Haploinsufficiency for human EYA1, a homologue of the Drosophila melanogaster gene eyes absent (eya), results in the dominantly inherited disorders branchio-oto-renal (BOR) syndrome and branchio-oto (BO) syndrome, which are characterized by craniofacial abnormalities and hearing loss with (BOR) or without (BO) kidney defects. To understand the developmental pathogenesis of organs affected in these syndromes, we inactivated the gene Eya1 in mice. Eya1 heterozygotes show renal abnormalities and a conductive hearing loss similar to BOR syndrome, whereas Eya1 homozygotes lack ears and kidneys due to defective inductive tissue interactions and apoptotic regression of the organ primordia. Inner ear development in Eya1 homozygotes arrests at the otic vesicle stage and all components of the inner ear and specific cranial sensory ganglia fail to form. In the kidney, Eya1 homozygosity results in an absence of ureteric bud outgrowth and a subsequent failure of metanephric induction. Gdnf expression, which is required to direct ureteric bud outgrowth via activation of the c-ret Rtk (refs 5, 6, 7, 8), is not detected in Eya1-/- metanephric mesenchyme. In Eya1-/- ear and kidney development, Six but not Pax expression is Eya1 dependent, similar to a genetic pathway elucidated in the Drosophila eye imaginal disc. Our results indicate that Eya1 controls critical early inductive signalling events involved in ear and kidney formation and integrate Eya1 into the genetic regulatory cascade controlling kidney formation upstream of Gdnf. In addition, our results suggest that an evolutionarily conserved Pax-Eya-Six regulatory hierarchy is used in mammalian ear and kidney development.

Thrombospondins are evolutionarily conserved, calcium-binding glycoproteins that undergo transient or longer-term interactions with other extracellular matrix components. They share properties with other matrix molecules, cytokines, adaptor proteins, and chaperones, modulate the organization of collagen fibrils, and bind and localize an array of growth factors or proteases. At cell surfaces, interactions with an array of receptors activate celldependent signaling and phenotypic outcomes. Through these dynamic, pleiotropic, and context-dependent pathways, mammalian thrombospondins contribute to wound healing and angiogenesis, vessel wall biology, connective tissue organization, and synaptogenesis. We overview the domain organization and structure of thrombospondins, key features of their evolution, and their cell biology. We discuss their roles in vivo, associations with human disease, and ongoing translational applications. In many respects, we are only beginning to appreciate the important roles of these proteins in physiology and pathology.T hrombospondins (TSPs) comprise a conserved family of extracellular, oligomeric, multidomain, calcium-binding glycoproteins. In general, basal metazoa and protostomes encode a single TSP in their genomes and deuterostomes have multiple TSP genes. The TSPs of mammals have many complex tissue-specific roles, including activities in wound healing and angiogenesis, vessel wall biology, connective tissue organization, and synaptogenesis. These activities derive mechanistically from interactions with cell surfaces, growth factors, cytokines, or components of the extracellular matrix (ECM) that collectively regulate many aspects of cell phenotype. Emerging evidence on the functions of TSPs in invertebrates suggests that ancient functions include bridging activities in cell-cell and cell-ECM interactions. Knowledge of TSP domain structures provides a rational basis for understanding their roles in vivo and associations with human disease and is assisting ongoing translational applications. DOMAIN ARCHITECTURE AND DOMAIN STRUCTURESThe domain architectures of representative TSP polypeptides are shown in Figure 1A. The invariant carboxy-terminal regions comprise a series of EGF-like domains, thirteen calcium-binding type 3 repeats, and a carboxy-terminal domain structurally homologous to the L-type lectin

In the epidermis proliferation of keratinocytes is restricted to the basal layer, which is in contact with the basement membrane, and cells undergo terminal differentiation as they move upwards through the suprabasal layers. In stratified cultures of human keratinocytes, upward migration is a consequence, not a cause, of terminal differentiation and occurs because keratinocytes become less adhesive to their substratum and to one another. Most keratinocytes can be induced to differentiate to completion by placing them in suspension in methylcellulose: within 12 h DNA synthesis is irreversibly inhibited and by 24 h most cells express involucrin (ref 4; P. A. Hall, J.C.A. and F.M.W., unpublished observations). Here we report that when fibronectin is added to the methylcellulose, keratinocytes still withdraw from the cell cycle, but induction of involucrin expression is largely inhibited. The effect of fibronectin is concentration- and time-dependent and is mediated by a receptor of the integrin family. These results provide an explanation for why overt terminal differentiation is normally restricted to suprabasal cells, whereas cell-cycle withdrawal occurs within the basal layer; they also have important implications for the mechanism of epidermal wound healing. Furthermore, our data show that the binding of an extracellular matrix protein to its receptor can regulate differentiated gene expression in the absence of changes in cell shape.

