Pulmonary, Allergy, Critical Care and Sleep Medicine Division, Department of Medicine, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
Am J Physiol Lung Cell Mol Physiol. 2011 Nov;301(5):L765-71. doi: 10.1152/ajplung.00151.2011. Epub 2011 Aug 12.
We previously reported that the 3,5,3'-triiodo-L-thyronine (T3)-induced increase of Na-K-ATPase activity in rat alveolar epithelial cells (AECs) required activation of Src kinase, PI3K, and MAPK/ERK1/2. In the present study, we assessed the role of Akt in Na-K-ATPase activity and the interaction between the PI3K and MAPK in response to T3 by using MP48 cells, inhibitors, and constitutively active mutants in the MP48 (alveolar type II-like) cell line. The Akt inhibitor VIII blocked T3-induced increases in Na-K-ATPase activity and amount of plasma membrane Na-K-ATPase protein. The Akt inhibitor VIII also abolished the increase in Na-K-ATPase activity induced by constitutively active mutants of either Src kinase or PI3K. Moreover, constitutively active mutants of Akt increased Na-K-ATPase activity in the absence of T3. Thus activation of Akt was required for T3-induced Na-K-ATPase activity in AECs and is sufficient in the absence of T3. Inhibitors of Src kinase (PP1), PI3K (wortmannin), and ERK1/2 (U0126) all blocked the T3-induced Na-K-ATPase activity. PP1 blocked the activation of PI3K and also ERK1/2 by T3, whereas U0126 did not prevent T3 activation of Src kinase or PI3K activity. Wortmannin did not significantly alter T3-increased MAPK/ERK1/2 activity, suggesting that T3-activated PI3K/Akt and MAPK/ERK1/2 pathways acted downstream of the Src kinase. Furthermore, in the absence of T3, a constitutively active mutant of Src kinase increased activities of Na-K-ATPase, PI3K, and MAPK/ERK1/2. A constitutively active mutant of PI3K enhanced Na-K-ATPase activity but did not alter the MAPK/ERK1/2 activity significantly. In summary, in adult rat AECs T3-stimulated Src kinase activity can activate both PI3K/Akt and MAPK/ERK1/2, and activation of Akt is necessary for T3-induced Na-K-ATPase activity.
我们之前曾报道，三碘甲腺原氨酸（T3）诱导大鼠肺泡上皮细胞（AEC）中钠钾-ATP 酶活性增加需要激活Src 激酶、PI3K 和 MAPK/ERK1/2。在本研究中，我们通过使用 MP48 细胞、抑制剂和在 MP48（肺泡 II 型样）细胞系中组成型激活的突变体，评估 Akt 在钠钾-ATP 酶活性以及 PI3K 和 MAPK 相互作用对 T3 反应中的作用。Akt 抑制剂 VIII 阻断 T3 诱导的钠钾-ATP 酶活性和质膜钠钾-ATP 酶蛋白含量的增加。Akt 抑制剂 VIII 还消除了 Src 激酶或 PI3K 的组成型激活突变体诱导的钠钾-ATP 酶活性的增加。此外，Akt 的组成型激活突变体在没有 T3 的情况下增加钠钾-ATP 酶活性。因此，Akt 的激活对于 AEC 中 T3 诱导的钠钾-ATP 酶活性是必需的，并且在没有 T3 的情况下是足够的。Src 激酶抑制剂（PP1）、PI3K（wortmannin）和 ERK1/2（U0126）抑制剂均阻断 T3 诱导的钠钾-ATP 酶活性。PP1 阻断了 T3 对 PI3K 和 ERK1/2 的激活，而 U0126 并未阻止 T3 激活 Src 激酶或 PI3K 活性。wortmannin 并未显著改变 T3 增加的 MAPK/ERK1/2 活性，表明 T3 激活的 PI3K/Akt 和 MAPK/ERK1/2 途径位于 Src 激酶的下游。此外，在没有 T3 的情况下，Src 激酶的组成型激活突变体增加了钠钾-ATP 酶、PI3K 和 MAPK/ERK1/2 的活性。PI3K 的组成型激活突变体增强了钠钾-ATP 酶活性，但并未显著改变 MAPK/ERK1/2 活性。总之，在成年大鼠 AEC 中，T3 刺激的 Src 激酶活性可以激活 PI3K/Akt 和 MAPK/ERK1/2，而 Akt 的激活是 T3 诱导的钠钾-ATP 酶活性所必需的。
