 also enhances migration through PI3K, but PI3K is not associated with either the binding affinity of the alpha3beta1 integrin or its adhesion to betaig-h3.     

Recognition of the neural chemoattractant Netrin-1 by integrins alpha6beta4 and alpha3beta1 regulates epithelial cell adhesion and migration

Netrins, axon guidance cues in the CNS, have also been detected in epithelial tissues. In this study, using the embryonic pancreas as a model system, we show that Netrin-1 is expressed in a discrete population of epithelial cells, localizes to basal membranes, and specifically associates with elements of the extracellular matrix. We demonstrate that alpha6beta4 integrin mediates pancreatic epithelial cell adhesion to Netrin-1, whereas recruitment of alpha6beta4 and alpha3beta1 regulate the migration of CK19+/PDX1+ putative pancreatic progenitors on Netrin-1. These results provide evidence for the activation of epithelial cell adhesion and migration by a neural chemoattractant, and identify Netrin-1/integrin interactions as adhesive/guidance cues for epithelial cells.     

Identification of a novel integrin alphaMbeta2 binding site in CCN1 (CYR61), a matricellular protein expressed in healing wounds and atherosclerotic lesions

CCN1 (cysteine-rich 61) and CCN2 (connective tissue growth factor) are growth factor-inducible immediate-early gene products found in atherosclerotic lesions, restenosed blood vessels, and healing cutaneous wounds. Both CCN proteins have been shown to support cell adhesion and induce cell migration through interaction with integrin receptors. Recently, we have identified integrin alphaMbeta2 as the major adhesion receptor mediating monocyte adhesion to CCN1 and CCN2 and have shown that the alphaMI domain binds specifically to both proteins. In the present study, we demonstrated that activated monocytes adhered to a synthetic peptide (CCN1-H2, SSVKKYRPKYCGS) derived from a conserved region within the CCN1 C-terminal domain, and this process was blocked by the anti-alphaM monoclonal antibody 2LPM19c. Consistently, a glutathione S-transferase (GST) fusion protein containing the alphaMI domain (GST-alphaMI) bound to immobilized CCN1-H2 as well as to the corresponding H2 sequence in CCN2 (CCN2-H2, TSVKTYRAKFCGV). By contrast, a scrambled CCN1-H2 peptide and an 18-residue peptide derived from an adjacent sequence of CCN1-H2 failed to support monocyte adhesion or alphaMI domain binding. To confirm that the CCN1-H2 sequence within the CCN1 protein mediates alphaMbeta2 interaction, we developed an anti-peptide antibody against CCN1-H2 and showed that it specifically blocked GST-alphaMI binding to intact CCN1. Collectively, these results identify the H2 sequence in CCN1 and CCN2 as a novel integrin alphaMbeta2 binding motif that bears no apparent homology to any alphaMbeta2 binding sequence reported to date.     

SVEP1 influences monocyte to macrophage differentiation via integrin α4β1/α9β1 and Rho/Rac signalling

BackgroundThe large extracellular matrix protein SVEP1 mediates cell adhesion via integrin α9β1. Recent studies have identified an association between a missense variant in SVEP1 and increased risk of coronary artery disease (CAD) in humans and in mice Svep1 deficiency alters the development of atherosclerotic plaques. However how SVEP1 functionally contributes to CAD pathogenesis is not fully understood. Monocyte recruitment and differentiation to macrophages is a key step in the development of atherosclerosis. Here, we investigated the requirement for SVEP1 in this process.MethodsSVEP1 expression was measured during monocyte–macrophage differentiation in primary monocytes and THP-1 human monocytic cells. SVEP1 knockout THP-1 cell lines and the dual integrin α4β1/α9β1 inhibitor, BOP, were utilised to investigate the effect of these proteins in THP-1 cell adhesion, migration and cell spreading assays. Subsequent activation of downstream integrin signalling intermediaries was quantified by western blotting.ResultsSVEP1 gene expression increases in monocyte to macrophage differentiation in human primary monocytes and THP-1 cells. Using two SVEP1 knockout THP-1 cells we observed reduction in monocyte adhesion, migration, and cell spreading compared to control cells. Similar results were found with integrin α4β1/α9β1 inhibition. We demonstrate reduced activity of Rho and Rac1 in SVEP1 knockout THP-1 cells.ConclusionsSVEP1 regulates monocyte recruitment and differentiation phenotypes through an integrin α4β1/α9β1 dependent mechanism.General significanceThese results describe a novel role for SVEP1 in monocyte behaviour relevant to CAD pathophysiology.     

