Differential utilization of VLA-4 (alpha 4 beta 1) and -5 (alpha 5 beta 1) integrins during the development of mouse bone marrow-derived mast cells

Matrix-regulated integrin αvβ5 maintains α5β1-dependent desmoplastic traits prognostic of neoplastic recurrence

Desmoplasia, a fibrotic mass including cancer-associated fibroblasts (CAFs) and self-sustaining extracellular matrix (D-ECM), is a puzzling feature of pancreatic ductal adenocarcinoma (PDACs). Conflicting studies have identified tumor-restricting and tumor-promoting roles of PDAC-associated desmoplasia, suggesting that individual CAF/D-ECM protein constituents have distinguishable tumorigenic and tumor-repressive functions. Using 3D culture of normal pancreatic versus PDAC-associated human fibroblasts, we identified a CAF/D-ECM phenotype that correlates with improved patient outcomes, and that includes CAFs enriched in plasma membrane-localized, active α₅β₁-integrin. Mechanistically, we established that TGFβ is required for D-ECM production but dispensable for D-ECM-induced naïve fibroblast-to-CAF activation, which depends on α_vβ₅-integrin redistribution of pFAK-independent active α₅β₁-integrin to assorted endosomes. Importantly, the development of a simultaneous multi-channel immunofluorescence approach and new algorithms for computational batch-analysis and their application to a human PDAC panel, indicated that stromal localization and levels of active SMAD2/3 and α₅β₁-integrin distinguish patient-protective from patient-detrimental desmoplasia and foretell tumor recurrences, suggesting a useful new prognostic tool.

DOI:http://dx.doi.org/10.7554/eLife.20600.001

Tumors are not entirely made out of cancerous cells. They contain many other components – referred to as tumor stroma – that may either encourage or hinder the tumor’s growth. Tumor stroma includes non-cancerous cells and a framework of fibrous sugary proteins, called the extracellular matrix, which surround and signal to cells while providing physical support.

In the most common and aggressive form of pancreatic cancer, the stroma often makes up the majority of the tumor’s mass. Sometimes the stroma of these pancreatic tumors can protect the cancer cells from anti-cancer drugs. Researchers have therefore been interested in finding out exactly which aspects of the tumor stroma shield and support cancer cells, and which impede their growth and progression. Answering these questions could make it possible to develop new drugs that will change a tumor-supporting stroma into one that hinders the tumor’s growth and spread.

The most abundant cells in the stroma of pancreatic tumors are called cancer-associated fibroblasts. Healthy specialized fibroblasts – known as pancreatic stellate cells – help to build and maintain the ‘normal’ extracellular matrix and so these cells normally restrict a tumor’s development. However, cancer cells can adapt healthy fibroblasts into cancer-associated fibroblasts, which produce an altered extracellular matrix that could allow the tumor to grow.

Franco-Barraza et al. have now compared healthy and cancer-associated fibroblasts from patients’ pancreatic tumors. One of the main differences between these two cell types was the location of the activated form of a molecule called α₅β₁-integrin. Healthy fibroblasts, in a normal extracellular matrix, have active α₅β₁-integrin on the surface of the cell. However, a number of tumor-promoting signals, including some from the altered extracellular matrix, could force the active α₅β₁-integrins to relocate inside the fibroblasts instead. In further experiments, where the activated integrin was retained at the cell surface, the fibroblasts were able to resist the influence of the cancer-associated extracellular matrix. Then again, if the active α₅β₁-integrins were directed inside the cells, healthy cells turned into cancer-associated fibroblasts.

With this information in hand, Franco-Barraza et al. examined tumor samples from over a hundred pancreatic cancer patients using a new microscopy-based technique that distinguishes cancer cells from stroma cells. The analysis confirmed the pattern observed in the laboratory: those patients who appeared to produce more normal extracellular matrix and have active α₅β₁-integrin localized mostly to the surface of the cells survived longer without the cancer returning than those patients who lacked these stroma traits. Samples from patients with kidney cancer also showed similar results and, as before, an altered extracellular matrix was linked to a worse outcome of the disease.

Together these findings suggest that if future studies uncover ways to relocate or maintain active α₅β₁-integrin to the cell surface of fibroblasts they could lead to new treatments to restrict the growth of tumors in cancer patients.

DOI:http://dx.doi.org/10.7554/eLife.20600.002

Niche anchorage and signaling through membrane-bound Kit-ligand/c-kit receptor are kinase independent and imatinib insensitive

Kit ligand (KitL) and its tyrosine kinase receptor c-kit are critical for germ cells, melanocytes, mastocytes, and hematopoietic stem cells. Alternative splicing of KitL generates membrane-bound KitL (mb-KitL) or soluble KitL, providing survival or cell migration, respectively. Here we analyzed whether c-kit can function both as an adhesion and signaling receptor to mb-KitL presented by the environmental niche. At contacts between fibroblasts and MC/9 mast cells, mb-KitL, and c-kit formed ligand/receptor clusters that formed stable complexes, which resisted dissociation by c-kit blocking mAbs and provided cell anchorage under physiological shear stresses. Clusters recruited tyrosine-phosphorylated proteins and induced spatially restricted F-actin polymerization. Mutational analysis of c-kit demonstrated kinase-independent mb-KitL/c-kit clustering, anchorage, F-actin polymerization, and Tyr567-dependent cluster phosphorylation. Kinase inhibition of c-kit by imatinib reduced cluster coalescence, but allowed cluster phosphorylation and F-actin polymerization, which required PI3K recruitment and a newly identified juxtamembrane residue. Synergies between integrin and c-kit-mediated spreading and adhesion of MC/9 cells were studied in vitro on immobilized-KitL/fibronectin surfaces. While c-kit blocking antibodies prevented spreading, imatinib blocked spreading induced by soluble- but not immobilized KitL. Thus, "mechanical" activation of c-kit provides signaling, niche-anchorage, and synergies with integrin-mediated adhesion, which is independent of kinase function and resistant to c-kit kinase inhibitors.-

Development of mast cells and importance of their tryptase and chymase serine proteases in inflammation and wound healing

Mast cells (MCs) are active participants in blood coagulation and innate and acquired immunity. This review focuses on the development of mouse and human MCs, as well as the involvement of their granule serine proteases in inflammation and the connective tissue remodeling that occurs during the different phases of the healing process of wounded skin and other organs. The accumulated data suggest that MCs, their tryptases, and their chymases play important roles in tissue repair. While MCs initially promote healing, they can be detrimental if they are chronically stimulated or if too many MCs become activated at the same time. The possibility that MCs and their granule serine proteases contribute to the formation of keloid and hypertrophic scars makes them potential targets for therapeutic intervention in the repair of damaged skin.

