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Abstract

Integrin receptors are mediators of cell-extracellular matrix and cell-cell interactions. Biochemical and immunocytochemical evidence shows that the platelet integrin receptor αIIbβ3 is present on the cell surface, at focal adhesion plaques and in the perinuclear region of metastatic B16a murine melanoma cells. Antibody to the fibronectin receptor α5β1, inhibits basal adhesion by approx. 30%, whereas antibodies to αIIbβ3 are ineffective. The surface immunoreactivity of tumor cells for αIIbβ3 can be enhanced by pre-treatment (5 min) with a lipoxygenase metabolite of arachidonic acid [i.e. 12-(S)-HETE] in a dose-dependent manner (max. effect approx. 0.1 μM). Other lipoxygenase metabolites are ineffective. B16a cells possess a large intracellular pool of αIIbβ3, from which the receptor complex translocates to the cell surface following 12-(S)-HETE pre-treatment. This pre-treatment of tumor cells enhances their adhesion to fibronectin, which is mediated exclusively by αIIbβ3 receptors. 12-(S)-HETE also facilitates the redistribution of αIIbβ3 in the plasma membrane with localization at the focal adhesion plaques. The cytoskeleton of the B16a cell is characterized by an absence of distinct microtubules in interphase cells and the presence of prominent microfilaments and vimentin intermediate filaments. In B16a cells, the disruption of intermediate filaments and/or microfilaments prevents the 12-(S)-HETE-induced increase in plasma membrane αIIbβ3, and enhanced tumor-cell adhesion to fibronectin. The microtubule-disrupting agent, colchicine, is ineffective in both respects. We conclude that the lipoxygenase metabolite of arachidonic acid, 120-(s)-HETE, regulates the surface expression and function of the αIIbβ3, integrin in B16a cells. Further, these data support the hypothesis that microfilaments and intermediate filaments have a profound role in regulating the expression of a multifunctional integrin in B16a tumor cells.