INVESTIGATION OF THE ROLE OF SIGNAL-TRANSDUCTION IN ATTACHMENT OF OCULAR MELANOMA-CELLS TO MATRIX PROTEINS - INHIBITION OF ATTACHMENT BY CALMODULIN ANTAGONISTS INCLUDING TAMOXIFEN

We investigated the role of signal transduction systems in the attachm ent of human uveal melanoma cells to matrix proteins. Ocular melanoma cells established from primary tumours attached rapidly to all substra tes examined. Preferred substrates of attachment were collagens type I , III and IV and fibronectin rather than laminin, gelatin, arginine-gl ycine-aspartine, vitronectin, poly-L-lysine or plastic. All cells show ed rapid attachment to the preferred substrates (80% within 10 min). M anipulation of intracellular cyclic AMP or protein kinase C activity h ad relatively little effect on cell attachment. In contrast, attachmen t was significantly reduced by manipulating either intracellular calci um or calmodulin. After 15 min at 37 degrees C, the calcium ionophore ionomycin (5 mu M) reduced attachment to 25%, and TMB8 (50 mu M), whic h can reduce intracellular calcium, reduced attachment to 60%. The exp erimental, calmodulin antagonist J8 (25 mu M), a substituted naphthale ne sulphonamide, reduced attachment to 40%. Similarly tamoxifen (25 mu M), which has calmodulin antagonist activity in vitro, reduced attach ment to 55%. Both 58 and tamoxifen inhibited cell attachment, to a wid e range of matrix proteins, suggesting that this effect on attachment is not dependent on the presence of specific adhesion receptors. Reduc tion of ocular melanoma tumour cell/matrix interactions through manipu lation of intracellular calcium or calmodulin may therefore merit furt her investigation as a possible approach to reducing metastatic spread .