An essential role for platelet-activating factor in activating mast cell migration following ultraviolet irradiation

The UVB (290-320 nm) radiation in sunlight is responsible for inducing skin cancer. Exposure to UV radiation is also immunosuppressive, and the systemic immune suppression induced by UV is a well-recognized risk factor for cancer induction. As UVB radiation is absorbed within the upper layers of the skin, indirect mechanisms must play a role in activating systemic immune suppression. One prominent example is mast cell migration, which from the skin to the draining LN is an essential step in the cascade of events leading to immune suppression. What triggers mast cell migration is not entirely clear. Here, we tested the hypothesis that PAF, a lipid mediator of inflammation produced by the skin in response to UV exposure, is involved. Mast cell-deficient mice (Kit(W-sh/W-sh)) are resistant to the suppressive effect of UV radiation, and reconstituting mast cell-deficient mice with normal bone marrow-derived mast cells restores susceptibility to immunosuppression. However, when mast cells from PAFR-/- mice were used, the reconstituted mice were not susceptible to the suppressive effects of UV. Furthermore, PAFR-/- mice showed impaired UV-induced mast cell migration when compared with WT mice. Finally, injecting PAF into WT mice mimicked the effect of UV irradiation and induced mast cell migration but not in PAFR-/- mice. Our findings indicate that PAFR binding induces mast cells to migrate from the skin to the LNs, where they mediate immune suppression.

Bone marrow stromal cell line promotes the proliferation of mast cell progenitors derived from cord blood CD34+ cells under serum-free conditions with a combination of both cell-cell interaction and soluble factors

A higher production of functional mast cells (MCs) can be generated by co-culturing cord blood-derived CD34+ cells with a human bone marrow stromal cell line under serum-free conditions supplemented with stem cell factor and IL-6. We addressed the question of whether the higher proliferation of MCs in this co-culture system might be due to the higher proliferation of MC progenitors. The stromal cell line increased the cell numbers of MC progenitors derived from cord blood-derived CD34+ cells, in a combination of cell-cell interactions between stromal cells and CD34+ cells, and as yet unidentified soluble factors derived from stromal cells.

A critical role of conventional protein kinase C in morphological changes of rodent mast cells

In mast cells, crosslinking the high-affinity IgE receptor (FcɛRI) results in a dynamic reorganization of the actin cytoskeleton that is associated with membrane ruffling. Although the signaling involved in degranulation has been well described, it is less understood in morphological changes. In this study, we investigated the specific role of conventional protein kinase C (cPKC), a crucial signal for degranulation, in antigen-induced membrane ruffling of mast cells. In RBL-2H3 mast cells, antigen induced a long-lasting membrane ruffling, which was blocked with late-added Gö6976, a specific cPKC inhibitor, indicating that sustained activation of cPKC is required for maintaining the reaction. Immunofluorescence staining of endogenous PKCα/β and real-time imaging of transfected green fluorescent protein-tagged PKCα/β demonstrated that in response to antigen both PKCα and PKCβI quickly translocated to the plasma membrane and were colocalized with actin filaments at the ruffling sites. These reactions were blocked by expression of kinase-negative PKCβI, but not kinase-negative PKCα, and by treatment with a specific PKCβ inhibitor, LY333531. The adhesion, spreading and membrane ruffling of mouse bone marrow-derived mast cells (BMMCs), which are mostly nonadhesive, were promoted by both antigen and thymeleatoxin. Treatment with Gö6976 abolished all these reactions. Antigen-mediated migration of BMMC was also sensitive to Gö6076 and LY333531. In addition, BMMC adhesion by and migration toward stem cell factor were shown to be dependent on cPKC. Thus, cPKC, at least PKCβ subtype, may be critical for the dynamic morphological changes that lead to the migration of mast cells.

Adhesion of MC3T3-E1 cells to RGD peptides of different flanking residues: detachment strength and correlation with long-term cellular function

We synthesized a series of RGD peptides and immobilized them to an amine-functional self-assembled monolayer using a modified maleimide-based conjugate technique that minimizes nonspecific interactions. Using a spinning disc apparatus, a trend in the detachment strength (tau(50)) of RGD peptides of different flanking residues was found: RGDSPK > RGDSVVYGLR approximately RGDS > RGES. Using blocking monoclonal antibodies, cellular adhesion to the peptides was shown to be primarily alpha(v)-integrin-mediated. In contrast, the tau(50) value of the cells on fibronectin (Fn)-coated substrates of similar surface density was 6-7 times higher and involved both alpha(5)beta(1) and alpha(v)beta(3) integrins. Cellular spreading was enhanced on RGD peptides after 1 h when compared to RGE and unmodified substrates. However, no significant differences were observed between the different RGD peptides. Long-term function of MC3T3-E1 cells was also evaluated by measuring alkaline phosphatase (ALP) activity and mineral deposition. Among the four peptides, RGDSPK exhibited the highest level of ALP activity after 11 days and mineralization after 15 days and reached comparable levels as Fn substrates after 15 and 24 days, respectively. These findings collectively illustrate both the advantages and limitations of enhancing cellular adhesion and function by the design of RGD peptides.

Dendritic cell expression of the transcription factor T-bet regulates mast cell progenitor homing to mucosal tissue

The transcription factor T-bet was identified in CD4⁺ T cells, and it controls interferon γ production and T helper type 1 cell differentiation. T-bet is expressed in certain other leukocytes, and we recently showed (Lord, G.M., R.M. Rao, H. Choe, B.M. Sullivan, A.H. Lichtman, F.W. Luscinskas, and L.H. Glimcher. 2005. Blood. 106:3432–3439) that it regulates T cell trafficking. We examined whether T-bet influences homing of mast cell progenitors (MCp) to peripheral tissues. Surprisingly, we found that MCp homing to the lung or small intestine in T-bet^−/− mice is reduced. This is reproduced in adhesion studies using bone marrow–derived MCs (BMMCs) from T-bet^−/− mice, which showed diminished adhesion to mucosal addresin cellular adhesion molecule–1 (MAdCAM-1) and vascular cell adhesion molecule–1 (VCAM-1), endothelial ligands required for MCp intestinal homing. MCp, their precursors, and BMMCs do not express T-bet, suggesting that T-bet plays an indirect role in homing. However, adoptive transfer experiments revealed that T-bet expression by BM cells is required for MCp homing to the intestine. Furthermore, transfer of WT BM-derived dendritic cells (DCs) to T-bet^−/− mice restores normal MCp intestinal homing in vivo and MCp adhesion to MAdCAM-1 and VCAM-1 in vitro. Nonetheless, T-bet^−/− mice respond vigorously to intestinal infection with Trichinella spiralis, eliminating a role for T-bet in MC recruitment to sites of infection and their activation and function. Therefore, remarkably, T-bet expression by DCs indirectly controls MCp homing to mucosal tissues.