The chemorepellent Slit3 promotes monocyte migration

Directional migration is an essential step for monocytes to infiltrate sites of inflammation, a process primarily regulated by chemoattractants. Slits are large matrix proteins that are secreted by endothelial cells; they were reported to inhibit the chemoattractant-induced migration of different cell types, including leukocytes. The aim of this study was to determine the effect of Slit3 on primary monocyte migration and to address the underlying mechanisms. We show that Roundabout (Robo)1, one of the Robo receptors that recognize Slit3, is the only Robo homolog expressed by CD14(+) monocytes. Interestingly, we found that stimulation with Slit3 increased the spontaneous and chemoattractant-induced migration of primary monocytes in vitro and increased the myeloid cell recruitment during peritoneal inflammation in vivo. In addition, Slit3 did not seem to act as a chemoattractant itself; it promoted directed migration triggered by chemoattractants, such as CXCL12, by inducing a chemokinetic effect. We further show that Slit3 prevented monocyte spreading and induced rounding of spread monocytes without affecting monocyte adhesion. Stimulation with Slit3 was not associated with changes in the levels of phosphorylated p38, p42/p44, or Src, known regulators of monocyte migration, but it directly acts on molecular pathways involved in basal leukocyte migration by activating RhoA. These findings show an unexpected response of monocytes to Slit3 and add insights into the possible role of Slit proteins during inflammatory cell recruitment.     

Human blood monocytes interact with type I collagen through alpha x beta 2 integrin (CD11c-CD18, gp150-95)

Human blood monocytes are attracted into connective tissues during early steps of inflammation and wound healing, and locally interact with resident cells and extracellular matrix proteins. We studied the effects of type I collagen on monocyte adhesion and superoxide anion production, using human monocytes elutriated from peripheral blood and type I collagen obtained from rat tail tendon. Both acid-soluble and pepsin-digested type I collagens promoted the adhesion of monocytes, whereas only acid-soluble collagen with intact telopeptides induced the production of superoxide. Adhesion and activation of monocytes on acid-soluble type I collagen depended on the presence of divalent cations. mAbs directed against integrin subunits CD11c and CD18 specifically inhibited adhesion and activation of monocytes on type I collagen. Protein membrane extracts obtained from monocytes were submitted to affinity chromatography on collagen I-Sepharose 4B, and analyzed by Western blotting using specific anti-integrin subunit Abs. In the case of both acid-soluble and pepsin-digested collagens, two bands were revealed with mAbs against CD11c and CD18 integrin subunits. Our results demonstrate that monocytes interact with type I collagen through CD11c-CD18 (alpha x beta 2) integrins, which promote their adhesion and activation. For monocyte activation, specific domains of the type I collagen telopeptides are necessary. Interactions between monocytes and collagen are most likely involved in the cascade of events that characterize the initial phases of inflammation.     

TGFBIp/betaig-h3 protein: a versatile matrix molecule induced by TGF-beta

TGFBIp/βig-h3 protein is an extracellular matrix molecule initially cloned from human adenocarcinoma cells treated with TGF-β. Its precise function remains obscure but a number of studies have demonstrated it to be an intriguingly versatile molecule role in a wide range of physiological and pathological conditions. To date, the most extensively studied and reported action of TGFBIp/βig-h3 protein is in corneal dystrophy and several excellent reviews are available on this. Work from various laboratories on this molecule has compiled a tremendous amount of information over the past decade and a half. Here we review the current understanding on TGFBIp/βig-h3 protein and its functions in morphogenesis, extracellular matrix interactions, adhesion/migration, corneal dystrophy, tumorigenesis, angiogenesis, nephropathies, osteogenesis, wound healing and inflammation.     

