γ-Secretase is a multiprotein complex composed of presenilin (PS), nicastrin (NCT), Aph-1, and Pen-2, and it catalyzes the final proteolytic step in the processing of amyloid precursor protein to generate amyloid-β. Our previous results showed that tumor necrosis factor-α (TNF-α) can potently stimulate γ-secretase activity through a c-Jun N-terminal kinase (JNK)-dependent pathway. Here, we demonstrate that TNF-α triggers JNK-dependent serine/threonine phosphorylation of PS1 and NCT to stimulate γ-secretase activity. Blocking of JNK activity with a potent JNK inhibitor (SP600125) reduces TNF-α–triggered phosphorylation of PS1 and NCT. Consistent with this, we show that activated JNKs can be copurified with γ-secretase complexes and that active recombinant JNK2 can promote the phosphorylation of PS1 and NCT in vitro. Using site-directed mutagenesis and a synthetic peptide, we clearly show that the Ser319Thr320 motif in PS1 is an important JNK phosphorylation site that is critical for the TNF-α–elicited regulation of γ-secretase. This JNK phosphorylation of PS1 at Ser319Thr320 enhances the stability of the PS1 C-terminal fragment that is necessary for γ-secretase activity. Together, our findings strongly suggest that JNK is a critical intracellular mediator of TNF-α–elicited regulation of γ-secretase and governs the pivotal step in the assembly of functional γ-secretase.
Amyloid-β(1−42) Fibrillar Precursors Are Optimal for Inducing Tumor Necrosis Factor-α Production in the THP-1 Human Monocytic Cell Line
