A Nucleolin-Binding 3′ Untranslated Region Element Stabilizes β-Globin mRNA In Vivo

Abstract

ABSTRACT The normal expression of human β globin is critically dependent upon the constitutively high stability of its encoding mRNA. Unlike with α-globin mRNA, the specific cis -acting determinants and trans -acting factors that participate in stabilizing β-globin mRNA are poorly described. The current work uses a linker-scanning strategy to identify a previously unknown determinant of mRNA stability within the β-globin 3′ untranslated region (3′UTR). The new determinant is positioned on an mRNA half-stem opposite a pyrimidine-rich sequence targeted by αCP/hnRNP-E, a factor that plays a critical role in stabilizing human α-globin mRNA. Mutations within the new determinant destabilize β-globin mRNA in intact cells while also ablating its 3′UTR-specific interaction with the polyfunctional RNA-binding factor nucleolin. We speculate that 3′UTR-bound nucleolin enhances mRNA stability by optimizing αCP access to its functional binding site. This model is favored by in vitro evidence that αCP binding is enhanced both by cis -acting stem-destabilizing mutations and by the trans -acting effects of supplemental nucleolin. These studies suggest a mechanism for β-globin mRNA stability that is related to, but distinct from, the mechanism that stabilizes human α-globin mRNA.