The histamine-induced enhanced expression of vascular cell adhesion molecule-1 by nasal polyp-derived fibroblasts is inhibited by levocetirizine

BACKGROUND

Histamine, a key chemical mediator in allergic reaction, exhibits an array of pro-inflammatory effects that include the activation of fibroblasts. The aim of this study was to evaluate whether histamine could stimulate nasal polyp-derived fibroblasts to express vascular cell adhesion molecule (VCAM)-1, a surface molecule involved in structural-inflammatory cell interaction and whether levocetirizine could inhibit this induction.

METHODS

Primary nasal polyp tissue-derived fibroblasts were stimulated with histamine (10-1000 microM) or interleukin (IL)-4 plus tumor necrosis factor (TNF)-alpha (0.5-5 ng/mL) and VCAM-1 expression was evaluated by flow cytometry analysis. The inhibitory effect of the selective H1-antagonist levocetirizine (0.01-10.0 microM) on VCAM-1 expression was also tested.

RESULTS

Compared with unstimulated cultures, histamine or IL-4 + TNF-alpha, at the highest concentrations tested, significantly increase VCAM-1 expression (p < 0.05). To evaluate the ability of levocetirizine to downregulate VCAM-1 expression, fibroblasts were stimulated with histamine (1000 microM) or IL-4 + TNF-alpha (5 ng/mL), in the presence of the drug (0.01-10.0 microM). The histamine-induced VCAM-1 expression was effectively inhibited by levocetirizine (0.1-10.0 microM) (p < 0.05). No effect of the drug on IL-4 + TNF-alpha-induced VCAM-1 expression was observed.

CONCLUSIONS

Histamine upregulates VCAM-1 expression on nasal polyp-derived fibroblasts and this phenomenon, relevant to allergic late-phase inflammation, is effectively inhibited by levocetirizine.

Distinct mechanisms of integrin binding by Yersinia pseudotuberculosis adhesins determine the phagocytic response of host macrophages

The enteropathogenic yersiniae express two outer membrane adhesins, invasin and YadA, that contribute to pathogenesis. While invasin binds directly to beta1 integrin receptors with high affinity, YadA binds indirectly through extracellular matrix (ECM) components. In this study, Yersinia pseudotuberculosis inv and yadA mutants were used to investigate how these distinct binding mechanisms compare and potentially compete in activating signalling pathways and promoting bacterial uptake by host macrophages. The efficiency of adhesin-mediated phagocytic responses was found to be dependent on the relative expression of invasin and YadA on the bacterial surface as well as the expression of ECM proteins in the extracellular milieu. Under conditions of low concentrations of ECM, invasin was found to be the dominant adhesin, promoting high levels of phagocytosis coincident with robust and sustained activation of the protein tyrosine kinases Fak and Pyk2, phosphorylation of the adaptor molecule Cas and activation of the small GTPase Rac1. In the presence of higher concentrations of ECM, YadA became the dominant functional adhesin through its ability to engage integrin receptors via an ECM bridge. We propose a model whereby invasin promotes robust and prolonged activation of phagocytic signalling cascades by inducing a 'high-affinity' integrin conformation as well as integrin clustering. We postulate that YadA-ECM promotes phagocytosis through a more transient activation of signalling cascades that arises from integrin clustering in the context of a cross-linked fibrillar ECM network.

Regulation of highly cytokinergic IgE-induced mast cell adhesion by Src, Syk, Tec, and protein kinase C family kinases

Mast cells play a critical role in IgE-dependent immediate hypersensitivity. Recent studies have shown that, contrary to the traditional view, binding of monomeric IgE to Fc epsilon RI results in a number of biological outcomes in mast cells, including survival. However, IgE molecules display heterogeneity in inducing cytokine production; highly cytokinergic (HC) IgEs cause extensive Fc epsilon RI aggregation, which leads to potent enhancement of survival and other activation events, whereas poorly cytokinergic (PC) IgEs can do so inefficiently. The present study demonstrates that HC, but not PC, IgEs can efficiently induce adhesion and spreading of mouse mast cells on fibronectin-coated plates in slow and sustained kinetics. HC IgE-induced adhesion through beta1 and beta7 integrins promotes survival, IL-6 production, and DNA synthesis. Importantly, we have identified Lyn and Syk as requisite tyrosine kinases and Hck, Btk, and protein kinase C theta as contributory kinases in HC IgE-induced adhesion and spreading, whereas protein kinase C epsilon plays a negative role. Consistent with these results, Lyn, Syk, and Btk are activated in HC IgE-stimulated cells in a slower but more sustained manner, compared with cells stimulated with IgE and Ag. Thus, binding of HC IgEs to Fc epsilon RI induces adhesion of mast cells to fibronectin by modulating cellular activation signals in a unique fashion.

IgE- and IgE+Ag-mediated mast cell migration in an autocrine/paracrine fashion

Mast cells are the major effector cells for immediate hypersensitivity and chronic allergic reactions. These cells accumulate in mucosal tissues of allergic reactions, where immunoglobulin E (IgE) is produced locally. Here we provide evidence that, in addition to antigen that can attract IgE-bound mast cells, the type of IgE molecules that efficiently activate mast cells can promote the migration of mast cells in the absence of antigen. IgE- and IgE+Ag-mediated migration involves an autocrine/paracrine secretion of soluble factors including adenosine, leukotriene B4, and several chemokines. Their secretion depends on 2 tyrosine kinases, Lyn and Syk, and they are agonists of G-protein-coupled receptors and signal through phosphatidylinositol 3-kinase gamma, leading to mast cell migration. In mouse experiments, naive mast cells are attracted to IgE, and IgE-sensitized mast cells are attracted to antigen. Therefore, IgE and antigen are implicated in mast cell accumulation at allergic tissue sites with local high IgE levels.

