Distinct functions of wild-type and R273H mutant Δ133p53α differentially regulate glioblastoma aggressiveness and therapy-induced senescence.

Despite being mutated in 92% of TP53 mutant cancers, how mutations on p53 isoforms affect their activities remain largely unknown. Therefore, exploring the effect of mutations on p53 isoforms activities is a critical, albeit unexplored area in the p53 field. In this article, we report for the first time a mutant Δ133p53α-specific pathway which increases IL4I1 and IDO1 expression and activates AHR, a tumor-promoting mechanism. Accordingly, while WT Δ133p53α reduces apoptosis to promote DNA repair, mutant R273H also reduces apoptosis but fails to maintain genomic stability, increasing the risks of accumulation of mutations and tumor's deriving towards a more aggressive phenotype. Furthermore, using 2D and 3D spheroids culture, we show that WT Δ133p53α reduces cell proliferation, EMT, and invasion, while the mutant Δ133p53α R273H enhances all three processes, confirming its oncogenic potential and strongly suggesting a similar in vivo activity. Importantly, the effects on cell growth and invasion are independent of mutant full-length p53α, indicating that these activities are actively carried by mutant Δ133p53α R273H. Furthermore, both WT and mutant Δ133p53α reduce cellular senescence in a senescence inducer-dependent manner (temozolomide or radiation) because they regulate different senescence-associated target genes. Hence, WT Δ133p53α rescues temozolomide-induced but not radiation-induced senescence, while mutant Δ133p53α R273H rescues radiation-induced but not temozolomide-induced senescence. Lastly, we determined that IL4I1, IDO1, and AHR are significantly higher in GBMs compared to low-grade gliomas. Importantly, high expression of all three genes in LGG and IL4I1 in GBM is significantly associated with poorer patients' survival, confirming the clinical relevance of this pathway in glioblastomas. These data show that, compared to WT Δ133p53α, R273H mutation reorientates its activities toward carcinogenesis and activates the oncogenic IL4I1/IDO1/AHR pathway, a potential prognostic marker and therapeutic target in GBM by combining drugs specifically modulating Δ133p53α expression and IDO1/Il4I1/AHR inhibitors.

The Δ133p53 Isoforms, Tuners of the p53 Pathway.

The TP53 gene is a critical tumor suppressor and key determinant of cell fate which regulates numerous cellular functions including DNA repair, cell cycle arrest, cellular senescence, apoptosis, autophagy and metabolism. In the last 15 years, the p53 pathway has grown in complexity through the discovery that TP53 differentially expresses twelve p53 protein isoforms in human cells with both overlapping and unique biologic activities. Here, we summarize the current knowledge on the Δ133p53 isoforms (Δ133p53α, Δ133p53ß and Δ133p53γ), which are evolutionary derived and found only in human and higher order primates. All three isoforms lack both of the transactivation domains and the beginning of the DNA-binding domain. Despite the absence of these canonical domains, the Δ133p53 isoforms maintain critical functions in cancer, physiological and premature aging, neurodegenerative diseases, immunity and inflammation, and tissue repair. The ability of the Δ133p53 isoforms to modulate the p53 pathway functions underscores the need to include these p53 isoforms in our understanding of how the p53 pathway contributes to multiple physiological and pathological mechanisms. Critically, further characterization of p53 isoforms may identify novel regulatory modes of p53 pathway functions that contribute to disease progression and facilitate the development of new therapeutic strategies.

The Δ133p53ß isoform promotes an immunosuppressive environment leading to aggressive prostate cancer.

