Identification of motifs for cell adhesion within the repeated domains of transforming growth factor-beta-induced gene, betaig-h3

RGD peptides released from beta ig-h3, a TGF-beta-induced cell-adhesive molecule, mediate apoptosis

Beta ig-h3 is a transforming growth factor-beta (TGF-beta)-induced cell-adhesive molecule and has an RGD sequence at its C-terminus. A previous report suggested that beta ig-h3 normally undergoes carboxy-terminal processing that results in the loss of the RGD sequence. RGD peptides appear to play various roles in cell function. Here we show that the RGD peptides released from beta ig-h3 may facilitate TGF-beta-induced apoptosis. We found that carboxy-terminal cleavage of beta ig-h3 occurred after its secretion, and that overexpression of the wild-type beta ig-h3 induced apoptosis, unlike the C-terminal deleted but RGD-containing mutant beta ig-h3, which is resistant to C-terminal processing. The beta ig-h3-induced apoptosis was abolished by either deletion of the RGD sequence or mutation of RGD to RAE. Synthetic peptides of ERGDEL and GRGDSP derived from beta ig-h3 and fibronectin, respectively, also induced apoptosis, unlike ERGEEL and GRGESP. Culture supernatants of cells overexpressing beta ig-h3 filtered to isolate molecules smaller than 3 kDa also induced apoptosis. A fusion protein composed of the N-terminal 100 amino acids of fibronectin and the RGD-containing C-terminal part of beta ig-h3 was also subjected to C-terminal cleavage and overexpression resulted in apoptosis. The anti-beta ig-h3 antibody blocks TGF-beta-induced apoptosis. Thus, beta ig-h3 may be important in regulating cell apoptosis by providing soluble RGD peptides.

TGF-beta-induced protein beta ig-h3 is upregulated by high glucose in vascular smooth muscle cells

TGF-beta-induced gene-h3 (beta ig-h3) is an adhesive molecule that interacts with integrins. Because TGF-beta plays an important role in diabetic complications and beta ig-h3 serves as a cell substrate, we hypothesized that diabetic conditions might increase beta ig-h3 synthesis in vascular smooth muscle cells (VSMCs), which may subsequently contribute to the pathogenesis of diabetic angiopathy. The concentrations of beta ig-h3 and TGF-beta were measured in conditioned media using an enzyme-linked immunosorbent assay. An immunohistochemical study showed that beta ig-h3 was expressed in the VSMCs and the matrix of rat aortas. TGF-beta stimulated beta ig-h3 production, and high glucose induced beta ig-h3 as well as TGF-beta production in the VSMCs. The high glucose-induced beta ig-h3 expression was almost entirely blocked by an anti-TGF-beta antibody. beta ig-h3 protein mediated the adhesion, spreading, migration, and proliferation of rat VSMCs. These results suggest that the high glucose-induced beta ig-h3 in VSMCs regulates VSMC functions and may play an important role in diabetic angiopathy.

Novel fold revealed by the structure of a FAS1 domain pair from the insect cell adhesion molecule fasciclin I

Fasciclin I is an insect neural cell adhesion molecule consisting of four FAS1 domains, homologs of which are present in many bacterial, plant, and animal proteins. The crystal structure of FAS1 domains 3 and 4 of Drosophila fasciclin I reveals a novel domain fold, consisting of a seven-stranded beta wedge and a number of alpha helices. The two domains are arranged in a linear fashion and interact through a substantial polar interface. Missense mutations in the FAS1 domains of the human protein betaig-h3 cause corneal dystrophies. Many mutations alter highly conserved core residues, but the two most common mutations, affecting Arg-124 and Arg-555, map to exposed alpha-helical regions, suggesting reduced protein solubility as the disease mechanism.

