Activity of alpha-secretase as the common final effector of protein kinaseC-dependent and -independent modulation of amyloid precursor protein metabolism

The metabolic fate of the amyloid precursor protein (APP) is one of the key factors in the pathogenesis of Alzheimer's disease (AD). A complex cellula r mechanism regulates the rate at which the precursor is cleaved by alpha-s ecretase and released as soluble protein in the extracellular space. We sho w here that alpha-secretase constitutes the common final effector of severa l independent means of stimulation of soluble APP (sAPP) release. The relea se of sAPP by alpha-secretase resembles that of several other membrane-boun d proteins with soluble counterparts, a process that is sensitive to matrix metalloprotease inhibitors. The hydroxamic acid-based compound KD-IX-73-4 inhibits phorbol ester-mediated sAPP release from COS cells with an IC50 of 8 mu M, consistent with previous data for the same compound against leukoc yte L-selectin shedding. Beyond direct protein kinase C (PKC) activation we show that KD-IX-73-4 inhibits also receptor-mediated sAPP release induced by carbachol in SH-SY5Y cells and by bradykinin in human skin fibroblasts, with the latter being a PKC-independent mechanism. Altogether these data su ggest that all pharmacological means of stimulating sAPP release converge t o a hydroxamic acid-based inhibitor-sensitive proteolytic enzyme. Moreover, because KD-IX-73-4 was effective in the inhibition of stimulated but not c onstitutive sAPP release, these data suggest the existence of different enz ymes regulating the two metabolic pathways leading to sAPP secretion.