Synthesis and secretion of alpha 2-macroglobulin by human lung fibroblasts

Synthesis and secretion of alpha 2-macroglobulin were studied with the human lung fibroblast cell line GM 1379. After incubation with [3H]leucine the cells secreted radioactively labeled alpha 2-macroglobulin consisting of subunits with a molecular weight of 180,000. When the cells were treated with tunicamycin the unglycosylated alpha 2-macroglobulin subunit exhibited a molecular weight of 160,000. Poly(A) +RNA was isolated from the cultured cells and translated in a rabbit reticulocyte lysate. From the translation products an alpha 2-macroglobulin species with a molecular weight of 160,000 was immunoprecipitated. The addition of pancreatic microsoms to the translation mixture resulted in the synthesis of an alpha 2-macroglobulin subunit which had molecular weights of 180,000. Thus, a size of approximately 160,000 for the protein moiety and 20,000 for the carbohydrate portion can be estimated for a subunit of alpha 2-macroglobulin from human lung fibroblasts.