GPIIb (CD41) integrin is expressed on mast cells and influences their adhesion properties

OBJECTIVES

GPIIb integrin expression has been found on platelets and megakaryocytes, and more recently on immature hematopoietic progenitors. We set out to investigate expression of GPIIb in other hematopoietic cell lineages and, having detected it on mast cells, aimed to determine what possible role it might perform.

METHODS

We have made use of cultured human and murine bone marrow mast cells (BMMC) in order to characterize the expression of GPIIb. Further, BMMC cultures from wild type and GPIIb deficient (gpIIb-/-) mice were used for comparison of the adhesive properties mediated by this receptor. Finally, peritoneal mast cells were analyzed from both wild type and (gpIIb-/-) mice.

RESULTS

We demonstrate expression of GPIIb on cultured BMMC. Using cells derived from mice homozygous for a null allele of gbIIb we show that the absence of GPIIb has no effect on mast cells with respect to a number of measures of cell growth and differentiation. However, loss of GPIIb on BMMC results in an increase in surface expression of aV integrin, the alternative partner of GPIIIa.

CONCLUSION

The results in this study demonstrate that GPIIb is expressed in human and murine mast cells. A function for GPIIb on mast cells is suggested by the altered adhesion of gbIIb-/- BMMC to fibronectin- and vitronectin-coated surfaces. Moreover, comparison of mast cells from the peritoneal cavity of wild type and gbIIb-/- mice indicates that GPIIb could influence the in vivo differentiation or homing of tissue mast cells.

In vivo exit of c-kit+/CD49d(hi)/beta7+ mucosal mast cell precursors from the bone marrow following infection with the intestinal nematode Trichinella spiralis

We have used the parasite helminth Trichinella spiralis to study the generation and differentiation of mast cell progenitors in the bone marrow of mice, as this infection triggers an intestinal mastocytosis which correlates with parasite expulsion. C-kit+ mast cell progenitors have previously been defined by methylcellulose colony-forming units and by limiting dilution assays in vitro. In vivo experiments have demonstrated the essential requirement by mast cells for specific integrin expression. We have defined 2 c-kit+ populations in the bone marrow, one of which coexpresses CD49d/beta7 integrin, a marker essential for small intestine immigration. We have confirmed the phenotype of these cells by using antagonistic anti-c-kit antibody in vivo. Our data show that the loss of c-kit+/beta7+ cells from the bone marrow correlates with their appearance in the blood and precedes detection of mature mast cells in the gut by 3 days. This exit correlates with an increase in soluble stem cell factor (SCF) in the serum, suggesting that the c-kit/SCF interaction may be chemotactic or haptotactic in nature. This study shows that during infection the bone marrow environment generates mast cells destined for the intestinal mucosa before their exit into the periphery, indicating a clear interplay between infection site and hematopoietic tissue.

Localization of BCR-ABL to F-actin regulates cell adhesion but does not attenuate CML development

We have previously found that P210BCR-ABL increases the adhesion of hematopoietic cell lines to fibronectin by a mechanism that is independent of tyrosine kinase activity. To investigate the pathway(s) by which P210BCR-ABL influences cell adhesion, we used a quantitative cell adhesion device that can discern small changes in cell adhesion to assay P210BCR-ABL with mutations in several critical domains. We expressed P210BCR-ABL mutants in 32D myeloblast cells and found that binding to fibronectin is mediated primarily by the alpha5beta1 integrin. We performed a structure/function analysis to map domains important for cell adhesion. Increased adhesion was mediated by 3 domains: (1) the N-terminal coiled-coil domain that facilitates oligomerization and F-actin localization; (2) bcr sequences between aa 163 to 210; and (3) F-actin localization through the C-terminal actin-binding domain of c-abl. We compared our adhesion results with the ability of these mutants to cause a chronic myelogenous leukemia (CML)-like disease in a murine bone marrow transplantation assay and found that adhesion to fibronectin did not correlate with the ability of these mutants to cause CML. Together, our results suggest that F-actin localization may play a pivotal role in modulating adhesion but that it is dispensable for the development of CML.

IgE alone stimulates mast cell adhesion to fibronectin via pathways similar to those used by IgE + antigen but distinct from those used by Steel factor

We recently demonstrated that immunoglobulin E (IgE), in the absence of cross-linking agents, activates signaling pathways in healthy murine bone marrow-derived mast cells (BMMCs) and that this activation enhances BMMC survival, at least in part, via secretion of autocrine-acting cytokines. We report herein that IgE alone also triggers the adhesion of both BMMCs and connective tissue mast cells (CTMCs) to the connective tissue component, fibronectin (FN). This adhesion occurs to the same extent as that triggered by optimal levels of Steel factor (SF) or IgE + antigen (IgE + Ag) and is mediated by an increased avidity of the integrin very late antigen 5 (VLA-5). Moreover, this IgE-induced adhesion, which is prolonged compared with that elicited by SF or IgE + Ag, requires phosphatidylinositol 3-kinase (PI3K), phospholipase C gamma (PLCgamma), and extracellular calcium but not extracellular-regulated kinase (Erk) or p38. Interestingly, we found, using the calcium channel blocker, 2-APB (2-aminoethoxydiphenyl borate) and Lyn-/- BMMCs that both IgE- and IgE + Ag-induced adhesion to FN require extracellular calcium entry, whereas SF does not. Furthermore, our data suggest that FN acts synergistically with IgE to prolong intracellular phosphorylation events and to enhance IgE-induced inflammatory cytokine production and BMMC survival.

Differential expression of integrin subunits on adherent and nonadherent mast cells

Mast cell progenitors arise in bone marrow and then migrate to peripheral tissues where they mature. It is presumed that integrin receptors are involved in their migration and homing. In the present study, the expression of various integrin subunits was investigated in three systems of adherent and nonadherent mast cells. Mesentery mast cells, freshly isolated bone marrow-derived mast cells (BMMC) and RBL-2H3 cells grown attached to tissue culture flasks are all adherent mast cells and peritoneal mast cells, and cultured BMMC and RBL-2H3 cells grown in suspension represent nonadherent mast cell populations. Pure populations of mast cells were immunomagnetically isolated from bone marrow, mesentery and peritoneal lavage using the mast cell-specific monoclonal antibody AA4. By immunomicroscopy, we could demonstrate that all of these mast cells expressed alpha 4, alpha 5, alpha 6, beta 1 and beta 7 integrin subunits. The expression of the alpha 4 integrin subunit was 25% higher in freshly isolated mesentery mast cells and BMMC. Consistent with the results obtained by immunomicroscopy, mesentery mast cells expressed 65% more mRNA for the alpha 4 integrin subunit than peritoneal mast cells. In vitro studies were also conducted using the rat mast cell line RBL-2H3. RBL-2H3 cells grown attached to the tissue culture flasks or as suspension cultures expressed the same integrin subunits identified in bone marrow, mesenteric and peritoneal mast cells ex vivo. Similarly, the expression of alpha 4 integrin was higher in adherent cells. Therefore, alpha 4 integrins may play a critical role in the anchorage of mast cells to the extracellular matrix in bone marrow and in peripheral tissues.

