Accurate determination of carboxyl-terminal fragment of presenilin 1 in various tissues from rat and cell lines.

Presenilin 1 (PS1) has been identified as a causative gene for the early-onset of familial Alzheimer's disease, and it is mainly localized in the endoplasmic reticulum and the Golgi membrane as a multiple membrane-spanning protein. In the cell, PS1 is proteolytically processed to a 30-kDa N-terminal fragment and a 20-kDa C-terminal fragment (CTF), both of which exist as a stable high-molecular-weight protein complex, together with other components of gamma-secretase. However, as there has been no report about the precise amount of PS1 expressed in mammalian tissues, the aim of this study was to quantitatively determine PS1-CTF amounts in various tissues such as liver, kidney, brain and heart of rat by western blotting using a [(35)S]-methionine-labelled PS1-CTF as a standard synthesized in a wheat germ cell-free protein synthesizing system. PS1-CTF contents in kidney, liver, brain and heart were 17.0, 6.6, 6.4 and 0.2 fmol/mg protein, respectively. PS1-CTF contents were also determined in cultured cell lines such as HeLa, HEK293 and COS-1.