Genetics and Aging Unit, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129, USA
We have previously shown that the endogenous C-terminal fragment
of presenilin 1 coimmunoprecipitates with endogenous ß-catenin.
Since PS1 has been suggested to be involved in ß-catenin
stabilization, we further investigated whether GSK3ß,
responsible for ß-catenin phosphorylation and degradation,
is part of the PS1/ß-catenin complex. In naïve
H4 and CHO cells, PS1 co-immunoprecipitated with both endogenous
ß-catenin and GSK3ß. In addition, GSK3ß
endogenously binds to the PS1-CTF/NTF complex and ß-catenin
in naïve CHO cells. GSK3ß also co-immunoprecipitated
with PS1 full length in CHO cell lines overexpressing PS1 wild
type. Given that it has been recently shown that PS1 mutations
of aspartate 257 or 385 result in prevention of PS1 endoproteolysis
and inhibition of
-secretase activity, we also tested whether
PS1 endoproteolysis is required for ß-catenin/GSK3ß/PS1
binding and whether PS1 FAD-linked mutations affect GSK3ß
recruitment in the PS1/ß-catenin complex. GSK3ß
was detected in PS1 immunoprecipitates from H4 cell lines overexpressing
PS1 wild type,
E10, A286E, L246V and in CHO cell lines overexpressing
aspartate or M146L mutations. The latter data show that the
absence of PS1 endoproteolysis (D257A/D385A and
E10) or the
presence of PS1-FAD mutations does not interfere with ß-catenin/GSK3ß/PS1
complex formation.
