Mammalian APH-1 interacts with presenilin and nicastrin and is required for intramembrane proteolysis of amyloid-β precursor protein and Notch

Presenilin and nicastrin are essential components of the γ-secretase complex that is required for the intramembrane proteolysis of an increasing number of membrane proteins including the amyloid-β precursor protein (APP) and Notch. By using co-immunoprecipitation and nickel affinity pull-down approaches, we now show that mammalian APH-1 (mAPH-1), a conserved multipass membrane protein, physically associates with nicastrin and the heterodimers of the presenilin amino-and carboxyl-terminal fragments in human cell lines and in rat brain. Similar to the loss of presenilin or nicastrin, the inactivation of endogenous mAPH-1 using small interfering RNAs results in the decrease of presenilin levels, accumulation of γ-secretase substrates (APP carboxyl-terminal fragments), and reduction of γ-secretase products (amyloid-β peptides and the intracellular domains of APP and Notch). These data indicate that mAPH-1 is probably a functional component of the γ-secretase complex required for the intramembrane proteolysis of APP and Notch.