Identification of novel functional and spatial associations between sphingosine kinase 1, sphingosine 1-phosphate receptors and other signaling proteins that affect prognostic outcome in estrogen receptor-positive breast cancer

摘要

Sphingosine kinase is an enzyme that catalyses the phosphorylation of sphingosine to form sphingosine 1-phosphate. Sphingosine 1-phosphate is a bioactive lipid, which has been shown to have an important role in promoting the survival, growth and invasiveness of cancer cells. Sphingosine 1-phosphate binds to five different plasma membrane sphingosine 1-phosphate receptors (S1P1-5) and can regulate intracellular target proteins. We have used immunohistochemical analysis to determine the concurrent expression levels of sphingosine kinase 1 or S1P receptors and other signaling proteins in estrogen receptor-positive breast cancer tumors and have then assessed the impact of these combinations on clinical outcome. This approach has enabled identification of (i) novel biomarkers and (ii) several spatially controlled associations between either sphingosine kinase 1 or S1P1-3 and other signaling proteins whose combination affect prognosis. For instance, the translocation of sphingosine kinase 1 to the plasma membrane has been shown to be a critical determinant in cancer progression. However, our findings identify an additional novel role for the nuclear localization of sphingosine kinase 1 combined with either ERK-1/2 or SFK or LYN or AKT or NF-κB, which significantly shortens disease-specific survival and/or recurrence. We also demonstrate that nuclear S1P2 receptor and c-SRC are associated with improved prognosis and this is linked with a reduction in the nuclear localization of sphingosine kinase 1. These findings identify potential novel biomarker associations, which might serve as new targets for drug intervention designed to improve treatment of estrogen receptor-positive breast cancer. What's new? Sphingosine kinase-1 (SK1) and sphingosine 1-phosphate (S1P) have been implicated in promoting the survival, growth, and invasiveness of cancer cells. Immunohistochemical investigation of estrogen receptor-positive breast tumors and assessment of clinical outcome revealed that SK1 and S1P expression and subcellular localization, when analyzed in combination with other signaling proteins, yielded distinct associations with prognosis. These biomarker associations could serve an important role in new drug interventions for breast cancer.