Serotonin 5-HT7 Receptor is A Biomarker Poor Prognostic Factor and Induces Proliferation of Triple Negative Breast Cancer Cells Through FOXM1

Triple-negative breast cancer (TNBC) is an aggressive type of breast cancer and associated with poor prognosis and shorter survival due to significant genetic heterogeneity, drug resistance and lack of effective targeted therapeutics. Therefore, novel molecular targets and therapeutic strategies are needed to improve patient survival. Serotonin (5-hydroxytriptamine, 5-HT) has been shown to induce growth stimulatory effects in breast cancer. However, the molecular mechanisms by which 5-HT exerts its oncogenic effects in TNBC still are not well understood. In the present study, we demonstrated that 5-HT induces cell proliferation of TNBC cells and expression of 5-HT7 receptor and FOXM1 oncogenic transcription factor. We found that expression of 5-HT7 receptor is up-regulated in TNBC cells and higher 5-HT7 expression is associated with poor patient prognosis and shorter patient survival. Genetic and pharmacological inhibition of 5-HT7 by siRNA and metergoline, respectively, suppressed TNBC cell proliferation and FOXM1 and its downstream mediators, including eEF2-Kinase (eEF2K) and cyclin-D1. Overall, our findings suggest for the first time that the 5-HT7 receptor promotes FOXM1, eEF2K and cyclin D1 signaling to support TNBC cell proliferation, thus inhibition of 5-HT7/FOXM1 signaling may be used as a potential therapeutic strategy for targeting TNBC.