Overexpression of <scp>RGPR</scp>‐p117 reveals anticancer effects by regulating multiple signaling pathways in bone metastatic human breast cancer <scp>MDA</scp>‐<scp>MB</scp>‐231 cells

The role of RGPR-p117, a transcription factor, which binds to the TTGGC motif in the promoter region of the regucalcin gene, in cell regulation remains to be investigated. This study elucidated whether RGPR-p117 regulates the activity of triple-negative human breast cancer MDA-MB-231 cells in vitro. The wild-type and RGPR-p117-overexpressing cancer cells were cultured in DMEM supplemented with fetal bovine serum. RGPR-p117 overexpression suppressed colony formation and growth of cancer cells. Stimulatory effects of epidermal growth factor on cell growth were blocked by RGPR-p117 overexpression. Wild-type cell proliferation was repressed by cell cycle and intracellular signaling inhibitors. These effects were not potentiated in transfectants. Overexpressed RGPR-p117 protected cancer cells against apoptosis inducers. Mechanistic results showed that RGPR-p117 overexpression decreased the expression of Ras, PI3-kinase, Akt, mitogen-activated protein kinase, and mTOR, which are involved in cell growth, while it elevated the levels of the cancer cell suppressor p53, Rb, p21, and regucalcin. Overexpression of RGPR-p117 suppressed cancer cell migration and adhesion. Interestingly, osteoblastic MC3T3-E1 cells or macrophage RAW264.7 cells involved in the bone microenvironment were impaired by coculture with MDA-MB-231 cells. The effects of cancer cells were blocked by transfection. Coculture with conditioned medium obtained from breast cancer cells repressed proliferation and enhanced the death of osteoblastic cells and macrophages. A TNF-α signaling inhibitor blocked these effects. Thus, overexpressed RGPR-p117 was found to suppress the activity of breast cancer cells by regulating various signaling processes, providing new insight into cellular signaling regulation.