p53 directs conformational change and translation initiation blockade of human fibroblast growth factor 2 mRNA

Tumour suppressor p53 has been shown to inhibit fibroblast growth factor 2 expression post-transcriptionally in cultured cells. Here we have investiga ted the mechanism responsible for this post-transcriptional blockade. Delet ion mutagenesis of the FGF-2 mRNA leader revealed the requirement of at lea st four RNA cis-acting elements to mediate the inhibitory effect of p53 in SK-Hep-1 transfected cells, suggesting the involvement of RNA secondary or tertiary structures. Recombinant wild-type, but not Ala(143) mutant p53, wa s able to specifically repress FGF-2 mRNA translation in rabbit reticulocyt e lysate, in a dose dependent manner. Sucrose gradient experiments showed t hat p53 blocks translation initiation by preventing 80S ribosome formation on an mRNA bearing the FGF-2 mRNA leader sequence. Interaction of wild-type and mutant p53 with different RNAs showed no significant correlation betwe en p53 RNA binding activity and its translational inhibiting effect. Howeve r, by checking the accessibility of the FGF-2 mRNA leader to complementary oligonucleotide probes, we showed that the binding to RNA of wild-type, but not mutant p53, induced RNA conformational changes that might be responsib le for the translational blockade. This strongly suggests that p53 represse s FGF-2 mRNA translation by a direct mechanism involving its nucleic acid u nwinding-annealing activity.