The IGF1 signal pathway is highly activated in some subtype of gastric cancer(GC) that exhibits poor survival and chemotherapy resistance. Although the results of clinical trials of anti-IGF1R monoclonal antibodies and IGF-1R inhibitors have been mostly disappointing in unselected cancer patients, some patients benefit from anti-IGF1R therapy in these failed studies. Therefore, it is necessary to characterize the complex IGF signaling in GC and help refine the strategies targeting the IGF1 pathway. We found that GC cell lines exhibit differential responses to the specific IGF1R inhibitor OSI906. According to the phosphorylation status of Akt upon the OSI906 treatment, we divided the GC cell lines into IGF1R-dependent and IGF1R-independent cells. Both in vitro and in vivo experiments indicate that Dox-induced knockdown of NEDD4 significantly suppresses tumor growth of IGF1R-dependent GC cells and NEDD4 overexpression promotes tumor growth of IGF1R-dependent GC cells. In contrast, the proliferation of IGF1R-independent GC cells is not affected by NEDD4 silencing and overexpression. The rescue experiments show that a PTEN-IRS1 axis is required for NEDD4-mediated regulation of Akt activation and tumor growth in GC cells. Clinically, NEDD4 is expressed higher in IGF1-high GC tissues compared with IGF1-low GC tissues and normal tissues, and the co-high expression of NEDD4 and IGF1 predicts a worse prognosis in GC patients. Taken together, our study demonstrated that NEDD4 specifically promotes proliferation of GC cells dependent on IGF1/IGF1R signaling by antagonizing the protein phosphatase activity of PTEN to IRS1, and targeting NEDD4 may be a promising therapeutic strategy for IGF1 signal pathway-driven gastric cancer.
Hepatic glycogen is the main source of blood glucose and controls the intervals between meals in mammals. Hepatic glycogen storage in mammalian pups is insufficient compared to their adult counterparts; however, the detailed molecular mechanism is poorly understood. Here, we show that, similar to glycogen storage pattern, N6-methyladenosine (m6A) modification in mRNAs gradually increases during the growth of mice in liver. Strikingly, in the hepatocyte-specific Mettl3 knockout mice, loss of m6A modification disrupts liver glycogen storage. On the mechanism, mRNA of Gys2, the liver-specific glycogen synthase, is a substrate of METTL3 and plays a critical role in m6A-mediated glycogenesis. Furthermore, IGF2BP2, a “reader” protein of m6A, stabilizes the mRNA of Gys2. More importantly, reconstitution of GYS2 almost rescues liver glycogenesis in Mettl3-cKO mice. Collectively, a METTL3-IGF2BP2-GYS2 axis, in which METTL3 and IGF2BP2 regulate glycogenesis as “writer” and “reader” proteins respectively, is essential on maintenance of liver glycogenesis in mammals.
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