Sizer K M, Smith C L, Jacob C S, Swanson M L, Bleasdale J E
Upjohn Laboratories, Kalamazoo, MI 49001.
Mol Cell Endocrinol. 1994 Jul;103(1-2):1-12. doi: 10.1016/0303-7207(94)90063-9.
Activation of phosphoinositide 3-kinase (PI 3-kinase) is an early event in insulin signal transduction that is blocked completely in adipocytes from insulin-resistant KKAy mice. Treatment of KKAy mice with pioglitazone, an anti-diabetic thiazolidinedione, partially restores insulin-dependent changes in PI 3-kinase. The mechanism of this effect of pioglitazone was investigated using murine 3T3-L1 cells as an experimental model. Insulin and insulin-like growth factor I (IGF-I) each elicited rapid (within 2 min) and large (2-5-fold) increases in PI 3-kinase activity that could be immunoprecipitated using anti-phosphotyrosine (pY) antibodies. Maximal insulin-induced activity of PI 3-kinase in pY-immunoprecipitates was similar in 3T3-L1 adipocytes and mouse adipocytes, but the kinetics of activation differed. Insulin- and IGF-I-induced changes in PI 3-kinase were each half-maximal at 3-5 nM of hormone and were not additive. Increases in both insulin-induced and IGF-I-induced pY-immunoprecipitable PI 3-kinase activity were observed when 3T3-L1 fibroblasts became confluent and when they adopted the adipocyte phenotype. Pioglitazone (10 microM), administered either acutely or chronically to either 3T3-L1 adipocytes or 3T3-L1 fibroblasts, did not greatly alter the kinetics, magnitude or sensitivity of changes in PI 3-kinase elicited by either insulin or IGF-I. In contrast, the attenuation by isoproterenol of insulin-induced changes in PI 3-kinase was prevented in cells pretreated with pioglitazone. This effect of pioglitazone did not involve inhibition of isoproterenol-elicited accumulation of cyclic AMP. Pioglitazone also prevented attenuation of insulin induced changes in PI 3-kinase by cell penetrating analogs of cyclic AMP. Pioglitazone, therefore, has no direct effect on insulin-stimulated PI 3-kinase activity, but interferes with a cyclic AMP-dependent mechanism that normally antagonizes this action of insulin. These data support the proposition that the facilitation of insulin action by pioglitazone involves, at least in part, an inhibition of a negative control mechanism.
磷酸肌醇3激酶（PI 3激酶）的激活是胰岛素信号转导中的早期事件，在胰岛素抵抗的KKAy小鼠的脂肪细胞中该激活被完全阻断。用抗糖尿病噻唑烷二酮类药物吡格列酮治疗KKAy小鼠，可部分恢复PI 3激酶中胰岛素依赖性变化。使用鼠3T3-L1细胞作为实验模型研究了吡格列酮这种作用的机制。胰岛素和胰岛素样生长因子I（IGF-I）均可引起PI 3激酶活性迅速（2分钟内）且大幅（2至5倍）增加，这种增加的活性可用抗磷酸酪氨酸（pY）抗体进行免疫沉淀。在3T3-L1脂肪细胞和小鼠脂肪细胞中，胰岛素诱导的pY免疫沉淀物中PI 3激酶的最大活性相似，但激活动力学不同。胰岛素和IGF-I诱导的PI 3激酶变化在激素浓度为3至5 nM时均达到半数最大效应，且两者无相加作用。当3T3-L1成纤维细胞汇合以及转变为脂肪细胞表型时，胰岛素诱导和IGF-I诱导的pY免疫沉淀PI 3激酶活性均增加。急性或慢性给予3T3-L1脂肪细胞或3T3-L1成纤维细胞吡格列酮（10 microM），并不会显著改变胰岛素或IGF-I引起的PI 3激酶变化的动力学、幅度或敏感性。相反，在预先用吡格列酮处理的细胞中，异丙肾上腺素对胰岛素诱导的PI 3激酶变化的减弱作用被阻止。吡格列酮的这种作用并不涉及对异丙肾上腺素引起的环磷酸腺苷积累的抑制。吡格列酮还可防止环磷酸腺苷的细胞穿透类似物对胰岛素诱导的PI 3激酶变化的减弱作用。因此，吡格列酮对胰岛素刺激的PI 3激酶活性无直接作用，但可干扰通常拮抗胰岛素这种作用的环磷酸腺苷依赖性机制。这些数据支持这样的观点，即吡格列酮对胰岛素作用的促进至少部分涉及对负性控制机制的抑制。
