Abstract 2590: TP53 R249S mutation confers hepatic organoids with gain-of-function (GOF) tumorigenic features through transcriptional activation of ZMIZ2
Authors: Xu Mingjing , Lam Yin Kau , Yu Jianqing , Ng Kelvin Kwok Chai , Wong Nathalie 
Published: April 2023

Abstract
Hepatocellular Carcinoma (HCC) represents the third leading cause of cancer-related mortality worldwide. TP53 mutations are pivotal genomic drivers for HCC development through frequent concurrent loss-of-function (LOF) aberrations and protein-altering missense mutations. Over 90% of the TP53 missense mutations are distributed within the core DNA binding domain (DBD), where R249S is the most common. Cumulative studies have demonstrated the cancer-promoting properties of TP53R249S mutation in HCC, but its biological impact on tumor initiation remains to be defined. To mimic the early stages of liver carcinogenesis, we generated normal hepatic organoids from human liver tissues of 3 individuals. CRISPR-Cas9 mediated knockout of TP53 in liver organoids resulted in pleomorphic malignant features, including dysplasia, hyperchromasia, atypical and frequent mitosis, loss of polarity, and increased nuclear to cytoplasm ratio. To recapitulate TP53R249S genotype in HCC, we ectopically expressed R249S mutant in liver organoids through lentiviral infection. TP53R249S liver organoids displayed tumorigenic properties as evidenced by increased lesion forming incidence (37.5%) in subcutaneous xenografts when compared with TP53KO (17%) and TP53 wild-type (WT) organoids (0%). Chromatin immunoprecipitation sequencing (ChIP-seq) analysis with HCC cell lines substantiated the specific gain-of-function (GOF) transcriptional activities of R249S mutant. A unique subset of transcription start site-proximal peaks was exclusively found in R249S mutant cells when compared with other TP53 missense mutants and WT. Integration of ChIP-seq and RNA-seq analysis identified transcription factor ZMIZ2 as a direct transcription target of R249S mutant. Our results showed that ZMIZ2 is preferentially overexpressed in HCC patients carrying TP53R249S mutation and exerts a vital role for proliferation of R249S mutant HCC cells. Knockdown of ZMIZ2 profoundly suppressed global H3K27 acetylation (H3K27ac) and H3K4 trimethylation (H3K4me3) in HCC cells. Transcriptome profiling of ZMIZ2 knockdown cells identified multiple downstream targets enriched in chromatin binding and interaction with histone deacetylase, further reinforcing its involvement in epigenetic regulation. In summary, our study revealed that TP53R249S mutation confers distinct advantages in increased tumorigenicity to human liver organoids through GOF transcriptional activities. ZMIZ2 serves as a direct downstream effector contributing to the oncogenic growth arising from R249S mutation plausibly through altering chromatin remodelling.
Citation Format: Mingjing Xu, Yin Kau Lam, Jianqing Yu, Kelvin Kwok Chai Ng, Nathalie Wong. TP53 R249S mutation confers hepatic organoids with gain-of-function (GOF) tumorigenic features through transcriptional activation of ZMIZ2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2590.