Basement membranes are thin extracellular matrices that separate epithelial and mesenchymal cells and surround cells, such as endothelial, muscular, and neural cells. Basement membranes are the first extracellular matrix to appear in development and are critical for organ development and tissue repair. They not only provide the scaffold for cells and cell layers, but they also have an essential role in tissue morphogenesis that affects cell adhesion, migration, proliferation, and differentiation. Basement membranes provide major barriers in blood vessels to the passage of proteins and invasion by metastatic tumor cells. Basement membranes consist of collagen IV, laminin, perlecan, nidogen/entactin, and other molecules, which interact with each other to form the supramolecular structure and also bind cell surface receptors such as integrins and syndecans. Recently, molecular diversity in basement membrane components has been found and the existence of a large family of these molecules has been demonstrated. Our primary objectives have been to identify the specific functions of basement membrane components, to study their structure and function relationships, to elucidate the mechanisms by which they are regulated, and to describe related protein interactions in development and diseases. We have created animal models to study functions of basement membrane components in development and disease.? ? Laminins are heterotrimeric basement membrane proteins that exert multiple biological functions through interactions with extracellular matrix molecules and with cell surface receptors. The regulation of these interactions are critical to many biological processes, including cell adhesion and migration, angiogenesis, tumor progression, and neurite outgrowth. To date, at least fifteen laminin isoforms, laminin-1 through laminin-15, have been identified. The laminin family contains at least 11 chains (five alpha, three beta, and three gamma chains). The five laminin alpha chains share a large module at their C-terminal region (G domain), which contains five laminin G domain-like modules (LG1-5), and each module consists of about 200 amino acids. Laminin-1 (alpha-1, beta-1 and gamma-1; also called laminin-111, according to a recently proposed nomenclature) is the major laminin present in early embryonic stages. We previously identified active peptides AG73 and EF-1 from laminin alpha-1 LG4 for binding to heparin/syndecan and integrin alpha-2/beta-1, respectively. However, their activity and functional relationship within the laminin-1 protein and LG4 module are not known. To address this question, we prepared recombinant LG4 proteins that contain site-specific mutations within the AG73, EF-1, and alpha-dystroglycan binding sites and analyzed their binding activities to syndecans, integrins, and heparin and their activities for cell attachment and spreading in comparison to laminin-1. We found that recombinant proteins containing mutations within either the AG73 or alpha-dystroglycan binding site lost heparin-binding activity and did not attach to lymphoid cell lines expressing specific syndecans, suggesting that LG4 binds syndecans through these sites. These mutant LG4 proteins mediated significantly reduced fibroblast attachment, while mutant LG4 in EF-1 retained cell attachment activity but did not promote cell spreading. Fibroblast attachment to LG4 was inhibited by heparin but not by integrin antibodies, while cell spreading was inhibited by anti-integrin alpha-2 but not by alpha-6. In contrast, laminin-1-mediated fibroblast attachment and spreading were not inhibited by heparin or anti-integrin alpha-2, indicating that LG4 and laminin-1 have distinct mechanisms for cell attachment and spreading. These results suggest that, similar to other laminin alpha-chains, laminin alpha-1 LG4-5 may also be produced by a proteolytic cleavage of the laminin alpha-1 chain in certain tissues where it exerts its activity.? ? Perlecan is a major heparan sulfate proteoglycan in basement membrane and in some other tissues such as cartilage. The protein core of perlecan consists of five distinct domains that can be substituted primarily with heparan sulfate (HS) chains. Perlecan interacts with many extracellular molecules and cell surface receptors through HS chains and the protein core, which contribute to strengthening basement membrane structure and serving as a multifaceted functional proteoglycan. Our previous studies with gene knockout mice and human genetic diseases demonstrated that perlecan is essential for development and that the lack of perlecan results in either embryonic lethality due to defective myocardiac basement membrane or perinatal lethality due to cartilage defects. In addition, perlecan is implicated in many biological functions in tissue homeostasis and diseases.? Animal models are useful to determine the roles of perlecan in adult tissue function and disease. However, the lethal phenotype of perlecan KO mice has hampered these studies. To overcome the problem, we created perinatal lethality-rescued perlecan KO mice by expressing recombinant perlecan specifically to cartilage but not other tissues. The mutant mice survived but had small eyes and a myotonia phenotype, similar to patients with partial functional mutations in perlecan. Using the mutant mice, we found that in the absence of perlecan, tumor metastasis was decreased in an experimental metastasis model using B16-F10 melanoma cells. We also found that skin wound healing was accelerated and cell migration of keratinocytes and fibroblasts was increased in the absence of perlecan. Although the mechanisms of these phenotypes are not clear, our results suggest that perlecan plays important roles in cellular processes in various tissues in adults.
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