MULTIPLE PROTEINS INTERACT AT A UNIQUE CIS-ELEMENT IN THE 3'-UNTRANSLATED REGION OF AMYLOID PRECURSOR PROTEIN MESSENGER-RNA

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.