Phosphorylation of Human p53 at Serine 46 Determines Promoter Selection and whether Apoptosis Is Attenuated or Amplified

Abstract

The capacity of DNA damaging agents to induce apoptosis is regulated by target gene induction by p53. We found that p53 targeted MDM2 in cells in which DNA repair was occurring, but persistent DNA damage induced by chemotherapy led p53 to selectively target PTEN. High dose chemotherapy induced the phosphorylation of p53 on serine 46, whereas low dose chemotherapy did not. A nonphosphorylatable serine 46 to alanine p53 mutant (S46A) targeted the MDM2 promoter in preference to that for PTEN. A serine 46 to aspartate mutant (S46D, a phosphorylation mimic) targeted PTEN in preference to MDM2. These observations show that phosphorylation of serine 46 in p53 is sufficient for it to induce the PTEN (phosphatase and tensin homolog deleted on chromosome ten) tumor suppressor protein in preference to MDM2. S46A induced significantly less cell death than the S46D in cells. The phosphorylation-induced change of p53 promoter targeting suppresses the induction of MDM2 and the formation of the autoregulatory feedback loop. Induction of PTEN by p53 followed by expression of PTEN inhibits AKT-induced translocation of MDM2 into the nucleus and sustains p53 function. The protection of p53 from MDM2 by PTEN and the damage-induced activation of PTEN by phosphorylated p53 leads to the formation of an apoptotic amplification cycle in which p53 and PTEN coordinately increase cellular apoptosis.

Regulation of p53 activity by HIPK2: molecular mechanisms and therapeutical implications in human cancer cells

“…Exogenous HIPK2 was shown to correlate with the reduction of MDM2 protein levels (Wang et al, 2001). This regulation is in line with the model showing that Ser46 phosphorylation determines p53 promoter selection toward the lowaffinity proapoptotic ones, impairing MDM2 transcription (Oda et al, 2000;Mayo et al, 2005). Furthermore, HIPK2 and MDM2 can form a stable complex in vitro and in vivo and HIPK2 has been shown to phosphorylate MDM2 and to promote MDM2 proteasomal degradation also in a p53-independent manner (Di Stefano et al, 2005a).…”

“…Thus, deletion of the TAD2 abolishes this activity, and phosphorylation at both Ser46 and Thr55 enhances the binding of p62 and Tfb1 to p53, which have an important role in regulating p53-target genes activation (Di Lello et al, 2006). The specific p53Ser46 phosphorylation is considered to be a sensor for DNA-damage intensity that induces a fine change of p53 conformation varying the p53 affinity for different promoters with a shift from cell-cycle-arrestrelated genes (that is, p21 Waf1 and MDM2) toward proapoptotic genes (that is, p53AIP1) (Oda et al, 2000;Mayo et al, 2005 HIPK2/p53 function in tumor suppression R Puca et al is also regulated by the prolyl-isomerase Pin1 that promotes efficient recruitment of p53 to its target promoters and by p53Lys382 acetylation mediated by p300. After phosphorylation of p53 at Ser46 triggered by either ultraviolet, etoposide or ADR treatments, Pin1 promotes p53 dissociation from iASPP, a p53-negative regulator (Zacchi et al, 2002;Mantovani et al, 2007), thus linking p53 post-translational modifications with transcriptional activity.…”

Defect in serine 46 phosphorylation of p53 contributes to acquisition of p53 resistance in oral squamous cell carcinoma cells

“…Many lines of evidence have demonstrated the importance of Ser46 phosphorylation for the apoptotic function of p53 (Bulavin et al, 1999;Oda et al, 2000b;D'Orazi et al, 2002;Hofmann et al, 2002;Mayo et al, 2005). Specifically, the substitution of this site with Ala reduces the ability of p53 to induce apoptosis.…”

Mapping genetic alterations causing chemoresistance in cancer: identifying the roads by tracking the drivers

“…38 Phosphorylation occurs at multiple sites; although experimental evidence indicate phosphorylations at serine 15 and 20 by the ataxia telangiectasia mutated (ATM) and chk2 kinases to have a critical role in response to DNA damage, phosphorylation at serine 46, which is caused by other kinases, seems of major importance in the execution of apoptosis. [43][44][45] The mechanisms deciding between growth arrest versus apoptosis is incompletely understood, but there seems to be structural differences in the promoters of genes responding rapidly (like the CDKN1A coding for p21) as compared with the more slowly acting genes involved in apoptosis, 46,47 and integrated models for a time sequence involving protein phosphorylations and promoter activation has been proposed. 48 Drug doses may have influenced outcome as well; thus, multiple kinase inhibition by low doses of reversine were shown to induce apoptosis in a p53-dependent manner.…”