2‐Methoxyestradiol‐Mediated Induction of Frzb Contributes to Cell Death and Autophagy in MG63 Osteosarcoma Cells

ABSTRACT Osteosarcoma is a bone tumor that mainly affects children and adolescents. Although its pathogenesis is still not fully understood, activation of Wnt signaling has been implicated in the development and metastasis of osteosarcoma. In this report, we have investigated the effect of the anti‐tumor compound, 2‐methoxyestradiol (2‐ME) on Wnt antagonist frizzled‐related protein b (Frzb), also known as secreted frizzled‐related protein (sFRP)3 in human osteosarcoma (MG63) cells. Our results show that 2‐ME treatment induces Frzb gene promoter activity, and increases Frzb mRNA and protein levels in osteosarcoma cells. In addition, 2‐ME treatment regulates downstream Wnt signaling, increasing the cytoplasmic levels of β‐catenin, and blocking β‐catenin‐mediated Wnt activation in osteosarcoma cells. 2‐ME‐mediated induction of Frzb protein expression is specific to osteosarcoma cells, as it does not affect Frzb expression in normal primary human osteoblasts. Furthermore, 2‐ME‐induced apoptosis and autophagy are blocked in osteosarcoma cells transfected with Frzb siRNAs. Taken together, these studies demonstrate that Frzb protein plays an important role in 2‐ME‐mediated anti‐tumor mechanisms in osteosarcoma cells. J. Cell. Biochem. 118: 1497–1504, 2017. © 2016 Wiley Periodicals, Inc.