Protein kinase A phosphorylation of the proteasome: a contribution to the alpha-secretase pathway in human cells.

The beta-amyloid precursor protein undergoes a physiological cleavage by alpha-secretase that leads to the release of a secreted C-terminally truncated fragment called APP alpha and likely concomitantly reduces the formation of the amyloidogenic A beta peptide. Here we demonstrate that APP alpha secretion is increased by the protein kinase A (PKA) effectors 8-bromo cyclic AMP and forskolin in human embryonic kidney cells (HK293), and that this can be prevented by a proteasome inhibitor. Furthermore, we establish that PKA effectors but not protein kinase C agonists increase the chymotrypsin-like activity and phosphorylation state of the proteasome in vitro and in vivo in HK293 cells. Altogether, this report demonstrates that the alpha-secretase pathway is under the control of PKA in human cells and that the proteasome likely contributes, either directly or through yet unknown intermediates, to the PKA-stimulated APP alpha secretion in human cells.