The fibronectin-binding integrins alpha5beta1 and alphavbeta3 differentially modulate RhoA-GTP loading, organization of cell matrix adhesions, and fibronectin fibrillogenesis

We have studied the formation of different types of cell matrix adhesions in cells that bind to fibronectin via either alpha5beta1 or alphavbeta3. In both cases, cell adhesion to fibronectin leads to a rapid decrease in RhoA activity. However, alpha5beta1 but not alphavbeta3 supports high levels of RhoA activity at later stages of cell spreading, which are associated with a translocation of focal contacts to peripheral cell protrusions, recruitment of tensin into fibrillar adhesions, and fibronectin fibrillogenesis. Expression of an activated mutant of RhoA stimulates alphavbeta3-mediated fibrillogenesis. Despite the fact that alpha5beta1-mediated adhesion to the central cell-binding domain of fibronectin supports activation of RhoA, other regions of fibronectin are required for the development of alpha5beta1-mediated but not alphavbeta3-mediated focal contacts. Using chimeras of beta1 and beta3 subunits, we find that the extracellular domain of beta1 controls RhoA activity. By expressing both beta1 and beta3 at high levels, we show that beta1-mediated control of the levels of beta3 is important for the distribution of focal contacts. Our findings demonstrate that the pattern of fibronectin receptors expressed on a cell dictates the ability of fibronectin to stimulate RhoA-mediated organization of cell matrix adhesions.

TGF-beta 1 regulates adhesion of mucosal mast cell homologues to laminin-1 through expression of integrin alpha 7

Mucosal mast cells (MMC) or their precursors migrate through the intestinal lamina propria to reside intraepithelially, where expression of mouse mast cell protease-1 indicates the mature phenotype. Alterations in expression of integrins that govern cell adhesion to the extracellular matrix may regulate this process. As the key cytokine mediating differentiation of mouse mast cell protease-1-expressing MMC homologues in vitro, TGF-beta1 was considered a likely candidate for regulation of the integrins that facilitate intraepithelial migration of MMC. Therefore, we examined adhesion of bone marrow-derived mast cells cultured with and without TGF-beta1 to laminin-1, fibronectin, and vitronectin along with expression of integrins likely to regulate this adhesion. Adhesion of PMA-stimulated cultured mast cells to laminin-1 increased from 5.3 +/- 3.6% (mean +/- SEM) in the absence of TGF-beta1 to 58.7 +/- 4.0% (p < 0.05) when cultured mast cells had differentiated into MMC homologues in the presence of TGF-beta1. Increased adhesion of MMC homologues to laminin-1 was also stimulated by FcepsilonRI cross-linking and the calcium ionophore A23187. Expression of the laminin-binding integrin alpha(7) by MMC homologues grown in the presence of TGF-beta1 was demonstrated by RT-PCR and flow cytometry, and preincubation of MMC homologues with the alpha(7)-neutralizing Ab 6A11 inhibited adhesion to laminin-1 by 98% (p < 0.05), demonstrating a novel role for this molecule in adhesion of a hemopoietic cell to laminin-1.

Thrombin induces mast cell adhesion to fibronectin: evidence for involvement of protease-activated receptor-1

Thrombin activates mast cells to release inflammatory mediators through a mechanism involving protease-activated receptor-1 (PAR-1). We hypothesized that PAR-1 activation would induce mast cell adhesion to fibronectin (FN). Fluorescent adhesion assay was performed in 96-well plates coated with FN (20 microg/ml). Murine bone marrow cultured mast cells (BMCMC) were used after 3-5 wk of culture (>98% mast cells by flow cytometry for c-Kit expression). Thrombin induced beta-hexosaminidase, IL-6, and matrix metalloproteinase-9 release from BMCMC. Thrombin and the PAR-1-activating peptide AparafluoroFRCyclohexylACitY-NH(2) (cit) induced BMCMC adhesion to FN in a dose-dependent fashion, while the PAR-1-inactive peptide FSLLRY-NH(2) had no effect. Thrombin and cit induced also BMCMC adhesion to laminin. Thrombin-mediated adhesion to FN was inhibited by anti-alpha(5) integrin Ab (51.1 +/- 6.7%; n = 5). The combination of anti-alpha(5) and anti-alpha(4) Abs induced higher inhibition (65.7 +/- 7.1%; n = 5). Unlike what is known for FcepsilonRI-mediated adhesion, PAR-1-mediated adhesion to FN did not increase mediator release. We then explored the signaling pathways involved in PAR-1-mediated mast cell adhesion. Thrombin and cit induced p44/42 and p38 phosphorylation. Pertussis toxin inhibited PAR-1-mediated BMCMC adhesion by 57.3 +/- 7.3% (n = 4), indicating that G(i) proteins are involved. Wortmannin and calphostin almost completely inhibited PAR-1-mediated mast cell adhesion, indicating that PI-3 kinase and protein kinase C are involved. Adhesion was partially inhibited by the mitogen-activated protein kinase kinase 1/2 inhibitor U0126 (24.5 +/- 3.3%; n = 3) and the p38 inhibitor SB203580 (25.1 +/- 10.4%; n = 3). The two inhibitors had additive effects. Therefore, thrombin mediates mast cell adhesion through the activation of G(i) proteins, phosphoinositol 3-kinase, protein kinase C, and mitogen-activated protein kinase pathways.

