Fibronectin binds integrin α5β1 to regulate macular neovascularization through the Wnt/β-catenin signaling pathway

Age-related macular degeneration (AMD) is a progressive, degenerative disease of the macula. The formation of macular neovascularization (MNV) and subretinal fibrosis of AMD is the most classic cause of the loss of vision in older adults worldwide. While the underlying causes of MNV and subretinal fibrosis remain elusive, the common feature of many common retinal diseases is changes the proportions of protein deposition in extracellular matrix (ECM) when compared to normal tissue. In ECM, fibronectin (FN) is a crucial component and plays a pivotal part not only in fibrotic diseases but also in the process of angiogenesis. The study aims to understand the role of ligand FN and its common integrin receptor α5β1 on MNV, and to understand the molecular mechanism involved. To study this, the laser-induced MNV mouse model and the rhesus macaque choroid-retinal endothelial cell line (RF/6A) chemical hypoxia mode were established, and the FN-α5β1 expression levels were detected by immunohistochemistry (IHC) and quantitative real-time PCR analysis (qRT-PCR). Fibronectin expression was silenced using small interfering RNA (siRNA) targeting FN. The tube formation and vitro scratch assays were used to assess the ability to form blood vessels and cell migration. To measure the formation of MNV, immunofluorescence, and Western blot assays were used. These results revealed that the expressions of FN and integrin α5β1 were distinctly increased in the laser-induced MNV mouse model and in the RF/6A cytochemically induced hypoxia model, and the expression tendency was identical. After the use of FN siRNA, the tube formation and migration abilities of the RF/6A cells were lower, the ability of endothelial cells to proliferate was confined and the scope of damage caused by the laser in animal models was significantly cut down. In addition, FN gene knockdown dramatically inhibited the expression of Wnt/β-catenin signal. The interaction of FN with the integrin receptor α5β1 in the constructed model, which may act through the Wnt/β-catenin signaling pathway, was confirmed in this study. In conclusion, FN may be a potential new molecular target for the prevention and treatment of subretinal fibrosis and MNV.

Redox-active endosomes mediate α5β1 integrin signaling and promote chondrocyte matrix metalloproteinase production in osteoarthritis

Mechanical cues sensed by integrins induce cells to produce proteases to remodel the extracellular matrix. Excessive protease production occurs in many degenerative diseases, including osteoarthritis, in which articular cartilage degradation is associated with the genesis of matrix protein fragments that can activate integrins. We investigated the mechanisms by which integrin signals may promote protease production in response to matrix changes in osteoarthritis. Using a fragment of the matrix protein fibronectin (FN) to activate the α5β1 integrin in primary human chondrocytes, we found that endocytosis of the integrin and FN fragment complex drove the production of the matrix metalloproteinase MMP-13. Activation of α5β1 by the FN fragment, but not by intact FN, was accompanied by reactive oxygen species (ROS) production initially at the cell surface, then in early endosomes. These ROS-producing endosomes (called redoxosomes) contained the integrin-FN fragment complex, the ROS-producing enzyme NADPH oxidase 2 (NOX2), and SRC, a redox-regulated kinase that promotes MMP-13 production. In contrast, intact FN was endocytosed and trafficked to recycling endosomes without inducing ROS production. Articular cartilage from patients with osteoarthritis showed increased amounts of SRC and the NOX2 complex component p67phox. Furthermore, we observed enhanced localization of SRC and p67phox at early endosomes, suggesting that redoxosomes could transmit and sustain integrin signaling in response to matrix damage. This signaling mechanism not only amplifies the production of matrix-degrading proteases but also establishes a self-perpetuating cycle that contributes to the ongoing degradation of cartilage matrix in osteoarthritis.

Reticular adhesions are assembled at flat clathrin lattices and opposed by active integrin α5β1

Reticular adhesions (RAs) consist of integrin αvβ5 and harbor flat clathrin lattices (FCLs), long-lasting structures with similar molecular composition as clathrin-mediated endocytosis (CME) carriers. Why FCLs and RAs colocalize is not known. Here, we show that RAs are assembled at FCLs in a process controlled by fibronectin (FN) and its receptor, integrin α5β1. We observed that cells on FN-rich matrices displayed fewer FCLs and RAs. CME machinery inhibition abolished RAs and live-cell imaging showed that RA establishment requires FCL coassembly. The inhibitory activity of FN was mediated by the activation of integrin α5β1 at Tensin1-positive fibrillar adhesions. Conventionally, endocytosis disassembles cellular adhesions by internalizing their components. Our results present a novel paradigm in the relationship between these two processes by showing that endocytic proteins can actively function in the assembly of cell adhesions. Furthermore, we show this novel adhesion assembly mechanism is coupled to cell migration via unique crosstalk between cell-matrix adhesions.

SEMA7a primes integrin α5β1 engagement instructing fibroblast mechanotransduction, phenotype and transcriptional programming

Integrins are cellular receptors that bind the extracellular matrix (ECM) and facilitate the transduction of biochemical and biophysical microenvironment cues into cellular responses. Upon engaging the ECM, integrin heterodimers must rapidly strengthen their binding with the ECM, resulting in the assembly of force-resistant and force-sensitive integrin associated complexes (IACs). The IACs constitute an essential apparatus for downstream signaling and fibroblast phenotypes. During wound healing, integrin signaling is essential for fibroblast motility, proliferation, ECM reorganization and, ultimately, restoration of tissue homeostasis. Semaphorin 7A (SEMA7a) has been previously implicated in post-injury inflammation and tissue fibrosis, yet little is known about SEMA7a's role in directing stromal cell, particularly fibroblast, behaviors. We demonstrate that SEMA7a regulates integrin signaling through cis-coupling with active integrin α5β1 on the plasma membrane, enabling rapid integrin adhesion strengthening to fibronectin (Fn) and normal downstream mechanotransduction. This molecular function of SEMA7a potently regulates fibroblast adhesive, cytoskeletal, and migratory phenotype with strong evidence of downstream alterations in chromatin structure resulting in global transcriptomic reprogramming such that loss of SEMA7a expression is sufficient to impair the normal migratory and ECM assembly phenotype of fibroblasts resulting in significantly delayed tissue repair in vivo.

Receptor-binding domain of SARS-CoV-2 is a functional αv-integrin agonist

Among the novel mutations distinguishing SARS-CoV-2 from similar coronaviruses is a K403R substitution in the receptor-binding domain (RBD) of the viral spike (S) protein within its S1 region. This amino acid substitution occurs near the angiotensin-converting enzyme 2-binding interface and gives rise to a canonical RGD adhesion motif that is often found in native extracellular matrix proteins, including fibronectin. Here, the ability of recombinant S1-RBD to bind to cell surface integrins and trigger downstream signaling pathways was assessed and compared with RGD-containing, integrin-binding fragments of fibronectin. We determined that S1-RBD supported adhesion of fibronectin-null mouse embryonic fibroblasts as well as primary human small airway epithelial cells, while RBD-coated microparticles attached to epithelial monolayers in a cation-dependent manner. Cell adhesion to S1-RBD was RGD dependent and inhibited by blocking antibodies against αv and β3 but not α5 or β1 integrins. Similarly, we observed direct binding of S1-RBD to recombinant human αvβ3 and αvβ6 integrins, but not α5β1 integrins, using surface plasmon resonance. S1-RBD adhesion initiated cell spreading, focal adhesion formation, and actin stress fiber organization to a similar extent as fibronectin. Moreover, S1-RBD stimulated tyrosine phosphorylation of the adhesion mediators FAK, Src, and paxillin; triggered Akt activation; and supported cell proliferation. Thus, the RGD sequence of S1-RBD can function as an αv-selective integrin agonist. This study provides evidence that cell surface αv-containing integrins can respond functionally to spike protein and raises the possibility that S1-mediated dysregulation of extracellular matrix dynamics may contribute to the pathogenesis and/or post-acute sequelae of SARS-CoV-2 infection.

Dysregulation of integrin αvβ3 and α5β1 impedes migration of placental endothelial cells in fetal growth restriction

Placentas from pregnancies complicated by severe early-onset fetal growth restriction (FGR) exhibit diminished vascular development mediated by impaired angiogenesis, but underlying mechanisms remain unknown. In this study, we show that FGR endothelial cells demonstrate inherently reduced migratory capacity despite the presence of fibronectin, a matrix protein abundant in placental stroma that displays abnormal organization in FGR placentas. Thus, we hypothesized that aberrant endothelial-fibronectin interactions in FGR are a key mechanism underlying impaired FGR endothelial migration. Using human fetoplacental endothelial cells isolated from uncomplicated term control and FGR pregnancies, we assessed integrin α5β1 and αvβ3 regulation during cell migration. We show that endothelial integrin α5β1 and αvβ3 interactions with fibronectin are required for migration and that FGR endothelial cells responded differentially to integrin inhibition, indicating integrin dysregulation in FGR. Whole-cell expression was not different between groups. However, there were significantly more integrins in focal adhesions and reduced intracellular trafficking in FGR. These newly identified changes in FGR endothelial cellular processes represent previously unidentified mechanisms contributing to persistent angiogenic deficiencies in FGR.

Receptor and Molecular Mechanism of AGGF1 Signaling in Endothelial Cell Functions and Angiogenesis

Objective

Angiogenic factor AGGF1 (angiogenic factor with G-patch and FHA [Forkhead-associated] domain 1) promotes angiogenesis as potently as VEGFA (vascular endothelial growth factor A) and regulates endothelial cell (EC) proliferation, migration, specification of multipotent hemangioblasts and venous ECs, hematopoiesis, and vascular development and causes vascular disease Klippel-Trenaunay syndrome when mutated. However, the receptor for AGGF1 and the underlying molecular mechanisms remain to be defined.