Transforming growth factor-beta-inducible gene-h3 (beta(ig)-h3) promotes cell adhesion of human astrocytoma cells in vitro: implication of alpha6beta4 integrin

Beta(ig)-h3 is a secretory protein that is induced by transforming growth factor (TGF)-beta. We have recently found that beta(ig)-h3 expression is induced in cultured astrocytes by TGF-beta1 and in rat cerebral cortex by stab wound. The purpose of this study was to examine the effect of the secreted beta(ig)-h3 on cell adhesion of astrocytes and the underlying mechanisms. When U87 human astrocytoma cells were seeded on dishes coated with recombinant beta(ig)-h3, cell adhesion was significantly enhanced. Blocking experiments using various antibodies to the integrin subunit suggested alpha6beta4 integrin could be involved in the beta(ig)-h3-mediated astrocyte cell adhesion. Cell adhesion to beta(ig)-h3 substrate was substantially blocked by preincubation with the inhibitor to the src kinase. When cells were plated on beta(ig)-h3-coated dishes, tyrosine phosphorylation of focal adhesion kinase was prominently increased within 20 min in a beta4 integrin-dependent manner. The results suggest that alpha6beta4 integrin-mediated interactions of astrocytes with beta(ig)-h3 transduce intracellular signals through the focal adhesion proteins, which may regulate certain aspects of astrocyte response to brain injury.

The thrombospondin type 1 repeat (TSR) and neuronal differentiation: roles of SCO-spondin oligopeptides on neuronal cell types and cell lines

SCO-spondin is a large glycoprotein secreted by ependymal cells of the subcommissural organ. It shares functional domains called thrombospondin type 1 repeats (TSRs) with a number of developmental proteins expressed in the central nervous system, and involved in axonal pathfinding. Also, SCO-spondin is highly conserved in the chordate phylum and its multiple domain organization is probably a chordate innovation. The putative involvement of SCO-spondin in neuron/glia interaction in the course of development is assessed in various cell culture systems. SCO-spondin interferes with several developmental processes, including neuronal survival, neurite extension, neuronal aggregation, and fasciculation. The TSR motifs, and especially the WSGWSSCSVSCG sequence, are most important in these neuronal responses. Integrins and growth factor receptors may cooperate as integrative signals. We discuss the putative involvement of the subcommissural organ/Reissner's fiber complex in developmental events, as a particular extracellular signaling system.

BIGH3 (TGFBI) Arg124 mutations influence the amyloid conversion of related peptides in vitro

Amyloid deposits with Arg124 mutated TGFBI protein have been identified in autosomal dominant blinding corneal dystrophies. We assessed in vitro the mechanisms determining TGFBI protein amyloid transformation involving mutations of Arg124. Eight peptides synthesized following the TGFBI protein sequence, centered on codon Arg124 holding the previously reported amyloidogenic mutations and the respective controls were studied. Cys124 and His124 mutated peptide preparations contained significantly higher amounts of amyloid than the native peptide. Blocking the SH group of Cys124 and deleting the first four NH2-terminal amino acids including Val112-Val113 resulted in a decrease in amyloid fibril formation while deletion of the nine CONH2-terminal residues increased amyloid fibril concentration. Fourrier transformed-infrared spectroscopy analysis of the different peptide solutions showed an increase in beta-pleated sheet structures in those with enhanced amyloid yielding. We designed a peptide (BB1) likely to counteract the role of Val112-Val113 in amyloid fibril formation. Incubation of Cys124 peptide with BB1 indeed resulted in a 35% inhibition of amyloid fibril formation. Our results are in keeping with the clinical observations of Arg124 mutation-linked amyloidosis and show the importance of Val112-Val113, disulfide and hydrogen bonding in increasing the beta-pleated conformation and amyloid formation. These findings shed new light on the molecular mechanisms of TGFBI protein amyloidogenesis and encourage further research on the use of specifically designed peptides as putative therapeutic agents for these disabling diseases.