Function of linear and cyclic RGD-containing peptides in osteoprogenitor cells adhesion process

Cell adhesion directly influences cell growth, differentiation and migration as well as morphogenesis, integrity and repair. The extracellular matrix (ECM) elaborated by osteoblast cells constitutes a regulator of the cell adhesion process and then of the related phenomenon. These regulatory effects of ECM are mediated through integrins and some of them are able to bind RGD sequences. The aim of this study was to determine the role of the sequence and the structure of RGD-containing peptides (linear and cyclic) as well as their role in the cell adhesion process. Cell adhesion assays onto ECM proteins coated surfaces were performed using a range of linear and cyclic RGD-containing peptides. We showed a different human osteoprogenitor cell adhesion according to the coating for ECM proteins and for RGD-peptides. Inhibition assays using peptides showed different responses depending on the coated protein. Depending on the amino-acid sequence and the structure of the peptides (cyclic linear), we observed 100% inhibition of cell adhesion onto vitronectin. These results suggest the importance of sequence, structure and conformation of the peptide, which may play a crucial function in the ligand/receptor interaction and/or in the stability of the interaction.

Attenuation of very late antigen-5-mediated adhesion of bone marrow-derived mast cells to fibronectin by peptides with inverted hydropathy to EF-hands

Release of allergic mediators from mast cells is enhanced by very late Ag (VLA)-5-mediated interaction of these cells with fibronectin. In this report, we show that VLA-5-mediated adhesion of bone marrow-derived mast cells to fibronectin can be induced by two different pathways: first, FcepsilonRI clustering, which depends on calmodulin activation and extracellular Ca(2+), and, second, by Mn(2+) stimulation, which is independent of calmodulin activation and antagonized by Ca(2+). Previous studies have shown the presence of several cation-binding domains in VLA-5 that are homologous to the calcium-binding EF-hands of calmodulin. To show a role for EF-hands of different proteins in VLA-5-mediated adhesion, we used calcium-like peptides (CALP), CALP1 and CALP2, designed to bind to EF-hands based on inverted hydropathy. CALP1 and, more potently, CALP2 inhibited FcepsilonRI-induced adhesion to fibronectin via different mechanisms. The target for the effects of CALP1 and 2 on FcepsilonRI-induced adhesion and degranulation was intracellular and likely involved calmodulin. Interestingly only CALP2 was able to inhibit Mn(2+)-induced calmodulin-independent adhesion by interfering with an extracellular target, which is probably VLA-5. We conclude that CALP1 and 2 can inhibit VLA-5-mediated adhesion of mast cells to fibronectin through binding to EF-hands of multiple proteins, and that these peptides can be used as lead compounds for the development of future therapy against allergy.

Defects in adhesion and migration, but not in proliferation and differentiation, of embryonic stem cells upon replacement of integrin subunit beta1A by beta1D

Beta1D is a skeletal muscle-specific splice variant of the beta1 integrin subunit, while beta1A integrin subunit has a wide tissue distribution. We have previously shown that replacement of beta1A by beta1D by homologous recombination (knockin) in all mouse tissues was embryonic lethal. Through two successive rounds of homologous recombination, we have now produced embryonic stem (ES) cells expressing beta1D instead of beta1A, and analyzed the ability of beta1D to support ES cell differentiation in vitro and in teratomas in vivo. Beta1D knockin (KI) ES cells grew at a similar rate but as more compact colonies than the beta1A-expressing cells. Increased cell cohesiveness, however, did not appear to involve changes in cadherin activity. Although in both beta1A and beta1D-KI ES cells only one beta1 allele is active; the expression of beta1 integrins in the beta1D-KI ES cells was reduced by 50%, compared with that in the beta1A-expressing cells; this correlated with impaired adhesive and migratory capacities. It appeared that during in vitro cardiac differentiation, in spite of a slight delay in the induction of two cardiac-specific transcripts, the alpha- and beta-myosin heavy chains, contracting cardiomyocytes were detected in similar numbers and at the same time in embryoid bodies (EB) derived from beta1D-KI and from beta1A cells. Furthermore, replacement of beta1A by beta1D in ES cells did not affect neurite differentiation in embryoid bodies in the presence of retinoic acid suggesting that beta1D supports neurogenesis. However, the impaired migration of other cells from the EB, including endodermal cells, prevented the normal outgrowth of neurites in beta1D-KI EB. Finally, injection of beta1D-KI ES cells in the flank of syngeneic mice gave rise to fully developed teratomas containing simple and pluristratified epithelia, muscle, cartilage, blood vessels, and tissues from the neural lineage. These results show that the muscle-specific splice variant beta1D, in spite of its specific cytoplasmic domain, supports the differentiation of many cell types. This further suggests that the embryonic lethality in the beta1D-KI embryos was mainly due to the different ability of beta1 A and beta1D to mediate cell adhesion and migration.

Induction of cell scattering by expression of beta1 integrins in beta1-deficient epithelial cells requires activation of members of the rho family of GTPases and downregulation of cadherin and catenin function

Adhesion receptors, which connect cells to each other and to the surrounding extracellular matrix (ECM), play a crucial role in the control of tissue structure and of morphogenesis. In this work, we have studied how intercellular adhesion molecules and beta1 integrins influence each other using two different beta1-null cell lines, epithelial GE11 and fibroblast-like GD25 cells. Expression of beta1A or the cytoplasmic splice variant beta1D, induced the disruption of intercellular adherens junctions and cell scattering in both GE11 and GD25 cells. In GE11 cells, the morphological change correlated with the redistribution of zonula occluden (ZO)-1 from tight junctions to adherens junctions at high cell confluency. In addition, the expression of beta1 integrins caused a dramatic reorganization of the actin cytoskeleton and of focal contacts. Interaction of beta1 integrins with their respective ligands was required for a complete morphological transition towards the spindle-shaped fibroblast-like phenotype. The expression of an interleukin-2 receptor (IL2R)-beta1A chimera and its incorporation into focal adhesions also induced the disruption of cadherin-based adhesions and the reorganization of ECM-cell contacts, but failed to promote cell migration on fibronectin, in contrast to full-length beta1A. This indicates that the disruption of cell-cell adhesion is not simply the consequence of the stimulated cell migration. Expression of beta1 integrins in GE11 cells resulted in a decrease in cadherin and alpha-catenin protein levels accompanied by their redistribution from the cytoskeleton-associated fraction to the detergent-soluble fraction. Regulation of alpha-catenin protein levels by beta1 integrins is likely to play a role in the morphological transition, since overexpression of alpha-catenin in GE11 cells before beta1 prevented the disruption of intercellular adhesions and cell scattering. In addition, using biochemical activity assays for Rho-like GTPases, we show that the expression of beta1A, beta1D, or IL2R-beta1A in GE11 or GD25 cells triggers activation of both RhoA and Rac1, but not of Cdc42. Moreover, dominant negative Rac1 (N17Rac1) inhibited the disruption of cell-cell adhesions when expressed before beta1. However, all three GTPases might be involved in the morphological transition, since expression of either N19RhoA, N17Rac1, or N17Cdc42 reversed cell scattering and partially restored cadherin-based adhesions in GE11-beta1A cells. Our results indicate that beta1 integrins regulate the polarity and motility of epithelial cells by the induction of intracellular molecular events involving a downregulation of alpha-catenin function and the activation of the Rho-like G proteins Rac1 and RhoA.

