NEK9, a novel effector of IL-6/STAT3, regulates metastasis of gastric cancer by targeting ARHGEF2 phosphorylation

Rationale: Inflammatory stimuli from the tumor microenvironment play important roles in cancer progression. However, the mechanism of promotion of cancer metastasis by inflammation in gastric cancer (GC) is poorly understood. Methods: The roles of NEK9 were validated via loss-of-function and gain-of-function experiments in vitro and in an animal model of metastasis. Cytoskeletal reorganization-associated molecules were detected by GST pull-down. The regulation of ARHGEF2 by NEK9 was investigated by phosphoproteomics analysis, immunoprecipitation (IP) and in vitro kinase assay. The transcriptional regulation of miR-520f-3p was studied using luciferase reporter and chromatin immunoprecipitation (ChIP). The expression of these proteins in GC tissues was examined by immunohistochemistry. Results: NEK9 directly regulates cell motility and RhoA activation in GC. The phosphorylation of ARHGEF2 by NEK9 is the key step of this process. NEK9 is a direct target of miR-520f-3p, which is transcriptionally suppressed by IL-6-mediated activation of STAT3. A decrease in miR-520f-3p leads to the amplification of IL-6/STAT3 by targeting GP130. A simultaneous elevation of the levels of NEK9, GP130 and p-STAT3 was confirmed in the lymph nodes and distant metastases. An increase in NEK9, GP130 and STAT3 is associated with reduced overall survival of GC patients. Conclusion: This study demonstrates that activation of STAT3 by IL-6 transcriptionally suppresses miR-520f-3p and diminishes the inhibitory effects of miR-520f-3p on NEK9 and GP130. An increase in GP130 enhances this signaling, and NEK9 directly influences cell motility and RhoA activation by targeting the phosphorylation of ARHGEF2. Targeting the IL-6-STAT3-NEK9 pathway may be a new strategy for GC treatment.