Adhesion promoting property of laminin from normal tissue and from a tumorigenic cell line

The cell adhesion promoting activity of laminin isolated from normal human placenta was compared with that isolated from mouse EHS tumor and from the cultures of a mouse epithelial cell line B82 and its tumorigenic derivative, B82HT. The adhesion promoting properties of commercial merosin isolated from placenta was also compared with the above preparations using the human fibrosarcoma HT1080 cells. Percent attachment was defined as (radioactivity extracted from attached cells)/(radioactivity in cells added to assay) x 100. HT1080 cells adhered more efficiently on laminin (0.5 micrograms/well), isolated from the B82 rather than B82HT cell conditioned medium, (82% vs 64%). Percent attachment of HT1080 cells on isolated native placental laminin or commercial merosin was significantly higher compared to laminin from the EHS tumor (at 0.75 micrograms/well, 69%, 73% and 20% respectively). In parallel experiments the steady-state levels of mRNAs for subunits A, M, B1 and B2 in cultures of B82 and B82HT cells were determined. The ratio of mRNA for the laminin subunits in B82 and B82HT cells was 1:0.9 for the A chain, 1:0.6 for the M chain, 1:0.4 for the B1 chain, and 1:0.3 for the B2 chain. Protein studies indicated that the M subunit is absent in laminin preparations from the EHS tumor whereas it is abundant in the laminin from placenta and in commercial merosin. Laminin isolated from B82 cells contains a higher proportion of the M subunit compared to that from B82HT cells. The data suggest that there are functional differences between the laminin found in normal tissue and that present in a solid tumor. Functional differences were noted between the laminins synthesized by the B82 cell line and its tumorigenic counterpart, B82HT. These differences may result from the lack of gene expression for the laminin subunit M by the EHS tumor and by the lower degree of gene expression for this subunit by B82HT cells. The possibility that the laminin synthesized by the tumorigenic cell line may be structurally different from that synthesized by the B82 cells should also be considered.