<scp>TIE1</scp> Promotes Primary Tumor Growth by Inhibiting Apoptosis and Activating the <scp>AKT</scp> ‐ <scp>p70S6K</scp> Signaling Pathway in Breast Cancer

Triple-negative breast cancer (TNBC) is the most aggressive molecular subtype among all breast cancer types. Its treatment remains a significant challenge due to the lack of clearly defined molecular targets. We previously reported that lung-metastatic cell lines, established via orthotopic transplantation of a TNBC cell line, showed high expression of the TIE1 receptor-tyrosine kinase. In this study, we demonstrated that TIE1 expression correlates with poor prognosis in breast cancer patients and is highly elevated in the Claudin-low subtype, which largely overlaps with TNBC. Notably, TIE1 expression promoted tumorigenicity in a breast cancer cell line. Furthermore, in primary tumors formed by TIE1-expressing cells, we observed TIE1 cleavage, reduced apoptosis, and activation of the AKT-p70S6K signaling pathway. Our findings suggest that TIE1 may serve as a potential molecular target and biomarker for Claudin-low type breast cancer, and further research could have significant implications for its treatment.