Prostate cancer is the second most common cancer in men, for which there are no reliable biomarkers or targeted therapies. Here we demonstrate that elevated levels of Δ133TP53ß isoform characterize prostate cancers with immune cell infiltration, particularly T cells and CD163+ macrophages. These cancers are associated with shorter progression-free survival, Gleason scores ≥ 7, and an immunosuppressive environment defined by a higher proportion of PD-1, PD-L1 and colony-stimulating factor 1 receptor (CSF1R) positive cells. Consistent with this, RNA-seq of tumours showed enrichment for pathways associated with immune signalling and cell migration. We further show a role for hypoxia and wild-type p53 in upregulating Δ133TP53 levels. Finally, AUC analysis showed that Δ133TP53ß expression level alone predicted aggressive disease with 88% accuracy. Our data identify Δ133TP53ß as a highly accurate prognostic factor for aggressive prostate cancer.

Elevation of the TP53 isoform Δ133p53ß in glioblastomas: an alternative to mutant p53 in promoting tumor development.

As tumor protein 53 (p53) isoforms have tumor-promoting, migration, and inflammatory properties, this study investigated whether p53 isoforms contributed to glioblastoma progression. The expression levels of full-length TP53α (TAp53α) and six TP53 isoforms were quantitated by RT-qPCR in 89 glioblastomas and correlated with TP53 mutation status, tumor-associated macrophage content, and various immune cell markers. Elevated levels of Δ133p53ß mRNA characterised glioblastomas with increased CD163-positive macrophages and wild-type TP53. In situ-based analyses found Δ133p53ß expression localised to malignant cells in areas with increased hypoxia, and in cells with the monocyte chemoattractant protein C-C motif chemokine ligand 2 (CCL2) expressed. Tumors with increased Δ133p53ß had increased numbers of cells positive for macrophage colony-stimulating factor 1 receptor (CSF1R) and programmed death ligand 1 (PDL1). In addition, cells expressing a murine 'mimic' of Δ133p53 (Δ122p53) were resistant to temozolomide treatment and oxidative stress. Our findings suggest that elevated Δ133p53ß is an alternative pathway to TP53 mutation in glioblastoma that aids tumor progression by promoting an immunosuppressive and chemoresistant environment. Adding Δ133p53ß to a TP53 signature along with TP53 mutation status will better predict treatment resistance in glioblastoma. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

TP53 drives invasion through expression of its Δ133p53ß variant.

TP53 is conventionally thought to prevent cancer formation and progression to metastasis, while mutant TP53 has transforming activities. However, in the clinic, TP53 mutation status does not accurately predict cancer progression. Here we report, based on clinical analysis corroborated with experimental data, that the p53 isoform Δ133p53ß promotes cancer cell invasion, regardless of TP53 mutation status. Δ133p53ß increases risk of cancer recurrence and death in breast cancer patients. Furthermore Δ133p53ß is critical to define invasiveness in a panel of breast and colon cell lines, expressing WT or mutant TP53. Endogenous mutant Δ133p53ß depletion prevents invasiveness without affecting mutant full-length p53 protein expression. Mechanistically WT and mutant Δ133p53ß induces EMT. Our findings provide explanations to 2 long-lasting and important clinical conundrums: how WT TP53 can promote cancer cell invasion and reciprocally why mutant TP53 gene does not systematically induce cancer progression.

p53 Isoforms: Key Regulators of the Cell Fate Decision.

It is poorly understood how a single protein, p53, can be responsive to so many stress signals and orchestrates very diverse cell responses to maintain/restore cell/tissue functions. The uncovering that TP53 gene physiologically expresses, in a tissue-dependent manner, several p53 splice variants (isoforms) provides an explanation to its pleiotropic biological activities. Here, we summarize a decade of research on p53 isoforms. The clinical studies and the diverse cellular and animal models of p53 isoforms (zebrafish, Drosophila, and mouse) lead us to realize that a p53-mediated cell response is, in fact, the sum of the intrinsic activities of the coexpressed p53 isoforms and that unbalancing expression of different p53 isoforms leads to cancer, premature aging, (neuro)degenerative diseases, inflammation, embryo malformations, or defects in tissue regeneration. Cracking the p53 isoforms' code is, thus, a necessary step to improve cancer treatment. It also opens new exciting perspectives in tissue regeneration.