Integrin expression in malignant melanoma.

Invasion of melanoma cells into the underlying interstitial stromal matrix is the initial step for subsequent local and distant metastasis. The invading tumor cell must interact with the extracellular matrix during the early stages of invasion and later during penetration of lymphatic and blood vessels. This interaction with different types of extracellular matrix predicts that the invasive cell must possess surface adhesion receptors with diverse ligand specificities, including the capacity to bind different types of collagens and adhesive glycoproteins. Metastatic melanoma cells do in fact express multiple adhesion receptors, including several of the receptors from the integrin family of heterodimers. The integrin receptors can be either extremely specific for a single ligand or capable of binding multiple ligands. It is likely that the tumor cell's repertoire of adhesion receptors may influence not only its adhesive properties but its metastatic characteristics as well. There is evidence that normal melanocytes have an integrin profile distinct from that of melanoma cells. In particular, melanocytes adhere poorly to laminin while metastatic melanoma cells bind well to this ligand. This difference in adhesion between the two cell types appears to reflect the fact that melanoma cells express a melanoma-specific integrin (alpha 7 beta 1) that binds laminin and is not detectable in normal melanocytes. The presence of increased laminin receptors and enhanced laminin binding in melanoma cells may contribute to the malignant phenotype.