Relaxin inhibits early steps in vascular inflammation

Increased expression of endothelial adhesion molecules, high levels of the monocyte chemoattractant protein-1 (MCP-1) and enhanced VLA4 integrin/VCAM-1 and CCR-2/MCP-1 interactions are initial steps in vascular inflammation. We sought to determine whether relaxin, a potent vasodilatory and anti-fibrotic agent, mitigates these early events compromising endothelial integrity. The effect of relaxin coincubation on the TNF-α-stimulated expression of the adhesion molecules VCAM-1, ICAM-1 and E-selectin; the MCP-1 expression by human umbilical vein endothelial cells (HUVEC) and human aortic smooth muscle cells (HAoSMC); as well as on direct monocyte–endothelium cell adhesion was quantified by ELISA or adhesion assay. CCR-2 and PECAM expression on HUVEC and THP-1 monocytes was investigated by FACS analysis. Relaxin treatment suppressed significantly TNF-α-induced upregulation of VCAM-1 and PECAM, CCR-2, and MCP-1 levels and direct monocyte adhesion to HUVEC. Our findings identify relaxin as a promising inhibitory factor in early vascular inflammation. By attenuating the upregulation of VCAM-1, key adhesion molecule in early vascular inflammation, and of MCP-1, a chemokine pivotal to monocyte recruitment, relaxin decreased initial monocyte–endothelium contact. This may be of relevance for the prevention and treatment of atherosclerosis and of other pro-inflammatory states.     

The CD157-integrin partnership controls transendothelial migration and adhesion of human monocytes

CD157, a member of the CD38 gene family, is an NAD-metabolizing ectoenzyme and a signaling molecule whose role in polarization, migration, and diapedesis of human granulocytes has been documented; however, the molecular events underpinning this role remain to be elucidated. This study focused on the role exerted by CD157 in monocyte migration across the endothelial lining and adhesion to extracellular matrix proteins. The results demonstrated that anti-CD157 antibodies block monocyte transmigration and adhesion to fibronectin and fibrinogen but that CD157 cross-linking is sufficient to overcome the block, suggesting an active signaling role for the molecule. Consistent with this is the observation that CD157 is prevalently located within the detergent-resistant membrane microdomains to which, upon clustering, it promotes the recruitment of β(1) and β(2) integrin, which, in turn, leads to the formation of a multimolecular complex favoring signal transduction. This functional cross-talk with integrins allows CD157 to act as a receptor despite its intrinsic structural inability to do so on its own. Intracellular signals mediated by CD157 rely on the integrin/Src/FAK (focal adhesion kinase) pathway, resulting in increased activity of the MAPK/ERK1/2 and the PI3K/Akt downstream signaling pathways, which are crucial in the control of monocyte transendothelial migration. Collectively, these findings indicate that CD157 acts as a molecular organizer of signaling-competent membrane microdomains and that it forms part of a larger molecular machine ruled by integrins. The CD157-integrin partnership provides optimal adhesion and transmigration of human monocytes.     

GRO family chemokines are specialized for monocyte arrest from flow

Chemokines participate in various processes of monocyte recruitment including monocyte arrest and migration. Our group and others have demonstrated that growth-related oncogene (GRO)-alpha (CXCL1) can support monocyte arrest in models of inflammation. Here we employed a parallel plate-flow chamber and Transwell reconstitution assay to test whether GRO family chemokines were sufficient for Mono Mac 6 (a human monocytic cell line) and isolated human monocyte recruitment. Our study shows that 1) GRO-alpha, -beta (CXCL2), and -gamma (CXCL3) all act as arrest chemokines for monocyte adhesion on vascular cell adhesion molecule (VCAM)-1 under flow in the presence of P-selectin; 2) CXCR2 is the functional receptor for GRO-family chemokines in monocyte arrest; however, CXCR2 is not an arrest chemokine receptor in general, since epithelial neutrophil-activating peptide ENA-78 failed to arrest monocytes; 3) GRO-alpha, -beta, and -gamma all fail to increase intracellular free Ca2+ or mediate monocyte chemotaxis; and 4) signaling through G alpha(i) protein, phosphoinositide 3-kinase, and actin polymerization but not Ca2+ mobilization or the mitogen-activated kinases p38 and MAPK/extracellular signal-related kinase are necessary for GRO-alpha-mediated Mono Mac 6 cell arrest under flow. We conclude that the GRO-family chemokines are specialized monocyte-arrest chemokines. Their role in monocyte recruitment in inflammation can be inhibited by blocking CXCR2 function or downstream signaling events.     

