Expression of p53 and p53/47 are controlled by alternative mechanisms of messenger RNA translation initiation

Abstract

P53 controls the growth and survival of cells by acting in response to a multitude of cellular stresses. It is, however, not yet fully understood how different p53 activation pathways result in either cell cycle arrest or apoptosis. We and others have described an N-terminally truncated p53 protein (p53/47) originating from a second translation initiation site in the p53 messenger RNA (mRNA), which can interact with p53 and impose altered stability and transactivation properties to p53 complexes. Here we show that cap-dependent and cap-independent mechanisms of initiation govern the translation of the p53 mRNA. Changes in synthesis of full-length p53 or p53/47 are regulated through distinct cell stress-induced pathways acting through separate regions of the p53 mRNA. We also show that some cytotoxic drugs require the presence of full-length p53 to induce apoptosis, whereas for others p53/47 is sufficient. This indicates that by harbouring alternative translation initiation sites, the p53 mRNA gives rise to different levels of the p53 isoforms which help to orchestrate the cell biological outcome of p53 activation in response to different types of cell stress. This sheds new light into the way p53 can integrate and differentiate a large multiplicity of changes in the cellular environment.

p53 isoforms gain functions

“…p53 isoforms gain functions V Olivares-Illana and R Fåhraeus the p53 response (Candeias et al, 2006). Further work showed that suppression of PERK activity, through overexpression of either a dominant-negative PERK or small interfering RNA, resulted in the suppression of p53/47 expression, indicating that PERK is the signal transducer between the ER and p53/47 expression ( Figure 2) (Bourougaa et al, 2010).…”

“…In fact, p53/47 was discovered due to the fact Mdm2 can promote the initiation of translation of both p53 and p53/47, but only targets the former for degradation (Yin et al, 2002). Later work showed that translation initiation of p53 and p53/47 can be controlled by separate and, to some extent, competing mechanisms of translation, so that suppression of capdependent translation of p53 results in an increase in the synthesis of p53/47 (Candeias et al, 2006). Insertion of an open-reading frame followed by a hairpin structure in the 5 0 -untranslated region of p53 resulted in an increase in p53/47 synthesis and a decrease in p53, indicating that cap-independent mechanisms of initiation control p53/47 translation via an internal ribosome entry site (IRES) structure located in the region of þ 1 to þ 120 of p53.…”

“…Insertion of an open-reading frame followed by a hairpin structure in the 5 0 -untranslated region of p53 resulted in an increase in p53/47 synthesis and a decrease in p53, indicating that cap-independent mechanisms of initiation control p53/47 translation via an internal ribosome entry site (IRES) structure located in the region of þ 1 to þ 120 of p53. Hence, the coding region of p53 serves as IRES for p53/47 (Candeias et al, 2006;Ray et al, 2006;Grover et al, 2009). It has also been shown that p53/47 could be generated by alternative splicing (Ghosh et al, 2004), but it should be a rare event as the full-length p53 mRNA was evident after 20 quantitative PCR cycles, whereas the p53/47 message required 40 quantitative PCR cycles, which represents approximately 2 Â 10 20 times less amount of p53/47 mRNA.…”

β-arrestin 2 oligomerization controls the Mdm2-dependent inhibition of p53

“…The cDNA of human Mdm2 was kindly provided by N. Varin-Blank (Institut Cochin), and the p53 plasmid was described previously (34). Various tagged forms of ␤-arr2 have been described previously (16).…”

Genotoxic exposure: novel cause of selection for a functional ΔN-p53 isoform

“…Several isoforms of p53 have been identified (Courtois et al, 2002;Candeias et al, 2006;Grover et al, 2009;Marcel and Hainaut, 2009), and point mutations influencing the functionality of p53 were elucidated and mimicked in vivo (de Vries et al, 2002;Wijnhoven et al, 2005;Hoogervorst et al, 2005a;Iwakuma and Lozano, 2007;Heinlein et al, 2008). The p53 gene is the most frequently mutated gene in cancer and analysis of many different human tumor types have shown a high prevalence of missense mutations located primarily in the central DNA-binding domain (Levine, 1997).…”