αVβ6 Is a Novel Receptor for Human Fibrillin-1

Abstract

Human fibrillin-1, the major structural protein of connective tissue 10 -12 nm microfibrils, contains multiple calcium binding epidermal growth factor-like domains interspersed with transforming growth factor ␤-binding protein-like (TB) domains. TB4 contains a flexible RGD loop that mediates cell adhesion via ␣V␤3 and ␣5␤1 integrins. This study identifies integrin ␣V␤6 as a novel cellular receptor for fibrillin-1 with a K d of ϳ0.45 M. Analyses of this interaction by surface plasmon resonance and immunocytochemistry reveal different module requirements for ␣V␤6 activation compared with those of ␣V␤3, suggesting that a covalent linkage of an N-terminal calcium binding epidermal growth factor-like domain to TB4 can modulate ␣V integrin binding specificity. Furthermore, our data suggest ␣5␤1 is a low affinity fibrillin-1 receptor (K d > 1 M), thus providing a molecular explanation for the different ␣5␤1 distribution patterns seen when human keratinocytes and fibroblasts are plated on recombinant fibrillin fragments versus those derived from the physiological ligand fibronectin. Nonfocal contact distribution of ␣5␤1 suggests that its engagement by fibrillin-1 may elicit a lesser degree and/or different type of intracellular signaling compared with that seen with a high affinity ligand.Human fibrillin-1, a 350-kDa extracellular matrix glycoprotein, is the major structural component of the 10 -12-nm connective tissue microfibrils (1). It has a modular structure dominated by 43 calcium binding epidermal growth factor-like (cbEGF) 3 domains, tandem repeats of which are separated by transforming growth factor ␤-binding protein-like (TB) domains. Mutations in the fibrillin-1 gene (FBN1) give rise to the connective tissue disease Marfan syndrome and related disorders.In elastic tissues such as arteries, lung, and elastic ligaments, fibrillin microfibrils appear attached to cell membranes. These areas of attachment resemble focal contacts with an abundance of actin microfilaments on the cytoplasmic side of the membrane. Clustering of microfilaments at the cell surface at points of contact with the microfibrils suggest that microfibrillar components interact with cell-surface receptors which in turn serve as a dynamic link between cells and their microenvironment (2, 3).Fibrillin-1 is one of the microfibrillar proteins shown to mediate cell adhesion through binding to heterodimeric cell surface receptors of the integrin family (4, 5). This binding is at least in part mediated by the TB4 domain that contains an RGD (Arg-Gly-Asp) motif, a minimal integrin binding motif found in a number of extracellular matrix proteins. Fibrillin-integrin interactions are likely to be particularly important in tissues where microfibrils are in close proximity to cells, such as in the elastic lamellae, and may play a role in the assembly of the microfibril network, as has been shown in the case of fibronectin fibrillogenesis (6). Furthermore, the loss of cell-matrix interactions is likely to underlie some of the pleiotropic manifestations of Ma...

p38 MAPK Is an Early Determinant of Promiscuous Smad2/3 Signaling in the Aortas of Fibrillin-1 (Fbn1)-null Mice

“…1B) (27). Identical results were obtained using the TGF-␤-responsive plasmid (CAGA) 12 MLP-Luc, (data not shown). Quantitative differences in Smad2/3 signaling between VSMC of different mutant genotypes and between individual cell strains of the same mutant genotype are likely to reflect variances in disease progression and penetrance (Fig.…”

“…The choice of Fbn1-null cells was based on the assumption that the extremely rapid physical collapse of the aortic wall in mgN/mgN mice might eliminate the confounding effects of secondary cellular events that characterize late onset vascular disease in the other two mouse models of MFS (5-7). The results revealed that inhibition of either p38 MAPK or JNK activity negatively affects the expression of the p3TP-Lux and (CAGA) 12 MLP-Luc reporter plasmids ( Fig. 2A) (data not shown).…”

“…Cells were transiently co-transfected with 400 ng of the TGF-␤-responsive plasmid p3TP-Lux or (CAGA) 12 MLP-Luc (kind gifts of Drs. Joan Massagué and Peter ten Dijke, respectively) (25, 26) and 1 ng of the control plasmid SV40:Renilla-Luc (Promega, Madison, WI) using Lipofectamine 2000 (Invitrogen) (27).…”

Fibrillin-1 and alpha8 integrin are co-expressed in the glomerulus and interact to convey adhesion of mesangial cells

“…5 Attachment of cells to fibrillin-1 is mediated via the integrin receptors avb3, a5b1, and avb6. [6][7][8] Recently, a8b1 integrin was also described to interact with fibrillin-1. 9 In the kidney, the a8 integrin chain is expressed on vascular smooth muscle cells and mesangial cells.…”

Engineered mutations in fibrillin-1 leading to Marfan syndrome act at the protein, cellular and organismal levels

“…These mutations are located in TB4 relatively close to the sole integrin-interacting RGD sequence in fibrillin-1 [87][88][89]. A significant loss of attachment and spreading of human foreskin dermal fibroblasts to mutated fibrillin-1 fragments, was observed for these mutations suggesting that the fibrillin-1 interaction with integrins avb3 and/or a5b1 was affected [42].…”