Downregulation of AKT3 increases migration and metastasis in triple negative breast cancer cells by upregulating S100A4

Introduction: Morbidity and mortality of breast cancer are mainly determined by the occurrence of distant metastases. Therefore, a better understanding of mechanisms promoting the development of metastases is of high clinical relevance. The serine/threonine kinase AKT was shown to drive cancer progression and metastasis. However, there is emerging data that single AKT isoforms (AKT1, AKT2, AKT3) have different or even opposing functions in the regulation of cancer cell migration in vitro, suggesting that inhibition of distinct AKT isoforms might have undesirable effects on cancer dissemination. Methods: The triple negative breast cancer cell line MDA-MB-231 was used to investigate the functional roles of AKT in migration and metastasis. AKT single and double knockdown cells were generated using isoform specific shRNAs. Migration was analyzed using live cell imaging, chemotaxis and transwell assays. The metastatic potential was evaluated in a subcutaneous xenograft mouse model. Results: Depletion of AKT3, but not AKT1 or AKT2, resulted in increased migration in vitro. This effect was even more prominent in AKT2/3 double knockdown cells. Furthermore, combined downregulation of AKT2 and AKT3, as well as AKT1 and AKT3 significantly increased metastasis formation in vivo. Screening for promigratory proteins revealed that downregulation of AKT3 increases the expression of S100A4 protein. In accordance, depletion of S100A4 by siRNA approach reverses the increased migration induced by knockdown of AKT3. Conclusion: We demonstrated that knockdown of AKT3 can increase the metastatic potential of triple negative breast cancer cells. Therefore, our results provide a rationale for the development of AKT isoform specific inhibitors.