Approach and Results

Using functional blocking studies with neutralizing antibodies, we identified [alpha]5[beta]1 as the receptor for AGGF1 on ECs. AGGF1 interacts with [alpha]5[beta]1 and activates FAK (focal adhesion kinase), Src (proto-oncogene tyrosine-protein kinase), and AKT (protein kinase B). Functional analysis of 12 serial N-terminal deletions and 13 C-terminal deletions by every 50 amino acids mapped the angiogenic domain of AGGF1 to a domain between amino acids 604-613 (FQRDDAPAS). The angiogenic domain is required for EC adhesion and migration, capillary tube formation, and AKT activation. The deletion of the angiogenic domain eliminated the effects of AGGF1 on therapeutic angiogenesis and increased blood flow in a mouse model for peripheral artery disease. A 40-mer or 15-mer peptide containing the angiogenic domain blocks AGGF1 function, however, a 15-mer peptide containing a single amino acid mutation from -RDD- to -RGD- (a classical RGD integrin-binding motif) failed to block AGGF1 function.

Conclusions

We have identified integrin [alpha]5[beta]1 as an EC receptor for AGGF1 and a novel AGGF1-mediated signaling pathway of [alpha]5[beta]1-FAK-Src-AKT for angiogenesis. Our results identify an FQRDDAPAS angiogenic domain of AGGF1 crucial for its interaction with [alpha]5[beta]1 and signaling.

CYRI-A limits invasive migration through macropinosome formation and integrin uptake regulation

The Scar/WAVE complex drives actin nucleation during cell migration. Interestingly, the same complex is important in forming membrane ruffles during macropinocytosis, a process mediating nutrient uptake and membrane receptor trafficking. Mammalian CYRI-B is a recently described negative regulator of the Scar/WAVE complex by RAC1 sequestration, but its other paralogue, CYRI-A, has not been characterized. Here, we implicate CYRI-A as a key regulator of macropinosome formation and integrin internalization. We find that CYRI-A is transiently recruited to nascent macropinosomes, dependent on PI3K and RAC1 activity. CYRI-A recruitment precedes RAB5A recruitment but follows sharply after RAC1 and actin signaling, consistent with it being a local inhibitor of actin polymerization. Depletion of both CYRI-A and -B results in enhanced surface expression of the α5β1 integrin via reduced internalization. CYRI depletion enhanced migration, invasion, and anchorage-independent growth in 3D. Thus, CYRI-A is a dynamic regulator of macropinocytosis, functioning together with CYRI-B to regulate integrin trafficking.

Cell-Extracellular Matrix Interactions Play Multiple Essential Roles in Aortic Arch Development

RATIONALE

Defects in the morphogenesis of the fourth pharyngeal arch arteries (PAAs) give rise to lethal birth defects. Understanding genes and mechanisms regulating PAA formation will provide important insights into the etiology and treatments for congenital heart disease.

OBJECTIVE

Cell-ECM (extracellular matrix) interactions play essential roles in the morphogenesis of PAAs and their derivatives, the aortic arch artery and its major branches; however, their specific functions are not well-understood. Previously, we demonstrated that integrin α5β1 and Fn1 (fibronectin) expressed in the Isl1 lineages regulate PAA formation. The objective of the current studies was to investigate cellular mechanisms by which integrin α5β1 and Fn1 regulate aortic arch artery morphogenesis.

METHODS AND RESULTS

Using temporal lineage tracing, whole-mount confocal imaging, and quantitative analysis of the second heart field (SHF) and endothelial cell (EC) dynamics, we show that the majority of PAA EC progenitors arise by E7.5 in the SHF and contribute to pharyngeal arch endothelium between E7.5 and E9.5. Consequently, SHF-derived ECs in the pharyngeal arches form a plexus of small blood vessels, which remodels into the PAAs by 35 somites. The remodeling of the vascular plexus is orchestrated by signals dependent on the pharyngeal ECM microenvironment, extrinsic to the endothelium. Conditional ablation of integrin α5β1 or Fn1 in the Isl1 lineages showed that signaling by the ECM regulates aortic arch artery morphogenesis at multiple steps: (1) accumulation of SHF-derived ECs in the pharyngeal arches, (2) remodeling of the EC plexus in the fourth arches into the PAAs, and (3) differentiation of neural crest-derived cells adjacent to the PAA endothelium into vascular smooth muscle cells.

CONCLUSIONS

PAA formation is a multistep process entailing dynamic contribution of SHF-derived ECs to pharyngeal arches, the remodeling of endothelial plexus into the PAAs, and the remodeling of the PAAs into the aortic arch artery and its major branches. Cell-ECM interactions regulated by integrin α5β1 and Fn1 play essential roles at each of these developmental stages.

Implication of integrins α3β1 and α5β1 in invasion and anoikis of SK-Mel-147 human melanoma cells: non-canonical functions of protein kinase Akt

Downregulation of integrins α3β1 and α5β1 strongly decreased cell colony formation and in vitro invasion and markedly enhanced anoikis in SK-Mel-147 human melanoma cells. These modifications were accompanied by a marked increase in the levels of active Akt protein kinase, which indicated it played a non-canonical function in the melanoma cells. Pharmacological inhibition of Akt1, an Akt isozyme, in cells depleted of α3β1 or α5β1 restored their invasive activity, while inhibition of the Akt 2 isoform did not cause a visible effect. Similar to our previous results with the α2β1 integrin, this finding suggested that in signaling pathways initiated by α3β1 and α5β1, the Akt1 isoform performs a non-canonical function in regulating invasive phenotype of melanoma cells. In contrast, when the effects of Akt inhibitors on anoikis of the melanoma cells were compared, the Akt2 isoform demonstrated a non-canonical activity in which Akt2 suppression led to a significant attenuation of apoptosis in cells with downregulated α3β1 or α5β1. Our results were the first evidence that, in the same tumor cells, different integrins can control various manifestations of tumor progression through distinct signaling pathways that are both common to various integrins and specific to a particular receptor.

RhoJ Regulates α5β1 Integrin Trafficking to Control Fibronectin Remodeling during Angiogenesis

Rho guanosine triphosphatases (GTPases) are master regulators of cell shape and cell movement [1]. The archetypal family members RhoA, Rac1, and Cdc42 arose early in eukaryotic evolution and coordinate a diverse range of cell morphologies and migrations. Evolution of the vertebrates was paralleled by expansion of this family through gene duplication. Emergence of an adaptive immune system and more complex neural systems presented new roles for Rho GTPases, filled by new family members. Cdc42 underwent gene duplication to produce two related proteins-RhoQ and RhoJ [2]. RhoQ is active in neural dynamics; however, RhoJ is highly expressed in endothelial cells under control of the endothelial-specific promoter ERG [3, 4]. RhoJ is required for angiogenesis [5, 6] and has multiple roles in this process [7, 8]. We recently demonstrated that RhoJ regulates the endosomal trafficking of podocalyxin during angiogenesis to control lumen formation [9]. Here, we use vesicle purification and proteomic analysis to identify the endothelial targets of RhoJ-mediated trafficking. We identify α5β1 integrin as a major RhoJ cargo and show that RhoJ regulates the intracellular trafficking of active α5β1 integrin in endothelial cells to repress fibronectin fibrillogenesis. Accordingly, mice lacking RhoJ show deregulated deposition of fibronectin around vessels during developmental angiogenesis. Intriguingly, we show that RhoJ acts in opposition to Cdc42 in this process through competition for a shared partner, PAK3. These studies identify a critical role for RhoJ in matrix remodeling during blood vessel formation and demonstrate a functional interrelationship between RhoJ and its evolutionary parent.

Two new, near-infrared, fluorescent probes as potential tools for imaging bone repair

A precise imaging technique to evaluate osteogenesis, osteodifferentiation, and osseointegration following peri-implant surgery is in high clinical demand. Herein, we report the generation of two new, near-infrared (NIR) fluorescent probes for use in the molecular imaging of bone repair. The first probe aims to monitor the in vitro differentiation of human mesenchymal stem cells (MSCs) into osteoblasts. A NIR fluorochrome was conjugated to a cyclic peptide that binds to integrin α5β1, a factor that promotes osteogenesis in MSCs and therefore functioned as an osteoblast-specific marker. The second probe aims to monitor osteogenesis, and was generated by conjugating the drug pamidronate to a NIR fluorescent gold nanocluster. Pamidronate specifically binds to hydroxyapatite (HA), a mineral present in bone that is produced by osteoblasts, and therefore provides a functional marker for new bone formation. Our results show that both probes bind to their specific targets in vitro-differentiated osteoblasts, and not to undifferentiated MSCs, and emit NIR fluorescence for functional detection. This in vitro work demonstrates the ability of these probes to bind to active osteoblasts and their mineral deposits and highlight their potential utility as clinical tools for the imaging of the osseointegration process at the molecular level.

