Elberg G, Li J, Shechter Y
Department of Hormone Research, Weizmann Institute of Science, Rehovot, Israel.
J Biol Chem. 1994 Apr 1;269(13):9521-7.
We have shown that vanadium mimics several insulin effects in rat adipocytes, via a staurosporine sensitive cytosolic protein tyrosine kinase (CytPTK; Shisheva, A., and Shechter, Y. (1993) J. Biol. Chem. 268, 6463). Here we demonstrate that vanadium effects on protein tyrosine kinases are preserved after cell disintegration. Vanadium inhibits or activates protein tyrosine kinases depending on its oxidation state and the tyrosine kinase studied. Vanadyl (4+) but not vanadate (5+) inhibits receptor tyrosine kinases such as the insulin receptor (IC50 value = 23 +/- 4 microM) and the insulin-like growth factor-I receptor (IC50 = 19 +/- 3 microM). Inhibition is non-competitive with respect to ATP, Mn2+, or substrate concentrations. Preincubation of adipocytes with vanadyl (0.4 mM), and staurosporine (which arrests the cytosolic enzyme) substantially inhibited insulin-stimulated lipogenesis. Vanadyl is readily oxidized to vanadate by hydrogen peroxide. In contrast, CytPTKs were poorly inhibited by vanadyl, and vanadate stimulated several CytPTKs 2-6 fold. CytPTK derived from rat adipocytes, liver and brain were activated, and CytPTK from Nb2 lymphoma cells was not affected. CytPTK extracted from insulin-responsive tissues are more sensitive to vanadate activation (ED50 = 3 +/- 0.7 microM), whereas the brain enzyme is less sensitive (ED50 = 27 +/- 3 microM). Tungstate, molybdate, and phenylarsine oxide also stimulate CytPTK, suggesting that the vanadate effect is secondary to inhibiting protein phosphotyrosine phosphatases. This study supports a working hypothesis implicating the intracellular vanadyl pool in modulating CytPTK activity. Any physiological conditions converting vanadyl to vanadate (i.e. H2O2 production) will activate CytPTK and consequently CytPTK-dependent bioeffects.
我们已经表明，钒通过一种对星形孢菌素敏感的胞质蛋白酪氨酸激酶（CytPTK；希舍娃，A.，和谢克特，Y.（1993年）《生物化学杂志》268卷，6463页）模拟了大鼠脂肪细胞中的几种胰岛素效应。在此我们证明，细胞裂解后钒对蛋白酪氨酸激酶的作用依然存在。钒对蛋白酪氨酸激酶的抑制或激活作用取决于其氧化态以及所研究的酪氨酸激酶。氧钒根离子（4 +）而非钒酸根离子（5 +）抑制受体酪氨酸激酶，如胰岛素受体（IC50值 = 23 ± 4微摩尔）和胰岛素样生长因子 - I受体（IC50 = 19 ± 3微摩尔）。这种抑制作用对于ATP、Mn2 +或底物浓度而言是非竞争性的。用氧钒根离子（0.4毫摩尔）和星形孢菌素（它能抑制胞质酶）预孵育脂肪细胞，可显著抑制胰岛素刺激的脂肪生成。氧钒根离子很容易被过氧化氢氧化成钒酸根离子。相比之下，氧钒根离子对CytPTK的抑制作用较弱，而钒酸根离子可使几种CytPTK的活性提高2 - 6倍。源自大鼠脂肪细胞、肝脏和大脑的CytPTK被激活，而来自Nb2淋巴瘤细胞的CytPTK未受影响。从胰岛素反应性组织中提取的CytPTK对钒酸根离子激活更为敏感（ED50 = 3 ± 0.7微摩尔），而脑内的该酶则较不敏感（ED50 = 27 ± 3微摩尔）。钨酸盐、钼酸盐和苯砷氧化物也能刺激CytPTK，这表明钒酸根离子的作用是抑制蛋白酪氨酸磷酸酶的继发效应。本研究支持了一个工作假说，即细胞内的氧钒根离子库参与调节CytPTK的活性。任何将氧钒根离子转化为钒酸根离子的生理条件（即产生过氧化氢）都将激活CytPTK，进而激活依赖于CytPTK的生物效应。
