Abstract
Breast cancer is currently the fourth leading cause of cancer-related death worldwide, with New Zealand and Australia reporting the highest incidence rates. The majority of deaths result from the metastatic spread of breast cancer rather than the primary tumour itself. Among its subtypes, triple-negative breast cancer (TNBC) is the most aggressive due to its increased metastatic potential and the absence of hormone receptors, making targeted treatment difficult. A key mechanism underlying the aggressive characteristics of TNBC is a process termed, epithelial-mesenchymal transition (EMT). Cells undergoing EMT lose epithelial characteristics such as polarity and E-cadherin mediated cell adhesion, and are instead replaced by alternative cadherins such as N-Cadherin and OB-cadherin (CDH11) that promote migration and invasion. This switch to CDH11 in TNBC promotes hallmarks of cancer such as increased proliferation, cancer stemness, and metastasis. In contrast, the epithelial sodium channel α-subunit (αENaC), involved in sodium regulation, has been associated with reduced proliferation and migration when overexpressed. The apical localization of αENaC in epithelial cells is thought to contribute to the preservation of epithelial polarity and thereby restricting EMT progression. RNA-sequencing analysis suggests that αENaC overexpression in TNBC cells is associated with significant downregulation of CDH11. The purpose of this project was to investigate whether αENaC overexpression regulates CDH11 expression and function in TNBC cells, and to determine whether this correlation contributes to reduced migratory potential. To examine whether αENaC downregulated CDH11 expression, CDH11 mRNA levels were quantified by RT-qPCR, revealing a significant reduction in αENaC-overexpressing TNBC cells compared to controls (p<0.0286).To determine whether this transcriptional change translated into protein differences, western blot analysis was performed but showed no significant change in CDH11 protein levels. Finally, to assess whether reduced migration in αENaC-overexpressing cells was mediated by CDH11, scratch assays were performed using celecoxib, a repurposed COX-2 selective inhibitor reported to inhibit CDH11. As expected, αENaC-overexpressing cells exhibited decreased migration when compared to controls. However, no change with migration was observed with celecoxib treatment. Collectively, the data suggests αENaC-CDH11 cross-talk as a possible regulatory mechanism in TNBC. By linking αENaC-overexpressing to transcriptional suppression of CDH11 by possible upregulation of miR335 or downregulation of ILF3 resulting in decreased migratory capacity in these cells. This study identifies a potential regulatory axis with prognostic and therapeutic relevance in the treatment of TNBC.