Tumor necrosis factor-alpha, interleukin-1beta, and interferon-gamma stimulate gamma-secretase-mediated cleavage of amyloid precursor protein through a JNK-dependent MAPK pathway.
The deposition of the amyloid beta (Abeta) peptide in neuritic plaques plays a critical role in the pathogenesis of Alzheimer's disease (AD). Abeta is generated through the proteolysis of amyloid precursor protein (APP) by the sequential actions of beta- and gamma-secretases. Although recent evidence has unveiled much about the biochemical identity and characteristics of gamma-secretase, the mechanism regulating endogenous gamma-secretase activity remains elusive. To identify possible extracellular signals and associated signaling cascades that could regulate APP proteolysis by gamma-secretase activity, we have developed a cell-based reporter gene assay by stably cotransfecting HEK293 cells with the Gal4-driven luciferase reporter gene and the Gal4/VP16-tagged C-terminal fragment of APP (C99-GV), the immediate substrate of gamma-secretase. The cleavage of C99-GV by gamma-secretase releases the transcription factor that activates luciferase expression, providing a quantitative measurement of gamma-secretase activity. Using this reporter assay, we have demonstrated that interferon-gamma, interleukin-1beta, and tumor necrosis factor-alpha can specifically stimulate gamma-secretase activity, concomitant with increased production of Abeta and the intracellular domain of APP (AICD). The gamma-secretase-dependent cleavage of Notch is also enhanced upon the stimulation of these cytokines. The cytokine-enhanced gamma-secretase activity can be suppressed by a potent inhibitor of c-Jun N-terminal kinase (JNK). Furthermore, cells transfected with dominant-positive MEKK1, one of the most potent activators of the JNK cascade, exhibit increased gamma-secretase activity, suggesting that the JNK-dependent mitogen-activated protein kinase pathway could mediate the cytokine-elicited regulation of gamma-secretase. Our studies provide direct evidence that cytokine-elicited signaling cascades control Abeta production by modulating gamma-secretase activity.
Liao
Yung-Feng
YF
Laboratory of Molecular Neurobiology, Institute of Zoology, Academia Sinica, Taipei 115, Taiwan. yliao@sinica.edu.tw
Wang
Bo-Jeng
BJ
Cheng
Hui-Ting
HT
Kuo
Lan-Hsin
LH
Wolfe
Michael S
MS
D053829:Amyloid Precursor Protein Secretases; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D000818:Animals; D016282:Aspartic Acid Endopeptidases; D015153:Blotting, Western; D019556:COS Cells; D002460:Cell Line; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005799:Genes, Dominant; D017930:Genes, Reporter; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism*; D007375:Interleukin-1 / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008156:Luciferases / Q000378:metabolism; D048670:MAP Kinase Kinase 4; D020935:MAP Kinase Signaling System; D008565:Membrane Proteins / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D009154:Mutation; D017434:Protein Structure, Tertiary; D051880:Receptors, Notch; D015398:Signal Transduction; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
D016564:Amyloid beta-Protein Precursor; D016895:Culture Media, Serum-Free; D007375:Interleukin-1; D008565:Membrane Proteins; D051880:Receptors, Notch; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D004247:DNA; D008156:Luciferases; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human