Retinoic Acid Inhibition of Human Melanoma Cell Invasion through a Reconstituted Basement Membrane and Its Relation to Decreases in the Expression of Proteolytic Enzymes and Motility Factor Receptor

Treatment of four A375 human melanoma sublines (A375, A375P, A375P-5, A375M), exhibiting distinct metastatic potentials in viVo, with β-all-trans-retinoic acid in vitro caused a dose- and time-dependent inhibition of the ability of these cells to penetrate Matrigel-coated filters using a reconstituted basement membrane invasion assay. The possible mechanisms of action responsible for the antiinvasive effect were further investigated, and the data showed that compared with untreated cells the retinoic acid-treated cells: (a) secreted lower levels of collagenolytic enzymes, as demonstrated by a decreased ability of the cells to degrade [3H]proline-labeled type IV collagen substrate and by a reduction in the activity of a secreted MT 64,000 collagenolytic enzyme detected in type IV collagen-containing Polyacrylamide gels; (b) expressed lower levels of the human type IV collagenase mRNA (except in the A375P cells), as detected by Northern blot analysis; (c) exhibited decreased levels of tissue plasminogen activator activity, as demonstrated by a chromogenic assay; (d) were 10–40% less adhesive to a reconstituted basement membrane matrix, as determined by a 60-min Na251Cr04-labeled cell attachment assay; (e) exhibited an increase in the high affinity metastasis-associated cell surface laminin receptor, as determined by flow cytometry after binding of fluorescently labeled laminin receptor antibody; and (/) expressed decreased amounts of gp78, a cell surface receptor for motility factor, demonstrated by immunoblotting and immunofluorescence. Collectively, these data suggest that retinoic acid inhibits tumor cell invasion through a basement membrane-like matrix by suppressing matrix degradation and by altering cell surface receptors.