Expression of Laminin α3, α4, and α5 Chains by Alveolar Epithelial Cells and Fibroblasts

Laminins are principal components of basement membranes. Eleven laminin isoforms are known, each a heterotrimer composed of polypeptide chains designated α, β, and γ. Five α chains have been identified to date: α1, α2, α3, α4, and α5. Recent studies of fetal and adult mouse lung show prominence of α3, α4, and α5 in alveolar tissue, and point to differences in the cellular expression of these α chains in the developing alveolus. We examined isolated rat alveolar type II cells and lung fibroblasts for expression of laminins α3, α4, and α5. We found that laminin α3 was expressed only by alveolar epithelial cells, that laminin α4 was expressed only by lung fibroblasts, and that laminin α5 was expressed primarily by alveolar epithelial cells. Metabolic labeling and immunoprecipitation confirmed the production of laminin α4 by fibroblasts and laminin α5 by alveolar epithelial cells in culture. These studies indicate that different alveolar cell types contribute different laminin α chains to the laminin isoforms...