amyloid-beta-peptides and pifithrin

Inhibition of basal JNK activity by JNK inhibitor SP600125 or JNK1siRNA repressed presenilin-1 (PS1) expression in SK-N-SH cells by augmenting the level of p53, a repressor of the PS1 gene (1). We now showed that repression of PS1 transcription by JNK inhibitor SP600125 inhibited gamma-secretase mediated processing of amyloid precursor protein (APP) resulting in the accumulation of C99 fragment and the reduction of secreted Abeta40 level without altering the expression of nicastrin (NCT). Co-treatment of cells with SP600125 and p53 inhibitor, pifithrin-alpha, partially nullified the suppressive effects of SP610025 on PS1 expression and secreted Abeta40 level. Suppression of JNK1 by JNK1siRNA also decreased Abeta40 level. Furthermore, overexpression of the repressors p53, ZNF237 and CHD3 of the PS1 gene also suppressed the processing of APP through repression of PS1 transcription by deacetylation of histone at the PS1 promoter. Transcriptional activator Ets2 increased PS1 protein and secreted Abeta40 levels without affecting the expression of NCT by activating PS1 transcription via hyper-acetylation of histone at the PS1 promoter. Therefore, regulation of PS1 transcription modulates gamma-secretase activity.

Topics: Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Amyloid Precursor Protein Secretases; Analysis of Variance; Anthracenes; Benzothiazoles; Blotting, Western; Cell Line, Tumor; Chromatin Immunoprecipitation; DNA Primers; Enzyme-Linked Immunosorbent Assay; Gene Expression Regulation; Genetic Vectors; Humans; JNK Mitogen-Activated Protein Kinases; Peptide Fragments; Presenilin-1; Reverse Transcriptase Polymerase Chain Reaction; Toluene

Current evidence suggests that amyloid beta peptides (Abeta) may play a major role in the pathogenesis of Alzheimer's disease by eliciting oxidative stress and neuronal apoptosis. In this study we have used differentiated SK-N-BE neurons to investigate molecular mechanisms and regulatory pathways underlying apoptotic neuronal cell death elicited by Abeta(1-40) and Abeta(1-42) peptides as well as the relationships between apoptosis and oxidative stress. Abeta peptides, used at concentrations able to induce oxidative stress, elicit a classic type of neuronal apoptosis involving mitochondrial regulatory proteins and pathways (i.e. affecting Bax and Bcl-2 protein levels as well as release of cytochrome c in the cytosol), poly-ADP rybose polymerase cleavage and activation of caspase 3. This pattern of neuronal apoptosis, that is significantly prevented by alpha-tocopherol and N-acetylcysteine and completely abolished by specific inhibitors of stress-activated protein kinases (SAPK) such as JNKs and p38(MAPK), involved early elevation of p53 protein levels. Pretreatment of neurons with alpha-pifithrin, a specific p53 inhibitor, resulted in a 50-60% prevention of Abeta induced apoptosis. These results suggest that oxidative stress - mediated neuronal apoptosis induced by amyloid beta operates by eliciting a SAPK-dependent multiple regulation of pro-apoptotic mitochondrial pathways involving both p53 and bcl-2.

Topics: Acetylcysteine; alpha-Tocopherol; Amyloid beta-Peptides; Apoptosis; bcl-2-Associated X Protein; Benzothiazoles; Caspase 3; Caspases; Cell Differentiation; Cytochromes c; Enzyme Activation; Enzyme Inhibitors; Humans; Hydrogen Peroxide; JNK Mitogen-Activated Protein Kinases; MAP Kinase Kinase 4; Mitochondria; Mitogen-Activated Protein Kinase Kinases; Mitogen-Activated Protein Kinases; Neuroblastoma; Oxidative Stress; p38 Mitogen-Activated Protein Kinases; Peptide Fragments; Poly(ADP-ribose) Polymerases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; Thiazoles; Toluene; Tumor Cells, Cultured; Tumor Suppressor Protein p53