Extracellular regucalcin reveals anti-cancer activity by suppressing cell growth and metastatic activity by blocking EGF signaling pathway in human glioblastoma cells in vitro.

Glioblastoma is a malignant brain tumor, which is insistent and deadly tumor. It is vital to adjust outcomes for patients with brain tumors. There are no effective treatments for malignant glioblastoma. Glioblastoma is characterized by overexpression of epidermal growth factor (EGF) receptors in a ligand-independent manner. EGF receptor signaling stimulates tumorigenesis by increasing the proliferation and metastatic activity of glioblastoma cells. Regucalcin is a critical regulator of signaling in non-tumor and tumor cells. Interestingly, extracellular regucalcin is reported to inhibit cancer cell proliferation. Furthermore, the current study elucidates the inhibitory effects of extracellular regucalcin on human glioblastoma cells in vitro. Glioblastoma cells were cultured in DMEM-low glucose containing 10 % fetal bovine serum (FBS) with the addition of regucalcin (0.001-10 nM). The proliferation of glioblastoma cells increased in culture with EGF or FBS. This augmentation was blocked by the treatment with extracellular regucalcin (0.001-10 nM) by the independent mechanism of altering EGF receptor levels and cell death. The suppressive effects of regucalcin on cell growth were not attenuated by treatment with various intracellular signaling inhibitors, including genistein, a tyrosine kinase inhibitor, and MAPK inhibitor. Mechanistically, culture with regucalcin reduced the expression levels of PI3-kinase 100α, Akt, MAPK, phosphor-MAPK, and mTOR, which promote cell growth, and regucalcin, which is an inhibitor of cancer cell growth. In addition, treatment with regucalcin inhibited metastatic activity, including adhesion, invasion, and migration of glioblastoma cells. Thus, extracellular regucalcin inhibited the activity of human glioblastoma cells, suggesting a suppressive role in the cancer microenvironment.