Control of Liver Glycogen Synthase Activity and Intracellular Distribution by Phosphorylation
Control of Liver Glycogen Synthase Activity and Intracellular Distribution by Phosphorylation
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DOI：
10.1074/jbc.m808576200
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发表时间：
2009-03-06
影响因子：
4.8
通讯作者：
Guinovart, Joan J.
中科院分区：
文献类型：
--
作者：
Ros, Susana;Garcia-Rocha, Mar;Guinovart, Joan J.
真核糖原合酶活性由多个位点的可逆磷酸化调节。在哺乳动物中发现的两种 GS 亚型中，肌肉酶（肌糖原合酶）受到了更多关注，并且之前已经讨论了每个已知磷酸化位点在控制其活性和细胞内分布方面的相对重要性。我们分析了糖原合酶肝 (LGS) 亚型同源位点去磷酸化的影响。这些位点的丝氨酸残基被不可磷酸化的丙氨酸残基单独或成对取代，并且使用腺病毒载体在培养的细胞中表达所得的LGS变体。位点 2 (Ser(7)) 的唯一突变产生了一种几乎完全活跃的酶，能够在缺乏葡萄糖的情况下培养的原代肝细胞和 FTO2B 细胞（一种通常不合成糖原的细胞系）中诱导糖原沉积。在没有葡萄糖的情况下，位点 2 的突变也足以触发 LGS 从细胞质聚集并易位到肝细胞皮质。然而，当引入导致酶失活的额外突变（E509A）时，在无葡萄糖孵育的肝细胞中没有观察到这种重新分布。这一结果表明 LGS 易位严格依赖于糖原合成。
Eukaryotic glycogen synthase activity is regulated by reversible phosphorylation at multiple sites. Of the two GS isoforms found in mammals, the muscle enzyme (muscle glycogen synthase) has received more attention and the relative importance of every known phosphorylation site in the control of its activity and intracellular distribution has been previously addressed. We have analyzed the impact of the dephosphorylation at the homologous sites of the glycogen synthase liver (LGS) isoform. Serine residues at these sites were replaced by non-phosphorylatable alanine residues, singly or in pairs, and the resultant LGS variants were expressed in cultured cells using adenoviral vectors. The sole mutation at site 2 (Ser(7)) yielded an enzyme that was almost fully active and able to induce glycogen deposition in primary hepatocytes incubated in the absence of glucose and in FTO2B cells, a cell line that does not normally synthesize glycogen. Mutation at site 2 was also sufficient to trigger the aggregation and translocation of LGS from the cytoplasm to the hepatocyte cell cortex in the absence of glucose. However, this redistribution was not observed in hepatocytes incubated without glucose when an additional mutation (E509A), which renders the enzyme inactive, was introduced. This result suggests that LGS translocation is strictly dependent on glycogen synthesis.