In epithelial tissue, cell-matrix and cell-cell adhesive interactions have important roles in the normal organization and stabilization of the cell layer. The malignant conversion of epithelial cells involves alterations in the expression and function of these adhesion systems that enable a switch to a migratory phenotype in tumor invasion and metastasis. Fascin is an actin-crosslinking protein that is found in the core actin bundles of cell-surface spikes and projections that are implicated in cell motility. We demonstrate that fascin is not detectable in normal colonic epithelium, but is dramatically up-regulated in colorectal adenocarcinoma. To test the hypothesis that fascin could participate in tumor invasive behavior, we developed a cell culture model to examine the effect of fascin expression on the adhesive interactions, invasiveness, and differentiation of colonic epithelial cells. We report marked effects on the organization of cell-surface protrusions, actin cytoskeleton, and focal adhesions in the absence of alterations in the protein levels of the major components of these structures. These effects correlate with alterations in cell movements on two-dimensional matrix, and increased invasiveness in three-dimensional matrix. The cells also show increased proliferation and decreased capacity for normal glandular differentiation in collagen gels. We propose that up-regulation of fascin, by promoting the formation of protrusive, actin-based, cell-motility structures, could be a significant component in the acquisition of invasive phe- Epithelial cell differentiation is fundamentally influenced by cell-matrix and cell-cell interactions. [1][2][3] In colonic epithelial cells, both the integrin and cadherin superfamilies of adhesion molecules are important contributors to the establishment of cell polarity and epithelial cell differentiation, and have been shown to play a role in the control of colorectal differentiation in tumor cells. 4,5 This is partly achieved through the formation of intracellular protein assemblies that anchor cytoskeletal actin filaments at defined areas within the cell membrane. In epithelial cells, these zones correspond to integrin-dependent focal adhesions and cadherin-containing adherens junctions and desmosomes. 6 These assemblies also function as important links in the integration of multiple cell signaling pathways. 3 Cell-matrix and cell-cell adhesive interactions normally stabilize the epithelial cell layer and maintain the cells in a nonmigratory state. However, the malignant conversion of epithelial cells involves a phenotypic switch to a migratory state that enables tumor invasion beyond the basement membrane and metastasis. The process of cell migration is poorly understood in epithelial cells, but studies in many types of carcinoma cells have documented increased formation of cell protrusions at cell margins, release of cell-cell contacts, and group movement of sheets of cells. In the models of cell motility that have been developed from studies of fibroblasts, protru...

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Cell adhesion to individual macromolecules of the extracellular matrix has dramatic effects on the subcellular localization of the actin-bundling protein fascin and on the ability of cells to form stable fascin microspikes. The actin-binding activity of fascin is down-regulated by phosphorylation, and we used two differentiated cell types, C2C12 skeletal myoblasts and LLC-PK1 kidney epithelial cells, to examine the hypothesis that cell adhesion to the matrix components fibronectin, laminin-1, and thrombospondin-1 differentially regulates fascin phosphorylation. In both cell types, treatment with the PKC activator 12-tetradecanoyl phorbol 13-acetate (TPA) or adhesion to fibronectin led to a diffuse distribution of fascin after 1 h. C2C12 cells contain the PKC family members alpha, gamma, and lambda, and PKCalpha localization was altered upon cell adhesion to fibronectin. Two-dimensional isoelectric focusing/SDS-polyacrylamide gels were used to determine that fascin became phosphorylated in cells adherent to fibronectin and was inhibited by the PKC inhibitors calphostin C and chelerythrine chloride. Phosphorylation of fascin was not detected in cells adherent to thrombospondin-1 or to laminin-1. LLC-PK1 cells expressing green fluorescent protein (GFP)-fascin also displayed similar regulation of fascin phosphorylation. LLC-PK1 cells expressing GFP-fascin S39A, a nonphosphorylatable mutant, did not undergo spreading and focal contact organization on fibronectin, whereas cells expressing a GFP-fascin S39D mutant with constitutive negative charge spread more extensively than wild-type cells. In contrast, C2C12 cells coexpressing S39A fascin with endogenous fascin remained competent to form microspikes on thrombospondin-1, and cells that expressed fascin S39D attached to thrombospondin-1 but did not form microspikes. Blockade of PKCalpha activity by TPA-induced down-regulation led to actin association of wild-type fascin in fibronectin-adherent C2C12 and LLC-PK1 cells but did not alter the distribution of S39A or S39D fascins. The association of fascin with actin in fibronectin-adherent cells was also evident in the presence of an inhibitory antibody to integrin alpha5 subunit. These novel results establish matrix-initiated PKC-dependent regulation of fascin phosphorylation at serine 39 as a mechanism whereby matrix adhesion is coupled to the organization of cytoskeletal structure.

