Focal adhesion kinase expressed by nerve cell lines shows increased tyrosine phosphorylation in response to Alzheimer's Aβ peptide

Aβ is a 39-43-amino acid peptide that accumulates as extracellular aggregates in Alzheimer's disease-afflicted brain tissue. Contact between these aggregates and neurons is potentially pathogenic, although little is known about the cellular transduction mechanisms. We have investigated the impact of Aβ aggregates on the neuronal control of protein tyrosine phosphorylation, which underlies signal transduction for multiple families of growth factor and adhesion receptors. Added to cultures of rat and human nerve cell lines, Aβ aggregates evoked a non-desensitizing increase (1.3- 3.6-fold) in tyrosine phosphorylation in a band at 118 kDa. The 118-kDa protein was determined by immunoprecipitation to be pp125(FAK), not previously documented in cells of neuronal lineage. Immunoblots with anti- focal adhesion kinase (FAK) showed that Aβ aggregates had no effect on FAK protein levels. The increase in FAK tyrosine phosphorylation occurred at doses of Aβ aggregates that evoked lactate dehydrogenase release; evoked tyrosine phosphorylation preceded the first detectable lactate dehydrogenase release by 4 h. Like degeneration, the FAK response was dependent on Aβ aggregation and neuronal differentiation. Since tyrosine phosphorylation of FAK is essential to its activity as a transduction component of integrin-, peptide-, and lysophosphatidic acid-mediated signaling, the data establish a link between Aβ aggregates and signal transduction pathways implicated in diverse cell functions including neurite outgrowth, control of the cell cycle, and apoptosis.