Physical and functional interaction between the α- and γ-secretases: A new model of regulated intramembrane proteolysis

Many single-transmembrane proteins are sequentially cleaved by ectodomain-shedding alpha-secretases and the gamma-secretase complex, a process called regulated intramembrane proteolysis (RIP). These cleavages are thought to be spatially and temporally separate. In contrast, we provide evidence for a hitherto unrecognized multiprotease complex containing both alpha- and gamma-secretase. ADAM10 (A10), the principal neuronal alpha-secretase, interacted and cofractionated with gamma-secretase endogenously in cells and mouse brain. A10 immunoprecipitation yielded gamma-secretase proteolytic activity and vice versa. In agreement, superresolution microscopy showed that portions of A10 and gamma-secretase colocalize. Moreover, multiple gamma-secretase inhibitors significantly increased alpha-secretase processing (r = 0.86) and decreased beta-secretase processing of beta-amyloid precursor protein. Select members of the tetraspanin web were important both in the association between A10 and gamma-secretase and the gamma ->alpha feedback mechanism. Portions of endogenous BACE1 coimmunoprecipitated with gamma-secretase but not A10, suggesting that beta- and alpha-secretases can form distinct complexes with gamma-secretase. Thus, cells possess large multiprotease complexes capable of sequentially and efficiently processing transmembrane substrates through a spatially coordinated RIP mechanism.