APP Phosphorylation at S655 Correlates with F-actin Cytoskeleton Dynamics—Relevance in Neuronal Differentiation

The Alzheimer’s Amyloid Precursor Protein (APP) is a type 1 transmembranar protein that has been implicated in roles such as cell adherence, survival, migration and differentiation. Although a role in neuritogenesis has been attributed to APP, some contradictory results have been reported regarding the benefits of knocking-down or overexpressing APP. Our preliminary work indicated that pAPP (APP phosphorylated at the S655 residue) may potentially modulate APP-mediated neuronal differentiation, through mechanisms that may involve increased APP trafficking and cleavage, and altered APP-mediated cytoskeleton rearrangements. In order to address the ability of APP and pAPP to mediate neuronal differentiation, we used APP cDNA constructs fused to the Green Fluorescent Protein (GFP): wild-type APP and APP S655 mutants (S655A dephosphomimicking and S655E phosphomimicking mutants). SH-SY5Y neuroblastoma cells, a well documented neuronal-like cell model, were used, and the conditions for their retinoic-acid mediated differentiation and concomitant APP-GFP transfection were first optimized.