Key result
Heterogeneous nuclear ribonucleoprotein A1 binds to the FGF-2 IRES and stimulates in vitro translation at IRES-dependent initiation codons, while its knockdown specifically inhibits this translation.
hnRNP A1 acts as a novel internal ribosome entry site trans-acting factor that modulates alternative initiation of translation of FGF-2 mRNA.
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.
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Bonnal et al. (2004) studied this question. hnRNP A1 was evaluated on Translation at IRES-dependent initiation codons. Heterogeneous nuclear ribonucleoprotein A1 binds to the FGF-2 IRES and stimulates in vitro translation at IRES-dependent initiation codons, while its knockdown specifically inhibits this translation.
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