RESUMEN
Presenilin-1 (PS1) is the catalytic subunit of γ-secretase, and mutations in this protein cause familial Alzheimer Disease (FAD). However, little is known about how these mutations affect the active site of γ-secretase. Here, we show that PS1 mutations alter the S2 subsite within the active site of γ-secretase using a multiple photoaffinity probe approach called "photophore walking." Moreover, we developed a unique in vitro assay with a biotinylated recombinant Notch1 substrate and demonstrated that PS1 FAD mutations directly and significantly reduced γ-secretase activity for Notch1 cleavage. Substitution of the Notch Cys-1752 residue, which interacts with the S2 subsite, with Val, Met, or Ile has little effect on wild-type PS1 but leads to more efficient substrates for mutant PS1s. This study indicates that alteration of this S2 subsite plays an important role in determining the activity and specificity of γ-secretase for APP and Notch1 processing, which provides structural basis and insights on how certain PS1 FAD mutations lead to AD pathogenesis.
Asunto(s)
Enfermedad de Alzheimer/metabolismo , Secretasas de la Proteína Precursora del Amiloide/metabolismo , Enfermedades Genéticas Congénitas/metabolismo , Mutación Missense , Presenilina-1/metabolismo , Enfermedad de Alzheimer/genética , Sustitución de Aminoácidos , Secretasas de la Proteína Precursora del Amiloide/genética , Dominio Catalítico , Enfermedades Genéticas Congénitas/genética , Células HEK293 , Humanos , Presenilina-1/genética , Receptor Notch1/genética , Receptor Notch1/metabolismoRESUMEN
γ-Secretase is composed of four proteins that are obligatory for protease activity: presenilin, nicastrin, Aph1, and Pen-2. Despite the progress toward understanding the function of these individual subunits, there is no information available pertaining to the modulation of γ-secretase in response to environmental changes in cells. Here, we show that hypoxia upregulates γ-secretase activity through a direct interaction with Hif-1α, revealing an unconventional function for Hif-1α as an enzyme subunit, which is distinct from its canonical role as a transcription factor. Moreover, hypoxia-induced cell invasion and metastasis are alleviated by either γ-secretase inhibitors or a dominant-negative Notch coactivator, indicating that γ-secretase/Notch signaling plays an essential role in controlling these cellular processes. The present study reveals a mechanism in which γ-secretase can achieve temporal control through conditional interactions with regulatory proteins, such as Hif-1α, under select physiological and pathological conditions.