Integrin Subtypes and Nanoscale Ligand Presentation Influence Drug Sensitivity in Cancer Cells

Cancer cell-matrix interactions have been shown to enhance cancer cell survival via the activation of pro-survival signaling pathways. These pathways are initiated at the site of interaction, i.e., integrins, and thus, their inhibition has been the target of therapeutic strategies. Individual roles for fibronectin-binding integrin subtypes α_vβ₃ and α₅β₁ have been shown for various cellular processes; however, a systematic comparison of their function in adhesion-dependent chemoresistance is lacking. Here, we utilize integrin subtype-specific peptidomimetics for α_vβ₃ and α₅β₁, both as blocking agents on fibronectin-coated surfaces and as surface-immobilized adhesion sites, in order to parse out their role in breast cancer cell survival. Block copolymer micelle nanolithography is utilized to immobilize peptidomimetics onto highly ordered gold nanoparticle arrays with biologically relevant interparticle spacings (35, 50, or 70 nm), thereby providing a platform for ascertaining the dependence of ligand spacing in chemoprotection. We show that several cellular properties-morphology, focal adhesion formation, and migration-are intricately linked to both the integrin subtype and their nanospacing. Importantly, we show that chemotherapeutic drug sensitivity is highly dependent on both parameters, with smaller ligand spacing generally hindering survival. Furthermore, we identify ligand type-specific patterns of drug sensitivity, with enhanced chemosurvival when cells engage α_vβ₃ vs α₅β₁ on fibronectin; however, this is heavily reliant on nanoscale spacing, as the opposite is observed when ligands are spaced at 70 nm. These data imply that even nanoscale alterations in extracellular matrix properties have profound effects on cancer cell survival and can thus inform future therapies and drug testing platforms.

Reappraising the role of α5 integrin and the microenvironmental support in stress erythropoiesis

We previously studied the role of β1 integrin and some of its different α partners relevant to erythropoiesis. Although clear and consistent answers regarding the role of α4β1 (VLA-4) were evident, the role of its companion integrin α5β1 (VLA-5) was clouded by inconsistent outcomes in all prior publications. Furthermore, the functional consequences of integrin deficiencies only in microenvironmental (ME) cells supporting erythroid cell expansion and maturation post stress have never been explored. In the study described here, we created several additional mouse models in the aim of addressing unanswered questions regarding functional consequences of single or combined integrin deficiencies in erythroid cells or only in ME supporting cells. Our novel and expansive data solidified the intrinsic requirement of both α4 and α5 integrins in erythroid cells for their proliferative expansion and maturation in response to stress; α5 integrin alone, deleted either early in all hematopoietic cells or only in erythroid cell, has only a redundant role in proliferative expansion and is dispensable for erythroid maturation. By contrast, α4 integrin, on its own, exerts a dominant effect on timely and optimal erythroid maturation. Deficiency of both α4 and α5 integrins in ME cells, including macrophages, does not negatively influence stress response by normal erythroid cells, in great contrast to the effect of ME cells deficient in all β1 integrins. Collectively the present data offer deeper insight into the coordination of different β1 integrin functional activities in erythroid cells or in ME cells for optimal erythroid stress response.

Integrin α5β1 regulates PP2A complex assembly through PDE4D in atherosclerosis

Fibronectin in the vascular wall promotes inflammatory activation of the endothelium during vascular remodeling and atherosclerosis. These effects are mediated in part by fibronectin binding to integrin α5, which recruits and activates phosphodiesterase 4D5 (PDE4D5) by inducing its dephosphorylation on an inhibitory site Ser651. Active PDE then hydrolyzes anti-inflammatory cAMP to facilitate inflammatory signaling. To test this model in vivo, we mutated the integrin binding site in PDE4D5 in mice. This mutation reduced endothelial inflammatory activation in athero-prone regions of arteries, and, in a hyperlipidemia model, reduced atherosclerotic plaque size while increasing markers of plaque stability. We then investigated the mechanism of PDE4D5 activation. Proteomics identified the PP2A regulatory subunit B55α as the factor recruiting PP2A to PDE4D5. The B55α-PP2A complex localized to adhesions and directly dephosphorylated PDE4D5. This interaction also unexpectedly stabilized the PP2A-B55α complex. The integrin-regulated, pro-atherosclerotic transcription factor Yap is also dephosphorylated and activated through this pathway. PDE4D5 therefore mediates matrix-specific regulation of EC phenotype via an unconventional adapter role, assembling and anchoring a multifunctional PP2A complex with other targets. These results are likely to have widespread consequences for control of cell function by integrins.

c-Abl regulates YAPY357 phosphorylation to activate endothelial atherogenic responses to disturbed flow

Local flow patterns determine the uneven distribution of atherosclerotic lesions. This research aims to elucidate the mechanism of regulation of nuclear translocation of Yes-associated protein (YAP) under oscillatory shear stress (OSS) in the atheroprone phenotype of endothelial cells (ECs). We report here that OSS led to tyrosine phosphorylation and strong, continuous nuclear translocation of YAP in ECs that is dependent on integrin α5β1 activation. YAP overexpression in ECs blunted the anti-atheroprone effect of an integrin α5β1-blocking peptide (ATN161) in Apoe-/- mice. Activation of integrin α5β1 induced tyrosine, but not serine, phosphorylation of YAP in ECs. Blockage of integrin α5β1 with ATN161 abolished the phosphorylation of YAP at Y357 induced by OSS. Mechanistic studies showed that c-Abl inhibitor attenuated the integrin α5β1-induced YAP tyrosine phosphorylation. Furthermore, the phosphorylation of c-Abl and YAPY357 was significantly increased in ECs in atherosclerotic vessels of mice and in human plaques versus normal vessels. Finally, bosutinib, a tyrosine kinase inhibitor, markedly reduced the level of YAPY357 and the development of atherosclerosis in Apoe-/- mice. The c-Abl/YAPY357 pathway serves as a mechanism for the activation of integrin α5β1 and the atherogenic phenotype of ECs in response to OSS, and provides a potential therapeutic strategy for atherogenesis.

Inhibition of integrin α5β1 ameliorates VEGF-induced retinal neovascularization and leakage by suppressing NLRP3 inflammasome signaling in a mouse model

PURPOSE

To assess the effect of inhibiting integrin α5β1 by ATN-161 on vascular endothelial growth factor (VEGF)-induced neovascularization (NV) and leakage causing retinal detachment in adult Tet/opsin/VEGF transgenic mice, and characterize the underlying mechanism of its function.

METHOD

Retinas from adult Tet/opsin/VEGF transgenic mice and human retinal endothelial cells (HRECs) exposed to VEGF (treated with ATN-161 or PBS) were used to carry out immunofluorescence, RT-PCR and western blot to examine expression levels of integrin α5β1 and the NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome. Retinal frozen section analysis was used to assess NV and leakage causing retinal detachment.

RESULTS

In comparison to normal-treated mice, doxycycline-treated Tet/opsin/VEGF transgenic mice showed severe retinal detachment and higher integrin α5β1 expression. Furthermore, the retinal detachment was inhibited significantly by ATN-161. Additionally, ATN-161 treatment was associated with a conspicuous reduction in NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC), cleaved caspase-1, and mature interleukin-1β expression levels in the retinas of Tet/opsin/VEGF transgenic mice treated with doxycycline as well as in HRECs exposed to VEGF.

CONCLUSION

ATN-161, an antagonist of integrin α5β1, is a promising treatment for retinal neovascularization (RNV), and its retinal protection role appears to take effect through inhibition of NLRP3 inflammasome activity.

Fibronectin-bound α5β1 integrins sense load and signal to reinforce adhesion in less than a second

Integrin-mediated mechanosensing of the extracellular environment allows cells to control adhesion and signalling. Whether cells sense and respond to force immediately upon ligand-binding is unknown. Here, we report that during adhesion initiation, fibroblasts respond to mechanical load by strengthening integrin-mediated adhesion to fibronectin (FN) in a biphasic manner. In the first phase, which depends on talin and kindlin as well as on the actin nucleators Arp2/3 and mDia, FN-engaged α5β1 integrins activate focal adhesion kinase (FAK) and c-Src in less than 0.5 s to steeply strengthen α5β1- and αV-class integrin-mediated adhesion. When the mechanical load exceeds a certain threshold, fibroblasts decrease adhesion and initiate the second phase, which is characterized by less steep adhesion strengthening. This unique, biphasic cellular adhesion response is mediated by α5β1 integrins, which form catch bonds with FN and signal to FN-binding integrins to reinforce cell adhesion much before visible adhesion clusters are formed.

Galectin-3 alters the lateral mobility and clustering of β1-integrin receptors

Glycoprotein receptors are influenced by myriad intermolecular interactions at the cell surface. Specific glycan structures may interact with endogenous lectins that enforce or disrupt receptor-receptor interactions. Glycoproteins bound by multivalent lectins may form extended oligomers or lattices, altering the lateral mobility of the receptor and influencing its function through endocytosis or changes in activation. In this study, we have examined the interaction of Galectin-3 (Gal-3), a human lectin, with adhesion receptors. We measured the effect of recombinant Gal-3 added exogenously on the lateral mobility of the α5β1 integrin on HeLa cells. Using single-particle tracking (SPT) we detected increased lateral mobility of the integrin in the presence of Gal-3, while its truncated C-terminal domain (Gal-3C) showed only minor reductions in lateral mobility. Treatment of cells with Gal-3 increased β1-integrin mediated migration with no apparent changes in viability. In contrast, Gal-3C decreased both cell migration and viability. Fluorescence microscopy allowed us to confirm that exogenous Gal-3 resulted in reorganization of the integrin into larger clusters. We used a proteomics analysis to confirm that cells expressed endogenous Gal-3, and found that addition of competitive oligosaccharide ligands for the lectin altered the lateral mobility of the integrin. Together, our results are consistent with a Gal-3-integrin lattice model of binding and confirm that the lateral mobility of integrins is natively regulated, in part, by galectins.

