The tumour suppressor p53 actually exists as 9 protein isoforms. Among them, D133p53a, b and g result from the use of an alternative promoter and lack the N-terminal transactivation domain. In addition to its multiple functions maintaining cell integrity, p53 is also able to block angiogenesis, a process strongly contributing in tumour development. Here I have examined the role of p5 isoforms in the regulation of angiogenesis and tumor progression. I also focused my work on FGF-2 regulation by p53. In a first part, full length p53 (p53) and/or D133p53 isoforms were selectively knocked-down with siRNAs in human glioblastoma cells U87. Conditioned medium produced by tumour cells knocked- down for D133p53 inhibited endothelial cell - EC - migration and tubulogenesis. Furthermore, in the chicken chorioallantoïd membrane CAM, D133p53 knockdown gave rise to smaller tumours devoid of vessels, whereas, in mice, it strongly inhibited tumour growth. Interestingly, the double knockdown of p53 and D133p53 also slowed town tumour growth in mice. Taqman Low Density Array revealed distinct gene expression profiles of pro and anti-angiogenic factors regulation following D133p53 and/or p53 knockdown. In particular, D133p53 knockdown resulted in specific down-regulation of Angiogenin and hepatocyte growth factor, whereas the main angiogenic factors FGF-2 and VEGF-A were not significantly affected. Secondly we investigated the regulation of FGF-2 by p53 and its isoforms D133p53 in a human osteosarcoma cell line U2OS, at translational, transcriptional and secretion levels. It resulted in a sophisticated mode of regulation mediated by a transient IRES-dependent translation inhibition of FGF-2. Our data reveal D133p53 isoforms as activators of angiogenesis and tumour progression, through a specific modulation of the angiogenic balance. These isoforms exhibit dominant-negative effect towards p53 but also intrinsic activities, while underlining the importance of considering D133p53 expression in cancers, as well as the potential antitumoural interest of drugs targeting this p53 isoform.
|Date of Award||2010|
|Sponsors||Ligue nationale contre le cancer, Association de la recherche contre le cancer, Université Paul Sabatier, Institut de Médicine Moléculaire de Rangueil & Institut national de la santé et de la recherche médicale|
|Supervisor||Jean-Christophe Bourdon (Supervisor)|
- In vivo