Attenuation of aggressive tumor progression of anaplastic thyroid cancer by p53.

Anaplastic thyroid cancer (ATC) is the most aggressive thyroid cancer, with very limited treatment options. Mutations of p53 are associated with lethal outcomes of ATC. In this study, we tested the hypothesis that wild type p53 (WTp53) mitigates its aggressive progression. We used human 8505C cells (from human ATC tumors) as a model, harboring a BRAF^V600E mutation and single of mutated p53^C742G allele. We exogenously expressed WTp53 or mutant p53^C742G into 8505C cells (8505C-WTp53 or 8505C-MTp53, respectively). The expressed WTp53 inhibited cell proliferation, decreased cell migration, and induced apoptosis via induction of proapoptotic WTp53 target BAX and PUMA genes in vitro. Mouse xenograft studies showed suppression of tumors induced by 8505C-WTp53 but not by 8505C-MTp53 cells. Consistent with in vitro findings, WTp53 inhibited proliferation of tumor cells, evidenced by decreased proliferation marker Ki-67 in tumors. WTp53 also induced apoptosis in xenograft tumors as shown by increased cleaved caspase-3 proteins and pro-apoptotic regulators, BAX and PUMA. Single cells RNA-sequencing (scRNA-seq) of tumors induced by 8505C, 8505C-WTp53, and 8505C-MTp53 cells demonstrated differential expression gene (DEG) patterns between 8505C-WTp53 and 8505C tumors. DEGs analysis identified alteration of multiple pathways, leading to attenuating the oncogenic actions of mutant p53. The discovery of the suppression of TNFα via NFκB pathway topped the pathways list, resulting in subduing the deleterious inflammatory responses caused by mutant p53. Our findings that exogenously expressed WTp53 could counter act the oncogenic actions of p53 has heightened the feasibility of using CRISPR/Cas9 genome editing to modify the p53 alleles for potential treatment of ATC.