Poster Presentation 35th Lorne Cancer Conference 2023

p53 isoform expression promotes a stemness phenotype and drives therapy resistance in breast cancer. (#108)

Luiza Steffens Reinhardt 1 2 , Kira Groen 1 3 , Xiajie Zhang 1 2 , Brianna Morten 1 , Kelly Avery-Kiejda 1 2
  1. School of Biomedical Sciences and Pharmacy, College of Health, Medicine and Wellbeing, The University of Newcastle, Callaghan, NSW, Australia
  2. Cancer Detection & Therapy Research Program, Hunter Medical Research Institute, New Lambton Heights, NSW, Australia
  3. Immune Health Research Program, Hunter Medical Research Institute, New Lambton Heights, NSW, Australia

Chemotherapies such as doxorubicin (DOX) trigger cell death via the p53 pathway and are frequently used in breast cancer treatment. We have previously shown that a high ∆40p53:p53 ratio is associated with worse disease-free survival and that high levels of the p53 isoform Δ40p53 inhibit the canonical DOX response in breast cancer1,2. Thus, Δ40p53 may adversely affect survival by promoting treatment resistance and recurrence, traits typically associated with cancer stem cells (CSCs).

To determine the association of Δ40p53 with CSC regulation and treatment response.

To infer aberrant activity of cellular pathways in tumours with high or low ∆40p53 expression, cDNA microarray data from our previous studies on 64 invasive ductal carcinomas (IDCs) was analyzed using Partek Genomic Suite 7.0 as previously described3. Stable ∆40p53 knockdown, overexpression, and control MCF-7 breast cancer sublines were generated through lentiviral transduction3. Cell sorting, mammosphere and colony formation assays, immunofluorescence, and RT-qPCR for stem cell and epithelial to mesenchymal transition markers and p53-target microRNAs (miR) were performed on sublines in vitro as previously described1. Sublines were orthotopically injected into immunocompromised mice, which were subsequently treated with DOX. Extracted tumours were stained by immunohistochemistry for Ki67 and Sox2.

Gene ontology analysis revealed downregulation of cell differentiation associated genes and upregulation of stem cell regulation genes in IDCs with high ∆40p53 compared to low ∆40p53. In vitro, ∆40p53 co-localised with stem cell markers. Further, in cells expressing high ∆40p53, increased expression of stem cell markers and greater mammospheres and colony formation capacities were observed compared to the control subline. Both miR-145 and miR-200c (repressors of stem cell markers) were found downregulated in Δ40p53 cells when compared to control cells. In vivo, high expression of ∆40p53 led increased tumour growth, Ki67 and Sox2 expression, and increased blood microvessel areas in vehicle-treated mice. High expression of ∆40p53 also reduced tumour sensitivity to DOX compared to controls.

Our results indicate that Δ40p53 may be a CSC regulator, promoting tumour aggressiveness and treatment resistance. Targeting Δ40p53 could enhance the efficacy of currently used treatments for breast cancer such as DOX.

  1. Steffens Reinhardt L, Zhang X, Groen K, Morten BC, De Iuliis GN, Braithwaite AW, Bourdon JC and Avery-Kiejda KA. Alterations in the p53 isoform ratio govern breast cancer cell fate in response to DNA damage. Cell Death and Disease 2022;13(10):907. doi: 10.1038/s41419-022-05349-9.
  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 Δ40p53:p53 ratio and better outcome. Carcinogenesis 2016; 37(1): 81-6. doi: 10.1093/carcin/bgv164.
  3. Zhang X, Groen K, Morten BC, Steffens Reinhardt L, Campbell HG, Braithwaite AW, Bourdon JC and Avery-Kiejda KA. Effect of p53 and its N‐terminally truncated isoform, Δ40p53, on breast cancer migration and invasion. Molecular Oncology 2021, 16, 447-465. doi: 10.1002/1878-0261.13118