Targeting integrin α5β1 ameliorates severe airway hyperresponsiveness in experimental asthma

Treatment options are limited for severe asthma, and the need for additional therapies remains great. Previously, we demonstrated that integrin αvβ6-deficient mice are protected from airway hyperresponsiveness, due in part to increased expression of the murine ortholog of human chymase. Here, we determined that chymase protects against cytokine-enhanced bronchoconstriction by cleaving fibronectin to impair tension transmission in airway smooth muscle (ASM). Additionally, we identified a pathway that can be therapeutically targeted to mitigate the effects of airway hyperresponsiveness. Administration of chymase to human bronchial rings abrogated IL-13-enhanced contraction, and this effect was not due to alterations in calcium homeostasis or myosin light chain phosphorylation. Rather, chymase cleaved fibronectin, inhibited ASM adhesion, and attenuated focal adhesion phosphorylation. Disruption of integrin ligation with an RGD-containing peptide abrogated IL-13-enhanced contraction, with no further effect from chymase. We identified α5β1 as the primary fibronectin-binding integrin in ASM, and α5β1-specific blockade inhibited focal adhesion phosphorylation and IL-13-enhanced contraction, with no additional effect from chymase. Delivery of an α5β1 inhibitor into murine airways abrogated the exaggerated bronchoconstriction induced by allergen sensitization and challenge. Finally, α5β1 blockade enhanced the effect of the bronchodilator isoproterenol on airway relaxation. Our data identify the α5β1 integrin as a potential therapeutic target to mitigate the severity of airway contraction in asthma.

PPFIA1 drives active α5β1 integrin recycling and controls fibronectin fibrillogenesis and vascular morphogenesis

Basolateral polymerization of cellular fibronectin (FN) into a meshwork drives endothelial cell (EC) polarity and vascular remodelling. However, mechanisms coordinating α5β1 integrin-mediated extracellular FN endocytosis and exocytosis of newly synthesized FN remain elusive. Here we show that, on Rab21-elicited internalization, FN-bound/active α5β1 is recycled to the EC surface. We identify a pathway, comprising the regulators of post-Golgi carrier formation PI4KB and AP-1A, the small GTPase Rab11B, the surface tyrosine phosphatase receptor PTPRF and its adaptor PPFIA1, which we propose acts as a funnel combining FN secretion and recycling of active α5β1 integrin from the trans-Golgi network (TGN) to the EC surface, thus allowing FN fibrillogenesis. In this framework, PPFIA1 interacts with active α5β1 integrin and localizes close to EC adhesions where post-Golgi carriers are targeted. We show that PPFIA1 is required for FN polymerization-dependent vascular morphogenesis, both in vitro and in the developing zebrafish embryo.

Constitutive Association of Tie1 and Tie2 with Endothelial Integrins is Functionally Modulated by Angiopoietin-1 and Fibronectin

Functional cross-talk between Tie2 and Integrin signaling pathways is essential to coordinate endothelial cell adhesion and migration in response to the extracellular matrix, yet the mechanisms behind this phenomenon are unclear. Here, we examine the possibility that receptor cross-talk is driven through uncharacterized Tie-integrin interactions on the endothelial surface. Using a live cell FRET-based proximity assay, we monitor Tie-integrin receptor recognition and demonstrate that both Tie1 and Tie2 readily associate with integrins α₅ß₁ and α_Vß₃ through their respective ectodomains. Although not required, Tie2-integrin association is significantly enhanced in the presence of the extracellular component and integrin ligand fibronectin. In vitro binding assays with purified components reveal that Tie-integrin recognition is direct, and further demonstrate that the receptor binding domain of the Tie2 ligand Ang-1, but not the receptor binding domain of Ang-2, can independently associate with α₅ß₁ or α_Vß₃. Finally, we reveal that cooperative Tie/integrin interactions selectively stimulate ERK/MAPK signaling in the presence of both Ang-1 and fibronectin, suggesting a molecular mechanism to sensitize Tie2 to extracellular matrix. We provide a mechanistic model highlighting the role of receptor localization and association in regulating distinct signaling cascades and in turn, the angiogenic switch.

Ligand-induced Epitope Masking: DISSOCIATION OF INTEGRIN α5β1-FIBRONECTIN COMPLEXES ONLY BY MONOCLONAL ANTIBODIES WITH AN ALLOSTERIC MODE OF ACTION

We previously demonstrated that Arg-Gly-Asp (RGD)-containing ligand-mimetic inhibitors of integrins are unable to dissociate pre-formed integrin-fibronectin complexes (IFCs). These observations suggested that amino acid residues involved in integrin-fibronectin binding become obscured in the ligand-occupied state. Because the epitopes of some function-blocking anti-integrin monoclonal antibodies (mAbs) lie near the ligand-binding pocket, it follows that the epitopes of these mAbs may become shielded in the ligand-occupied state. Here, we tested whether function-blocking mAbs directed against α5β1 can interact with the integrin after it forms a complex with an RGD-containing fragment of fibronectin. We showed that the anti-α5 subunit mAbs JBS5, SNAKA52, 16, and P1D6 failed to disrupt IFCs and hence appeared unable to bind to the ligand-occupied state. In contrast, the allosteric anti-β1 subunit mAbs 13, 4B4, and AIIB2 could dissociate IFCs and therefore were able to interact with the ligand-bound state. However, another class of function-blocking anti-β1 mAbs, exemplified by Lia1/2, could not disrupt IFCs. This second class of mAbs was also distinguished from 13, 4B4, and AIIB2 by their ability to induce homotypic cell aggregation. Although the epitope of Lia1/2 was closely overlapping with those of 13, 4B4, and AIIB2, it appeared to lie closer to the ligand-binding pocket. A new model of the α5β1-fibronectin complex supports our hypothesis that the epitopes of mAbs that fail to bind to the ligand-occupied state lie within, or very close to, the integrin-fibronectin interface. Importantly, our findings imply that the efficacy of some therapeutic anti-integrin mAbs could be limited by epitope masking.

Allosteric Regulation of Fibronectin/α5β1 Interaction by Fibronectin-Binding MSCRAMMs

Adherence of microbes to host tissues is a hallmark of infectious disease and is often mediated by a class of adhesins termed MSCRAMMs (Microbial Surface Components Recognizing Adhesive Matrix Molecules). Numerous pathogens express MSCRAMMs that specifically bind the heterodimeric human glycoprotein fibronectin (Fn). In addition to roles in adhesion, Fn-binding MSCRAMMs exploit physiological Fn functions. For example, several pathogens can invade host cells by a mechanism whereby MSCRAMM-bound Fn bridges interaction with α₅β₁ integrin. Here, we investigate two Fn-binding MSCRAMMs, FnBPA (Staphylococcus aureus) and BBK32 (Borrelia burgdorferi) to probe structure-activity relationships of MSCRAMM-induced Fn/α₅β₁integrin activation. Circular dichroism, fluorescence resonance energy transfer, and dynamic light scattering techniques uncover a conformational rearrangement of Fn involving domains distant from the MSCRAMM binding site. Surface plasmon resonance experiments demonstrate a significant enhancement of Fn/α₅β₁ integrin affinity in the presence of FnBPA or BBK32. Detailed kinetic analysis of these interactions reveal that this change in affinity can be attributed solely to an increase in the initial Fn/α₅β₁ on-rate and that this rate-enhancement is dependent on high-affinity Fn-binding by MSCRAMMs. These data implicate MSCRAMM-induced perturbation of specific intramolecular contacts within the Fn heterodimer resulting in activation by exposing previously cryptic α₅β₁ interaction motifs. By correlating structural changes in Fn to a direct measurement of increased Fn/α₅β₁ affinity, this work significantly advances our understanding of the structural basis for the modulation of integrin function by Fn-binding MSCRAMMs.

Endostatin inhibits the tumorigenesis of hemangioendothelioma via downregulation of CXCL1

Hemangioendotheliomas could be repressed by various anti-angiogenic agents in animal models. It was unclear whether the agents target hemangioendothelioma cells directly. This study elucidated the mechanism by which endostatin inhibited hemangioendothelioma progression. Expression of the endostatin receptors nucleolin and integrin α5β1 in hemangioendothelioma was assessed by immunohistochemistry. The effects of endostatin on the hemangioendothelioma-derived cells (EOMA) were evaluated by proliferation and apoptosis assays and by angiogenesis array screening. This revealed the contribution of the Chemokine (C-X-C motif) ligand 1 (CXCL1) to hemangioendothelioma progression, which was explored in vitro and in vivo. The clinical relevance of CXCL1 expression in hemangioendothelioma was also evaluated using tissue array. EOMA cells expressed nucleolin and integrin α5β1 and bound to endostatin. Endostatin did not alter proliferation or hypoxia-induced apoptosis in EOMA cells but it did impair the pro-angiogenic capacity of the cells. Endothelial cell migration was induced by CXCL1 produced by EOMA cells and endostatin downregulated CXCL1 production by inactivating its transcriptional factor, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). In vivo, the knockdown of CXCL1 significantly impaired EOMA cell growth in nude mice; endostatin had no effect when CXCL1 was overexpressed. A strong correlation was observed between CXCL1 levels and hemangioendothelioma occurrence in patients. CXCL1, which was responsible for hemangioendothelioma progression by stimulating angiogenesis, was impaired by endostatin via inactivation of NF-κB in an animal model. In vascular lesions in patients, CXCL1 expression was a negative prognostic factor. CXCL1-inhibting agents such as endostatin may constitute a useful approach to treat the malignant or intermediate vascular lesions.

