Regulation of the ‘molecular scissor’ ADAM10 by tetraspanin Tspan15

ADAM10 is a ubiquitously-expressed ‘molecular scissor’ that regulates a variety of important transmembrane proteins by proteolytically cleaving their extracellular regions. The cellular localisation and substrate specificity of ADAM10 is regulated by one of six tetraspanin membrane proteins, termed TspanC8s, comprising Tspan5, 10, 14, 15, 17 and 33. This has led to the hypothesis that ADAM10 exists as six different scissors, depending on its interacting TspanC8. This thesis investigates the function of Tspan15, which is of interest due to its recent implication in cancer, deep vein thrombosis and bacterial infection. The new discoveries of this study are as follows. (1) Tspan15 expression is dependent on ADAM10. (2) Tspan15 is required for cleavage of neural-, epithelial- and vascular endothelial-cadherin in cell lines. (3) Two of four newly-generated anti-Tspan15 monoclonal antibodies have inhibitory activity directed against ADAM10-mediated cleavage of VE-cadherin, which cannot be explained by recognition of different epitopes or differential effects on Tspan15 internalisation or ADAM10 expression. (4) Loss of ADAM10 in human endothelial cells promotes migration, increases proliferation and impairs network formation, but loss of Tspan15 has no effect. These findings support the six-scissor hypothesis, suggest that the major function of Tspan15 is to regulate ADAM10, and demonstrate the therapeutic potential of TspanC8 monoclonal antibodies.