Identification of Motifs in the Fasciclin Domains of the Transforming Growth Factor-β-induced Matrix Protein βig-h3 That Interact with the αvβ5 Integrin

betaig-h3 is a TGF-beta-induced matrix protein known to mediate the adhesion of several cell types. In this study, we found that all four of the fas-1 domains in betaig-h3 mediate MRC-5 fibroblast adhesion and that this was specifically inhibited by a function-blocking monoclonal antibody specific for the alphavbeta5 integrin. Using deletion mutants of the fourth fas-1 domain revealed the MRC-5 cell adhesion motif (denoted the YH motif) is located in amino acids 548-614. Experiments with substitution mutants showed that tyrosine 571, histidine 572, and their flanking leucine and isoleucine amino acids, which are all highly conserved in many fas-1 domains, are essential for mediating MRC-5 cell adhesion. A synthetic 18-amino acid peptide encompassing these conserved amino acids could effectively block MRC-5 cell adhesion to betaig-h3. Using HEK293 cells stably transfected with the beta5 integrin cDNA, we confirmed that the alphavbeta5 integrin is a functional receptor for the YH motif. In conclusion, we have identified a new alphavbeta5 integrin-interacting motif that is highly conserved in the fas-1 domains of many proteins. This suggests that fas-1 domain-containing proteins may perform their biological functions by interacting with integrins.

Induction of TGF-beta-inducible gene-h3 (betaig-h3) by TGF-beta1 in astrocytes: implications for astrocyte response to brain injury

Transforming growth factor (TGF)-beta-inducible gene-h3 (betaig-h3) product is a secreted protein that is induced by TGF-beta in several cell types and implicated in various tissue pathologies. The aims of this study were to determine the effect of TGF-beta1 on betaig-h3 expression in cultured astrocytes and to examine whether betaig-h3 is expressed in the brain after traumatic injury. The results showed that betaig-h3 mRNA and protein increased in response to TGF-beta1 in U87 human astrocytoma cells and mouse cortical astrocytes. Treatment with other cytokines, including tumor necrosis factor-alpha and fibroblast growth factor-2, did not enhance the expression of betaig-h3 in astrocytes. betaig-h3 was significantly expressed in reactive astrocytes at the site of a stab wound in the cerebral cortex of adult rats. These results provide an insight into understanding a novel role for betaig-h3 protein in the response of astrocytes to brain injury.

Induction and expression of betaig-h3 in pancreatic cancer cells

betaig-h3 (TGFBI, keratoepithelin) was first identified as a transforming growth factor-beta1 (TGF-beta1)-inducible gene in a human lung adenocarcinoma cell line. It encodes for a secreted extracellular matrix (ECM) protein, which is thought to act on cell attachment and ECM composition. Mutations of the betaig-h3 gene are involved in several corneal dystrophies. Pancreatic cancers display multiple alterations in the TGF-beta signaling pathway and in TGF-beta response genes, such as overexpression of all three TGF-beta isoforms and Smad4 mutations. In this report, we determined that betaig-h3 mRNA levels were induced by TGF-beta1 in two out of five examined pancreatic cancer cell lines (CAPAN-1, PANC-1). In CAPAN-1 cells, which harbor a Smad4 mutation, betaig-h3 but not PAI-1 was induced by TGF-beta1, whereas in PANC-1 cells that express wild-type Smad4, TGF-beta1 induced both PAI-1 and betaig-h3. In human pancreatic tissues, there was a 32.4-fold increase in betaig-h3 mRNA levels in pancreatic cancers in comparison to normal control tissues. In situ hybridization analysis revealed that betaig-h3 mRNA was expressed mainly in the cancer cells within the pancreatic tumor mass. These findings suggest that betaig-h3 is induced by TGF-betas in pancreatic cancer cells even in the presence of Smad4 mutations, which might explain, in part, the increased betaig-h3 mRNA levels observed in pancreatic cancer cells in vivo.

FEEL-1, a novel scavenger receptor with in vitro bacteria-binding and angiogenesis-modulating activities

