epidermal-growth-factor and acetyl-aspartyl-glutamyl-valyl-aspartal

The biological function of full-length amyloid-beta protein precursor (AbetaPP), the precursor of Abeta, is not fully understood. Multiple laboratories have reported that antibody binding to cell surface AbetaPP causes neuronal cell death. Here we examined whether induced dimerization of the cytoplasmic domain of AbetaPP (AbetaPPCD) triggers neuronal cell death. In neurohybrid cells expressing fusion constructs of the epidermal growth factor (EGF) receptor with AbetaPPCD (EGFR/AbetaPP hybrids), EGF drastically enhanced neuronal cell death in a manner sensitive to acetyl-l-aspartyl-l-glutamyl-l-valyl-l-aspartyl-aldehyde (Ac-DEVD-CHO; DEVD), GSH-ethyl ester (GEE), and pertussis toxin (PTX). Dominant-negative apoptosis signal-regulating kinase 1 (ASK1) blocked this neuronal cell death, but not alpha-synuclein-induced cell death. Constitutively active ASK1 (caASK1) caused DEVD/GEE-sensitive cell death in a manner resistant to PTX and sensitive to Humanin, which also suppressed neuronal cell death by EGFR/AbetaPP hybrid. ASK1 formed a complex with AbetaPPCD via JIP-1b, the c-Jun N-terminal kinase (JNK)-interacting protein. EGFR/AbetaPP hybrid-induced and caASK1-induced neuronal cell deaths were specifically blocked by SP600125 (anthra[1,9-cd]pyrazol-6(2H)-one), a specific JNK inhibitor. Combined with our earlier study, these data indicate that dimerization of AbetaPPCD triggers ASK1/JNK-mediated neuronal cell death. We also noticed a potential role of ASK1/JNK in sustaining the activity of this mechanism after initial activation by AbetaPP, which allows for the achievement of cell death by short-term anti-AbetaPP antibody treatment. Understanding the function of AbetaPPCD and its downstream pathway should lead to effective anti-Alzheimer's disease therapeutics.

Topics: Adaptor Proteins, Signal Transducing; Alzheimer Disease; Amyloid beta-Protein Precursor; Animals; Anthracenes; Carrier Proteins; Dimerization; Epidermal Growth Factor; ErbB Receptors; Flavonoids; Humans; Hybrid Cells; Imidazoles; Intracellular Signaling Peptides and Proteins; JNK Mitogen-Activated Protein Kinases; MAP Kinase Kinase Kinase 5; MAP Kinase Kinase Kinases; Mice; Mitogen-Activated Protein Kinases; Neurons; Oligopeptides; p38 Mitogen-Activated Protein Kinases; Protein Structure, Tertiary; Proteins; Pyridines; Rats; Signal Transduction

Normal epithelial cells undergo apoptosis when they are denied contact with the extracellular matrix, in a process termed "anoikis." Conversely, malignant epithelial cells typically acquire anchorage independence, i.e., the capacity to survive and grow in the absence of matrix interaction. Here we asked the question whether anoikis is affected by signaling through the EGF receptor (EGFR). We focused on the EGFR because EGFR signaling is frequently deregulated in malignant epithelial cells. We demonstrate that EGFR activation markedly alleviated the requirement of matrix engagement for survival of primary and immortalized human keratinocytes in suspension culture. Protection of epithelial cells through EGFR activation against anoikis was associated with and required sustained MAPK phosphorylation during the early phase of suspension culture. Interestingly, high levels of MAPK phosphorylation were not only required for EGFR-mediated protection against anoikis but also occurred as a consequence of caspase activation at later stages of suspension culture. These results demonstrate that EGFR activation contributes to anchorage-independent epithelial cell survival and identify MAPK activation as an important mechanism in this process.

Topics: bcl-X Protein; Calcium-Calmodulin-Dependent Protein Kinases; Caspase Inhibitors; Caspases; Cell Survival; Cells, Cultured; Chromones; Cysteine Proteinase Inhibitors; Enzyme Inhibitors; Epidermal Growth Factor; ErbB Receptors; Extracellular Matrix; Flavonoids; Humans; In Situ Nick-End Labeling; Keratinocytes; MAP Kinase Signaling System; Mitogen-Activated Protein Kinase Kinases; Mitogen-Activated Protein Kinases; Morpholines; Oligopeptides; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Protein Tyrosine Phosphatases; Proto-Oncogene Proteins c-bcl-2; Quinazolines; Tyrphostins