Distinct functions of wild-type and mutant ?133p53a R273H differentially regulate glioblastoma aggressiveness and therapy-induced senescence
Mutations effects on p53 isoforms' activities remain largely unknown, although they are mutated in 92% of TP53 mutant cancers. Therefore, exploring the effect of mutations on p53 isoforms activities is a critical, albeit unexplored area in the p53 field. Current glioblastoma treatments, including temozolomide chemotherapy and radiations, induce cellular senescence through a p53-dependent mechanism. Nevertheless, GBMs still have a poor 6.8% five-year survival indicating a need to better understand underlying mechanisms affecting the response to treatments. The progression from low-grade astrocytoma to glioblastoma is accompanied by TP53 mutations. Since ?133p53a prevents cellular senescence, studying the impact of its mutation in glioblastoma is relevant to determine if it affects the progression and response to treatment of GBM cells. In this aim, we stably overexpressed wild-type (WT) ?133p53a in WT glioblastoma multiforme (GBM) cells, and ?133p53a R273H in R273H mutant GBM cells. We used mRNA-sequencing to identify mutant ?133p53a-specific target genes. We examined proliferation, invasion, DNA repair, apoptosis, and senescence regulation by WT and mutant ?133p53a. All results were confirmed by siRNA knock-down. Finally, using TCGA data, we investigated the association of the mutant ?133p53a-specific target genes to clinical outcome of GBM and low-grade glioma (LGG) patients.   This study provides the first and most in-depth characterization of a mutant p53 isoform's activities to date and demonstrate that mutant ?133p53a R273H is an active contributor to glioblastoma carcinogenesis and response to treatment. Furthermore, by discovering the link between TP53 mutation and IL4I1/IDO1/AhR pathway, we show strong evidence of ?133p53a R273H clinical relevance in mutant TP53 glioblastoma development and aggressiveness, and as a potential therapeutic target and biomarker. Overall design: Wild-type (WT) ?133p53a was stably overexpressed in two WT glioblastoma multiforme (GBM) cells (U87 and A172) and mutant ?133p53a R273H in as stably overexpressed in two R273H mutant GBM cells (SF268 and SNB19). Each control or ?133p53a overexpressing cells were either treated with DMSO, Temozolomide, or radiations. mRNA sequensing was then performed on threee independent experiments.