The NLRP3 Inflammasome Is a Pathogen Sensor for Invasive Entamoeba histolytica via Activation of α5β1 Integrin at the Macrophage-Amebae Intercellular Junction

Entamoeba histolytica (Eh) is an extracellular protozoan parasite of humans that invades the colon to cause life-threatening intestinal and extra-intestinal amebiasis. Colonized Eh is asymptomatic, however, when trophozoites adhere to host cells there is a considerable inflammatory response that is critical in the pathogenesis of amebiasis. The host and/or parasite factors that trigger the inflammatory response to invading Eh are not well understood. We recently identified that Eh adherence to macrophages induces inflammasome activation and in the present study we sought to determine the molecular events upon contact that coordinates this response. Here we report that Eh contact-dependent activation of α₅β₁ integrin is critical for activation of the NLRP3 inflammasome. Eh-macrophage contact triggered recruitment of α₅β₁ integrin and NLRP3 into the intercellular junction, where α₅β₁ integrin underwent activation by an integrin-binding cysteine protease on the parasite surface, termed EhCP5. As a result of its activation, α₅β₁ integrin induced ATP release into the extracellular space through opening of pannexin-1 channels that signalled through P2X₇ receptors to deliver a critical co-stimulatory signal that activated the NLRP3 inflammasome. Both the cysteine protease activity and integrin-binding domain of EhCP5 were required to trigger α₅β₁ integrin that led to ATP release and NLRP3 inflammasome activation. These findings reveal engagement of α₅β₁ integrin across the parasite-host junction is a key regulatory step that initiates robust inflammatory responses to Eh. We propose that α₅β₁ integrin distinguishes Eh direct contact and functions with NLRP3 as pathogenicity sensor for invasive Eh infection.

Amebiasis caused by the enteric protozoan parasite Entamoeba histolytica is among the three top causes of death from parasitic infections worldwide, as a result of amebic colitis (dysentery) and liver or brain abscess. When Eh invades the intestinal barrier and contacts host tissue there is a profound inflammatory response, which is thought to drive the disease. One of the central outstanding questions has been how the immune response is escalated at sites of invasion. Adherence of the parasite to host cells has long been appreciated in the pathogenesis of amebiasis, but was never considered as a “cue” that host cells use to detect Eh and initiate host defense. Here we introduce the idea, and demonstrate, that an intercellular junction forms between Eh and host cells upon contact that engages the NLRP3 inflammasome. The NLRP3 inflammasome belongs to a group of “danger” sensors that are uniquely designed to rapidly activate highly inflammatory host defenses. In this work, we identified a surface receptor on macrophages that normally functions in adhesion and polarization recognizes a protein on the outer surface of Eh. Intriguingly, Eh also secretes this protein. However, the full activation of the surface receptor leading to inflammasome activation only occurs when the Eh protein is immobilized on the parasite surface. Thus, we uncovered a molecular mechanism though which host cells distinguish direct contact, and therefore recognize parasites that are immediately present in the tissue, to mobilize a highly inflammatory response. We believe this concept is central to understanding the biology of amebiasis.

Regulation of the ITGA2 gene by epigenetic mechanisms in prostate cancer

BACKGROUND

Integrin alpha2 beta1 (α2 β1 ) plays an integral role in tumour cell invasion, metastasis and angiogenesis, and altered expression of the receptor has been linked to tumour prognosis in several solid tumours. However, the relationship is complex, with both increased and decreased expression associated with different stages of tumour metastases in several tumour types. The ITGA2 gene, which codes for the α2 subunit, was examined to investigate whether a large CpG island associated with its promoter region is involved in the differential expression of ITGA2 observed in prostate cancer.

METHODS

Bisulphite sequencing of the ITGA2 promoter was used to assess methylation in formalin-fixed paraffin-embedded (FFPE) prostate tumour specimens and prostate cancer cell lines, PC3, 22Rv1 and LNCaP. Changes in ITGA2 mRNA expression were measured using quantitative PCR. ITGA2 functionality was interrogated using cell migration scratch assays and siRNA knockdown experiments.

RESULTS

Bisulphite sequencing revealed strikingly decreased methylation at key CpG sites within the promoter of tumour samples, when compared with normal prostate tissue. Altered methylation of this CpG island is also associated with differences in expression in the non-invasive LNCaP, and the highly metastatic PC3 and 22Rv1 prostate cancer cell lines. Further bisulphite sequencing confirmed that selected CpGs were highly methylated in LNCaP cells, whilst only low levels of methylation were observed in PC3 and 22Rv1 cells, correlating with ITGA2 transcript levels. Examination of the increased expression of ITGA2 was shown to influence migratory potential via scratch assay in PC3, 22Rv1 and LNCaP cells, and was confirmed by siRNA knockdown experiments.

CONCLUSIONS

Taken together, our data supports the assertion that epigenetic modification of the ITGA2 promoter is a mechanism by which ITGA2 expression is regulated.

H. pylori CagL-Y58/E59 prime higher integrin α5β1 in adverse pH condition to enhance hypochlorhydria vicious cycle for gastric carcinogenesis

Background/Aims

H. pylori CagL amino acid polymorphisms such as Y58/E59 can increase integrin α5β1 expression and gastric cancer risk. Hypochlorhydria during chronic H. pylori infection promotes gastric carcinogenesis. The study test whether CagL-Y58/E59 isolates may regulate integrin α5β1 to translocate CagA via the type IV secretory system even under adverse pH conditions, and whether the integrin α5β1 expression primed by H. pylori is a pH-dependent process involving hypochlorhydria in a vicious cycle to promote gastric carcinogenesis.

Methods

The expressions of integrin α5 and β1, CagA phosphorylation, IL-8, FAK, EGFR, and AKT activation of AGS cells exposed to CagL-Y58/E59 H. pylori, isogenic mutants, and different H. pylori CagL amino acid replacement mutants under different pH values were determined. Differences in the pepsinogen I/II ratio (indirectly indicating gastric acidity) and gastric integrin α5β1 expression were compared among the 172 H. pylori-infected patients with different cancer risks.

Results

Even under adversely low pH condition, H. pylori CagL-Y58/E59 still keep active integrin β1 with stronger binding affinity, CagA translocation, IL-8, FAK, EGFR, and AKT activation than the other mutants (p<0.05). The in vitro assay revealed higher priming of integrin α5β1 by H. pylori under elevated pH as hypochlorhydria (p<0.05). In the H. pylori-infected patients, the gastric integrin α5β1 expressions were higher in those with pepsinogen I/II ratio <6 than in those without (p<0.05).

Conclusions

H. pylori CagL-Y58/E59 prime higher integrin under adverse pH and may involve to enhance hypochlorhydria vicious cycle for gastric carcinogenesis, and thus require an early eradication.

The role of TG2 in regulating S100A4-mediated mammary tumour cell migration

The importance of S100A4, a Ca(2+)-binding protein, in mediating tumour cell migration, both intracellularly and extracellularly, is well documented. Tissue transglutaminase (TG2) a Ca(2+)-dependent protein crosslinking enzyme, has also been shown to enhance cell migration. Here by using the well characterised non-metastatic rat mammary R37 cells (transfected with empty vector) and highly metastatic KP1 cells (R37 cells transfected with S100A4), we demonstrate that inhibition of TG2 either by TG2 inhibitors or transfection of cells with TG2 shRNA block S100A4-accelerated cell migration in the KP1cells and in R37 cells treated with exogenous S100A4. Cell migration was also blocked by the treatment with the non-cell permeabilizing TG2 inhibitor R294, in the human breast cancer cell line MDA-MB-231 (Clone 16, which has a high level of TG2 expression). Inhibition was paralleled by a decrease in S100A4 polymer formation. In vitro co-immunoprecipitation and Far Western blotting assays and cross-linking assays showed not only the direct interaction between TG2 and S100A4, but also confirmed S100A4 as a substrate for TG2. Using specific functional blocking antibodies, a targeting peptide and a recombinant protein as a competitive treatment, we revealed the involvement of syndecan-4 and α5β1 integrin co-signalling pathways linked by activation of PKCα in this TG2 and S100A4-mediated cell migration. We propose a mechanism for TG2-regulated S100A4-related mediated cell migration, which is dependent on TG2 crosslinking.

Tetraspanin CO-029 inhibits colorectal cancer cell movement by deregulating cell-matrix and cell-cell adhesions

Alterations in tetraspanin CO-029 expression are associated with the progression and metastasis of cancers in the digestive system. However, how CO-029 promotes cancer metastasis is still poorly understood. To determine the mechanism, we silenced CO-029 expression in HT29 colon cancer cells and found that the CO-029 knockdown significantly reduced cell migratory ability. The diminished cell migration was accompanied by the upregulation of both integrin-dependent cell-matrix adhesion on laminin and calcium-dependent cell-cell adhesion. The cell surface levels of laminin-binding integrin α3β1 and fibronectin-integrin α5β1 were increased while the level of CD44 was decreased upon CO-029 silencing. These changes contribute to the altered cell-matrix adhesion. The deregulated cell-cell adhesion results, at least partially, from increased activity of cadherins and reduced level of MelCAM. In conclusion, CO-029 functions as a regulator of both cell-matrix and cell-cell adhesion. During colon cancer progression, CO-029 promotes cancer cell movement by deregulating cell adhesions.