Cell adhesion to thrombospondin-1 (TSP-1) correlates with assembly of cell-substratum contact structures that contain fascin microspikes. In this analysis, cell-matrix requirements for assembly of fascin microspikes were examined in detail. In six cell lines, cell spreading on a TSP-1 substratum correlated with expression of fascin protein and formation of fascin microspikes. Microspikes were not formed by H9c2 cells adherent on fibronectin, vitronectin, collagen IV, or platelet factor 4. However, both fascin microspikes and focal contacts were assembled by cells adherent on laminin-1. Using mixed substrata containing different proportions of TSP-1, and fibronectin, fascin microspike formation by H9c2 and C2C12 cells was found to be reduced on substrata containing 25% fibronectin and abolished on substrata containing 75% fibronectin. Adhesion to intermediate mixtures of TSP-1 and fibronectin resulted in coassembly of fascin microspikes and focal contacts, colocalization of fascin with actin stress fiber bundles and altered distributions of ␤1 integrins, cortical ␣-actinin, and tropomyosin. In cells adherent on 50% TSP-1:50% fibronectin, GRGDSP peptide treatment decreased focal contact assembly and altered cytoskeletal organization but did not inhibit microspike assembly. Treatment with chondroitin sulfate A or p-nitrophenol ␤-d-xylopyranoside decreased microspike formation and modified cytoskeletal organization but did not inhibit focal contact formation. In polarized migratory and postmitotic C2C12 cells, fascin microspikes and ruffles were localized at leading edges and TSP matrix deposition was also concentrated in this region. Depletion of matrix TSP by heparin treatment correlated with decreased microspike formation and cell motility. Thus, the balance of adhesive receptors ligated at the cell surface during initial cell-matrix attachment serves to regulate the type of substratum adhesion contact assembled and subsequent cytoskeletal organization. A role for fascin microspikes in cell motile behavior is indicated. INTRODUCTIONIt has long been appreciated that the interactions of cells with extracellular matrix (ECM) macromolecules play a role in regulating cell adhesion, shape, and movement: processes that are central to tissue organization in metazoan organisms and that contribute to many pathological conditions if disregulated (reviewed by Hynes and Lander, 1992;Gumbiner, 1996).To date, the cell-substratum contact structure most thoroughly studied in vitro has been the focal contact, or focal adhesion, that corresponds morphologically to a site of very close apposition between the ventral plasma membrane of a cell and its substratum (Abercrombie et al., 1971;Izzard and Lochner, 1976;Heath and Dunn, 1978). In molecular terms, focal contacts are distinguished by the colocalization of ligand-occupied clustered integrins on the cell surface with the termini of actin microfilament bundles and a characteristic assembly of intracellular proteins including talin, vinculin, paxillin, and focal adhesion kinase (FAK...

Abstract. We have compared the adhesive properties and integrin expression profiles of cultured human epidermal keratinocytes and a strain of nondifferentiating keratinocytes (ndk). Both cell types adhered to fibronectin, laminin, and collagen types I and IV, but ndk adhered more rapidly and at lower coating concentrations of the proteins . Antibody blocking experiments showed that adhesion of both cell types to fibronectin was mediated by the a5ß, integrin and to laminin by a 3ß1 in synergy with a2ß1 . Keratinocytes adhered to collagen with 01201, but an antibody to a2 did not inhibit adhesion of ndk to collagen . Both cell types adhered to vitronectin by a, containing integrins. Immunoprecipitation of surface-iodinated and metabolically labeled cells showed that in addition to a 2ß1, a3ß1, and a5ß1, both keratinocytes and ndk expressed a6ß4 and T HE integrins constitute a large family of cell surface molecules involved in cell-cell and cell-matrix interactions. Integrins are heterodimers, consisting of non-covalently associated a and ß subunits, both of which are transmembrane glycoproteins (Hynes, 1987) . The integrins are presently classified on the basis that one ß subunit can associate with several different a subunits : the 01 and 03 subgroups are widely expressed and are principally involved in cell-matrix interactions, whereas 0, integrins are expressed on leukocytes and are involved in cell-cell interactions (reviewed by Hemler, 1990) . However, it is now apparent that one a subunit can also associate with different ß subunits, examples being the a6ß, and a6ß4 integrins (Sonnenberg et al ., 1988a,b ;Kajiji et al., 1989) and the a,ß,, C1 .ß3, or a,ß5 integrins (Bodary and McLean, 1990;Vogel et al., 1990;Cheresh et al., 1989 ;Ramaswamy et al., 1990) . Heterodimer composition is important in determining ligand specificity (Cheresh et al., 1989; Bodary andMcLean, 1990; Sonnenberg etal ., 1990x ;Vogel et al., 1990), but there is also evidence that the same integrin can have different functions when expressed on different cell types (Elices and Hemler, 1989;Languino et al., 1989).Dr. Adams' present address