ZnRF3 Induces Apoptosis of Gastric Cancer Cells by Antagonizing Wnt and Hedgehog Signaling

A large proportion of malignant cancers of the stomach are gastric adenocarcinoma type. In spite of many studies, the molecular basis for this cancer is still unclear. Deregulated cell proliferative signaling via Wnt/β-catenin and Hedgehog pathways is considered important in the pathogenesis of many cancers including the gastric cancer. Recent studies identified ZnRF3 protein, which is a E3-ubiquitin ligase and which is either deleted or mutated in cancers, to inhibit Wnt signaling. However, the significance of ZnRF3 in the control of gastric cancer and whether it also regulates Hedgehog signaling pathway, is not known. In the present study, we assessed the expression of ZnRF3 in gastric tumors and paracancerous tissues from 58 patients (44 male and 14 female) of different ages and related this to patient survival. We observed a clear relationship between ZnRF3 expression in paracancerous tissue and tumor size. Also, ZnRF3 expression was much higher in tumors from aged patients. Male patients showed higher mortality than the females. Mechanistic studies using normal gastric cells (GES1) and gastric cancer cells (MGC-803) infected with either AdZnRF3 or AdGFP viral vectors, revealed that ZnRF3 overexpression causes significantly more apoptosis and lowered proliferation of cancer cells. ZnRF3 overexpression led to greatly reduced levels of Lgr5, a component of Wnt signaling and also Gli1, a component of Hedgehog signaling. Thus, ZnRF3 negatively influences both the Wnt and Hedgehog proliferative pathways, and probably this way it negatively regulates cancer progression. These results suggest the importance of normal ZnRF3 function in checking the progression of cancer cell growth and indicate that a lack of this protein can lead to poorer clinical outcomes for gastric cancer patients.