Knockdown of RNF6 inhibits gastric cancer cell growth by suppressing STAT3 signaling

Background and objective: RNF6, an E3 ligase, has been reported to play an important role in the tumorigenesis in several tissues, but its role in gastric cancer is still unknown. In this study, we aimed to investigate the biological function and molecular mechanisms of RNF6 in gastric cancer. Materials and methods: The expression levels of RNF6 were detected by quantitative real-time PCR (qRT-PCR) and immunoblotting in gastric cancer tissues and cell lines. Cell Counting Kit-8 assay was performed to evaluate cell proliferation. Cell apoptosis was analyzed by flow cytometer and immunoblotting. Luciferase assay, immunoblotting and qRT-PCR were performed to explore the activation of STAT3. Immunoprecipitation was performed to evaluate the ubiquitination of SHIP-1. Results: In this study, RNF6 was found to be upregulated in both primary tissues and cell lines of gastric cancer. Knockdown or overexpression of RNF6 inhibited or promoted cell growth of gastric cancer cells. Knockdown of RNF6 also induced the cleavage of PARP and promoted cell apoptosis in gastric cancer cells. In addition, knockdown of RNF6 also increased the cytotoxicity of doxorubicin against gastric cancer. Moreover, knockdown of RNF6 inhibited STAT3-derived luciferase activity and downregulated the phosphorylation of STAT3, but upregulated the protein level of SHIP-I. Knockdown of RNF6 downregulated the expression of MC L I and XIAP, which are target genes of STAT3. Further studies showed that RNF6 regulated the stability of SHIP-1 by inducing its polyubiquitination. Conclusion: These results demonstrated that RNF6 was highly expressed in gastric cancer and regulated the growth of gastric cancer cells by affecting SHIP-1/STAT3 signaling, which suggested that RNF6 could be a novel target for gastric cancer therapy.