Prematurely elevating estradiol in early baboon pregnancy suppresses uterine artery remodeling and expression of extravillous placental vascular endothelial growth factor and α1β1 and α5β1 integrins

We previously showed that advancing the increase in estradiol levels from the second to the first third of baboon pregnancy suppressed placental extravillous trophoblast (EVT) invasion and remodeling of the uterine spiral arteries. Cell culture studies show that vascular endothelial cell growth factor (VEGF) plays a central role in regulating EVT migration and remodeling of the uterine spiral arteries by increasing the expression/action of certain integrins that control extracellular matrix remodeling. To test the hypothesis that the estradiol-induced reduction in vessel remodeling in baboons is associated with an alteration in VEGF and integrin expression, extravillous placental VEGF and integrin expression was determined on d 60 of gestation (term is 184 d) in baboons in which uterine artery transformation was suppressed by maternal estradiol administration on d 25-59. EVT uterine spiral artery invasion was 5-fold lower (P < 0.01), and VEGF protein expression, quantified by in situ proximity ligation assay, was 50% lower (P < 0.05) in the placenta anchoring villi of estradiol-treated than in untreated baboons. α1β1 and α5β1 mRNA levels in cells isolated by laser capture microdissection from the anchoring villi and cytotrophoblastic shell of estradiol-treated baboons were over 2-fold (P < 0.01) and 40% (P < 0.05) lower, respectively, than in untreated animals. In contrast, placental extravillous αvβ3 mRNA expression was unaltered by estradiol treatment. In summary, extravillous placental expression of VEGF and α1β1 and α5β1 integrins was decreased in a cell- and integrin-specific manner in baboons in which EVT invasion and remodeling of the uterine spiral arteries were suppressed by prematurely elevating estradiol levels in early pregnancy. We propose that estrogen normally controls the extent to which the uterine arteries are transformed by placental EVT in primate pregnancy by regulating expression of VEGF and particular integrin extracellular remodeling molecules that mediate this process.

Slit2/Robo4 signaling modulates HIV-1 gp120-induced lymphatic hyperpermeability

Dissemination of HIV in the host involves transit of the virus and virus-infected cells across the lymphatic endothelium. HIV may alter lymphatic endothelial permeability to foster dissemination, but the mechanism is largely unexplored. Using a primary human lymphatic endothelial cell model, we found that HIV-1 envelope protein gp120 induced lymphatic hyperpermeability by disturbing the normal function of Robo4, a novel regulator of endothelial permeability. HIV-1 gp120 induced fibronectin expression and integrin α₅β₁ phosphorylation, which led to the complexing of these three proteins, and their subsequent interaction with Robo4 through its fibronectin type III repeats. Moreover, pretreatment with an active N-terminus fragment of Slit2, a Robo4 agonist, protected lymphatic endothelial cells from HIV-1 gp120-induced hyperpermeability by inhibiting c-Src kinase activation. Our results indicate that targeting Slit2/Robo4 signaling may protect the integrity of the lymphatic barrier and limit the dissemination of HIV in the host.

Cell-cell interactions mediate the response of vascular smooth muscle cells to substrate stiffness

The vessel wall experiences progressive stiffening with age and the development of cardiovascular disease, which alters the micromechanical environment experienced by resident vascular smooth muscle cells (VSMCs). In vitro studies have shown that VSMCs are sensitive to substrate stiffness, but the exact molecular mechanisms of their response to stiffness remains unknown. Studies have also shown that cell-cell interactions can affect mechanotransduction at the cell-substrate interface. Using flexible substrates, we show that the expression of proteins associated with cell-matrix adhesion and cytoskeletal tension is regulated by substrate stiffness, and that an increase in cell density selectively attenuates some of these effects. We also show that cell-cell interactions exert a strong effect on cell morphology in a substrate-stiffness dependent manner. Collectively, the data suggest that as VSMCs form cell-cell contacts, substrate stiffness becomes a less potent regulator of focal adhesion signaling. This study provides insight into the mechanisms by which VSMCs respond to the mechanical environment of the blood vessel wall, and point to cell-cell interactions as critical mediators of VSMC response to vascular injury.

Cancer cells regulate biomechanical properties of human microvascular endothelial cells

Metastasis is a key event of malignant tumor progression. The capability to metastasize depends on the ability of the cancer cell to migrate into connective tissue, adhere, and possibly transmigrate through the endothelium. Previously we reported that the endothelium does not generally act as barrier for cancer cells to migrate in three-dimensional extracellular matrices (3D-ECMs). Instead, the endothelium acts as an enhancer or a promoter for the invasiveness of certain cancer cells. How invasive cancer cells diminish the endothelial barrier function still remains elusive. Therefore, this study investigates whether invasive cancer cells can decrease the endothelial barrier function through alterations of endothelial biomechanical properties. To address this, MDA-MB-231 breast cancer cells were used that invade deeper and more numerous into 3D-ECMs when co-cultured with microvascular endothelial cells. Using magnetic tweezer measurements, MDA-MB-231 cells were found to alter the mechanical properties of endothelial cells by reducing endothelial cell stiffness. Using spontaneous bead diffusion, actin cytoskeletal remodeling dynamics were shown to be increased in endothelial cells co-cultured with MDA-MB-231 cells compared with mono-cultured endothelial cells. In addition, knockdown of the α5 integrin subunit in highly transmigrating α5β1(high) cells derived from breast, bladder, and kidney cancer cells abolished the endothelial invasion-enhancing effect comparable with the inhibition of myosin light chain kinase. These results indicate that the endothelial invasion-enhancing effect is α5β1 integrin-dependent. Moreover, inhibition of Rac-1, Rho kinase, MEK kinase, and PI3K reduced the endothelial invasion-enhancing effect, indicating that signaling via small GTPases may play a role in the endothelial facilitated increased invasiveness of cancer cells. In conclusion, decreased stiffness and increased cytoskeletal remodeling dynamics of endothelial cells may account for the breakdown of endothelial barrier function, suggesting that biomechanical alterations are sufficient to facilitate the transmigration and invasion of invasive cancer cells into 3D-ECMs.

The Arp2/3 activator WASH regulates α5β1-integrin-mediated invasive migration

The actin cytoskeleton provides scaffolding and physical force to effect fundamental processes such as motility, cytokinesis and vesicle trafficking. The Arp2/3 complex nucleates actin structures and contributes to endocytic vesicle invagination and trafficking away from the plasma membrane. Internalisation and directed recycling of integrins are major driving forces for invasive cell motility and potentially for cancer metastasis. Here, we describe a direct requirement for WASH and Arp2/3-mediated actin polymerisation on the endosomal membrane system for α5β1 integrin recycling. WASH regulates the trafficking of endosomal α5β1 integrin to the plasma membrane and is fundamental for integrin-driven cell morphology changes and integrin-mediated cancer cell invasion. Thus, we implicate WASH and Arp2/3-driven actin nucleation in receptor recycling leading to invasive motility.

[Implication of integrin alpha5beta1 in human breast carcinoma apoptosis and drug resistance]

Doxorubicin-resistant MCF-7Dox line, which is a derivative of the drug-sensitive MCF-7 human breast carcinoma line, differs from the latter by a strongly reduced expression of the alpha2beta1 integrin and a highly increased expression of the alpha5beta1 receptor. Silencing of this integrin in the MCF-7Dox cells by transfection with alpha5-specific siRNA markedly stimulated anoikis and increased sensitivity of the cells to doxorubicin. Alpha5beta1 silencing also leads to significant inhibition of the activity of kinases Akt and Erk2 in MCF-7Dox cells. Our results suggest that integrins alpha5beta1-induced signals, controlling distinct aspects of cell behavior, are conducted through the common signal pathways.

A New alpha5beta1 integrin-dependent survival pathway through GSK3beta activation in leukemic cells

Background

Cell survival mediated by integrin engagement has been implicated in cell adhesion-mediated drug resistance. We have recently demonstrated that the activation of glycogen synthase kinase 3 β (GSK3β) is a new pathway supporting the chemoresistance of leukemic cells adhered to fibronectin.

Methodology and Principal Findings

We show here that in conditions of serum starvation, the fibronectin receptor α₅β₁ integrin, but not α₄β₁, induced activation of GSK3β through Ser-9 dephosphorylation in adherent U937 cells. The GSK3β-dependent survival pathway occurred in adherent leukemic cells from patients but not in the HL-60 and KG1 cell lines. In adhesion, activated GSK3β was found in the cytosol/plasma membrane compartment and was co-immunoprecipitated with α₅ integrin, the phosphatase PP2A and the scaffolding protein RACK1. PP2A and its regulatory subunit B' regulated the Ser-9 phosphorylation of GSK3β. In adherent leukemic cells, α₅β₁ integrin but not α₄β₁ upregulated the resistance to TNFα-induced apoptosis. Both extrinsic and intrinsic apoptotic pathways were under the control of α₅β₁ and GSK3β.

Conclusions and Significance

Our data show that, upon serum starvation, α₅β₁ integrin engagement could regulate specific pro-survival functions through the activation of GSK3β.

