Post-transcriptional contribution of a cAMP-dependent pathway to the formation of alpha- and beta/gamma-secretases-derived products of beta APP maturation in human cells expressing wildtype and Swedish mutated beta APP

Background: The physiopathological maturation of the beta-amyloid precursor protein can be modulated by effecters targeting a protein kinase C-depende nt pathway. These agents increase the recovery of APP alpha, the physiologi cal alpha-secretase-derived product of beta APP processing, and concomittan tly lower the production of the pathogenic beta/gamma-secretase-derived A b eta fragment. Methods: We set up stably transfected HEK293 cells expressing wild-type or Swedish mutated beta APP. By combined metabolic labeling and/or immunopreci pitation procedures, we assessed the effect of various cAMP effecters on th e production of the beta APP maturation products A beta 40, A beta 42, APP alpha, and its C-terminal counterpart. Results: We show here that the cAMP-dependent protein kinase (PKA) effecter s, dibutyryl-cAMP (dBut-cAMP) and forskolin, but not the inactive analog di deoxyforskolin, enhance the secretion of APP alpha and the intracellular pr oduction of its C-terminal counterpart (p10) in stably transfected HEK293 c ells. The above agonists also drastically increase both A beta 40 and A bet a 42 secretions and intracellular A beta recovery. The same influence was o bserved with HEK293 cells overexpressing the Swedish mutated beta APP. We a ttempted to delineate the relative contribution of transcriptional and post -transcriptional events in the cAMP-mediated response. We show here that th e dBut-cAMP and forskolin-induced increase of APP alpha and A beta s secret ions is not prevented by the transcription inhibitor actinomycin D. Conclusion: Our data suggest a major contribution of post-transcriptional e vents in the cAMP-dependent effect on beta APP maturation. It appears likel y that cAMP triggers the PKA-dependent phosphorylation of a protein involve d in beta APP maturation and occuring upstream to alpha- and beta/gamma-sec retase cleavages.