She. Zaidi et al., MULTIPLE PROTEINS INTERACT AT A UNIQUE CIS-ELEMENT IN THE 3'-UNTRANSLATED REGION OF AMYLOID PRECURSOR PROTEIN MESSENGER-RNA, The Journal of biological chemistry, 269(39), 1994, pp. 24000-24006
Growing evidence suggests that Alzheimer's disease results from dysreg
ulated production and deposition of beta-amyloid in the central nervou
s system. beta-Amyloid is derived from proteolytic processing of one o
f multiple amyloid precursor protein (APP) isoforms. The production of
APP in many somatic tissues and tumor cell lines provides a more acce
ssible model to study the regulation of APP gene expression. Recent da
ta suggest that APP mRNAs accumulate in activated lymphocytes and neur
onal tumor lines. We are interested in defining the contribution of al
terations in stability to changes in steady-state APP mRNA levels in t
hese model systems. Herein we demonstrate by mobility shift assay that
the 3'-untranslated region of APP RNAs which contain a contiguous 29-
base region interacts in vitro with multiple mRNA-binding proteins fou
nd in cytosolic lysates prepared from normal and transformed human cel
ls. UV cross-linking of radiolabeled APP RNAs to cytosolic protein ext
racts followed by sodium dodecyl sulfate-polyacrylamide gel electropho
resis identified six distinct RNA-protein complexes of 42, 47, 65, 73,
84, and 104 kDa Competition assays with APP, AU-rich, or irrelevant R
NAs demonstrated that binding was specific and in some cases preferent
ial for AU- or U-rich sequences by which we tentatively place the bind
ing site of the proteins along the 29-base region. APP mRNA-binding pr
oteins were constitutively active in all tumor lines examined as web a
s at diminished levels in whole human brain cytosolic lysates. The cor
e element is AU-rich and highly conserved between human and some murin
e APP mRNAs. In the accompanying paper (Zaidi, S. H. E. and Malter, J.
S. (1994) J. Biol. Chem. 269, 24007-24013) we show that this 29-base
element in the 3'-untranslated region regulates the stability of APP m
RNA. Cumulatively these data suggest that steady-state APP mRNA levels
are modulated by cytosolic protein-RNA interactions.