Employing the expression cloning technique, we cloned a novel scavenger receptor that is structurally unrelated to other scavenger receptors. The cloned receptor contained fasciclin (Fas-1), epidermal growth factor (EGF)-like, laminin-type EGF-like, and link domains. Based on the domain structures, we temporarily named it FEEL-1 (fasciclin, EGF-like, laminin-type EGF-like, and link domain-containing scavenger receptor-1). A data base search suggested the presence of a paralogous gene of FEEL-1, the full-length cDNA of this gene was also cloned, and its nucleotide sequence was determined. The deduced amino acid sequence of the clone indicated that its domain organization is similar to FEEL-1, and we named this clone FEEL-2. The effect of monoclonal antibodies against FEEL-1 indicated that FEEL-1 is the major receptor for 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbo-cyanine perchlorate (DiI)-labeled acetylated low density lipoprotein (DiI-Ac-LDL) in human umbilical vein endothelial cells. Reverse transcription and PCR analysis revealed that both FEEL-1 and FEEL-2 were expressed in several tissues and expressed highly in the spleen and lymph node. On the other hand, only FEEL-1 was expressed in mononuclear cells, particularly resting CD14(+) cells. The transient expression of FEEL-1 and FEEL-2 in Chinese hamster ovary cells demonstrated that both FEELs could bind to DiI-Ac-LDL. Both receptors were also found to bind to Gram-negative and Gram-positive bacteria. These results suggest that FEELs play important roles in the defense mechanisms against bacterial infection. Finally, the phenotypic effect of the inhibition of FEEL-1 on vascular remodeling was tested in vitro using the Matrigel tube formation assay, and we found a marked reduction in the degree of cell-cell interaction in anti-FEEL-1 monoclonal antibody-treated cells, suggesting the role of this receptor in angiogenesis.

The transforming growth factor-beta-inducible matrix protein (beta)ig-h3 interacts with fibronectin

Proper growth and development require the orderly synthesis and deposition of individual components of the extracellular matrix (ECM) into well ordered networks. Once formed, the ECM maintains tissue structure and houses resident cells. One ECM component, (beta)ig-h3, is a highly conserved transforming growth factor-beta-inducible protein that has been hypothesized to function as a bifunctional linker between individual matrix components and resident cells. To gain insights into its physiological function, full-length (beta)ig-h3 protein was produced using a baculovirus expression system and purified under native conditions. Human fibroblasts attached and spread on (beta)ig-h3-coated plates and developed actin stress fibers. Purified (beta)ig-h3 binds fibronectin (FN) and type I collagen (Col I) but does not bind gelatin. Using defined fragments of FN, we localized the (beta)ig-h3 recognition region to the gelatin/collagen binding domain present in the N-terminal region of the FN molecule. Our results identify FN and Col I as two ligands of (beta)ig-h3 in the ECM.

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

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

Overexpression of Betaig-h3 gene downregulates integrin alpha5beta1 and suppresses tumorigenicity in radiation-induced tumorigenic human bronchial epithelial cells

Interaction between cell and extracellular matrix plays a crucial role in tumour invasion and metastasis. Using an immortalised human bronchial epithelial (BEP2D) cell model, the study here shows that expression of Betaig-h3 gene, which encodes a secreted adhesion molecule induced by transforming growth factor-beta, is markedly decreased in several independently generated, radiation-induced tumour cell lines (TL1-TL5) relative to parental BEP2D cells. Transfection of Betaig-h3 gene into tumour cells resulted in a significant reduction in tumour growth. While integrin receptor alpha5beta1 was overexpressed in tumour cells, its expression was corrected to the level found in control BEP2D cells after Betaig-h3 transfection. These data suggest that Betaig-h3 gene is involved in tumour progression by regulating integrin receptor alpha5beta1. The findings provide strong evidence that the Betaig-h3 gene has tumour suppressor function in human BEP2D cell model and suggest a potential target for interventional therapy.

Prediction of glycosylphosphatidylinositol-anchored proteins in Arabidopsis. A genomic analysis

