Inoue Yosuke, Moriwaki Kazumasa, Ueda Yasuhiro, Takeuchi Toshihisa, Higuchi Kazuhide, Asahi Michio
Department of Internal Medicine II, Faculty of Medicine, Osaka Medical College, Osaka 569-8686, Japan.
Department of Pharmacology, Faculty of Medicine, Osaka Medical College, Osaka 569-8686, Japan.
Biochem Biophys Res Commun. 2018 Jan 8;495(2):1681-1687. doi: 10.1016/j.bbrc.2017.11.179. Epub 2017 Dec 2.
O-GlcNAcylation is a dynamic post-translational modification of cytonuclear proteins for intracellular signaling. Elevated O-GlcNAcylation is a general feature of cancer and contributes to cancer progression, and recent studies indicate the contribution to increasing incidence of various types of cancer in diabetic patients. However, the role of O-GlcNAcylation in tumor progression is not fully elucidated. Forkhead box M1 (FOXM1), a master mitotic transcription factor, has been implicated in all major hallmarks of cancer, and is wildly expressed in solid tumors. Given that FOXM1 expression was reported to be elevated in gastric cancer, we examined the effect of high glucose or an inhibitor of O-GlcNAc hydrolase, Thiamet G (TMG), on FOXM1 protein expression in a human gastric cancer cell line, MKN45 cells, and confirmed that FOXM1 protein level and the cell proliferation were upregulated. To investigate the molecular mechanisms by which FOXM1 protein expression is regulated by O-GlcNAcylation, the effect of high glucose and TMG on FOXM1 ubiquitination was examined in MKN45 cells. As a result, the ubiquitination and degradation of FOXM1 protein were both suppressed by high glucose and TMG treatment. However, the O-GlcNAcylation was not detected on FOXM1 but not on GSK-3β. High glucose and TMG treatment increased phospho-serine 9 GSK-3β, an inactive form, and the degradation of FOXM1 protein was suppressed by treatment of GSK-3β inhibitors in MKN45 cells. Taken together, we suggest that high glucose and elevated O-GlcNAcylation stabilize FOXM1 protein by its reduced degradation via GSK-3β inactivation in MKN45 cells, suggesting that the higher risk of gastric cancer in diabetic patients could be partially due to O-GlcNAcylation-mediated FOXM1 stabilization.
O-连接的N-乙酰葡糖胺化（O-GlcNAcylation）是一种用于细胞内信号传导的细胞核蛋白动态翻译后修饰。O-GlcNAcylation水平升高是癌症的一个普遍特征，并促进癌症进展，最近的研究表明其与糖尿病患者中各类癌症发病率增加有关。然而，O-GlcNAcylation在肿瘤进展中的作用尚未完全阐明。叉头框M1（FOXM1）是一种主要的有丝分裂转录因子，与癌症的所有主要特征相关，在实体瘤中广泛表达。鉴于有报道称FOXM1在胃癌中表达升高，我们检测了高糖或O-GlcNAc水解酶抑制剂噻美司钠（TMG）对人胃癌细胞系MKN45细胞中FOXM1蛋白表达的影响，并证实FOXM1蛋白水平和细胞增殖均上调。为了研究O-GlcNAcylation调节FOXM1蛋白表达的分子机制，我们检测了高糖和TMG对MKN45细胞中FOXM1泛素化的影响。结果显示，高糖和TMG处理均抑制了FOXM1蛋白的泛素化和降解。然而，在FOXM1上未检测到O-GlcNAcylation，但在糖原合成酶激酶-3β（GSK-3β）上检测到了。高糖和TMG处理增加了无活性形式的磷酸化丝氨酸9 GSK-3β，并且在MKN45细胞中，GSK-3β抑制剂处理可抑制FOXM1蛋白的降解。综上所述，我们认为高糖和升高的O-GlcNAcylation通过使MKN45细胞中的GSK-3β失活，减少FOXM1蛋白降解，从而使其稳定，这表明糖尿病患者患胃癌风险较高可能部分归因于O-GlcNAcylation介导的FOXM1稳定化。