A Role for the αvβ3 Integrin in the Transmigration of Monocytes

The β2 integrins and intercellular adhesion molecule-1 (ICAM-1) are important for monocyte migration through inflammatory endothelium. Here we demonstrate that the integrin αvβ3 is also a key player in this process. In an in vitro transendothelial migration assay, monocytes lacking β3 integrins revealed weak migratory ability, whereas monocytes expressing β3 integrins engaged in stronger migration. This migration could be partially blocked by antibodies against the integrin chains αL, β2, αv, or IAP, a protein functionally associated with αvβ3 integrin. Transfection of β3 integrin chain cDNA into monocytes lacking β3 integrins resulted in expression of the αvβ3 integrin and conferred on these cells an enhanced ability to transmigrate through cell monolayers expressing ICAM-1. These monocytes also engaged in αLβ2-dependent locomotion on recombinant ICAM-1 which was enhanced by αvβ3 integrin occupancy. Antibodies against IAP were able to revert this αvβ3 integrin-dependent cell locomotion to control levels. Finally, adhesion assays revealed that occupancy of αvβ3 integrin could decrease monocyte binding to ICAM-1.In conclusion, we show that αvβ3 integrin modulates αLβ2 integrin-dependent monocyte adhesion to and migration on ICAM-1. This could represent a novel mechanism to promote monocyte motility on vascular ICAM-1 and initiate subsequent transendothelial migration.     

TGFBIp mediates lymphatic sprouting in corneal lymphangiogenesis

Corneal lymphangiogenesis plays a key role in diverse pathological conditions of the eye. Here, we demonstrate that a versatile extracellular matrix protein, transforming growth factor‐β induced protein (TGFBIp), promotes lymphatic sprouting in corneal lymphangiogenesis. TGFBIp is highly up‐regulated in inflamed mouse corneas. Immunolocalization of TGFBIp is detected in infiltrating macrophages in inflamed mouse corneas. Subconjunctival injection of liposomal clodronate can significantly reduce macrophage infiltration in inflamed mouse cornea, and decrease the expression of TGFBIp and areas of corneal lymphangiogenesis and angiogenesis after corneal suture placement. In brief, these results indicate that the up‐regulation of TGFBIp in sutured cornea correlates with macrophage infiltration. Although TGFBIp alone cannot significantly stimulate corneal lymph vessel ingrowth in vivo, it can enhance the effect of vascular endothelial growth factor‐C in promoting corneal lymphangiogenesis. The in vitro results show that TGFBIp promotes migration, tube formation and adhesion of human lymphatic endothelial cells (HLECs), but it has no effect on HLECs' proliferation. We also find that the in vitro effect of TGFBIp is mediated by the integrin α5β1‐FAK pathway. Additionally, integrin α5β1 blockade can significantly inhibit lymphatic sprouting induced by TGFBIp. Taken together, these findings reveal a new molecular mechanism of lymphangiogenesis in which the TGFBIp‐integrin pathways plays a pivotal role in lymphatic sprouting.     

