Regulation of amyloid precursor protein (APP) secretion by protein kinase Cα in human ntera 2 neurons (NT2N)

Cleavage of amyloid precursor protein (APP) by beta-secretase generates beta-amyloid (A beta), the major component of senile plaques in Alzheimer's disease. Cleavage of APP by alpha-secretase prevents A beta formation, producing nonamyloidogenic APP products. Protein kinase C (PKC) has been shown to regulate APPs secretion, and PKC alpha and PKC epsilon have been implicated in APPs secretion in fibroblasts. This study examined the PKC isoform involved in regulated APPs secretion in human NT2N neurons and in CHO cells stably expressing APP(695) Inhibition of PMA-induced APPs secretion with the PKC inhibitors Calphostin C and GF109203X demonstrated that PKC is involved in PMA-regulated APPs secretion in NT2N cells. The specific PKC isoforms present in NT2N and CHO695 cells were identified, and PKC alpha and PKC epsilon were found to translocate from cytosol to membranes in NT2N and CHO695 cells. Translocation of PKC to the membrane allows for activation of the enzyme, as well as for positioning of the enzyme close to its substrate. Long-term PMA treatment led to complete downregulation of PKC alpha in NT2N cells and to downregulation of PKC alpha and PKC epsilon in CHO695 cells. PKC alpha downregulation in the NT2N cells resulted in loss of PMA-regulated APPs secretion and a substantial reduction in constitutive APPs secretion. Downregulation of PKC alpha and PKC epsilon in CHO695 cells resulted in loss of PMA-regulated APPs secretion; however, constitutive APPs secretion was unaffected. These findings suggest that PKC alpha is involved in PMA-regulated APPs secretion in NT2N cells and PKC alpha and/or PKC epsilon is involved in PMA-regulated APPs secretion in CHO695 cells.