Glycosylphosphatidylinositol (GPI) anchoring of proteins provides a potential mechanism for targeting to the plant plasma membrane and cell wall. However, relatively few such proteins have been identified. Here, we develop a procedure for database analysis to identify GPI-anchored proteins (GAP) based on their possession of common features. In a comprehensive search of the annotated Arabidopsis genome, we identified 167 novel putative GAP in addition to the 43 previously described candidates. Many of these 210 proteins show similarity to characterized cell surface proteins. The predicted GAP include homologs of beta-1,3-glucanases (16), metallo- and aspartyl proteases (13), glycerophosphodiesterases (6), phytocyanins (25), multi-copper oxidases (2), extensins (6), plasma membrane receptors (19), and lipid-transfer-proteins (18). Classical arabinogalactan (AG) proteins (13), AG peptides (9), fasciclin-like proteins (20), COBRA and 10 homologs, and novel potential signaling peptides that we name GAPEPs (8) were also identified. A further 34 proteins of unknown function were predicted to be GPI anchored. A surprising finding was that over 40% of the proteins identified here have probable AG glycosylation modules, suggesting that AG glycosylation of cell surface proteins is widespread. This analysis shows that GPI anchoring is likely to be a major modification in plants that is used to target a specific subset of proteins to the cell surface for extracellular matrix remodeling and signaling.

Role of BMP, betaig-h3, and chitosan in early bony consolidation in distraction osteogenesis in a dog model

The purpose of this investigation was to study the effect of bone morphogenetic protein (BMP), transforming growth factor beta-induced gene h3 (betaig-h3), and chitosan on early bony consolidation in distraction osteogenesis in a dog model. Sixteen dogs were used for this study. The lateral surface of the mandibular body was exposed in the subperiosteal plane and the vertical osteotomy on the mandibular body was extended downward. An external distraction device was applied to the mandibular body, and the mandibular distraction was started 5 days after the operation at a rate of 2 mm/day up to a 10-mm distraction after 5 days. The experimental group was then divided into a control group, a BMP group, a betaig-h3 group, and a chitosan group, depending on the type of implantation material used in the distracted area. On the same day after completing the distraction, BMP, betaig-h3, or chitosan was implanted into the distracted area. No material was implanted into the distracted area in the control group. After implanting the materials, the distraction device was left in place for 7 weeks to allow for bony consolidation. Four dogs were allocated to each group. Two dogs in each group, a total of eight dogs, were killed 4 weeks after completing the distraction and the other eight dogs were killed after 7 weeks. Serial radiographs were obtained every week after completing the distraction. New bone was generated in the distracted zone in all groups. In the BMP group, the formation of active woven bone was observed throughout the distracted zone, and the new bone appeared to be nearly normal cortical bone 7 weeks after implantation. In the betaig-h3 and chitosan groups, the development of new bone was observed in the distracted zone after 7 weeks; however, the amount was less than that in the BMP group. In the control group, the new bone was observed at the edges of the distracted zone. These findings suggest that BMP seems to be very effective in early bony consolidation in distraction osteogenesis.

Stabilin-1 and -2 constitute a novel family of fasciclin-like hyaluronan receptor homologues

MS-1, a high-molecular-mass protein expressed by non-continuous and angiogenic endothelial cells and by alternatively activated macrophages (Mphi2), and the hepatic sinusoidal endothelial hyaluronan clearance receptor are similar with respect to tissue distribution and biochemical characteristics. In the present study we purified these proteins by immuno- and hyaluronan-affinity chromatography respectively, sequenced tryptic peptides and generated full-length cDNA sequences in both mouse and human. The novel genes, i.e. stabilin-1 and stabilin-2, code for homologous transmembrane proteins featuring seven fasciclin-like adhesion domains, 18-20 epidermal-growth-factor domains, one X-link domain and three to six B-(X(7))-B hyaluronan-binding motifs. Northern-blotting experiments revealed the presence of both stabilins in organs with predominant endothelial sinuses such as liver, spleen and lymph node: stabilin-1 mRNA was also detected in organs with predominant Mphi2 cells, such as placenta, and in interleukin-4/glucocorticoid-stimulated Mphi2 cells in vitro. A polyclonal antibody made against human recombinant stabilin-1 confirmed the expression of stabilin-1 protein in splenic sinus endothelial cells in vivo and in Mphi2 in vitro. On the basis of high similarity at the protein level and the unique domain composition, which differs from that of all other known fasciclin-like proteins and hyaluronan receptors, stabilin-1 and stabilin-2 define a novel family of fasciclin-like hyaluronan receptor homologues that might play a role in cell-cell and cell-matrix interactions in vascular function and inflammatory processes.