WAVE2 regulates high-affinity integrin binding by recruiting vinculin and talin to the immunological synapse

T-cell-receptor (TCR)-mediated integrin activation is required for T-cell-antigen-presenting cell conjugation and adhesion to extracellular matrix components. While it has been demonstrated that the actin cytoskeleton and its regulators play an essential role in this process, no mechanism has been established which directly links TCR-induced actin polymerization to the activation of integrins. Here, we demonstrate that TCR stimulation results in WAVE2-ARP2/3-dependent F-actin nucleation and the formation of a complex containing WAVE2, ARP2/3, vinculin, and talin. The verprolin-connecting-acidic (VCA) domain of WAVE2 mediates the formation of the ARP2/3-vinculin-talin signaling complex and talin recruitment to the immunological synapse (IS). Interestingly, although vinculin is not required for F-actin or integrin accumulation at the IS, it is required for the recruitment of talin. In addition, RNA interference of either WAVE2 or vinculin inhibits activation-dependent induction of high-affinity integrin binding to VCAM-1. Overall, these findings demonstrate a mechanism in which signals from the TCR produce WAVE2-ARP2/3-mediated de novo actin polymerization, leading to integrin clustering and high-affinity binding through the recruitment of vinculin and talin.     

Human Thy-1 (CD90) on activated endothelial cells is a counterreceptor for the leukocyte integrin Mac-1 (CD11b/CD18)

Leukocyte recruitment in response to inflammatory signals is in part governed by interactions between endothelial cell receptors belonging to the Ig superfamily and leukocyte integrins. In our previous work, the human Ig superfamily glycoprotein Thy-1 (CD90) was identified as an activation-associated cell adhesion molecule on human dermal microvascular endothelial cells. Furthermore, the interaction of Thy-1 with a corresponding ligand on monocytes and polymorphonuclear cells was shown to be involved in the adhesion of these leukocytes to activated Thy-1-expressing endothelial cells. In this study, we have identified the specific interaction between human Thy-1 and the leukocyte integrin Mac-1 (CD11b/CD18; alphaMbeta2) both in cellular systems and in purified form. Monocytes and polymorphonuclear cells were shown to adhere to transfectants expressing human Thy-1 as well as to primary Thy-1-expressing human dermal microvascular endothelial cells. Furthermore, leukocyte adhesion to activated endothelium as well as the subsequent transendothelial migration was mediated by the interaction between Thy-1 and Mac-1. This additional pathway in leukocyte-endothelium interaction may play an important role in the regulation of leukocyte recruitment to sites of inflammation.     

The Matricellular Protein Cyr61 Is a Key Mediator of Platelet-derived Growth Factor-induced Cell Migration

Platelet-derived growth factor (PDGF), a potent chemoattractant, induces cell migration via the MAPK and PI3K/Akt pathways. However, the downstream mediators are still elusive. In particular, the role of extracellular mediators is largely unknown. In this study, we identified the matricellular protein Cyr61, which is de novo synthesized in response to PDGF stimulation, as the key downstream mediator of the ERK and JNK pathways, independent of the p38 MAPK and AKT pathways, and, thereby, it mediates PDGF-induced smooth muscle cell migration but not proliferation. Our results revealed that, when Cyr61 was newly synthesized by PDGF, it was promptly translocated to the extracellular matrix and physically interacted with the plasma membrane integrins α6β1 and αvβ3. We further demonstrate that Cyr61 and integrins are integral components of the PDGF signaling pathway via an “outside-in” signaling route to activate intracellular focal adhesion kinase (FAK), leading to cell migration. Therefore, this study provides the first evidence that the PDGF-induced endogenous extracellular matrix component Cyr61 is a key mediator in modulating cell migration by connecting intracellular PDGF-ERK and JNK signals with integrin/FAK signaling. Therefore, extracellular Cyr61 convergence with growth factor signaling and integrin/FAK signaling is a new concept of growth factor-induced cell migration. The discovered signaling pathway may represent an important therapeutic target in growth factor-mediated cell migration/invasion-related vascular diseases and tumorigenesis.     

