Departament de Bioquímica i Biomedicina Molecular, Facultat de Biologia, Universitat de Barcelona, Spain; Institut de Biomedicina de la Universitat de Barcelona (IBUB), Spain; Institut de Recerca Sant Joan de Déu (IRSJD), Esplugues de Llobregat, Barcelona, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM)-Instituto de Salud Carlos III, Spain; Departament de Farmacologia, Toxicologia i Química Terapéutica, Facultat de Farmàcia i Ciències de l'Alimentació, Universitat de Barcelona, Spain.
Departament de Bioquímica i Biomedicina Molecular, Facultat de Biologia, Universitat de Barcelona, Spain.
Metabolism. 2018 Jun;83:177-187. doi: 10.1016/j.metabol.2018.02.005. Epub 2018 Feb 18.
Glycogenin-interacting protein 1 (GNIP1) is a tripartite motif (TRIM) protein with E3 ubiquitin ligase activity that interacts with glycogenin. These data suggest that GNIP1 could play a major role in the control of glycogen metabolism. However, direct evidence based on functional analysis remains to be obtained.
The aim of this study was 1) to define the expression pattern of glycogenin-interacting protein/Tripartite motif containing protein 7 (GNIP/TRIM7) isoforms in humans, 2) to test their ubiquitin E3 ligase activity, and 3) to analyze the functional effects of GNIP1 on muscle glucose/glycogen metabolism both in human cultured cells and in vivo in mice.
We show that GNIP1 was the most abundant GNIP/TRIM7 isoform in human skeletal muscle, whereas in cardiac muscle only TRIM7 was expressed. GNIP1 and TRIM7 had autoubiquitination activity in vitro and were localized in the Golgi apparatus and cytosol respectively in LHCN-M2 myoblasts. GNIP1 overexpression increased glucose uptake in LHCN-M2 myotubes. Overexpression of GNIP1 in mouse muscle in vivo increased glycogen content, glycogen synthase (GS) activity and phospho-GSK-3α/β (Ser21/9) and phospho-Akt (Ser473) content, whereas decreased GS phosphorylation in Ser640. These modifications led to decreased blood glucose levels, lactate levels and body weight, without changing whole-body insulin or glucose tolerance in mouse.
GNIP1 is an ubiquitin ligase with a markedly glycogenic effect in skeletal muscle.
糖原合酶相互作用蛋白 1（GNIP1）是一种具有 E3 泛素连接酶活性的三联基序（TRIM）蛋白，与糖原合酶相互作用。这些数据表明，GNIP1 可能在控制糖原代谢中发挥重要作用。然而，基于功能分析的直接证据仍有待获得。
本研究的目的是 1）确定糖原合酶相互作用蛋白/三联基序蛋白 7（GNIP/TRIM7）同工型在人体中的表达模式，2）检测其泛素 E3 连接酶活性，3）分析 GNIP1 对人培养细胞和体内小鼠肌肉葡萄糖/糖原代谢的功能影响。
我们表明，GNIP1 是人体骨骼肌中含量最丰富的 GNIP/TRIM7 同工型，而在心肌中仅表达 TRIM7。GNIP1 和 TRIM7 在体外具有自身泛素化活性，分别在 LHCN-M2 成肌细胞中定位于高尔基器和细胞质。GNIP1 的过表达增加了 LHCN-M2 肌管中的葡萄糖摄取。体内过表达 GNIP1 增加了小鼠肌肉中的糖原含量、糖原合酶（GS）活性和磷酸化 GSK-3α/β（Ser21/9）和磷酸化 Akt（Ser473）含量，而降低了 GS 在 Ser640 的磷酸化。这些修饰导致血糖水平、乳酸水平和体重降低，而不改变小鼠的全身胰岛素或葡萄糖耐量。
GNIP1 是一种具有明显糖原生成作用的泛素连接酶，在骨骼肌中起作用。
