Triple Negative Breast Cancer Depends on Sphingosine Kinase 1 (SphK1)/Sphingosine-1-Phosphate (S1P)/Sphingosine 1-Phosphate Receptor 3 (S1PR3)/Notch Signaling for Metastasis

Abstract

BackgroundTriple negative breast cancer (TNBC) has a more aggressive recurrence. Previous reports have demonstrated that sphingosine kinase 1 (SphK1) is a crucial regulator of breast cancer progression. However, the correlation of SphK1 with clinical prognosis has been poorly investigated. Thus, we aimed to elaborate the role of SphK1 in TNBC metastasis.Material/MethodsWe first determined the level of SphK1 in breast cancer tissue samples and breast cancer cells. Furthermore, the expression of HER2 and phosphor-SphK1 (pSphK1) in human breast cancer tissue samples was determined by immunohistochemical analysis. Associations between SphK1 and clinical parameters of tumors were analyzed. The activity of SphK1 was measured by fluorescence analysis. Extracellular sphingosine-1-phosphate (S1P) was detected using an ELISA kit. Associations between SphK1 and metastasis potential were analyzed by Transwell assay.ResultsLevels of SphK1 in TNBC patients were significantly higher than levels in other patients with other breast tumors. The expression of SphK1 was positively correlated with poor overall survival (OS) and progression-free survival (PFS), as well as poor response to 5-FU and doxorubicin. The depression of SphK1 thus could repress the Notch signaling pathway, reduce migration, and invasion of TNBC cells in vivo and in vitro. Furthermore, silencing of SphK1 by Ad-SPHK1-siRNA or SphK1 inhibitor PF543 sensitized TNBCs to 5-FU and doxorubicin. Our results also indicated that SphK1 inhibition could effectively counteracts tumors metastasis via Notch signaling pathways, indicating a potentially anti-tumor strategy in TNBC.ConclusionsWe found that elevated levels of pSphK1 were positive correlation with high expression of S1P, which in turn promoted metastasis of TNBC through S1P/S1PR3/Notch signaling pathway.

Sphingosine Kinase 1 in Breast Cancer—A New Molecular Marker and a Therapy Target

“…Cytotoxic effects of doxorubicin and fluorouracil in triple negative breast cancer cells (MDA-MB-231 and its variant LM2-4) were enhanced by silencing of SK1 (97). Functionally, SK1 was shown to regulate the levels of Notch signaling target gene Hes1 via S1P receptor (S1PR) 3-mediated upregulation of Notch intracellular domain (97). Collectively, pharmacological inhibition of SK1 appears to be an effective therapeutic strategy for the treatment of triple negative breast cancer (please see more details in the section SK1 Inhibition as a Therapeutic Tool-Preclinical Evidence).…”

“…In breast tumors, SK1 mRNA expression was shown to increase through the four stages of breast cancer and was associated with disease progression (93). High levels of SK1 correlated with poorer survival and prognosis in breast cancer patients (97). In patients with invasive ductal carcinoma, high SK1 expression was an independent factor for predicting shorter recurrence-free survival and was significantly associated with more aggressive oncogenic behavior, including higher histological grade, development of distant metastasis, negativity for estrogen, progesterone and HER2 receptors, and triple negativity (91).…”

“…In patients with invasive ductal carcinoma, high SK1 expression was an independent factor for predicting shorter recurrence-free survival and was significantly associated with more aggressive oncogenic behavior, including higher histological grade, development of distant metastasis, negativity for estrogen, progesterone and HER2 receptors, and triple negativity (91). Triple negative breast cancer cells (97) and basal-like subtypes (which often lack the ER) exhibited the highest SK1 gene expression among the various molecular subtypes (95)(96)(97). In a study of 65 ER-negative tumors from patients with locally advanced or metastatic breast cancer who were receiving doxorubicin or docetaxel-based chemotherapy, it was shown that the tumors that failed to respond to chemotherapy exhibited significantly higher levels of SK mRNA compared to tumors that partially or completely responded to treatment (95).…”

“…SK1 is a constitutively active enzyme, which can also be phosphorylated, increasing its activity (83). Phosphorylation of SK1 was significantly associated with higher S1P levels in breast cancer tissue (97,128), which correlated with lymph node metastasis (128). High SK1 expression was associated with a greater relative risk of development of distant metastasis compared to the risk of pathological T and N stages (91).…”

SphK2/S1P promotes metastasis in triple negative breast cancer through PAK1/LIMK1/Cofilin1 signaling pathway

“…The promoting functions of SphK1/S1P in TNBC are well defined by compelling evidence. Previous studies reported that SphK1/S1P promoted TNBC metastasis through the Notch signaling pathway [6] and that inhibition of SphK1 reduced TNBC cells growth through the ERK1/2 and AKT pathways [7]. However, the role of SphK2/S1P in these processes is not decisively recognized.…”