Eosinophil tissue recruitment to sites of allergic inflammation in the lung is platelet endothelial cell adhesion molecule independent

Platelet endothelial cell adhesion molecule (PECAM or CD31) is a cell adhesion molecule expressed on circulating leukocytes and endothelial cells that plays an important role in mediating neutrophil and monocyte transendothelial migration in vivo. In this study, we investigated whether eosinophils, like neutrophils and monocytes, utilize PECAM for tissue recruitment to sites of allergic inflammation in vivo. Eosinophils express similar levels of PECAM as neutrophils as assessed by FACS analysis. RT-PCR studies demonstrate that eosinophils like neutrophils express the six extracellular domains of PECAM. Eosinophils exhibit homophilic binding to recombinant PECAM as assessed in a single-cell micropipette adhesion assay able to measure the biophysical strength of adhesion of eosinophils to recombinant PECAM. The strength of eosinophil adhesion to recombinant PECAM is the same as that of neutrophil binding to recombinant PECAM and can be inhibited with an anti-PECAM Ab. Although eosinophils express functional PECAM, anti-PECAM Abs did not inhibit bronchoalveolar lavage eosinophilia, lung eosinophilia, and airway hyperreactivity to methacholine in a mouse model of OVA-induced asthma in vivo. Thus, in contrast to studies that have demonstrated that neutrophil and monocyte tissue recruitment is PECAM dependent, these studies demonstrate that eosinophil tissue recruitment in vivo in this model is PECAM independent.     

Monocyte migration and LFA-1-mediated attachment to brain microvascular endothelia is regulated by SDF-1 alpha through Lyn kinase

Infiltration of activated monocytes into the brain is a prerequisite for the development of various neurological disorders such as HIV-associated dementia, multiple sclerosis, and other inflammatory processes. In these pathologies, the chemokine SDF-1alpha (CXCL12) is over-expressed and might attract monocytes into the CNS. We demonstrate here that SDF-1alpha stimulates migration of monocytes through its receptor, CXCR4, and decreases monocyte adherence to surfaces coated with ICAM-1, a ligand for beta(2) integrins. SDF-1alpha also decreases monocyte adherence to brain microvascular endothelial cells (BMVEC) that are activated with TNF-alpha, IL-1beta, or recombinant envelope glycoprotein from HIV-1, which increase BMVEC expression of ICAM-1. The decreased adherence is linked to down-regulation on monocytes of the activation-dependent epitope of the beta(2) integrin LFA-1 by SDF-1alpha. Knockdown of Lyn in monocytes using small interfering RNA decreases SDF-1alpha-mediated migration and prevents the inhibition of monocyte attachment to ICAM-1 and activated BMVEC. Thus, in SDF-1alpha-stimulated monocytes, Lyn acts as a positive regulator of migration and a negative regulator of adhesion to BMVEC through the LFA-1 integrin. These results provide a novel Lyn-mediated signaling mechanism for the regulation of monocyte movement at the blood-brain barrier.     

Augmentation of monocyte chemotaxis by 1 alpha,25-dihydroxyvitamin D3. Stimulation of defective migration of AIDS patients

Preincubation for 20 h with 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) markedly augmented the chemotactic responsiveness of human blood monocytes to the classical chemoattractant, FMLP. A modest enhancement of monocyte spontaneous locomotion in the absence of chemoattractants was also observed. Maximal increase of monocyte migration was observed after pretreatment with 10(-9) M 1,25(OH)2D3 and was detectable at FMLP concentrations ranging from 10(-10) to 10(-7) M. Pretreatment with 1,25(OH)2D3 augmented the number of monocyte high affinity FMLP receptors (1500 +/- 220 and 3800 +/- 300 sites per cell for untreated and 1,25(OH)2D3-pretreated cells, respectively) with no significant changes in Kd values (2 +/- 0.5 nM and 4 +/- 1 nM, for untreated and 1,25(OH)2D3-pretreated monocytes). Enhanced chemotaxis was not restricted to FMLP, because 1,25(OH)2D3-treated monocytes showed enhanced migration also in response to activated C components and chemotactic cytokines. In agreement with previous observations, monocytes from AIDS patients showed defective migration capacity. In vitro exposure to 1,25(OH)2D3 stimulated monocyte migration in all 10 patients examined with considerable quantitative differences among individuals. Regulating the responsiveness of mature monocytes to chemo-attractants, 1,25(OH)2D3, produced systemically or in situ by immunocompetent cells, could play a role in the regulation of the recruitment of monocytes at sites of inflammation, cell-mediated immunity, or bone resorption. The potential of 1,25(OH)2D3 as a restorative agent under conditions of defective phagocyte recruitment deserves further exploration.