Post-transcriptional contribution of a cAMP-dependent pathway to the formation of α- and β/y-secretases-derived products of βAPP maturation in human cells expressing wildtype and swedish mutated βAPP

Abstract

Background: The physiopathological maturation of the β-amyloid precursor protein can be modulated by effectors targeting a protein kinase C-dependent pathway. These agents increase the recovery of APPα, the physiological α-secretase-derived product of βAPP processing, and concomittantly lower the production of the pathogenic β/γ-secretase-derived Aβ fragment. Methods: We set up stably transfected HEK293 cells expressing wild-type or Swedish mutated βAPP. By combined metabolic labeling and/or immunoprecipitation procedures, we assessed the effect of various cAMP effectors on the production of the βAPP maturation products Aβ40, Aβ42, APPα, and its C-terminal counterpart. Results: We show here that the cAMP-dependent protein kinase (PKA) effectors, dibutyryl-cAMP (dButcAMP) and forskolin, but not the inactive analog dideoxyforskolin, enhance the secretion of APPa and the intracellular production of its C-terminal counterpart (plO) in stably transfected HEK293 cells. The above agonists also drastically increase both Aβ40 and Aβ42 secretions and intracellular Aβ recovery. The same influence was observed with HEK293 cells overexpressing the Swedish mutated βAPP. We attempted to delineate the relative contribution of transcriptional and post-transcriptional events in the cAMP-mediated response. We show here that the dBut-cAMP and forskolin-induced increase of APP and Aβs secretions is not prevented by the transcription inhibitor actinomycin D. Conclusion: Our data suggest a major contribution of post-transcriptional events in the cAMP-dependent effect on βAPP maturation. It appears likely that cAMP triggers the PKA-dependent phosphorylation of a protein involved in βAPP maturation and occuring upstream to α- and β/γ-secretase cleavages. © 1998 The Picower Institute Press.