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

Abstract

BackgroundThe 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.MethodsWe 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.ResultsIn 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.ConclusionΔ40p53 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.

The Emerging Landscape of p53 Isoforms in Physiology, Cancer and Degenerative Diseases

“…In contrast, ∆40p53α and ∆133p53α isoforms which retain the complete oligomerisation domain can directly interact with p53α (and probably other α-isoforms) to form distinct permutation of hetero-oligomers, which would differentially expose amino-acid domains to protein partners (i.e., Mdm2, MDMx) or cell protein machineries (i.e., transcriptional machinery, splicing machinery, microRNA machinery). ∆40p53α/p53α complexes can mediate biological responses by modulating the transcriptional activity of promoters of IGF1-receptor and Nanog, thus controlling the switch from pluripotency to differentiation [24,64,80]. In A375 melanoma cells, ∆40p53α/p53α complexes had modified promoter activity at LRDD and CDKN1A genes contributing to shifting cell-fate outcome in favour of apoptosis compared to cell-cycle arrest (upregulation of PIDD and downregulation of p21) despite exposure to γ-irradiation, an established trigger for p53-mediated DNA damage and cell cycle arrest [66].…”

A Study of TP53 RNA Splicing Illustrates Pitfalls of RNA-seq Methodology

“…Multiple studies have now shown that p53 isoforms have distinct functions and frequently contribute to diseases including cancer (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Elevated expression of the D40p53 isoform has been associated with metastatic melanoma and triple-negative breast cancers (7,19).…”

Aberrant splicing of the DMP1‐ARF‐MDM2‐p53 pathway in cancer

“…However, low D40p53/FLp53 expression ratio increased p53 transcriptional activity over FLp53 alone due to D40p53 protection of FLp53 from Mdm2-mediated degradation. 71 Thus, D40p53 has differential effects on FL53 dependent on its level of expression: high D40p53 blocks FLp53 activity while low D40p53 stimulates it. The second largest DNp53 isoform, D133p53, lacks both TAD1/2 and PRD, and inhibits FLp53 activity 72 (Fig.…”

“…In p53 ‐null cells, Δ40p53 expression alone was insufficient to mimic the transcriptional activity of a p53‐response element reporter, and co‐transfection of Δ40p53 with FLp53 decreased total p53 transcriptional activity in a dose‐dependent manner. However, low Δ40p53/FLp53 expression ratio increased p53 transcriptional activity over FLp53 alone due to Δ40p53 protection of FLp53 from Mdm2‐mediated degradation . Thus, Δ40p53 has differential effects on FL53 dependent on its level of expression: high Δ40p53 blocks FLp53 activity while low Δ40p53 stimulates it.…”