Integrins Alpha-2 and Beta-1 increase through Multiple Generations of the EDW01 Patient-Derived Xenograft Model of Breast Cancer – Markers but not Drivers of Epithelial Mesenchymal Transition

Background: Breast cancers acquire aggressive capabilities via epithelial to mesenchymal transition (EMT), in which various integrins/integrin linked kinase signalling are upregulated. Methods: We investigated this in two patient-derived xenografts (PDXs) developed from breast-to-bone metastases, and it’s functional significance in a breast cancer cell line system. ED03 and EDW01 PDXs were grown subcutaneously in immunocompromised SCID mice through 11 passages and 7 passages, respectively. Tumour tissue was assessed using immunohistochemistry (IHC) for estrogen receptor (ER)-alpha, E-cadherin, vimentin, Twist1, beta-catenin, P120-RasGAP, CD44, CD24 and Ki67, and RT-qPCR of EMT-related factors (CDH1, VIM, CD44, CD24), integrins beta-1 (ITGB1), alpha-2 (ITGA2) and ILK. Integrin and ILK expression in epidermal growth factor (EGF) induced EMT of the PMC42-ET breast cancer cell line was assessed by RT-qPCR and Western blotting, as were the effects of their transient knockdown via small interfering RNA +/- EGF. Cell migration, changes in cell morphology and adhesion of siRNA-transfected PMC42-ET cells to various extracellular matrix (ECM) substrates was assessed. Results: The ED03 (ER+/PR-/HER2-/lobular) and EDW01 (ER+/PR-/HER2-/ductal) PDXs were both classified as molecular subtype luminal A. ED03 xenografts exhibited mutated E-cadherin with minimal expression, but remained vimentin-negative across all passages. In EDW01, the hypoxic indicator gene CAIX and Twist1 were co-ordinately upregulated at passage 4-5, corresponding with a decrease in E-cadherin. At passages 6-7, vimentin was upregulated along with ITGB1 and ITGA2, consistent with an increasing EMT. The ED03 PDX displayed minimal change over passages in mice, for all genes examined. ILK, ITGB1 and ITGA2 were also increased in the EGF-induced EMT of PMC42-ET cells (in which E-cadherin was downregulated) although siRNA against these targets revealed that this induction was not necessary for the observed EMT. However, their knockdown significantly reduced EMT-associated adhesion and Transwell migration. Conclusion: Our data suggest that despite an increase in integrins alpha-2 and beta-1 in the EMT exhibited by EDW01 PDX over multiple generations, this pathway may not necessarily drive the EMT process.