EXPRESSION OF THE ALPHA-2-SUBUNIT OF LAMININ CORRELATES WITH INCREASED CELL-ADHESION AND METASTATIC PROPENSITY

Previous studies have indicated that laminin from neoplastic cells of high tumorigenicity is less active in promoting cell adhesion than aminin from normal cells or tissues. In the present study, we tested the hypothesis that laminin of metastatic tumor cells differs from that of nonmetastatic cells. Accordingly, we determined the subunit composition of laminin in highly metastatic, ras-transformed cells (4R) and compared it with laminin produced by nonmetastatic cells transformed with ras plus E1a (RE4). Metastatic 4R cells produced three to four times more of the alpha 2-subunit of laminin than RE4 cells did. Furthermore, the highly metastatic human melanoma cells (1205 and A2058) made and secreted into the medium, laminin containing significantly more of the alpha 2-subunit than laminin from the highly tumorigenic but nonmetastatic melanoma WM793 or HT1080 fibrosarcoma cells. Using HT1080 cells, laminin (250 ng/well) from 4R cells showed more adhesion promoting activity (68%) than laminin from RE4 cells (39%). Similarly, laminin isolated from human placenta, which expresses bot the alpha 1 beta 1 gamma 1 and alpha 2 beta 1 gamma 1 isoforms, promoted cell adhesion better (63%) than EHS laminin (26%), which contains only the former isoform, at 250 ng/well. In addition, both 4R and RE4 cells attached more efficiently to 4R laminin-coated substratum than to RE4 laminin at 0.3 and 0.6 mu g/well. Using an oligonucleotide probe and a cDNA probe, specific for the human merosin sequence, we measured the steady-state levels of the alpha 2-mRNA in both 4R and RE4 cells and found ten times more mRNA for the alpha 2-subunit in the 4R cells than in RE4 cells. These studies suggest that tumor cells with metastatic propensity secrete more of the alpha 2-subunit than nonmetastatic tumor cells do, and that laminin containing the alpha 2-subunit promotes cell adhesion better than laminin which does not.