Dexamethasone enhances cell resistance to chemotherapy by increasing adhesion to extracellular matrix in human ovarian cancer cells

Glucocorticoids (GCs) are widely used as co-medication in the therapy of solid malignant tumors to relieve some of the side effects of chemotherapeutic drugs. However, recent studies have shown that GCs could render cancer cells more resistant to cytotoxic drug-induced apoptosis, but the mechanism is largely unknown. In the present study, we found that the treatment of human ovarian cancer cell lines HO-8910 and SKOV3 with synthetic GCs dexamethasone (Dex) significantly increased their adhesion to extracellular matrix (ECM) and their resistance to apoptosis induced by cytotoxic drugs cisplatin and paclitaxel. Dex also increased the protein levels of adhesion molecules integrins beta1, alpha 4, and alpha 5 in HO-8910 cells. The neutralizing antibody against integrin beta1 prevented Dex-induced adhesion and significantly abrogated the protective effect of Dex toward cytotoxic agents. We further found that transforming growth factor-beta1 (TGF-beta1) alone not only increased cell adhesion and cell survival of HO-8910 cells in the presence of cisplatin, but also had synergistic pro-adhesion and pro-survival effects with Dex. Moreover, TGF-beta1-neutralizing antibody that could block TGF-beta1-induced cell adhesion and apoptosis resistance markedly abrogated the synergistic pro-adhesion and pro-survival effects of Dex and TGF-beta1. Finally, we further demonstrated that Dex could up-regulate the expression of TGF-beta receptor type II and enhance the responsiveness of cells to TGF-beta1. In conclusion, our results indicate that increased adhesion to ECM through the enhancement of integrin beta1 signaling and TGF-beta1 signaling plays an important role in chemoresistance induced by GCs in ovarian cancer cells.

17β-estradiol enhances α(5) integrin subunit gene expression through ERα-Sp1 interaction and reduces cell motility and invasion of ERα-positive breast cancer cells

In breast tumors the expression of estrogen receptor alpha (ERα) is known to be associated with a more favorable prognosis. ERα expression has been reported to reduce the metastatic potential of breast cancer cells. Recently, we have observed that extracellular matrix proteins activate ERα and that both liganded and unliganded receptor modulate cell invasiveness acting at nuclear level. To explain the mechanisms by which ERα regulates cell adhesion, we have evaluated the expression of α(5)β(1) integrin, prevalently expressed in stationary cells, in response to 17β-estradiol (E2). Here we show that E2/ERα increases the expression of integrin α(5)β(1) through Sp1-mediated binding to a GC-rich region located upstream of an ERE half-site in the 5' flanking region of the α(5) gene forming a ternary ERα-Sp1-DNA complex. Estrogen responsiveness of the α(5) gene promoter, as observed in HeLa cells, underlies a general mechanism of regulation which is not strictly linked to the cell type. Our data reveal novel insight into the molecular mechanisms sustaining the reduced invasiveness of ERα expressing cells demonstrating that α(5)β(1) integrin expression is related to the maintenance of the stationary status of the cells, counteracting E2/ERα capability to enhance breast cancer cell migration and invasion.

Adiponectin increases motility of human prostate cancer cells via adipoR, p38, AMPK, and NF-kappaB pathways

BACKGROUND

Prostate cancer is the most commonly diagnosed malignancy in men. Prostate cancer shows a predilection for metastasis to the bone. Adiponectin is a protein hormone secreted predominantly by differentiated adipocytes and involved in energy homeostasis. The aim of this study was to investigate whether adiponectin is associated with migration of prostate cancer cells.

METHOD

Cancer cells migration activity was examined using the Transwell assay. The p38 and AMPK phosphorylation was examined by using Western blot method. The cell surface expression of integrins was examined by using flow cytometry. The qPCR was used to examine the mRNA expression of integrin. A transient transfection protocol was used to examine NF-kappaB activity.

RESULTS

We found that adiponectin increased the migration and the expression of alpha5beta1 integrin of human prostate cancer cells. Adiponectin-mediated migration and integrins expression was attenuated by p38 inhibitor (SB203580), p38 mutant, AMPK siRNA, AMPK inhibitor (araA and compound C). Activations of p38, AMPK and NF-kappaB pathways after adiponectin treatment was demonstrated, and adiponectin-induced expression of integrins and migration activity was inhibited by the specific inhibitor and mutant of p38, AMPK, and NF-kappaB cascades.

CONCLUSIONS

This study showed for the first time that the adiponectin mediates migration of human prostate cancer cells. One of the mechanisms underlying adiponectin directed migration was transcriptional up-regulation of alpha5beta1 integrin and activation of AdipoR1 receptor, p38, AMPK, and NF-kappaB pathways.

Therapeutic ultrasound bypasses canonical syndecan-4 signaling to activate rac1

The application of pulsed, low intensity ultrasound is emerging as a potent therapy for the treatment of complex bone fractures and tissue damage. Ultrasonic stimuli accelerate fracture healing by up to 40% and enhance tendon and ligament healing by promoting cell proliferation, migration, and matrix synthesis through an unresolved mechanism. Ultrasound treatment also induces closure of nonunion fractures, at a success rate (85% of cases) similar to that of surgical intervention (68-96%) while avoiding the complications associated with surgery. The regulation of cell adhesion necessary for wound healing depends on cooperative engagement of the extracellular matrix receptors, integrin and syndecan, as exemplified by the wound healing defects observed in syndecan- and integrin-knock-out mice. This report distinguishes the influence of ultrasound on signals downstream of the prototypic fibronectin receptors, alpha(5)beta(1) integrin and syndecan-4, which cooperate to regulate Rac1 and RhoA. Ultrasonic stimulation fails to activate integrins or induce cell spreading on poor, electrostatic ligands. By contrast, ultrasound treatment overcomes the necessity of engagement or expression of syndecan-4 during the process of focal adhesion formation, which normally requires simultaneous engagement of both receptors. Ultrasound exerts an influence downstream of syndecan-4 and PKCalpha to specifically activate Rac1, itself a critical regulator of tissue repair, and to a lesser extent RhoA. The ability of ultrasound to bypass syndecan-4 signaling, which is known to facilitate efficient tissue repair, explains the reduction in healing times observed in ultrasound-treated patients. By substituting for one of the key axes of adhesion-dependent signaling, ultrasound therapy has considerable potential as a clinical technique.

Targeting colon cancer cells using PEGylated liposomes modified with a fibronectin-mimetic peptide

Integrin alpha(5)beta(1) is expressed on several types of cancer cells, including colon cancer, and plays an important role in tumor growth and metastasis. The ability to target the integrin alpha(5)beta(1) using an appropriate drug delivery nano-vector can significantly help in inhibiting tumor growth, reducing tumor metastasis, and decreasing deleterious side effects associated with different cancer therapies. Liposomes are nano-sized phospholipid bilayer vesicles that have been extensively studied as drug delivery carriers. The goal of this study is to design stealth liposomes (liposomes covered with polyethylene glycol (PEG)) that will target colon cancer cells that express the integrin alpha(5)beta(1). The PEG provides a steric barrier allowing the liposomes to circulate in the blood and the functionalizing moiety, PR_b peptide, will specifically recognize and bind to alpha(5)beta(1) expressing cells. PR_b is a novel peptide sequence that mimics the cell adhesion domain of fibronectin, and includes four building blocks, RGDSP (the primary recognition site for alpha(5)beta(1)), PHSRN (the synergy site for alpha(5)beta(1)), a (SG)(5) linker, and a KSS spacer. In this study we have demonstrated that by varying the amount of PEG (PEG750 or PEG2000) and PR_b on the liposomal interface we can engineer nano-vectors that bind to CT26.WT, HCT116, and RKO colon cancer cells in a specific manner and are internalized through most likely alpha(5)beta(1)-mediated endocytosis. GRGDSP-targeted stealth liposomes bind to colon cancer cells and internalize, but they have much lesser efficiency than PR_b-targeted stealth liposomes, and more importantly they are not as specific since many integrins bind to RGD peptides. PR_b-targeted stealth liposomes are as cytotoxic as free 5-Fluorouracil (5-FU) and exert the highest cytotoxicity on CT26.WT cells compared to GRGDSP-targeted stealth liposomes and non-targeted stealth liposomes. Thus, the proposed targeted delivery system has the great potential to deliver a therapeutic load directly to colon cancer cells, in an efficient and specific manner.

Caveolin-1 regulates glioblastoma aggressiveness through the control of alpha(5)beta(1) integrin expression and modulates glioblastoma responsiveness to SJ749, an alpha(5)beta(1) integrin antagonist

Caveolin-1 plays a checkpoint function in the regulation of processes often altered in cancer. Although increased expression of caveolin-1 seems to be the norm in the glioma family of malignancies, populations of caveolin-1 positive and negative cells coexist among glioblastoma specimens. As no data are available to date on the contribution of such cells to the phenotype of glioblastoma, we manipulated caveolin-1 in the glioblastoma cell line U87MG. We showed that caveolin-1 plays a critical role in the aggressiveness of glioblastoma. We identified integrins as the main set of genes affected by caveolin-1. We reported here that the phenotypic changes observed after caveolin-1 modulation were mediated by alpha(5)beta(1) integrins. As a consequence of the regulation of alpha(5)beta(1) levels by caveolin-1, the sensitivity of cells to the specific alpha(5)beta(1) integrin antagonist, SJ749, was affected. Mediator of caveolin-1 effects, alpha(5)beta(1) integrin, is also a marker for glioma aggressiveness and an efficient target for the treatment of glioma especially the ones exerting the highest aggressive phenotype.

