p53Ψ is a transcriptionally inactive p53 isoform able to reprogram cells toward a metastatic-like state

Abstract

Although much is known about the underlying mechanisms of p53 activity and regulation, the factors that influence the diversity and duration of p53 responses are not well understood. Here we describe a unique mode of p53 regulation involving alternative splicing of the TP53 gene. We found that the use of an alternative 3′ splice site in intron 6 generates a unique p53 isoform, dubbed p53Ψ. At the molecular level, p53Ψ is unable to bind to DNA and does not transactivate canonical p53 target genes. However, like certain p53 gain-offunction mutants, p53Ψ attenuates the expression of E-cadherin, induces expression of markers of the epithelial-mesenchymal transition, and enhances the motility and invasive capacity of cells through a unique mechanism involving the regulation of cyclophilin D activity, a component of the mitochondrial inner pore permeability. Hence, we propose that p53Ψ encodes a separation-of-function isoform that, although lacking canonical p53 tumor suppressor/transcriptional activities, is able to induce a prometastatic program in a transcriptionally independent manner. reactive oxygen species | cancer A n evolutionarily conserved transcription factor, p53 has origins that can be traced back to the early metazoans, ∼700 Mya (1). This transcription factor plays a critical role in regulating many fundamental aspects of reversible and irreversible cellular stress responses, genome surveillance, and suppression of oncogenic transformation (1). In response to strong cellular stresses such as DNA damage or oncogenic signals, p53 regulates the expression of a large cohort of genes that affect cell cycle arrest, senescence, and apoptosis (1). Recent work has uncovered additional roles for p53 under basal physiological conditions, such as regulation of development, reproduction, metabolism, and self-renewal capacity (2-5). However, the factors that influence the diversity and duration of p53 responses are not well understood. Here we describe a unique mode of p53 regulation that involves alternative splicing of the TP53 gene. We found that the use of an alternative 3′ splice site in intron 6 generates a previously uncharacterized p53 isoform that we named p53Ψ. Interestingly, this isoform is highly expressed in cells characterized by a CD44 high /CD24 low immune type. At the molecular level, p53Ψ lacks major portions of the DNA-binding domain, the nuclear localization sequence, and the tetramerization domain, features that are normally present in full-length p53 (p53FL). Consequently, this isoform proved incapable of sequence-specific DNA binding and transactivation of canonical p53 target genes. However, expression of the p53Ψ isoform attenuated the expression of E-cadherin, induced expression of markers associated with epithelial-mesenchymal transition (EMT), and enhanced the motility and invasive capacity of normal and malignant cells. Consistent with a role of these features in enhancing the prometastatic capabilities of cells, we observed that in patients with early-stage nonsmall cell lung carcinoma (...

Metformin and mTOR Inhibitors: Allies against Ovarian and Breast Cancers

“…The analysis of 500 high grade serous ovarian tumors was conducted by the Cancer Genome Atlas (TCGA) project, revealing that 96% of all ovarian cancer subtypes present mutations in the TP53 gene [65,68]. In agreement, a systematic analysis of the ovarian clear cell tumors present mutations in the PIK3CA, TP53, KRAS, PTEN genes with a frequency of 33%, 15%, 7%, and 5%, respectively [70,71], whereas endometrioid ovarian tumors frequently have mutated CTNNB1 (encoding β-catenin), ARID1A, member of the SWI/SNF family, and PIK3CA genes [64]. The mucinous ovarian tumors present prevalent KRAS gene mutations [63,64,72].…”

The Paradox of p53: What, How, and Why?

“…In line with these observations, it has been proposed that increased D133p53 and decreased p53-b expression in colon carcinomas may reflect an escape from the senescence barrier during progression from adenoma to carcinoma (Fujita et al 2009). Recently, a new isoform, p53C, was shown to promote cell motility and invasion in a transcription-independent manner (Senturk et al 2014), widening the "noncanonical" repertoire of p53. These multiple p53 isoforms, which increase greatly the level of complexity of p53-mediated transcription, might contribute significantly to the generation of discordant p53 programs.…”

Roles of alternative splicing in the pathogenesis of lung cancer

“…Although much is known about the suppressor role of P53 and its regulation, the alternative splicing of P53 is not well understood. A recent study described an alternatively spliced form of P53, P53Ψ, which uses an alternative 3' splice site in intron 6 [10] . P53Ψ was detected in approximately 22% of early stage adenocarcinomas, and patients with tumors expressing P53Ψ displayed a decrease in overall survival compared with the P53Ψ negative patients.…”

“…P53Ψ was detected in approximately 22% of early stage adenocarcinomas, and patients with tumors expressing P53Ψ displayed a decrease in overall survival compared with the P53Ψ negative patients. P53Ψ does not transactivate canonical P53 target genes, while it attenuates E-cadherin expression, induces those markers of the epithelial-mesenchymal transition (EMT), and consequently increases the motility and invasive capacity of lung cancer cells [10] . Different isoforms of neuropilins (NRP1 and NRP2) are generated by alternative splicing.…”