ADAMs are a sub-family of enzymes called “metalloproteases” which are implicated in a variety of physiological as well as pathological processes through their ability to cleave a number of substrates including growth factors, cytokines or adhesion proteins. Despite numerous studies on ADAM activity, very little is known about their regulation.Tetraspanins form a super-family of membrane proteins with a common conserved structure. They are implicated in numerous biological processes including migration, intercellular interactions, immune response, gamete fusion… Tetraspanins are known to interact with one another and with a restricted number of protein partners at the cell surface, thus forming a multi-molecular network referred to as « the tetraspanin web ». Previous studies in our laboratory have shown that the metalloprotease ADAM10 is associated to the tetraspanin web. Nevertheless, the tetraspanin in direct interaction with ADAM10 enabling it to be part of the web was not identified at the time. To begin with, in order to establish a model providing a read-out for a modulation of ADAM10 activity by tetraspanins, we demonstrate that tetraspanin engagement by monoclonal antibodies enhances E-cadherin shedding by ADAM10. Furthermore, muscarinic receptor activation also augments E-cadherin shedding but this time in an ADAM17-dependent manner. This occurs without the intervention of EGFR transactivation whereas a direct EGFR activation is able to stimulate E-cadherin shedding. Refocusing on the initial subject of the consequences of an interaction between ADAM10 and the tetraspanins, we conclusively show that the metalloprotease ADAM10 interacts with members of the conserved TspanC8 subfamily consisting of tetraspanins Tspan5, Tspan17, Tspan14, Tspan15, Tspan10 and Tspan33. These interactions and the relative expression of each of the TspanC8 members play a role in ADAM10 trafficking. ADAM10 and TspanC8 interactions are conserved throughout the Evolution and play a role in Notch signaling pathway regulation. When we examined in more details the particular interaction between the tetraspanin Tspan5 and ADAM10, we discovered that it had a negative effect on ADAM10 membrane as well as total expression. Moreover, this interaction seems to have implications on prostate cancer PC3 cell proliferation as Tspan5 overexpression causes a diminished growth rate. This inhibition could be caused by one or more soluble factors which could be less secreted by cells overexpressing Tspan5 than wild-type counterparts. Furthermore, oddly enough, PC3 cells overexpressing Tspan5 were completely unaffected by drugs targeted against the tyrosine-kinase receptor EGFR whereas this type of treatment impaired PC3 WT cell growth which therefore seems at least partly dependent on EGFR signalling. Finally, we reveal that another tyrosine-kinase receptor called EphA2 could play the proeminent role of regulating EGFR signalling-dependence in PC3 cells.
