Department of Anatomy, Korea University College of Medicine, Seoul, Korea.
J Cell Physiol. 2011 Apr;226(4):974-81. doi: 10.1002/jcp.22410.
Metformin is a major oral anti-diabetic drug and is known as an insulin sensitizer. However, the mechanism by which metformin acts is unclear. In this study, we found that AICAR, an AMPK activator, and metformin increased the expression of Rab4 mRNA and protein levels in skeletal muscle C2C12 cells. The promoter activity of Rab4 was increased by metformin in an AMPK-dependent manner. Metformin stimulated the phosphorylation of AS160, Akt substrate, and Rab GTPase activating protein (GAP), and also increased the phosphorylation of PKC-zeta, which is a critical molecule for glucose uptake. Knockdown of AMPK blocked the metformin-induced phosphorylation of AS160/PKC-zeta. In addition, a colorimetric absorbance assay showed that insulin-induced translocation of GLUT4 was suppressed in Rab4 knockdown cells. Moreover, Rab4 interacted with PKC-zeta but not with GLUT4. The C-terminal-deleted Rab4 mutant, Rab4ΔCT, showed diffuse sub-cellular localization, while wild-type Rab4 localized exclusively to the perinuclear membrane. Unlike Rab4ΔCT, wild-type Rab4 co-localized with PKC-zeta. Together, these results demonstrate that metformin induces Rab4 expression via AMPK-AS160-PKC-zeta and modulates insulin-mediated GLUT4 translocation.
二甲双胍是一种主要的口服抗糖尿病药物，被称为胰岛素增敏剂。然而，二甲双胍的作用机制尚不清楚。在这项研究中，我们发现 AMPK 激活剂 AICAR 和二甲双胍均可增加骨骼肌 C2C12 细胞中 Rab4 mRNA 和蛋白水平的表达。二甲双胍以 AMPK 依赖的方式增加 Rab4 的启动子活性。二甲双胍刺激 AS160、Akt 底物和 Rab GTP 酶激活蛋白（GAP）的磷酸化，还增加了葡萄糖摄取的关键分子 PKC-ζ的磷酸化。AMPK 的敲低阻断了二甲双胍诱导的 AS160/ PKC-ζ的磷酸化。此外，比色吸收测定表明 Rab4 敲低细胞中胰岛素诱导的 GLUT4 易位受到抑制。此外，Rab4 与 PKC-ζ相互作用，但与 GLUT4 不相互作用。C 端缺失的 Rab4 突变体 Rab4ΔCT 显示弥散的亚细胞定位，而野生型 Rab4 仅定位于核周膜。与 Rab4ΔCT 不同，野生型 Rab4 与 PKC-ζ共定位。总之，这些结果表明，二甲双胍通过 AMPK-AS160-PKC-ζ诱导 Rab4 表达，并调节胰岛素介导的 GLUT4 易位。
