Inhibition of PI3-kinase signaling by glucocorticoids results in increased branched-chain amino acid degradation in renal epithelial cells.
Inhibition of PI3-kinase signaling by glucocorticoids results in increased branched-chain amino acid degradation in renal epithelial cells.
复制标题
DOI：
10.1152/ajpcell.00617.2006
复制
发表时间：
2007-05
期刊：
影响因子：
--
通讯作者：
Xiaonan H. Wang;Junping Hu;S. Price
中科院分区：
文献类型：
--
作者：
Xiaonan H. Wang;Junping Hu;S. Price
磷脂酰肌醇3-激酶（PI 3 K）是一种参与多种代谢功能调控的关键酶。糖皮质激素已被证明在某些非肾细胞类型中减弱PI 3 K信号传导，这提高了糖皮质激素在肾细胞中的某些生理作用可能通过类似机制实现的可能性。因此，我们测试了糖皮质激素是否通过LLC-PK 1-GR 101肾上皮细胞中的胰岛素受体底物（IRS）-1/PI3K/Akt信号级联影响信号传导。用地塞米松处理细胞24小时：1）抑制IRS-1相关的PI 3 K活性和Akt磷酸化，2）增加PI 3 K p85调节亚基的水平，但不增加p110催化亚基的水平，3）诱导IRS-1在抑制性Ser（307）上的磷酸化。我们以前曾报道，糖皮质激素增加支链酮酸脱氢酶（BCKD）的活性在LLC-PK 1-GR 101细胞。这种反应部分是通过改变BCKD亚基和BCKD激酶的转录来实现的，BCKD激酶通过磷酸化使酶复合物失活。因此，我们测试了PI 3 K信号传导的抑制是否会通过增加支链氨基酸降解来模拟糖皮质激素。显性负性PI 3 K p85调节亚基（Adp 85 DeltaiSH 2）的表达增加BCKD活性，并且地塞米松没有进一步刺激酶活性。使用LY-294002抑制PI 3 K增加了BCKD E2亚基的转录，但不增加E1 α亚基或BCKD激酶的转录。因此，糖皮质激素通过IRS-1/PI 3 K/Akt途径抑制信号传导，结果增加支链氨基酸催化剂。
Phosphatidylinositol 3-kinase(PI3K) is a pivotal enzyme involved in the control of a variety of diverse metabolic functions. Glucocorticoids have been shown to attenuate PI3K signaling in some nonrenal cell types, raising the possibility that some physiological effects of glucocorticoids in renal cells may be achieved by a similar mechanism. Therefore, we tested whether glucocorticoids affect signaling through the insulin receptor substrate (IRS)-1/PI3K/Akt signaling cascade in LLC-PK1-GR101 renal epithelial cells. Treatment of cells with dexamethasone for 24 h: 1) suppressed IRS-1-associated PI3K activity and Akt phosphorylation, 2) increased the level of the PI3K p85 regulatory subunit but not the p110 catalytic subunit, and 3) induced the phosphorylation of IRS-1 on inhibitory Ser(307). We have previously reported that glucocorticoids increase branched-chain ketoacid dehydrogenase (BCKD) activity in LLC-PK1-GR101 cells. This response was achieved, in part, by alterations in the transcription of BCKD subunits and BCKD kinase, which inactivates the enzyme complex by phosphorylation. Therefore, we tested whether inhibition of PI3K signaling would mimick glucocorticoids by increasing branched-chain amino acid degradation. Expression of a dominant negative PI3K p85 regulatory subunit (Adp85DeltaiSH2) increased BCKD activity, and dexamethasone did not further stimulate enzyme activity. Inhibition of PI3K using LY-294002 increased the transcription of the BCKD E2 subunit but not the E1alpha subunit or BCKD kinase. Thus, glucocorticoids inhibit signaling through the IRS-1/PI3K/Akt pathway with a consequence of increased branched-chain amino acid catabolism.