Evaluation of selective γ-secretase inhibitors as novel modulators of TNF-α-mediated apoptosis

Abstract

The presenilin proteins (presenilin 1 and presenilin 2) were identified in mutagenesis screens causing the early onset forms of familial Alzheimer’s disease (FAD) in 1995. Subsequently characterized as the catalytic subunits of the γ-secretase protease complexes, the presenilins are responsible for the cleavage of the amyloid precursor protein (APP) and generation of amyloid beta (Aβ). To date, γ-secretase proteases have over 120 substrates which demonstrate contribution to a diverse range of cellular processes and signalling events. However, recent findings have revealed several γ-secretase-independent presenilin functions, including calcium signalling, autophagy and apoptosis. We and others have previously reported members of the TNF receptor super-family as substrates for γ-secretase proteolysis, and that presenilin-deficient cells have increased resistance to TNFα-induced apoptosis. In this study, we sought to determine whether loss of presenilin expression or loss of γ-secretase protease activity is associated with increased resistance to TNFα-induced apoptosis. Utilizing the cleavage of caspase 3 and Poly ADP ribose polymerase (PARP) in target cells as a readout, we tested the anti-apoptotic characteristics of a panel of well characterized γ-secretase inhibitors. In this study, we show that loss of presenilin expression is associated with increased resistance to TNFα-induced apoptosis, and that loss of γ-secretase protease activity does not affect sensitivity to TNFα-induced apoptosis. These observations suggest a γ-secretase-independent role of presenilins in the regulation of TNFα-induced apoptosis.