Heterogeneous Nuclear Ribonucleoprotein A1 Is a Novel Internal Ribosome Entry Site trans-Acting Factor That Modulates Alternative Initiation of Translation of the Fibroblast Growth Factor 2 mRNA

doi:10.1074/jbc.M411492200

Heterogeneous Nuclear Ribonucleoprotein A1 Is a Novel Internal Ribosome Entry Site trans-Acting Factor That Modulates Alternative Initiation of Translation of the Fibroblast Growth Factor 2 mRNA*

^‡INSERM U589, Institut Louis Bugnard, Hopital Rangueil, TSA 50032, 31059 Toulouse Cedex 9, and ^∥Sanofi-Aventis CRVA, 13 Quai Jules Guesdes, 94403 Vitry-sur-Seine, France

** Present address: INSERM U563, Institut Claudius Régaud, Rue du Pont Sain-Pierre, 31052 Toulouse, France. To whom correspondence should be addressed. Tel.: 33-561-32-31-28; Fax: 33-561-32-21-41; E-mail: vagner{at}toulouse.inserm.fr.

Abstract

Alternative initiation of translation of the human fibroblast growth factor 2 (FGF-2) mRNA at five in-frame CUG or AUG translation initiation codons requires various RNA cis-acting elements, including an internal ribosome entry site (IRES). Here we describe the purification of a trans-acting factor controlling FGF-2 mRNA translation achieved by several biochemical purification approaches. We have identified the heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) as a factor that binds to the FGF-2 5′-leader RNA and that also complements defective FGF-2 translation in vitro in rabbit reticulocyte lysate. Recombinant hnRNP A1 stimulates in vitro translation at the four IRES-dependent initiation codons but has no effect on the cap-dependent initiation codon. Consistent with a role of hnRNP A1 in the control of alternative initiation of translation, short interfering RNA-mediated knock down of hnRNP A1 specifically inhibits translation at the four IRES-dependent initiation codons. Furthermore, hnRNP A1 binds to the FGF-2 IRES, implicating this interaction in the control of alternative initiation of translation.

Footnotes

↵1 The abbreviations used are: FGF-2, fibroblast growth factor 2; hnRNP A1, heterogeneous nuclear ribonucleoprotein A1; IRES, internal ribosome entry site; siRNA, short interfering RNAs; snRNP, small nuclear ribonucleoprotein; RRL, rabbit reticulocyte lysate; GST, glutathione S-transferase; nts, nucleotides; CAT, chloramphenicol acetyltransferase; ORF, open reading frame; UTR, untranslated region; RNAi, RNA interference; WT, wild type; MUT, mutant; VEGF, vascular endothelial growth factor; EMCV, encephalomyocarditis virus; ITAF, IRES trans-acting factor; PTB, polypyrimidine tract binding protein.
↵2 S. Bonnal and S. Vagner, unpublished observations.
↵* This work was supported in part by INSERM, European Commission FP5, QoL Cell Factory, Contract QLRT-2000-00721, Association pour la Recherche sur le Cancer, Fondation de France, and the French Ministry of Research (ACI “Jeunes Chercheurs”). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵§ Supported by a Poste d'Accueil INSERM pour Ingénieurs des Grandes Écoles and by an Association pour la Recherche sur le Cancer pre-doctoral fellowship.
↵¶ Supported by a post-doctoral fellowship from Fondation de France.
- Received October 8, 2004.
The American Society for Biochemistry and Molecular Biology, Inc.