Alzheimer's disease associated presenilin 1 interacts with HC5 and ZETA, subunits of the catalytic 20S proteasome

Proteolytic processing and degradation tightly regulate the amount of stabl e, functional presenilin 1 (PSEN1) in the cell. The similar to 46-kDa PSEN1 holoprotein is cleaved into a similar to 30-kDa N-terminal fragment (NTF) and a similar to 20-kDa C-terminal fragment (CTF) by an unknown protease. T he fragments are stabilized in a high molecular weight complex and noncorpo rated fragments and excess holoprotein are degraded by the 26S proteasome. The fight balance between, on the one hand, processing and incorporation in to the stable complex and, on the other hand, proteolytic degradation of ex cess PSEN1, indicates that minor changes in one of these two processes coul d be pathologically relevant. Here we demonstrate the direct physical inter action between PSEN1 and two subunits, HC5 and ZETA, of the 20S proteasome. These interactions were identified using an interaction trap screening and were further established in an in vitro binding assay. Furthermore, we wer e able to coimmunoprecipitate the transfected binding partners, as well as the endogenous PSEN1 and ZETA proteins from HEK 293T cells. Finally, degrad ation of ubiquitinated wild-type and mutant PSEN1 by the 26S proteasome was demonstrated. In conclusion, we report a direct interaction between PSEN1 and subunits of the 20S catalytic particle of the 26S proteasome, further e stablishing the involvement of proteasomal degradation in the regulation of PSEN1 turnover. (C) 1999 Academic Press.