Rapid impact of β-amyloid on paxillin in a neural cell line

β-amyloid1-42 (Aβ) is a naturally occurring peptide whose accumulation in the brain is putatively coupled to Alzheimer's disease pathogenesis. Deleterious effects of Aβ on neurons have been linked to the inappropriate activation of signaling pathways within the cell (reviewed in Yankner, 1996), including tyrosine phosphorylation of focal adhesion kinase (FAK) (Zhang et al., 1994, 1996a,b). Here we have investigated the effects of Aβ on paxillin in a neural cell line. Paxillin, a substrate for FAK, is thought to act as a signal 'integrator,' functioning to link other proteins into multi-molecular signaling complexes (reviewed in Turner, 1994). Treatment of the rat central nervous system B103 cell line with aggregates of Aβ was found to induce the tyrosine phosphorylation of paxillin within 30 min, nearly 24 hr prior to significant cell death. Particularly striking was a subsequent 'mobilization' of paxillin to the cytoskeleton in Aβ-treated cells. The amount of paxillin associated with the cytoskeleton in Aβ-treated cells was increased 10-fold over controls. The Aβ-induced paxillin accumulation could be visualized immunocytochemically, with an increase in number and size of paxillin- labeled focal contacts upon treatment with Aβ. This effect was specific, in that vinculin, another focal contact protein, was unaffected by Aβ. Disruption of f-actin, which inhibits both Aβ-induced neurotoxicity (Furukawa and Mattson, 1995) and focal contact signaling in B103 cells (Zhang et al., 1996b) was found to block the cytoskeletal paxillin accumulation. The rapid tyrosine phosphorylation and cytoskeletal mobilization of paxillin links Aβ to the activation of focal contact signaling events that may influence neuronal cytoskeletal architecture, gene expression, synaptic plasticity and cell viability.