The RNA-binding protein HuD promotes neuronal differentiation by an unknown mechanism. Here we identify an enhancer function of HuD in translation. Translation stimulation by HuD requires both a 3' poly(A) tail and a 5' m(7)G cap structure. We also show that HuD directly interacts with eIF4A. This interaction and the poly(A)-binding activity of HuD are critical for its translational enhancer function because HuD-eIF4A- and HuD-poly(A)-binding mutants fail to stimulate translation. We show that translation of HCV IRES mRNA, which is eIF4A independent, is not stimulated by HuD. We also find that the eIF4A and poly(A)-binding activities of HuD are not only important for stimulating translation but also are essential for HuD-induced neurite outgrowth in PC12 cells. This example of cap-dependent translational regulation might explain at least in part how HuD triggers the induction of neuronal differentiation.
2009 Elsevier Inc.