Protein kinase C regulation of intracellular and cell surface amyloid precursor protein (APP) cleavage in CHO695 cells

Cleavage of amyloid precursor protein (APP) by beta -secretase generates be ta -amyloid (A beta), the major component of senile plaques in Alzheimer's disease. Cleavage of APP by alpha -secretase prevents A beta formation, pro ducing nonamyloidogenic secreted APPs products. PKC-regulated API, alpha -s ecretase cleavage has been shown to involve tumor necrosis factor alpha (TN F-alpha) converting enzyme (TACE). To determine the location of APP cleavag e, we examined PKC-regulated APPs secretion by examining cell surface versu s intracellular APP in CHO cells stably expressing APP(695) (CH0695). We de monstrate that PKC regulates cell surface and intracellular APP cleavage. T he majority of secreted APPs originates from the intracellular compartment, and PKC does not cause an increase in APP trafficking to the cell surface for cleavage. Therefore, intracellular APP regulated by PKC must be cleaved at an intracellular site. Experiments utilizing Brefeldin A suggest APP cl eavage occurs at the Golgi or late in the secretory pathway. Experiments us ing TAPI, an inhibitor of TACE, demonstrate PKC-regulated APPs secretion fr om the cell surface is inhibited after pretreatment with TAPI, and APPs sec retion from the intracellular pool is partially inhibited after pretreatmen t with TAPI. These findings suggest PKC-regulated APP cleavage occurs at mu ltiple locations within the cell and both events appear to involve TACE.