Increased expression of alpha IIb beta 3 integrin in subpopulations of murine melanoma cells with high lung-colonizing ability.

Abstract

Four subpopulations of B16 amelanotic melanoma cells, possessing different abilities to induce platelet aggregation (TCIPA) and to form lung colonies, were isolated by centrifugal elutriation. The expression of alpha IIb beta 3, alpha v beta 3 and alpha 5 beta 1 integrins was examined in the 4 subpopulations in order to determine the relationship between integrin receptor expression and tumor-cell metastatic potential. The mRNA of alpha IIb, alpha 5, beta 1 and beta 3 was detectable in the 4 subpopulations by Northern blotting. A gradual increase in mRNAs and cell-surface immunoreactivity of the alpha IIb beta 3 receptor, but not in their gene copies, was observed from the low to the high metastatic subpopulations. The ability of tumor cells to adhere to fibronectin and subendothelial matrix (SEM) increased in parallel. In the high metastatic cells, the alpha IIb beta 3 receptors, but not the alpha 5 beta 1 receptors, were localized to focal adhesion plaques. Incubation of the high metastatic cells with alpha IIb beta 3-specific antibodies reduced their matrix adhesion, TCIPA and lung-colonizing abilities. In contrast, in the low met- astatic cells, SEM adhesion and lung-colony formation were not affected by anti-alpha IIb beta 3 antibody treatment. Incubation of either the low or the high metastatic subpopulation with an alpha 5 beta 1-specific antibody had no effect in vitro and showed a slight inhibition of lung colonization in vivo. Our results suggest that several phenotypic characteristics of the enhanced metastatic potential of B16a subpopulations may be mediated by increased expression of alpha IIb beta 3 receptors and that expression of these receptors may be regulated at the transcriptional level.