Biomedical subjects

D M Ramos

Publications and source records attributed to D M Ramos.

21 records · Page 2Linked to original sources

PubMed1991

Role of laminin-binding integrin in the invasion of basement membrane matrices by fibrosarcoma cells.

Laminin is a large glycoprotein that is found in basement membranes and promotes cell adhesion and migration. In human fibrosarcoma cells we detected the presence of an integrin complex, with a Mr of 140,000/120,000 under nonreducing conditions, that bound specifically to laminin-Sepharose columns. Immunoprecipitation with monoclonal antibodies characterized this complex as alpha 6 beta 1. Attachment of the fibrosarcoma cells to laminin substrates was completely inhibited in the presence of anti-alpha 6 beta 1 antibody, while attachment to fibronectin and type IV collagen was unaffected. When seeded onto reconstituted basement membrane, the fibrosarcoma cells spread out, migrated, and invaded the matrix. In the presence of anti-beta 1 or anti-alpha 6 beta 1 antibodies, initial invasion through the matrix was inhibited. The results indicate that the HT1080 cells express the alpha 6 beta 1 complex and that it mediates their attachment to laminin. Furthermore, this receptor appears to be important during initial attachment and subsequent invasion of basement membrane-like matrices.

Amino Acid Sequence↗

PubMed1990

Analysis of integrin receptors for laminin and type IV collagen on metastatic B16 melanoma cells.

As tumor cells invade surrounding tissue, they adhere to various extracellular matrix components. Previously we reported that B16-BL6 melanoma cell adhesion to both basement membrane and purified protein substrates was blocked by antibody to beta 1-integrin adhesion receptors (R. H. Kramer et al., Cancer Res., 49: 393-402, 1989). In the present study we found, using immunofluorescent staining, that beta 1-integrin complexes were colocalized with vinculin in focal adhesion plaques on laminin, type IV collagen, and fibronectin substrates. To identify potential adhesion receptors on B16 cells, the cells were surface-labeled with 125I, solubilized with detergent, and chromatographed on laminin-, type IV collagen-, and fibronectin-Sepharose columns. On laminin-Sepharose, an integrin heterodimer complex was eluted with EDTA that contained a beta 1 chain at Mr 120,000 and an alpha subunit at Mr 140,000 (nonreduced). This complex was specific for laminin and failed to bind to collagen- or fibronectin-Sepharose columns. Immunoprecipitation with specific monoclonal antibody identified this complex as alpha 6 beta 1 (VLA-6). Furthermore, monoclonal antibody to the alpha 6 beta 1 complex effectively blocked the attachment of B16-BL6 cells to laminin but did not affect adhesion to fibronectin or type IV collagen. We recovered a different integrin complex from type IV collagen-Sepharose columns that was composed of a beta 1 chain and an alpha chain of Mr 180,000 (nonreduced). This same complex also exhibited a weak affinity for laminin-affinity chromatography. The laminin-binding complex and the type IV collagen-binding complex were clearly distinct from the fibronectin-binding receptor and were not eluted by arginyl-glycyl-aspartate-containing peptides. The results suggest that the B16 melanoma cells express multiple integrin-related receptors that appear to mediate cell adhesion to basement membrane matrices.

Animals↗

PubMed1989

Melanoma cell adhesion to basement membrane mediated by integrin-related complexes.

During invasion and metastasis, tumor cells use a variety of surface adhesion receptors to attach to and invade basement membranes and interstitial stroma. We examined the role of the cell surface integrin-like complex in the attachment of the invasive murine B16-BL6 melanoma cell line to basement membrane. Polyclonal antibodies prepared against integrin-related complexes isolated from hamster BHK cells (anti-ECMR) or mouse erythroleukemia cells (anti-mouse FnR) inhibited the attachment of B16 cells to complex basement membrane matrices and to substrates coated with purified extracellular matrix components (fibronectin, laminin, and type IV collagen). The expression of integrin-like receptors on the surface of B16 cells was confirmed by selective immunoprecipitation of radiolabeled and solubilized membrane proteins with the antibodies. Both antibodies also reacted with an integrin-related fibronectin-binding receptor complex purified by ligand affinity chromatography on fibronectin-Sepharose columns. The anti-integrin antibodies failed to react with the Mr 68,000 laminin-binding protein, suggesting that their inhibition of cell attachment to laminin and complex basement membrane was not due to contaminating antibodies against the Mr 68,000 laminin receptor. The results indicate that the integrin receptor complexes on B16-BL6 cells either interact directly with a diverse set of extracellular-matrix-associated components or somehow modulate the activity and function of other receptors. Thus integrins may have an important role in tumor cell invasion of tissue barriers.

Animals↗