A 30 KD SULFATED EXTRACELLULAR-MATRIX PROTEIN IMMUNOLOGICALLY CROSS-REACTIVE WITH VITRONECTIN

In this study we describe a human sulfated 30kD protein (sp30) that is recognized by a monoclonal antibody raised against human vitronectin (mAb 8E6). Another monoclonal antibody raised against human vitronecti n, mAb MaSp, and a polyclonal antiserum against vitronectin did not re act detectably with sp30. Sp30, unlike vitronectin, is synthesized by a variety of non-hepatic human cell lines in culture, including cells of lymphoid origin. It is synthesized in sulfated form as indicated by metabolic labeling of MG-63 human osteosarcoma cells with (SO4)-S-35. Sp30 is an extracellular matrix protein as indicated by its associati on with the matrix of MG-63 cells after removal of the cells with EDTA and its fibrillar pattern by immunofluorescence of non-permeabilized confluent MG-63 cell monolayers detected with mAb 8E6. This antibody a lso stained short fibrils in human embryonic tissue. This pattern was distinct from the fainter diffuse staining obtained with mAb MaSp and the polyclonal antiserum to vitronectin, suggesting that the 8E6 stain ing in embryonic tissues was mostly due to sp30 rather than vitronecti n. A polyclonal antiserum against bovine microfibril associated glycop rotein (MAGP) precipitated a [(SO4)-S-35]-30kD protein from [(SO4)-S-3 5]-labeled MG-63 medium that co-migrated with a band precipitated by m Ab 8E6. Double-labeling immunofluorescence studies of embryonic tissue s showed an identical distribution of anti-bovine MAGP antiserum and m Ab 8E6 staining. These data indicate that sp30 is the human homolog of bovine MAGP. Distinction between sp30 and vitronectin will be importa nt in ascertaining the localization and function of both proteins. The findings that sp30 is sulfated and synthesized and secreted by a vari ety of cells in culture should aid in defining its role in microfibril logenesis. That sp30 is secreted by cells of lymphoid origin suggests that it might also have a heretofore unsuspected role in immune respon ses.