Differences in phosphatase modulation of α4 β1 and α5 β1 integrin-mediated adhesion and migration of B16F1 cells

It is well established that a biphasic relationship exists between the adhesive strength of β1 integrins and their ability to mediate cell movement. Thus, cell movement increases progressively with adhesive strength, but beyond a certain point of optimal interaction, cell movement is reduced with further increases in adhesive function. The interplay between the various kinase and phosphatase activities provides the balance in β1 integrin-mediated cell adhesion and migration. In the present study, the significance of protein tyrosine phosphatases (PTP) and ser/thr protein phosphatases (PP) in α4β1 and α5β1 integrin-mediated mouse melanoma B16F1 cell anchorage and migration on fibronectin was characterized using phosphatase inhibitors. At low fibronectin concentration, α5β1 functioned as the predominant receptor for cell movement; a role for α4β1 in B16F1 cell migration increased progressively with fibronectin concentration. Treatment of B16F1 cells with PTP inhibitors, sodium orthovanadate (Na3VO4) and phenylarsine oxide (PAO), or PP-1/2A inhibitor, okadaic acid (OA), abolished cell movement. Inhibition of cell movement by PAO and OA was associated by a reduction in the adhesive strength of α4β1 and α5β1. In contrast, treatment of B16F1 cells with Na3VO4 resulted in selective stimulation of the adhesive function of α5β1, but not α4β1. Therefore, our results demonstrate that (i) both PTP and PP-1/2A have roles in cell movement, (ii) modulation of cell movement by PTP and PP-1/2A may involve either a stimulation or reduction of β1 integrin adhesive strength, and (iii) distinct phosphatase-mediated signaling pathways for differential regulation of the various β1 integrins exist. Key words: phosphatases, integrins, cell movement, cell adhesion.

Characterization of a functional relationship between hepatocyte growth factor and mouse bone marrow-derived mast cells

During the early stage (at 4 weeks) of interleukin-3 (IL-3)-induced development, mouse bone marrow-derived mast cells (BMMC) express alpha 4, alpha 5 and alpha 6 integrins, whereas with further maturation beyond 10 weeks, only alpha 5 integrin remains stably expressed. Hepatocyte growth factor (HGF) modulates the growth and movement of diverse cell types upon binding to its receptor, encoded by the proto-oncogene c-met. We report here the expression of c-met by BMMC throughout the course of their development. In addition, HGF stimulated migration of early week-4 BMMC, but not of the later stage week-10 BMMC, on fibronectin and laminin substrates. The developmental stage-dependent effect of HGF on BMMC was due to specific stimulation of the migratory function of alpha 4 and alpha 6, but not alpha 5 integrins. In addition, HGF had no effect on BMMC growth, either alone or in combination with IL-3. While HGF is stimulatory of the migratory function of BMMC, our results show that BMMC in turn can modulate HGF function. Thus, upon activation via the IgE receptors, BMMC released proteases that abolished HGF activities. Analyses of the degradation products by two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot using antisera prepared against recombinant HGF and the kringle 3 domain of HGF revealed specific degradation of HGF alpha but not beta/beta' subunits. Therefore, our results suggest that: 1) the motogenic effect of HGF on BMMC varies according to the stage of their development, 2) HGF stimulation of BMMC migration is due to selective activation of alpha 4 and alpha 6, but not alpha 5 integrin function, and 3) there exists a two-way relationship between BMMC and HGF such that HGF stimulates the beta 1 integrin-mediated migratory function of BMMC, which can, in turn, modulate HGF function by release of serine proteases.

Tenascin-R interferes with integrin-dependent oligodendrocyte precursor cell adhesion by a ganglioside-mediated signalling mechanism

Oligodendrocyte (OL) lineage progression is characterized by the transient expression of the disialoganglioside GD3 by OL precursor (preOL) cells followed by the sequential expression of myelin-specific lipids and proteins. Whereas GD3+ preOLs are highly motile cells, the migratory capacity of OLs committed to terminal differentiation is strongly reduced, and we have recently shown that the extracellular matrix protein tenascin-R (TN-R) promotes the stable adhesion and differentiation of O4+ OLs by a sulphatide-mediated autocrine mechanism (O4 is a monoclonal antibody recognizing sulphatides/seminolipids expressed by OLs and in myelin). Using culture conditions that allow the isolation of mouse OLs at distinct lineage stages, here we demonstrate that TN-R is antiadhesive for GD3+ preOLs and inhibits their integrin-dependent adhesion to fibronectin (FN) by a disialoganglioside-mediated signalling mechanism affecting the tyrosine phosphorylation of the focal adhesion kinase. This responsive mechanism appears to be common to various cell types expressing disialogangliosides as: (i) disialogangliosides interfered with the inhibition of cell adhesion of different neural and non-neural cells on substrata containing TN-R and FN or RGD-containing FN fragments. TN-R interacted specifically with disialoganglioside-expressing cells or immobilized gangliosides, and ganglioside treatment of TN-R substrata resulted in a delayed preOL cell detachment as a function of time. We conclude that OL response to one and the same signal in the extracellular matrix critically depends on the molecular repertoire expressed by OLs at different lineage stages and could thus define their final positioning.

