Binding and degradation of alpha 2-macroglobulin by cultured fibroblasts.
We studied the interactions of alpha 2-macroglobulin, a major protease inhibitor of plasma and of serum-containing culture medium, with cultured fibroblasts. Iodinated human alpha 2-macroglobulin bound specifically to washed cell layers of cultured human fibroblasts. At 0--4 degrees C, binding was saturated at a concentration of 10--20 micrograms/ml. At 37 degrees C, radiolabel appeared in the medium in a form soluble in 10% trichloroacetic acid. Sodium dodecyl sulfate polyacrylamide gel electrophoresis indicated that ingested iodinated alpha 2-macroglobulin transiently forms a complex with a trypsin-like protease. Indirect immunofluorescence demonstrated alpha 2-macroglobulin in vacuoles of fibroblasts grown in 10% human serum or incubated with purified alpha 2-macroglobulin. Fibroblasts transformed by SV-40 (VA-13 cells) bound and degraded less 125I-labeled alpha 2-macroglobulin than non-transformed fibroblasts and had fewer vacuoles containing alpha 2-macroglobulin. These observations indicate that cultured fibroblasts bind, take up by endocytosis, and degrade alpha 2-macroglobulin. Binding and endocytosis of alpha 2-macroglobulin by a cell may be a means of modulating proteases in the microenvironment of the cell and during endocytosis.
D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D003080:Cold Temperature; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006801:Humans; D007457:Iodine Radioisotopes; D010447:Peptide Hydrolases / Q000378:metabolism; D011485:Protein Binding; D013539:Simian virus 40; D000511:alpha-Macroglobulins / Q000378:metabolism*
D007457:Iodine Radioisotopes; D000511:alpha-Macroglobulins; D010447:Peptide Hydrolases