The fibronectin receptor is organized by extracellular matrix fibronectin: implications for oncogenic transformation and for cell recognition of fibronectin matrices.

Abstract

Abstract. Cells interact with extracellular fibronectin (FN) via adhesive fibronectin receptors (FNRs) that are members of the very late antigens (VLAs) subgroup of the integrin family. In stationary fibroblasts, the FNR is highly organized and distributed identically to extracellular FN fibrils. However, in highly migratory neural crest cells and embryonic somatic fibroblasts, this organization is lost and the FNR appears diffuse. Similarly, oncogenic transformation typically leads to disorganization of the FN receptor and loss of matrix FN. Two models can account for these observations. First, the FN matrix may organize the FN receptor at extracellular matrix contacts on the cell surface. Motile cells not depositing FN matrices thus lack organized receptors. Alternatively, as the FNR is required for optimal FN matrix assembly, (McDonald, J. A., B. J. Quade, T. J. Broekelmann, R. LaChance, K. Forseman, K. Hasegawa, and S. Akiyama. 1987. J. Biol. Chem. 272:2957-2967; Roman, J., R. M. LaChance, T. J. Broekelmann, C. J. R. Kennedy, E. A. Wayner, W. G. Carter, J. A. McDonald. 1989. J. Cell Biol. 108:2529-2543 and has putative cytoskeletal links, it could be organized from within the cell helping to position newly forming FN fibrils. To study this question, we developed peptide antibodies specifically recognizing the a5 subunit of the FNR.Using these antibodies, we examined the organization of FN and of the FNR in normal, matrix assembly inhibited, and SV40-transformed human fibroblasts. On FN-coated substrates, the FNR is found in focal contacts rather than diffusely on the basal cell surface, suggesting FNR interaction with intracellular components. However, when FN fibrils are deposited, the FNR is co-distributed with these fibrils. Preventing FN matrix assembly prevents organization of the FNR. Moreover, when fibroblasts with well established FN matrices and co-distributed FNR are incubated briefly with monoclonal antibodies that block FNR binding to FN, the FNR is no longer co-distributed with the FN matrix. Thus, the FN receptor is organized in fibrils on the cell surface in response to extracellular FN. Because exogenous FN restores a FN matrix and receptor organization to SV40-transformed cells, the diffuse FN receptor phenotype appears to be related to loss of the FN matrix rather than to impaired FNR function. These results explain diffusely distributed FNRs in migratory neural crest and embryonic fibroblasts lacking well organized FN matrices and emphasize the existence of separate but related systems controlling FN deposition and recognition by receptor-armed cells.

Regulation of fibronectin receptor distribution [published erratum appears in J Cell Biol 1992 Jul;118(2):491]

“…Similarly the distribution of the fibronectin receptor with plasma membrane-associated fibronectin fibrils requires the interaction of the fibronectin receptor with extracellular fibrils (Chen et al, 1986;Giancotti et al, 1986;Akiyama et al, 1989;Roman et al, 1989) . These previous experiments demonstrated that the regulation of integrin receptor distribution requires the interaction of the receptor with its ligand and that the distribution of ligand determines the distribution of its receptor.…”

Expression, topography, and function of integrin receptors are severely altered in keratinocytes from involved and uninvolved psoriatic skin.

“…However, contrasting data exist in terms ofits cytoskeleton association and adhesive functions since a5/3, has been reported to be poorly and diffusely expressed on the keratinocyte plasma membrane (17) and not organized in defined adhesive structures (9), or expressed in focal contacts mediating keratinocyte adhesion (15,18). Recently, the clustering of the fibronectin receptor in defined adhesive structures has been correlated with keratinocyte migration during wound healing (39 Savoia, R. Cancedda, and P. C. Marchisio, submitted for publication) all might alter integrin polarization and/or trigger the organization of the fibronectin receptor in defined adhesive structures (31,54). In fact a functionally comparable mechanism exists for platelets (55,56), for the fast activation-regulated function of a5/31 in CD4+ resting human T cells (57) and for the fibronectin dependent activation of the Na+/H+ antiporter in mouse fibroblasts (58).…”

Integrin-linked Protein Kinase Regulates Fibronectin Matrix Assembly, E-cadherin Expression, and Tumorigenicity

“…Fn fragments containing the RGD-containing integrin binding site or antibodies recognizing the integrin binding site inhibited Fn matrix assembly in cultured cells and developing amphibian embryos (8,(21)(22)(23)(24). In addition, antibodies to ␣ 5 ␤ 1 integrin reduced the deposition of Fn into extracellular matrix by fibroblasts (25)(26)(27). The participation of Fn-binding integrins in Fn matrix assembly has been extensively studied in Chinese hamster ovary (CHO) cells.…”