Distinct FAK-Src activation events promote alpha5beta1 and alpha4beta1 integrin-stimulated neuroblastoma cell motility

Signals from fibronectin-binding integrins promote neural crest cell motility during development in part through protein-tyrosine kinase (PTK) activation. Neuroblastoma (NB) is a neural crest malignancy with high metastatic potential. We find that alpha4 and alpha5 integrins are present in late-stage NB tumors and cell lines derived thereof. To determine the signaling connections promoting either alpha4beta1- or alpha5beta1-initiated NB cell motility, pharmacological, dominant negative and short-hairpin RNA (shRNA) inhibitory approaches were undertaken. shRNA knockdown revealed that alpha5beta1-stimulated NB motility is dependent upon focal adhesion kinase (FAK) PTK, Src PTK and p130Cas adapter protein expression. Cell reconstitution showed that FAK catalytic activity is required for alpha5beta1-stimulated Src activation in part through direct FAK phosphorylation of Src at Tyr-418. Alternatively, alpha4beta1-stimulated NB cell motility is dependent upon Src and p130Cas but FAK is not essential. Catalytically inactive receptor protein-tyrosine phosphatase-alpha overexpression inhibited alpha4beta1-stimulated NB motility and Src activation consistent with alpha4-regulated Src activity occurring through Src Tyr-529 dephosphorylation. In alpha4 shRNA-expressing NB cells, alpha4beta1-stimulated Src activation and NB cell motility were rescued by wild type but not cytoplasmic domain-truncated alpha4 re-expression. These studies, supported by results using reconstituted fibroblasts, reveal that alpha4beta1-mediated Src activation is mechanistically distinct from FAK-mediated Src activation during alpha5beta1-mediated NB migration and support the evaluation of inhibitors to alpha4, Src and FAK in the control of NB tumor progression.

Mammalian NOTCH-1 Activates β1 Integrins via the Small GTPase R-Ras

Notch is a central regulator of important cell fate decisions. Notch activation produces diverse cellular effects suggesting the presence of context-dependent control mechanisms. Genetic studies have demonstrated that Notch and integrin mutations have related phenotypes in key developmental processes such as vascular development and somitogenesis. We show that the intracellular domain of mammalian Notch-1 activates integrins without affecting integrin expression. Integrin activation is dependent on gamma-secretase-mediated intramembranous cleavage of membrane-bound Notch releasing intracellular Notch that activates R-Ras, independent of CSL-transcription. Notch also reverses H-Ras and Raf-mediated integrin suppression without affecting ERK phosphorylation. Membrane-bound Notch mutants that are inefficiently cleaved or intracellular Notch mutants lacking the ankyrin repeat sequence do not activate R-Ras or integrins. Co-expression of Msx2-interacting nuclear target (MINT) protein with Notch or expression of intracellular Notch-1 truncation mutants lacking the C-terminal transactivation/PEST domain suppresses Notch transcriptional activity without affecting integrin activation. Notch ligand, Delta-like ligand-4, stimulates R-Ras-dependent alpha 5 beta 1 integrin-mediated adhesion, demonstrating the physiological relevance of this pathway. This new CSL-independent Notch/R-Ras pathway provides a molecular mechanism to explain Notch, integrin, and Ras cross-talk during the development of multicellular organisms.

alpha v beta3 and alpha5beta1 integrin recycling pathways dictate downstream Rho kinase signaling to regulate persistent cell migration

Accumulating evidence suggests that integrin recycling regulates cell migration. However, the lack of reagents to selectively target the trafficking of individual heterodimers, as opposed to endocytic transport as a whole, has made it difficult to define the contribution made by particular recycling pathways to directional cell movement. We show that autophosphorylation of protein kinase D1 (PKD1) at Ser⁹¹⁶ is necessary for its association with αvβ3 integrin. Expression of PKD1^916A or the use of mutants of β3 that do not bind to PKD1 selectively inhibits short-loop, Rab4-dependent recycling of αvβ3, and this suppresses the persistence of fibroblast migration. However, we report that short-loop recycling does not directly contribute to fibroblast migration by moving αvβ3 to the cell front, but by antagonizing α5β1 recycling, which, in turn, influences the cell's decision to migrate with persistence or to move randomly.

Ameloblastoma and adenomatoid odontogenic tumor: the role of α2β1, α3β1, and α5β1 integrins in local invasiveness and architectural characteristics

Ameloblastoma is an odontogenic neoplasm characterized by local invasiveness and a tendency toward recurrence, whereas adenomatoid odontogenic tumor (AOT) is an indolent neoplasm. The objective of the present study was to immunohistochemically analyze the role of alpha2beta1, alpha3beta1, and alpha5beta1 integrins in the cellular events and cell-matrix interactions that occur in these tumors and their consequent repercussions on the architectural arrangement and biologic behavior of these lesions. Paraffin-embedded specimens from 30 ameloblastomas (20 solid and 10 unicystic tumors) and 12 AOTs were submitted to immunohistochemistry using the catalyzed signal amplification system. A difference in the pattern of integrin expression was observed between the various histologic types of ameloblastoma. No significant difference in labeling intensity was observed between unicystic and solid ameloblastomas, but comparison between ameloblastomas and AOT showed a significantly stronger expression of alpha5beta1 integrin in the former (P < .05). Our findings suggest an important role of the integrins studied in the architectural characteristics of ameloblastomas and AOTs and a possible participation of alpha5beta1 integrin in the mechanism of local invasion of ameloblastomas.

Involvement of alpha5beta1-integrin and TNF-alpha in Staphylococcus aureus alpha-toxin-induced death of epithelial cells

Staphylococcus aureus causes suppurative infections which are often associated with tissue destruction and cell death. In the present study, we investigated the molecular and cellular basis of S. aureus-induced apoptosis and death in a human lung epithelial cell line (A549). We found that staphylococcal alpha-toxin is an important mediator of cytotoxicity in these epithelial cells. Specifically, we found that downregulating alpha-toxin production eliminated the cytotoxicity of S. aureus, whereas the addition of alpha-toxin to the cell culture medium significantly increased cell death in a dose-dependent manner. Importantly, we found that alpha-toxin-mediated cell death may partially function through alpha5beta1-integrin, because both the beta1-integrin antibody and the ligand fibronectin inhibited the cytotoxicity of alpha-toxin. Furthermore, we found that the overexpression of the inflammatory cytokine interferon (TNF)-alpha is associated with alpha-toxin-induced cell death, because both the TNF-alpha release inhibitor and antibody effectively inhibited the cytotoxicity of alpha-toxin. In contrast, the cytotoxicity of alpha-toxin was enhanced by the inhibition of the MAPK p38 and NF-kappaB pathways. Taken together, our results suggest that the activation of the MAPK p38 and NF-kappaB pathways are stress responses for survival, rather than direct contributes to alpha-toxin-induced cell death, and that the interaction of alpha-toxin with alpha5beta1-integrin and overproduction of TNF-alpha may contribute to destruction of epithelial cells during S. aureus infection.

Bacillus Calmette-Guérin induces p21 expression in human transitional carcinoma cell lines via an immediate early, p53 independent pathway

PURPOSE

Work by our group has shown that bacillus Calmette-Guérin (BCG) induces cell cycle arrest at the G1/S interface in human transitional carcinoma cell lines. This study evaluated the effect of BCG on cell cycle regulatory proteins relevant to this effect.

MATERIALS AND METHODS

The effect of BCG on selected cell cycle regulatory proteins, including cyclin D1, p27, and p21, was assessed in 2 human cell lines. After the identification of p21 as a candidate protein, p21 regulation was evaluated using a combination of Western, reverse transcriptase polymerase chain reaction, and promoter-reporter analysis. The immediate early versus delayed nature of p21 induction was determined. Finally, given the known potential for p21 to be regulated by both p53 dependent and independent pathways, the role of p53 in BCG induced expression of p21 was evaluated.

RESULTS

BCG increased p21 expression 2-fold relative to controls as measured by Western, and promoter-reporter analysis. Inhibition of protein synthesis had no effect on p21 messenger ribonucleic acid induction in response to BCG. T24 cells contained a previously reported mutation in p53. In the p53 wild-type 253J cells, deletion of one or both p53 response elements in the p21 reporter had no effect on BCG induced reporter transactivation.

CONCLUSIONS

BCG up-regulates expression of p21 in human transitional cell carcinoma lines. The transactivation of p21 in response to BCG occurs through an immediate early, p53 independent pathway. The finding of increased p21, together with the observation that BCG induces cell cycle arrest at the G1/S interface, supports a role for this protein in the biologic response to BCG.

Biological activity of rainbow trout Ea4-peptide of the pro-insulin-like growth factor (pro-IGF)-I on promoting attachment of breast cancer cells (MDA-MB-231) via alpha2- and beta1-integrin

E-peptide of pro-IGF-I was considered as biologically inactive. We have demonstrated that rainbow trout (rt) Ea4-peptide exerted biological activities in several established tumor cell lines [Chen et al., 2002; Kuo and Chen, 2002]. Here we report the activity of rtEa4-peptide in promoting attachment of human breast cancer cells (MDA-MB-231). While rtEa2-, rtEa3-, and rtEa4-peptides enhanced the attachment of MDA-MB-231 cells in a dose dependent manner, rtEa4-peptide possessed the highest activity. Antibodies specific to alpha2 and beta1 integrins significantly inhibited the attachment of cells to rtEa4-peptide coated-plates by 40%. In addition, rtEa4-peptide induced the expression of fibronectin 1 and laminin receptor genes in MDA-MB-231 cells. Blocking new protein synthesis by cycloheximide significantly reduced the attachment of MDA-MB-231 cells to rtEa4-peptide coated wells by 50%. These results suggest that rtEa4-peptide may promote cell attachment by interacting with alpha2/beta1 integrin receptors at the cell surface and by inducing the expression of fibronectin 1 and laminin receptor genes. Expression of fibronectin 1 gene induced by rtEa4-peptide in MDA-MB-231 cells was abolished by inhibitors of PI3K, PKC, Mek1/2, JNK1/2, and p38 MAPK signaling transduction molecules. These results suggested that induction of fibronectin 1 gene expression in MDA-MB-231 cells by rtEa4-peptide may be mediated via PI3K, PKC, Mek1/2, JNK1/2, and p38 MAPK signal transduction molecules.