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Open Access Research article

Effects of Δ40p53, an isoform of p53 lacking the N-terminus, on transactivation capacity of the tumor suppressor protein p53

Hind Hafsi1, Daniela Santos-Silva1, Stéphanie Courtois-Cox2 and Pierre Hainaut134*

Author Affiliations

1 International Agency for Research on Cancer, Lyon, France

2 Cancer Research Center, Lyon, France

3 International Prevention Research Institute, Lyon, France

4 International Prevention Research Institute, 15 Chemin du Saquin, Ecully, 69130, France

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BMC Cancer 2013, 13:134  doi:10.1186/1471-2407-13-134

Published: 20 March 2013

Abstract

Background

The p53 protein is expressed as multiple isoforms that differ in their N- and C-terminus due to alternative splicing, promoter or codon initiation usage. Δ40p53 lacks the first 39 residues containing the main transcriptional activation domain, resulting from initiation of translation at AUG +40 in fully spliced p53 mRNA or in a specific variant mRNA retaining intron 2. Overexpression of Δ40p53 antagonizes wild-type p53 in vitro. However, animal models of Δ40p53 in mouse or Zebrafish have shown complex phenotypes suggestive of p53-dependent growth suppressive effects.

Methods

We have co-transfected expression vectors for p53 and Δ40p53 in p53-null cell lines Saos-2 and H1299 to show that Δ40p53 forms mixed oligomers with p53 that bind to DNA and modulate the transcription of a generic p53-dependent reporter gene.

Results

In H1299 cells, co-expression of the two proteins induced a decrease in transcription with amplitude that depended upon the predicted composition of the hetero-tetramer. In Saos-2, a paradoxical effect was observed, with a small increase in activity for hetero-tetramers predicted to contain 1 or 2 monomers of Δ40p53 and a decrease at higher Δ40p53/p53 ratios. In this cell line, co-transfection of Δ40p53 prevented Hdm2-mediated degradation of p53.

Conclusion

Δ40p53 modulates transcriptional activity by interfering with the binding of Hdm2 to hetero-tetramers containing both Δ40p53 and p53. These results provide a basis for growth suppressive effects in animal models co-expressing roughly similar levels of p53 and Δ40p53.

Keywords:
P53; Isoforms; Hdm2; Δ40p53; Oligomerization