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肿瘤细胞的快速增殖和持续分裂依赖膜脂的加倍。因此旺盛的脂质合成被认为是肿瘤细胞代谢的关键特征之一【1-3】。ATP-柠檬酸裂解酶（ATP-citrate lyase, ACLY）是脂肪酸合成代谢途径的第一个关键酶，催化底物柠檬酸与CoA形成脂肪酸从头合成所需的二碳单位乙酰辅酶A。ACLY的表达和活性受到磷酸化、乙酰化和泛素化的调节【4-7】，而近期研究发现，ACLY也可以发生O-GlcNAc糖基化修饰。O-GlcNAc糖基化修饰被广泛认为是一种可以感受营养波动的“sensor”【8-12】，但ACLY的O-GlcNAc糖基化修饰如何感知营养丰度及其生物学意义亟待揭示。
2024年10月10日，东北师范大学分子表观遗传学教育部重点实验室魏民、冯云鹏研究团队在PNAS上发表的题为O-GlcNAcylation of ATP-citrate lyase couples glucose supply to lipogenesis for rapid tumor cell proliferation的研究论文，报道了O-GlcNAc糖基化修饰在ACLY活性调节中的关键作用。
研究阐释了ACLY通过 O-GlcNAc糖基化修饰感知葡萄糖浓度的升高，进而增强脂类合成促进肿瘤细胞快速增殖的分子机制。蛋白质谱分析显示，S979是ACLY的主要O-GlcNAc糖基化修饰位点。该位点的O-GlcNAc糖基化修饰能够显著增强底物CoA与ACLY的结合，从而提高ACLY的酶活性，促进脂肪酸及脂质的生成。基于 [U-13C] 葡萄糖的代谢流示踪分析发现， ACLY S979的O-GlcNAc糖基化修饰可以根据葡萄糖浓度的变化，对进入脂肪酸从头合成代谢途径的葡萄糖来源的碳单位进行动态调节。因此，ACLY S979的O-GlcNAc糖基化修饰可以响应葡萄糖浓度的变化，从而将葡萄糖供给与脂质合成连接在一起。研究人员发现，ACLY的O-GlcNAc糖基化修饰水平在肿瘤细胞/组织中显著升高。小鼠体内荷瘤实验显示，破坏ACLY S979的O-GlcNAc糖基化修饰能够显著抑制葡萄糖以及EGF对肿瘤生长产生的促进作用。
值得注意的是，已知生长因子EGF可以通过提高ACLY S455的磷酸化修饰，增强底物柠檬酸与ACLY的结合，提高ACLY的酶活性【6,13-17】。而该研究阐释的是ACLY S979的O-GlcNAc糖基化修饰增强另一底物底物CoA与ACLY的结合，且这两个位点的修饰对于产物的生成缺一不可。尽管ACLY S455的磷酸化与S979的糖基化两种修饰之间并不存在“cross-talk”，但EGF信号通过促进葡萄糖的吸收，进而上调ACLY的O-GlcNAc糖基化修饰。显然，决定ACLY活性的营养依赖的糖基化修饰和丝裂原信号指导的磷酸化修饰直接或间接地受EGF信号调控。该研究一方面阐释了细胞如何感知糖类物质的丰度指导脂肪酸合成进而促进细胞增殖的机制；另一方面也为从演化视角思考多细胞复杂有机体的细胞增殖调控机制增添了新的理解：虽然多细胞复杂有机体的增殖受丝裂原信号的控制，但决定单细胞生物增殖的古老的营养感知机制是保守的，丝裂原信号促进细胞增殖的过程依然需要通过特定的营养“检查点”（checkpoint）的核验。
东北师范大学刘佳博士、王杨博士和田苗苗博士为该研究的共同第一作者，冯云鹏教授、魏民教授和金鑫博士为共同通讯作者。浙江大学易文教授、中国科学院杨巍维研究员和复旦大学王永明教授为本论文提供了指导和帮助。
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