Integrin subunits responsible for adhesion of human osteoblast-like cells to biomimetic peptide surfaces

We have identified the integrin subunits responsible for the initial adhesion of human osteoblast-like cells to peptide-modified surfaces. Biomimetic peptide surfaces containing homogenous RGD (Arg-Gly-Asp), homogenous FHRRIKA (Phe-His-Arg-Arg-Ile-Lys-Ala), and a mixed ratio of FHRRIKA:RGD (25:75) were used to assess integrin-mediated adhesion. The RGD and FHRRIKA peptides were selected from the cell-binding and putative heparin-binding domains of bone sialoprotein. A panel of monoclonal antibodies against human alpha1, alpha2, alpha3, alpha4, alpha5, beta1, alpha(v), and alpha(v)beta3 was used to identify the subunits most dominant in mediating short-term (10 or 30 minutes) and long-term (4 hours) cell adhesion to the peptide surfaces. Anti-alpha2, anti-beta1, and anti-alpha(v) significantly (p < 0.05) diminished cell attachment to homogenous RGD surfaces following 30 minutes of incubation. After 4 hours of incubation on RGD-grafted surfaces, immunostaining of these integrin subunits revealed discrete localization of the alpha(v) subunit at the periphery of the cell (similar to focal contact points), whereas the alpha2 and beta1 subunits stained very diffusely throughout the cell. A radial-flow apparatus was used to determine the effect of anti-integrin antibodies on strength of cell detachment following 10 minutes of incubation on peptide-grafted surfaces. The strength of detachment from surfaces containing RGD was significantly reduced (p < 0.05) in the presence of anti-alpha2, anti-alpha(v), or anti-beta1 compared with controls (presence of preimmune mouse IgG). None of the antibodies significantly influenced cell attachment to homogenous FHRRIKA-grafted surfaces. These results demonstrate that initial (30 minutes) attachment of human osteoblast-like cells to homogenous RGD surfaces was mediated by the collagen receptor alpha2beta1 and the vitronectin receptor alpha(v)beta3, whereas only the vitronectin receptor governed longer term (longer than 30 minutes) adhesion (localization to focal contacts). The importance of distinct integrins in mediating the attachment of bone cells to RGD-immobilized surfaces indicates a strategy for engineering orthopaedic implants with a built-in surface specificity for cell adhesion.

Leukocytes utilize both alpha4 and alpha5 integrins for intraislet infiltration in non-obese diabetic mice

The loss of insulin-producing cells during the development of type 1 diabetes is dependent on leukocyte infiltration of beta-islets in the pancreas. Injection of antibodies to integrins and their ligands has been shown to prevent the development of diabetes in non-obese diabetic (NOD) mice. However, little is known about the progression of infiltration by leukocytes after their homing and extravasation into the pancreas. In the present study, the effect of monoclonal antibodies (mAbs) to alpha4 and alpha5 integrins on leukocytes that had infiltrated the islets was characterized in NOD mice at 10 weeks of age when insulitis was in progress, or in mice with recent onset of diabetes. Injection of mAbs to either alpha4 or alpha5 integrins had little effect on the extent of leukocyte infiltration in 10-week-old or diabetic mice. In contrast, leukocyte infiltration was significantly reduced upon injection of mAbs to both alpha4 and alpha5 integrins. The reduction in leukocyte infiltration was due to decreases in the percentage of islets with intraislet infiltration. However, the observed effect of mAbs to alpha4 and alpha5 integrins was reversible, since intraislet infiltration resumed upon termination of antibody treatment. Results suggest that after homing to the pancreas, leukocytes utilize both alpha4 and alpha5 integrins for intraislet infiltration.

Periodontal-derived cells attach to cementum attachment protein via alpha 5 beta 1 integrin

A specific collagenous cementum attachment protein (CAP) has been identified in human cementum which promotes selective cell migration towards and attachment of various periodontal derived cell populations to root surfaces in vitro. The CAP is known to support attachment of periodontal-derived cell via an RGD motif, which suggests an integrin-mediated mode of attachment. The purpose of the present study was to ascertain which integrin(s) are involved in the attachment of periodontal-derived cells to CAP. The integrins examined comprised subunits of the major receptors for fibronectin (alpha 5) and collagen (alpha 2, alpha 3), as well as the common beta 1 subunit which is present in many extracellular matrix receptors. The wells of 48-well non-tissue culture treated plates were coated with CAP (2 micrograms/ml). For negative and positive controls the wells were coated with bovine serum albumin and fibronectin (5 micrograms/ml), respectively. Human gingival fibroblasts and periodontal ligament fibroblasts were labeled with [3H]-proline, incubated with anti-integrin antibodies and added to the precoated wells. Attachment was assessed after incubating the cells for 1 h at 37 degrees C in the presence of the antibodies. Antibodies to alpha 5 and beta 1 inhibited the attachment of both human gingival fibroblasts and human periodontal ligament fibroblasts to CAP, while anti alpha 2 and alpha 3 antibodies did not affect the attachment. The binding of the fibroblasts to fibronectin was also inhibited by anti-alpha 5 and beta 1 antibodies, both of which are components of the "classical" fibronectin receptor and remained unaffected by the addition of anti-alpha 2 and alpha 3 antibodies. Proteins migrating in SDS-polyacrylamide gels in positions similar to the alpha 5 and beta 1 integrin subunits were present in fractions bound to a column of CAP coupled to Sepharose CL-4B. These results indicate that the attachment to CAP of the periodontal-derived cells, human gingival fibroblasts and human periodontal ligament fibroblasts, is mediated primarily via the integrin alpha 5 beta 1.

Essential Roles of Lyn in Fibronectin-Mediated Filamentous Actin Assembly and Cell Motility in Mast Cells

Although the requirement for c-Src in extracellular matrix (ECM)-mediated fibroblast motility has been well established, the roles of hemopoietic Src family protein tyrosine kinases in leukocyte migration have not been fully elucidated. To address the issue, we analyzed fibronectin (Fn)-mediated adhesion signaling in rat basophilic leukemia (RBL) 2H3 cells overexpressing 1) Csk, 2) a membrane-anchored, gain-of-function Csk (mCsk), and 3) a kinase-defective mCsk (mCsk(−)). Parent RBL2H3 cells, expressing autoactivated c-kit, readily adhered to Fn-coated surface, developed typical leukocyte adhesion machinery (podosome), and migrated toward Fn without cytokine priming, thus provided a simple experimental system to analyze Fn-mediated outside-in signaling. While overexpression of Csk or the Csk mutants did not significantly affect cell adhesion to the Fn surface or α5 integrin recruitment to the attachment sites, Csk suppressed and mCsk almost abolished Fn-mediated tyrosine phosphorylation of paxillin, filamentous actin assembly to podosomes, and cell migration, but mCsk(−) did not. Coexpression of LynA devoid of C-terminal negative regulatory tyrosine in mCsk cells successfully restored Fn-mediated podosome formation and cell migration. Coexpression of c-Src lacking the C-terminal tyrosine reconstructed podosomes, but could not restore the cell migration regardless of its expression level. Collectively, these observations provide evidence that Src family protein tyrosine kinases are required, and that Lyn could transmit sufficient signal for Fn-mediated cytoskeletal changes leading to cell locomotion in RBL2H3 cells, and they suggest that Lyn and c-Src are differentially involved in cell motility.