Investigation of the role of signal transduction in attachment of ocular melanoma cells to matrix proteins: inhibition of attachment by calmodulin antagonists including tamoxifen

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Abstract
We investigated the role of signal transduction systems in the attachment of human uveal melanoma cells to matrix proteins. Ocular melanoma cells established from primary tumours attached rapidly to all substrates examined. Preferred substrates of attachment were collagens type I, III and IV and fibronectin rather than laminin, gelatin, arginine-glycine-aspartine, vitronectin, poly-I -lysine or plastic. All cells showed rapid attachment to the preferred substrates (80% within 10 min). Manipulation of intracellular cyclic AMP or protein kinase C activity had relatively little effect on cell attachment. In contrast, attachment was significantly reduced by manipulating either intracellular calcium or calmodulin. After 15 min at 37°C, the calcium ionophore ionomycin (5 μm) reduced attachment to 25%, and TMB8 (50 μM), which can reduce intracellular calcium, reduced attachment to 60%. The experimental calmodulin antagonist J8 (25 μm), a substituted naphthalene sulphonamide, reduced attachment to 40%. Similarly tamoxifen (25 μM), which has calmodulin antagonist activity in vitro,reduced attachment to 55%. Both J8 and tamoxifen inhibited cell attachment to a wide range of matrix proteins, suggesting that this effect on attachment is not dependent on the presence of specific adhesion receptors. Reduction of ocular melanoma tumour cell/matrix interactions through manipulation of intracellular calcium or calmodulin may therefore merit further investigation as a possible approach to reducing metastatic spread.