MacAulay Katrina, Hajduch Eric, Blair Anne S, Coghlan Matthew P, Smith Stephen A, Hundal Harinder S
Division of Molecular Physiology, Faculty of Life Sciences, University of Dundee, UK.
Eur J Biochem. 2003 Sep;270(18):3829-38. doi: 10.1046/j.1432-1033.2003.03777.x.
Glycogen synthase kinase 3 (GSK3) is inactivated by insulin and lithium and, like insulin, Li also activates glycogen synthase (GS) via inhibition of GSK3. Li also mimics insulin's ability to stimulate glucose transport (GT), an observation that has led to the suggestion that GSK3 may coordinate hormonal increases in GT and glycogen synthesis. Here we have used Li and SB-415286, a selective GSK3 inhibitor, to establish the importance of GSK3 in the hormonal activation of GT in terms of its effect on GS in L6 myotubes and 3T3-L1 adipocytes. Insulin, Li and SB-415286 all induced a significant inhibition of GSK3, which was associated with a marked dephosphorylation and activation of GS. In L6 myotubes, SB-415286 induced a much greater activation of GS (6.8-fold) compared to that elicited by insulin (4.2-fold) or Li (4-fold). In adipocytes, insulin, Li and SB-415286 all caused a comparable activation of GS despite a substantial differentiation-linked reduction in GSK3 expression ( approximately 85%) indicating that GSK3 remains an important determinant of GS activation in fat cells. Whilst Li and SB-415286 both inhibit GSK3 in muscle and fat cells, only Li stimulated GT. This increase in GT was not sensitive to inhibitors of PI3-kinase, MAP kinase or mTOR, but was suppressed by the p38 MAP kinase inhibitor, SB-203580. Consistent with this, phosphorylation of p38 MAP kinase induced by Li correlated with its stimulatory effect on GT. Our findings support a crucial role for GSK3 in the regulation of GS, but based on the differential effects of Li and SB-415286, it is unlikely that acute inhibition of GSK3 contributes towards the rapid stimulation of GT by insulin in muscle and fat cells.
糖原合酶激酶3（GSK3）可被胰岛素和锂失活，并且与胰岛素一样，锂也通过抑制GSK3来激活糖原合酶（GS）。锂还模拟了胰岛素刺激葡萄糖转运（GT）的能力，这一观察结果提示GSK3可能协调激素诱导的GT增加和糖原合成。在这里，我们使用锂和选择性GSK3抑制剂SB - 415286，从其对L6肌管和3T3 - L1脂肪细胞中GS的影响方面，来确定GSK3在激素激活GT中的重要性。胰岛素、锂和SB - 415286均能显著抑制GSK3，这与GS的明显去磷酸化和激活相关。在L6肌管中，与胰岛素（4.2倍）或锂（4倍）相比，SB - 415286诱导的GS激活程度更高（6.8倍）。在脂肪细胞中，尽管与分化相关的GSK3表达大幅降低（约85%），胰岛素、锂和SB - 415286仍能引起相当程度的GS激活，这表明GSK3仍然是脂肪细胞中GS激活的重要决定因素。虽然锂和SB - 415286都能抑制肌肉和脂肪细胞中的GSK3，但只有锂能刺激GT。这种GT的增加对PI3激酶、MAP激酶或mTOR的抑制剂不敏感，但被p38 MAP激酶抑制剂SB - 203580抑制。与此一致的是，锂诱导的p38 MAP激酶磷酸化与其对GT的刺激作用相关。我们的研究结果支持GSK3在GS调节中起关键作用，但基于锂和SB - 415286的不同作用，急性抑制GSK3不太可能有助于胰岛素在肌肉和脂肪细胞中快速刺激GT。
