AMPHIREGULIN IN LUNG BRANCHING MORPHOGENESIS - INTERACTION WITH HEPARAN-SULFATE PROTEOGLYCAN MODULATES CELL-PROLIFERATION

Epithelial and mesenchymal cells isolated from mouse embryonic lungs s ynthesized and responded to amphiregulin (AR) in a different fashion. Mesenchymal cells produced and deposited 3- to 4-fold more AR than epi thelial cells, proliferated in the presence of exogenous AR, and their spontaneous growth was blocked by up to 85% by anti-AR antibodies. In contrast, epithelial cells exhibited a broad response to this growth regulator factor depending on whether they were supplemented with extr acellular matrix (ECM) and whether this ECM was of epithelial or mesen chymal origin. AR-treated epithelial cells proliferated by up to 3-fol d in the presence of mesenchymal-deposited ECM, remained unchanged in the presence of epithelial-deposited ECM, and decreased in their proli feration rate below controls in the absence of ECM supplementation. Th is effect was abolished by treatment with the glycosaminoglycan-degrad ing enzymes heparinase and heparitinase suggesting the specific involv ement of heparan sulfate proteoglycan (HSPG) in AR-mediated cell proli feration. In whole lung explants, branching morphogenesis was inhibite d by antibodies against the AR heparan sulfate binding site and stimul ated by exogenous AR. Since during development, epithelial cells are i n contact with mesenchymal ECM at the tips of the growing buds and alo ngside the basement membrane, focal variations in the proportion of ep ithelial and mesenchymal HSPG will focally affect epithelial prolifera tion rates. Therefore, AR-HSPG interaction may underlie the process of branching morphogenesis by inducing differential cell proliferation.