Receptor- and non-receptor tyrosine kinases induce processing of the amyloid precursor protein: Role of the low-density lipoprotein receptor-related protein

The Alzheimer's P-amyloid pepticles derive from the proteolytic processing of the P-amyloid precursor protein, APP, by beta- and -gamma-secretases. The regulation of this processing is not fully understood. Experimental evidence suggests that the activation of pathways involving protein tyrosine kinases, such as PDGFR and Src, could induce the cleavage of APP and in turn the generation of amyloid pepticles. In this paper we addressed the effect of receptor and nonreceptor protein tyrosine kinases on the cleavage of APP and the mechanisms of their action. To this aim, we developed an in vitro system based on the APP-Ga14 fusion protein stably transfected in SHSY5Y neuroblastoma cell line. The cleavage of this molecule, induced by various stimuli, results in the activation of the transcription of the luciferase gene under the control of Ga14 cis-elements. By using this experimental system we demonstrated that, similarly to Src, three tyrosine kinases, TrkA, Ret and EGFR, induced the cleavage of APP-Ga14. We excluded that this effect was mediated by the activation of Ras-MAPK, PI3K-Akt and IPLG- pathways. Furthermore, the direct phosphorylation of the APP cytosolic domain does not affect AP peptide generation. On the contrary, experiments in cells lacking the LDL-receptor related protein LIRP support the hypothesis that the interaction of APP with LRP is required for the induction of APP cleavage by tyrosine kinases.