Biosynthesis of sulfated extracellular matrices by alveolar type II cells increases with time in culture

The aim of this study was to determine the extent to which sulfate incorporated into biosynthesized basement membrane (BM) components increased as isolated type II cells progress toward a more type I cell-like phenotype from 7 to 21 days in culture. Specific sulfate cytochemistry, using high iron diamine, showed that type I-like cells in 21-day cultures deposited a more highly sulfated extracellular matrix. Biosynthetic labeling experiments using [35S]cysteine or [35S]sulfate as precursors confirmed the increased capacity of 21-day type I-like cells to biosynthesize sulfated BM components compared with type II-like cells in 7-day cultures, including a novel sulfated laminin. These biochemical changes in sulfation of BM components coincide with the established phenotypic transition from type II to type I cells during prolonged culture. More importantly, the data suggest that regulation of sulfation constitutes a potential mechanism by which type I and type II cells alter their environment in such a manner as to stabilize phenotype and modulate responses to growth factors.