Growth factor-mediated stabilization of amyloid precursor protein mRNA is mediated by a conserved 29-nucleotide sequence in the 3 '-untranslated region

Using a cell-free translation system, we previously demonstrated that the t urnover and translation of amyloid precursor protein (APP) mRNA was regulat ed by a 29-nucleotide instability element, located 200 nucleotides downstre am from the stop codon, Here we have examined the regulatory role of this e lement in primary human capillary endothelial cells under different nutriti onal conditions. Optimal proliferation required a growth medium (endothelia l cell growth medium) supplemented with epidermal, basic fibroblast, insuli n-like, and vascular endothelial growth factors. In vitro transcribed mRNAs with the 5'-untranslated region (UTR) and coding region of beta-globin and the entire 3'-UTR of APP 751 were transfected into cells cultured in endot helial cell growth medium. Wild-type globin-APP mRNA containing an intact A PP 3'-UTR and mutant globin-APP mRNA containing a mutated 29-nucleotide ele ment decayed with identical half-lives (t(1/2)= 60 min). Removal of all sup plemental growth factors from the culture medium significantly accelerated the decay of transfected wild-type mRNA (t(1/2) = 10 min), but caused only a moderate decrease in the half-life of transfected mutant mRNA (t(1/2) = 4 0 min). We therefore conclude that the 29-nucleotide 3'-UTR element is an m RNA destabilizer whose function can be inhibited by inclusion of the aforem entioned mixture of growth factors in the culture medium.