| Basement membranes (BM) are thin sheets of highly specialized extracellular matrices (ECMs) present at the epithelial/mesenchymal interface of most tissues and surround muscle, peripheral nerve fibers, and fat cells. BMs are biochemically complex, containing several collagenous and noncollagenous proteins. For about two decades it has been apparent that all BMs contain laminins, entactin-1/nidogen-1 (E/N-1), Type IV collagen, and proteoglycans (PGs). However, within the past few years this complexity has increased as new components are described. While these new BM components give rise to the ideas of redundancy and specificity, they create new obstacles in understanding the physical, biochemical, and physiological properties of BMs.; Marlin-Darby canine kidney (MDCK) cells are an epithelial cell line derived from canine kidney distal tubules. These cells display multiple characteristics of transporting epithelia. When MDCK cells are grown on permeable supports they can generate a transepithelial electrical resistance demonstrating the presence of functional tight junctions and a polarized phenotype. MDCK cells serve as an ideal in vitro model for investigating epithelial cell-ECM interactions and basal lamina deposition due to their ability to synthesize many BM components and their integrin receptors.; To facilitate future studies involving PGs of epithelial cells, we characterized the BM and interstitial PGs of MDCK cells. PGs were prepared from conditioned medium by DEAE anion exchange chromatography. Heparan sulfate proteoglycans expressed by MDCK cells are perlecan, agrin, and collagen XVIII. Various chondroitin sulfate proteoglycan core proteins are made by MDCK cells and have been identified as biglycan, bamacan, and versican (PG-M). These PGs are also associated with mammalian kidney tubules in vivo.; Little is known about the physiological role of the E/N-1 molecule, although multiple studies have furthered the understanding of its biochemical nature and localization. MDCK cells do not synthesize endogenous EN-1. We have established clonal MDCK cell lines that allow for tetracycline-controlled expression of murine E/N-1. Consequences of E/N-1 expression include an increase in fibronectin deposition accompanied by a reduction in laminin deposition at the basal surface, mislocalization of integrins to lateral plasma membranes, and disruption of basolateral polarity when cells were grown on collagen-coated transwells. These observations may provide clues for elucidation of epithelial transformation. |
