SPOCK1 promotes breast cancer progression via interacting with SIX1 and activating AKT/mTOR signaling pathway

SPOCK1 is highly expressed in many types of cancer, which has been recognized as a promoter of cancer progression, while its regulatory mechanism remains to be clear in breast cancer (BC). This study aimed to explore the precise function of SPOCK1 in BC progression and the mechanism by which SPOCK1 was involved in cell proliferation and epithelial-mesenchymal transition (EMT). Immunohistochemistry (IHC) and database analysis displayed that high expression of SPOCK1 was positively associated with histological grade, lymph node metastasis (LN) and poor clinical prognosis in BC. A series of assays both in vitro and in vivo elucidated that altering SPOCK1 level led to distinctly changes in BC cell proliferation and metastasis. Investigations of potential mechanisms revealed that SPOCK1 interacted with SIX1 could enhance cell proliferation, cell cycle and EMT process by activating the AKT/mTOR pathway, whereas inhibition of AKT/mTOR pathway or depletion of SIX1 reversed the effects of SPOCK1 overexpression. Furthermore, SPOCK1 and SIX1 were highly expressed in BC and might indicate poor prognoses. Altogether, SPOCK1/SIX1 promoted BC progression by activating AKT/mTOR pathway to accelerate cell proliferation and metastasis in BC, and SPOCK1/SIX1 might be promising clinical therapeutic targets to prevent BC progression. IMPORTANCEThe incidence of BC is alarmingly high and many patients initially diagnosed without detectable metastases will eventually develop metastatic lesions. The occurrence of metastasis is responsible for the death of many patients, which also represents a big challenge for researchers to improve the survival rates of BC patients. Hence the scientific community pays more attention on cancer targeted therapy. This research is significant for identifying the underlying mechanisms and capabilities of SPOCK1-induced BC activities, which will greatly apply novel targets and new treatment strategies for clinicians, leading to broader biomedical impacts.