Fine mapping of inhibitory anti-α5 monoclonal antibody epitopes that differentially affect integrin–ligand binding

The high-affinity interaction of integrin α5β1 with the central cell-binding domain of fibronectin requires both the Arg-Gly-Asp (RGD) sequence (in the tenth type III repeat) and a second site Pro-His-Ser-Arg-Asn (PHSRN) in the adjacent ninth type III repeat, which synergizes with RGD. Arg-Arg-Glu-Thr-Ala-Trp-Ala (RRETAWA) is a novel peptidic ligand for α5β1, identified by phage display, which blocks α5β1-mediated cell adhesion to fibronectin. A key question is the location of the binding sites for these ligand sequences within the integrin. In this study we have identified residues that form part of the epitopes of three inhibitory anti-α5 monoclonal antibodies (mAbs): 16, P1D6 and SNAKA52. These mAbs have distinct functional properties. mAb 16 blocks the recognition of RGD and RRETAWA, whereas P1D6 blocks binding to the synergy sequence. The binding of SNAKA52 is inhibited by anti-β1 mAbs, indicating that its epitope is close to the interface between the α and β subunits. Residues in human α5 were replaced with the corresponding residues in mouse α5 by site-directed mutagenesis; wild-type or mutant human α5 was expressed on the surface of α5-deficient Chinese hamster ovary cells. mAb binding was assessed by flow cytometry and by adhesion to the central cell-binding domain of fibronectin or RRETAWA by cell attachment assay. All three epitopes were located to different putative loops in the N-terminal domain of α5. As expected, disruption of these epitopes had no effect on ligand recognition by α5β1. The locations of these epitopes are consistent with the β-propeller model for integrin α-subunit structure and allow us to propose a topological image of the integrin-ligand complex.

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Role of type III homology repeats in cell adhesive function within the cell-binding domain of fibronectin.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(18)49952-8 ◽

1991 ◽

Vol 266 (5) ◽

pp. 3045-3051

Author(s):

F Kimizuka ◽

Y Ohdate ◽

Y Kawase ◽

T Shimojo ◽

Y Taguchi ◽

...

Keyword(s):

Binding Domain ◽

Cell Binding ◽

Type Iii ◽

Cell Adhesive ◽

Cell Binding Domain

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Role of Ninth Type-III Domain of Fibronectin in the Mediation of Cell-Binding Domain Adsorption on Surfaces with Different Chemistries

Langmuir ◽

10.1021/acs.langmuir.8b01937 ◽

2018 ◽

Vol 34 (33) ◽

pp. 9847-9855 ◽

Cited By ~ 3

Author(s):

Tianjie Li ◽

Lijing Hao ◽

Jiangyu Li ◽

Chang Du ◽

Yingjun Wang

Keyword(s):

Binding Domain ◽

Cell Binding ◽

Type Iii ◽

Cell Binding Domain

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Neurite extension of chicken peripheral nervous system neurons on fibronectin: relative importance of specific adhesion sites in the central cell-binding domain and the alternatively spliced type III connecting segment.

The Journal of Cell Biology ◽

10.1083/jcb.106.4.1289 ◽

1988 ◽

Vol 106 (4) ◽

pp. 1289-1297 ◽

Cited By ~ 77

Author(s):

M J Humphries ◽

S K Akiyama ◽

A Komoriya ◽

K Olden ◽

K M Yamada

Keyword(s):

