Poster Presentation 32nd Lorne Cancer 2020

Δ40p53 inhibits the p53-mediated response to DNA damaging therapies in breast cancer cells (#120)

Xiajie Zhang 1 2 , Brianna C Morten 1 2 , Luiza Steffens Reinhardt 3 , Hamish G Campbell 4 , Antony W Braithwaite 5 , Kelly A Avery-Kiejda 1 2
  1. Hunter Cancer Research Alliance, and Medical Genetics, Hunter Medical Research Institute, New Lambton Heights, NSW, Australia
  2. Priority Research Centre for Cancer Research, Innovation and Translation, School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, University of Newcastle, Callaghan, NSW, Australia
  3. Hunter Medical Research Institute, University of Newcastle, New Lambton Heights , NSW, Australia
  4. Children’s Medical Research Institute, University of Sydney, Sydney, NSW, Australia
  5. Department of Pathology, School of Medicine, University of Otago, Dunedin, New Zealand

Breast cancer is the most common malignancy in women. Nearly all deaths from breast cancer are a result of resistance to DNA-damaging therapies and the subsequent development of metastases. The tumour suppressor, p53, is a master regulator of cell fate outcome following DNA damage, by regulating the expression of target genes involved in cell cycle arrest, DNA repair or apoptosis. The mutation frequency (~25%) of p53 in breast cancer is less than expected for a protein that plays a pivotal role in maintaining genomic integrity, suggesting that p53 is inactivated or that its function is modulated by mechanisms other than mutation. The p53 isoforms play important roles in mediating the p53 response in a range of cancers. We have shown that the p53 isoform, Δ40p53, is abundantly expressed in breast cancer (1). Furthermore, a high Δ40p53:p53 ratio is associated with worse disease-free survival, indicating that disruption of p53 function by Δ40p53 may contribute to a more aggressive phenotype (2). However, the endogenous role of Δ40p53 in the response to DNA damage is unclear. This study aimed to investigate the role of Δ40p53 in the response to DNA-damaging therapies in breast cancer cells. We developed breast cancer cells that overexpress Δ40p53 or empty vector; as well as those where Δ40p53 had been knocked down using shRNA. The cells were treated with DNA damaging agents and downstream analysis was performed including real-time PCR, RNA-seq and functional assays. Our studies have shown that Δ40p53-knockdown is associated with increased DNA damage and apoptosis; and decreased G2 arrest in response to DNA-damaging therapies, as well as increased expression of p53 and the p53-dependent apoptosis-related genes including Bax, Noxa and Puma. In contrast, Δ40p53-overexpression led to increased G2 arrest and decreased expression of these genes. These results suggest that Δ40p53 can inhibit the p53-mediated DNA damage response. Inhibition of Δ40p53 expression may serve as a potential target to enhance effectiveness of DNA-damaging therapies in breast cancer.

  1. Avery-Kiejda KA, Morten B, Wong-Brown MW, Mathe A and Scott RJ. The relative mRNA expression of p53 isoforms in breast cancer is associated with clinical features and outcome. Carcinogenesis 2014; 35(3), 586-596. doi:10.1093/carcin/bgt411
  2. Morten BC, Wong-Brown MW, Scott RJ and Avery-Kiejda KA. The presence of the intron 3 16bp duplication polymorphism of p53 (rs17878362) in breast cancer is associated with a low Delta-40p53:p53 ratio and better outcome. Carcinogenesis 2016; 37(1): 81-6. doi: 10.1093/carcin/bgv164