The KH-Domain Protein αCP Has a Direct Role in mRNA Stabilization Independent of Its Cognate Binding Site

Abstract

Previous studies suggest that high-level stability of a subset of mammalian mRNAs is linked to a C-rich motif in the 3′ untranslated region (3′UTR). High-level expression of human α-globin mRNA (hα-globin mRNA) in erythroid cells has been specifically attributed to formation of an RNA-protein complex comprised of a 3′UTR C-rich motif and an associated 39-kDa poly(C) binding protein, αCP. Documentation of this RNA-protein α-complex has been limited to in vitro binding studies, and its impact has been monitored by alterations in steady-state mRNA. Here we demonstrate that αCP is stably bound to hα-globin mRNA in vivo, that α-complex assembly on the hα-globin mRNA is restricted to the 3′UTR C-rich motif, and that α-complex assembly extends the physical half-life of hα-globin mRNA selectively in erythroid cells. Significantly, these studies also reveal that an artificially tethered αCP has the same mRNA-stabilizing activity as the native α-complex. These data demonstrate a unique contribution of the α-complex to hα-globin mRNA stability and support a model in which the sole function of the C-rich motif is to selectively tether αCP to a subset of mRNAs. Once bound, αCP appears to be fully sufficient to trigger downstream events in the stabilization pathway.

ACKNOWLEDGMENTS

We thank Chenglu Liu and Faith Fox for technical support in several of these studies and members of the laboratory for invaluable suggestions and reagents.

This work was supported by NIH grants HL 65449 and CA72765 and by the generosity of the Doris Duke Foundation.