The identification of extracellular matrix (ECM) binding sites on the basal surface of embryonic corneal epithelium and the effect of ECM binding on epithelial collagen production.

Abstract

Abstract. Previously, we have shown that embryonic corneal epithelia can interact with, and respond to, soluble extracellular matrices (ECM) (laminin, collagen, and fibronectin). The basal surface of epithelia isolated free of the underlying ECM can be seen to be disrupted by numerous blebs that sprout from this formerly smooth surface. Laminin, collagen, or fibronectin added to the culture medium cause the epithelium to reorganize its cytoskeleton and flatten its basal surface. We show here that ECM molecules at concentrations that reorganize epithelial cytoskeletal morphology also increase the amount of collagen produced by the epithelial cells. However, molecules that do not reorganize basal epithelial morphology (concanavalin A, heparin, bovine serum albumin) have no effect on collagen production. We also report that fluorescently labeled laminin, collagen, and flbronectin, when added to the medium surrounding isolated corneal epithelia, bind to and flatten the basal epithelial cell surface. The binding site on the basal surface is protease sensitive and is specific for each ECM molecule. These results are compatible with the idea that the basal epithelial plasmalemma possesses a diverse population of binding sites for ECM that link cell surface matrix to the cytoskeleton, causing a dramatic cytoskeletal reorganization which in turn results in enhanced production of collagen by the cells. PITHELIAL cells exhibit highly polarized apical and basal cell surfaces. The apical surface expresses enzymes and other molecules that do not appear on the basolateral surface, whereas the basolateral surface is known to have sodium potassium ATPase, binding sites for hormones, and other molecules that do not occur on the apical surface (26). Epithelia confront the extracellular matrix (ECM) ~ only at their basal surfaces. From the work of Sabatini et al. (26), it seems that the contact of the epithelial cells with the substratum is one of the key events in the determination of the apical-basal polarity of the cells. In a study of hepatocytes attaching to collagen, Rubin et al. (25) postulated that receptors in the cell membrane for collagen are mobile and upon attachment to ECM, repolarize to the basal cell surface. Recently, specific laminin-binding, fibronectin-binding, and collagen-binding proteins have been reported for several cell types, as well as a heparan sulfate proteoglycan that seems to be membrane intercalated (for review see references 10, 28, 33).We have been investigating the interaction of ECM components with embryonic corneal epithelium and the role of this interaction in the maintenance of epithelial cytoarchitecture and differentiation. During development of the eye, the avian corneal epithelium secretes the primary stroma, which consists of an orthogonal array of striated fibrils containing several collagens, including types I and II (4,8). If the corneal epithelium is removed from basal lamina and underlying stroma by EDTA or trypsin collagenase, the basal surface extends cell processes called blebs...

Specific glycosphingolipids mediate epithelial-to-mesenchymal transition of human and mouse epithelial cell lines

“…For example, epithelial cells that come in contact with soluble extracellular matrix components acquire characteristics similar to those of mesenchymal fibroblasts, as originally observed by Hay and colleagues (1)(2)(3). After extensive further studies, a concept emerged that the transitional process from epithelial to mesenchymal phenotype is commonly associated with embryonic development, as well as pathological conditions, such as fibrosis or cancer metastasis, and the process was termed ''epithelial-to-mesenchymal transition'' (EMT) (4)(5)(6)(7)(8)(9)(10).…”

Modulation of the expression of an apical plasma membrane protein of Madin-Darby canine kidney epithelial cells: cell-cell interactions control the appearance of a novel intracellular storage compartment.

“…Likewise, ECM regulates hepatocyte proliferation and differentiation (18,21). Hay and co-workers have shown that collagen and other ECM components stimulate differentiation and ECM synthesis by corneal epithelium (27,(37)(38)(39)59). In fibroblasts, both messenger translatability and the synthesis of cytoskeletal components require cell-substratum interactions (4,19).…”

Induction of albumin gene transcription in hepatocytes by extracellular matrix proteins.

“…By utilizing different culture substrata, matrices have been identified which support differentiated function in a variety of cell types (8,15,16,18) including epithelial cells (2,10,17,20,23). In primary cultures of hepatocytes, albumin synthesis and secretion is maintained for several weeks when cells are plated on a basement membrane-like matrix derived from the Engelbreth-Holm-Swarm mouse sarcoma tumor (EHS gel; described in reference 19) (4).…”