Related Experiment Videos
Tumour suppressor p53 inhibits human fibroblast growth factor 2 expression by a post-transcriptional mechanism
B Galy1, L Créancier, C Zanibellato
1Institut National de la Santé et de la Recherche Médicale U397, Endocrinologie et Communication Cellulaire, Institut Fédératif de Recherche Louis Bugnard, CHU Rangueil, 31403 Toulouse Cedex 04, France.
Abstract:
Fibroblast growth factor-2 (FGF-2) is a powerful mitogen and angiogenic factor whose expression is strongly regulated at the translational level. The constitutive upregulation of FGF-2 isoforms in transformed cells prompted us to investigate the post-transcriptional effects of a tumour suppressor, p53, on FGF-2 expression. We show here in human primary skin fibroblasts that the cell density-dependent variation of FGF-2 mRNA translatability was inversely correlated with endogenous p53 expression. Transient cell transfection revealed an inhibitory effect of wild-type p53 on the expression of chimeric FGF--CAT proteins. RNAse mapping experiments ruled out any effect of p53 on FGF--CAT mRNA accumulation, suggesting a translational inhibition. This inhibition was mediated by the FGF-2 mRNA leader, but not by vascular endothelial growth factor or platelet derived growth factor mRNA leaders. Neither p53-like protein p73, nor p21/waf had any inhibitory activity. Furthermore a set of hot spot mutants of p53 bearing mutations in the DNA binding domain had no post-transcriptional inhibitory effect. In contrast a p53 mutant of the transactivating domain was still able to block FGF--CAT expression, indicating that the post-transcriptional activity of p53 described here was independent of the trans-activation of target genes. Such data reveal a novel mechanism by which p53 efficiently blocks the expression of a major proliferating, anti-apoptotic and angiogenic gene.
Insights
The tumor suppressor p53 inhibits the expression of fibroblast growth factor-2 (FGF-2) at the translational level. This novel mechanism, independent of gene transactivation, blocks FGF-2
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Fibroblast growth factor-2 (FGF-2) is a potent mitogen and angiogenic factor.
- FGF-2 expression is primarily regulated post-transcriptionally.
- Constitutive upregulation of FGF-2 in cancer cells suggests a role for tumor suppressors in its regulation.
Purpose of the Study:
- To investigate the post-transcriptional effects of the tumor suppressor p53 on FGF-2 expression.
- To elucidate the mechanism by which p53 influences FGF-2 translation.
- To determine if p53's inhibitory effect on FGF-2 is linked to its transactivation activity.
Main Methods:
- Human primary skin fibroblast culture and transfection.
- Reporter gene assays using chimeric FGF--CAT proteins.
- RNAse mapping to assess mRNA accumulation.
- Site-directed mutagenesis of p53.
Main Results:
- Endogenous p53 expression inversely correlated with FGF-2 mRNA translatability in a cell-density-dependent manner.
- Wild-type p53 significantly inhibited FGF--CAT protein expression.
- p53 mediated translational inhibition via the FGF-2 mRNA leader sequence, independent of mRNA accumulation.
- p53's inhibitory activity was independent of its DNA-binding and transactivating domains, and not mimicked by p73 or p21/waf.
Conclusions:
- p53 exerts a novel post-transcriptional inhibitory effect on FGF-2 expression.
- This inhibition occurs at the translational level and is mediated by the FGF-2 mRNA leader.
- p53's tumor suppressive function may involve blocking the expression of key pro-proliferative and angiogenic genes like FGF-2 through a non-canonical mechanism.