Tsiani E, Bogdanovic E, Sorisky A, Nagy L, Fantus I G
Department of Medicine, Banting and Best Diabetes Centre, Mount Sinai Hospital, and University of Toronto, Ontario, Canada.
Diabetes. 1998 Nov;47(11):1676-86. doi: 10.2337/diabetes.47.11.1676.
Vanadate and pervanadate (pV) are protein tyrosine phosphatase (PTP) inhibitors that mimic insulin to stimulate glucose transport. To determine whether phosphatidylinositol (PI) 3-kinase is required for vanadate and pV, as it is for insulin, cultured L6 myotubes were treated with vanadate and pV. The two compounds stimulated glucose transport to levels similar to those stimulated by insulin; however, while PI 3-kinase activity and the increase in the lipid products PI 3,4-bisphosphate and PI 3,4,5-trisphosphate were inhibited by wortmannin after stimulation by all three agents--insulin, vanadate, and pV--wortmannin blocked glucose transport stimulated by insulin but not vanadate or pV. Vanadate and pV stimulated the translocation of GLUTs from an intracellular compartment to the plasma membrane; this stimulation was not blocked by wortmannin, but insulin-induced GLUT translocation was inhibited. Similar results were obtained in cultured H9c2 cardiac muscle cells in which wortmannin did not inhibit glucose transport or the vanadate-induced translocation of GLUT4 in c-myc-GLUT4 transfected cells. The ser/thr kinase PKB (Akt/PKB/RAC-PK) is activated by insulin, lies downstream of PI 3-kinase, and has been implicated in signaling of glucose transport. Insulin and pV stimulated PKB activity, and both were inhibited by wortmannin. In contrast, vanadate, at concentrations that maximally stimulated glucose transport, did not significantly increase PKB activity. To determine the potential role of protein kinase C (PKC), L6 cells were incubated chronically with phorbol myristate acetate (PMA) or acutely with the PKC inhibitors calphostin C and bisindolylmaleimide. There was no inhibition of glucose transport stimulation by insulin, vanadate, or pV, and a combination of wortmannin and PKC inhibitors also failed to block the effect of vanadate and pV. In contrast, disassembly of the actin network with cytochalasin D blocked the stimulation of glucose transport by all three agents. In conclusion, vanadate and pV are able to stimulate glucose transport and GLUT translocation by a mechanism independent of PI 3-kinase and PKC. Similar to that by insulin, glucose transport stimulation by vanadate and pV requires the presence of an intact actin network.
钒酸盐和过钒酸盐（pV）是蛋白酪氨酸磷酸酶（PTP）抑制剂，可模拟胰岛素刺激葡萄糖转运。为了确定磷脂酰肌醇（PI）3激酶是否如对胰岛素一样，是钒酸盐和pV发挥作用所必需的，用钒酸盐和pV处理培养的L6肌管。这两种化合物刺激葡萄糖转运至与胰岛素刺激相似的水平；然而，虽然在胰岛素、钒酸盐和pV这三种物质刺激后，渥曼青霉素均抑制PI 3激酶活性以及脂质产物PI 3,4-二磷酸和PI 3,4,5-三磷酸的增加，但渥曼青霉素阻断胰岛素刺激的葡萄糖转运，却不阻断钒酸盐或pV刺激的葡萄糖转运。钒酸盐和pV刺激葡萄糖转运蛋白（GLUTs）从细胞内区室转位至质膜；这种刺激未被渥曼青霉素阻断，但胰岛素诱导的GLUT转位受到抑制。在培养的H9c2心肌细胞中也获得了类似结果，在c-myc-GLUT4转染细胞中，渥曼青霉素不抑制葡萄糖转运或钒酸盐诱导的GLUT4转位。丝氨酸/苏氨酸激酶蛋白激酶B（PKB，即Akt/PKB/RAC-PK）被胰岛素激活，位于PI 3激酶下游，且与葡萄糖转运信号传导有关。胰岛素和pV刺激PKB活性，二者均被渥曼青霉素抑制。相比之下，在最大程度刺激葡萄糖转运的浓度下，钒酸盐并未显著增加PKB活性。为了确定蛋白激酶C（PKC）的潜在作用，用佛波酯肉豆蔻酸酯（PMA）长期孵育L6细胞，或用PKC抑制剂钙泊三醇C和双吲哚马来酰胺急性处理L6细胞。胰岛素、钒酸盐或pV刺激的葡萄糖转运未受抑制，渥曼青霉素和PKC抑制剂联合使用也未能阻断钒酸盐和pV的作用。相比之下，用细胞松弛素D破坏肌动蛋白网络，阻断了这三种物质对葡萄糖转运的刺激。总之，钒酸盐和pV能够通过一种独立于PI 3激酶和PKC的机制刺激葡萄糖转运和GLUT转位。与胰岛素类似，钒酸盐和pV刺激葡萄糖转运需要完整的肌动蛋白网络存在。
