Hundal H S, Bilan P J, Tsakiridis T, Marette A, Klip A
Division of Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada.
Biochem J. 1994 Jan 15;297 ( Pt 2)(Pt 2):289-95. doi: 10.1042/bj2970289.
The effects of insulin-like growth factor I (IGF-I) on glucose and amino acid uptake were investigated in fully differentiated L6 muscle cells, in order to determine whether the two processes are functionally related. Transport of both glucose and amino acid (methylaminoisobutyric acid, MeAIB) was activated rapidly in response to IGF-I. Stimulation reached a peak within 30 min and was sustained for up to 90 min. Maximal activation of either glucose or MeAIB transport was achieved at 3 nM IGF-I; the half-maximal activation (ED50) of glucose transport was at 107 pM and that of MeAIB transport was at 36 pM. Stimulation of amino acid uptake occurred in the absence or presence of glucose, suggesting that this response is not secondary to increased glucose intake. Incubation of cells for 1 h with Brefeldin A (5 micrograms/ml), which disassembles the Golgi apparatus and inhibits the secretory pathway in eukaryotic cells, had no effect on the acute IGF-I activation of glucose and MeAIB transport. Moreover, Brefeldin A caused wide redistribution of the trans-Golgi antigen TGN38, as assessed by subcellular fractionation, without affecting the distribution of glucose transporters. The finding that the degree of activation, time response and sensitivity to IGF-I and Brefeldin A were similar for both glucose and MeAIB transport suggests commonalities in the IGF-I mechanism of recruitment of glucose transporters and stimulation of amino acid transport through System A. An integral trans-Golgi network does not appear to be required for the acute IGF-I stimulation of glucose or amino acid transport, even though stimulation of glucose transport occurs through recruitment of glucose transporters from intracellular stores in these cells. We propose that the donor site of glucose transporters (and perhaps of amino acid transporters) involved in the acute response to IGF-I lies beyond the trans-Golgi network, perhaps in an endosomal compartment in close proximity to the plasma membrane.
为了确定葡萄糖摄取和氨基酸摄取这两个过程在功能上是否相关，研究了胰岛素样生长因子I（IGF-I）对完全分化的L6肌肉细胞中葡萄糖和氨基酸摄取的影响。葡萄糖和氨基酸（甲基氨基异丁酸，MeAIB）的转运都因IGF-I而迅速被激活。刺激在30分钟内达到峰值，并持续长达90分钟。在3 nM IGF-I时可实现葡萄糖或MeAIB转运的最大激活；葡萄糖转运的半数最大激活（ED50）为107 pM，MeAIB转运的半数最大激活为36 pM。无论有无葡萄糖存在，氨基酸摄取均受到刺激，这表明该反应并非继发于葡萄糖摄入量的增加。用布雷菲德菌素A（5微克/毫升）处理细胞1小时，布雷菲德菌素A可拆解高尔基体并抑制真核细胞中的分泌途径，但对IGF-I对葡萄糖和MeAIB转运的急性激活没有影响。此外，通过亚细胞分级分离评估，布雷菲德菌素A导致反式高尔基体抗原TGN38广泛重新分布，而不影响葡萄糖转运体的分布。葡萄糖和MeAIB转运在激活程度、时间反应以及对IGF-I和布雷菲德菌素A的敏感性方面相似，这一发现表明在IGF-I募集葡萄糖转运体和通过A系统刺激氨基酸转运的机制中存在共性。即使在这些细胞中葡萄糖转运是通过从细胞内储存库募集葡萄糖转运体来实现的，但急性IGF-I刺激葡萄糖或氨基酸转运似乎并不需要完整的反式高尔基体网络。我们提出，参与对IGF-I急性反应的葡萄糖转运体（可能还有氨基酸转运体）的供体部位位于反式高尔基体网络之外，可能在紧邻质膜的内体区室中。
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