EXPRESSION OF LAMININ ALPHA(3), ALPHA(4), AND ALPHA(5) CHAINS BY ALVEOLAR EPITHELIAL-CELLS AND FIBROBLASTS

Laminins are principal components of basement membranes. Eleven lamini n isoforms an known, each a heterotrimer composed of polypeptide chain s designated alpha, beta, and gamma. Five alpha chains have been ident ified to date: alpha(1), alpha(2), alpha(3), alpha(4), and alpha(5). R ecent studies of fetal and adult mouse lung show prominence of alpha(3 ), alpha(4), and alpha(5) in alveolar tissue, and point to differences in the cellular expression of these alpha chains in the developing al veolus. We examined isolated rat alveolar type II cells and lung fibro blasts for expression oflaminins alpha(3), alpha(4), and alpha(5). We found that laminin alpha(3) was expressed only by alveolar epithelial cells, that laminin alpha(4) was expressed only by lung fibroblasts, a nd that laminin alpha(5) was expressed primarily by alveolar epithelia l cells. Metabolic labeling and immunoprecipitation confirmed the prod uction of laminin alpha(4) by fibroblasts and laminin alpha(5) by alve olar epithelial cells in culture. These studies indicate that differen t alveolar cell types contribute different laminin alpha chains to the laminin isoforms in alveolar basement membranes. Immunohistochemistry showed colocalization of these laminin a chains with the laminin beta (1), beta(2), and gamma(1) chains, indicating the likelihood that lami nins 6 to 11 an present in alveolar basement membranes.