Concurrent modulation of cell surface fibronectin and adhesion to fibronectin in hepatoma cells

In vitro adhesion of mouse fetal germ cells to extracellular matrix components

Mouse primordial germ cells (PGCs) isolated from the dorsal mesentery and gonadal ridges of 10.5-12.5 days post coitum (dpc) embryos showed a progressively increasing adhesiveness to laminin and fibronectin coated substrates, whereas type I collagen and various glycosaminoglycans (hyaluronic acid, heparin and chondroitin-sulphates) were poor adhesive substrates. At later stages germ cells appeared to lose their adhesiveness to fibronectin and laminin substrates; the ability to adhere to laminin decreased very rapidly in male and slowly in female germ cells. Oocytes and prospermatogonia from 15.5 dpc fetal gonads showed poor adhesiveness to all substrates tested. PGC adhesion to laminin and fibronectin substrates did not require calcium but was markedly trypsin sensitive. Antibodies against the fibronectin receptor of CHO fibroblasts and short peptides containing the Arg-Gly-Asp sequence greatly reduced PGC adhesion to fibronectin. Following adhesion to laminin or fibronectin, most PGCs did not exhibit a morphology typical of motile cells, but remained spherical. A significant proportion (about 30%) of oocytes from 13.5-14.5 dpc embryos appeared, however, able to spread and elongate following attachment to laminin. The results support the hypothesis that mouse PGCs may utilize laminin and/or fibronectin as adhesive substrates during migration and gonad colonization, but indicate that additional factors are probably required to promote PGC motility. In addition, our data provide indirect evidence that binding sites for specific components of extracellular matrix are present in PGCs, and that their expression may be developmentally regulated.

The early appearance of fibronectin in the course of metastatic tumor growth in lymph nodes

In order to study structural changes in the lymph node architecture in the course of metastatic involvement by carcinoma, 70 axillary lymph nodes of 45 female patients affected by breast carcinoma were examined. The following growth pattern of the metastasis was observed: (1) Involvement of vasa afferentia and (marginal) sinuses; (2) lysis of sinus wall and infiltration, causing replacement and lysis of reticulin fibres; (3) appearance of fibrillary fibronectin (FN) as the first noticeable sign of tumor stroma; (4) immigration of fibroblasts along these fibres, appearance of argyrophilic fibres codistributed with fibrillary FN; (5) formation of the complete tumor stroma, neovessels included. The appearance of FN is thus the first step of stroma formation and is interpreted as an "in situ" precipitation of soluble plasma FN.

Integral membrane antigens involved in cell-substratum adhesion of hepatocytes and hepatoma cells

Cell-substratum adhesion of rat hepatocytes was inhibited by antisera raised against purified plasma membranes of rat liver (anti-liver-antiserum) and Morris hepatoma 7777 (anti-hepatoma-antiserum). It is assumed that substances which block the adhesion-inhibiting activity of the antisera are involved in cell-substratum adhesion. Adhesion-involved molecules of rat liver monitored as 'blocking activity' were compared with those of Morris hepatoma 7777 and 9121. They were found to be integral membrane glycoproteins, which could be solubilized only by detergents. Fractionation of plasma membrane extracts by size exclusion HPLC revealed two blocking activity peaks representing molecules involved in the adhesion to plastic (P-AIM) and collagen (C-AIM). In rat liver both adhesion-involved molecules were found; yet P-AIM seemed to be the major type of adhesion-involved molecule. In the relatively well differentiated Morris hepatoma 9121 also both types were detected. In membrane extracts of the high malignant and poorly differentiated Morris hepatoma 7777, however, no P-AIM but only C-AIM were found. Estimation by size exclusion HPLC revealed molecular weights of 120 kD for C-AIM and approx. 105 kD for P-AIM. On SDS gel electrophoresis proteins in the region of 95 kD were found in C-AIM containing fractions, whereas proteins of 105 kD are likely candidates for P-AIM.