Nervous System ◽

Cell Adhesion ◽

Neurite Outgrowth ◽

Peripheral Nervous System ◽

Binding Domain ◽

Central Cell ◽

Cell Binding ◽

Alternatively Spliced ◽

Cell Binding Domain ◽

Iiics Region

Fibronectin contains at least two domains that support cell adhesion. One is the central cell-binding domain that is recognized by a variety of cell types, including fibroblasts. The second, originally identified by its ability to support melanoma cell adhesion, is located in the alternatively spliced type III connecting segment (IIICS). Using specific adhesive ligands and inhibitory probes, we have examined the role of each of these domains in fibronectin-mediated neurite extension of neurons from chick embryo dorsal root and sympathetic ganglia. In studies using explanted ganglia, both fl3, a 75-kD tryptic fragment of human plasma fibronectin containing the central cell-binding domain, and CS1-IgG, a synthetic peptide-IgG conjugate containing the principal cell adhesion site from the IIICS, supported neurite outgrowth after adsorption onto the substrate. The maximal activities of fl3 and CSl-IgG were 45-55% and 25-30% that of intact fibronectin, respectively. Co-coating of the substrate with f13 and CS1-IgG produced an additive stimulation of neurite outgrowth, the extent of which approached that obtained with fibronectin. Similar results were obtained with purified neuronal cell preparations isolated by tryptic dissociation of dorsal root ganglia. In complementary studies, blockage of the adhesive function of either the central cell-binding domain (with mAb 333, an antiadhesive monoclonal antibody) or the IIICS (with CS1 peptide), resulted in approximately 60 or 30% reduction in fibronectin-mediated neurite outgrowth, respectively. When tested in combination, the inhibitory activities of mAb 333 and CSl were additive. From these results, we conclude that neurons from the peripheral nervous system can extend neurites on both the central cell-binding domain and the IIICS region of fibronectin, and that these cells are therefore the first normal, embryonic cell type shown to adhere to the IIICS. These results suggest that spatiotemporal fluctuations in the alternative mRNA splicing of the IIICS region of fibronectin may be important in regulation of cell adhesive events during development of the peripheral nervous system.

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Monoclonal antibody characterization of two distant sites required for function of the central cell-binding domain of fibronectin in cell adhesion, cell migration, and matrix assembly.

The Journal of Cell Biology ◽

10.1083/jcb.114.6.1295 ◽

1991 ◽

Vol 114 (6) ◽

pp. 1295-1305 ◽

Cited By ~ 101

Author(s):

T Nagai ◽

N Yamakawa ◽

S Aota ◽

S S Yamada ◽

S K Akiyama ◽

...

Keyword(s):

Cell Spreading ◽

Binding Domain ◽

Central Cell ◽

Site Directed Mutagenesis ◽

Cell Binding ◽

Matrix Assembly ◽

Fibronectin Receptor ◽

Molar Basis ◽

Rgd Site ◽

Cell Binding Domain

Site-directed mutagenesis studies have suggested that additional peptide information in the central cell-binding domain of fibronectin besides the minimal Arg-Gly-Asp (RGD) sequence is required for its full adhesive activity. The nature of this second, synergistic site was analyzed further by protein chemical and immunological approaches using biological assays for adhesion, migration, and matrix assembly. Fragments derived from the cell-binding domain were coupled covalently to plates, and their specific molar activities in mediating BHK cell spreading were compared with that of intact fibronectin. A 37-kD fragment purified from chymotryptic digests of human plasma fibronectin had essentially the same specific molar activity as intact fibronectin. In contrast, other fragments such as an 11.5-kD fragment lacking NH2-terminal sequences of the 37-kD fragment had only poor spreading activity on a molar basis. Furthermore, in competitive inhibition assays of fibronectin-mediated cell spreading, the 37-kD fragment was approximately 325-fold more active than the GRGDS synthetic peptide on a molar basis. mAbs were produced using the 37-kD protein as an immunogen and their epitopes were characterized. Two separate mAbs, one binding close to the RGD site and the other to a site approximately 15 kD distant from the RGD site, individually inhibited BHK cell spreading on fibronectin by greater than 90%. In contrast, an antibody that bound between these two sites had minimal inhibitory activity. The antibodies found to be inhibitory in cell spreading assays for BHK cells also inhibited both fibronectin-mediated cell spreading and migration of human HT-1080 cells, functions which were also dependent on function of the alpha 5 beta 1 integrin (fibronectin receptor). Assembly of endogenously synthesized fibronectin into an extracellular matrix was not significantly inhibited by most of the anti-37-kD mAbs, but was strongly inhibited only by the antibodies binding close to the RGD site or the putative synergy site. These results indicate that a second site distant from the RGD site on fibronectin is crucial for its full biological activity in diverse functions dependent on the alpha 5 beta 1 fibronectin receptor. This site is mapped by mAbs closer to the RGD site than previously expected.

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