Meima Marcel E, Webb Bradley A, Witkowska H Ewa, Barber Diane L
Department of Cell and Tissue Biology, University of California, San Francisco, California 94143, USA.
J Biol Chem. 2009 Sep 25;284(39):26666-75. doi: 10.1074/jbc.M109.019448. Epub 2009 Jul 21.
The kinase Akt mediates signals from growth factor receptors for increased cell proliferation, survival, and migration, which contribute to the positive effects of Akt in cancer progression. Substrates are generally inhibited when phosphorylated by Akt; however, we show phosphorylation of the plasma membrane sodium-hydrogen exchanger NHE1 by Akt increases exchanger activity (H(+) efflux). Our data fulfill criteria for NHE1 being a bona fide Akt substrate, including direct phosphorylation in vitro, using mass spectrometry and Akt phospho-substrate antibodies to identify Ser(648) as the Akt phosphorylation site and loss of increased exchanger phosphorylation and activity by insulin and platelet-derived growth factor in fibroblasts expressing a mutant NHE1-S648A. How Akt induces actin cytoskeleton remodeling to promote cell migration and tumor cell metastasis is unclear, but disassembly of actin stress fibers by platelet-derived growth factor and insulin and increased proliferation in growth medium are inhibited in fibroblasts expressing NHE1-S648A. We predict that other functions shared by Akt and NHE1, including cell growth and survival, might be regulated by increased H(+) efflux.
激酶Akt介导来自生长因子受体的信号，促进细胞增殖、存活和迁移，这些作用对Akt在癌症进展中的积极影响有贡献。一般来说，Akt磷酸化其底物时底物会受到抑制；然而，我们发现Akt对质膜钠氢交换体NHE1的磷酸化会增加交换体活性（H⁺外流）。我们的数据符合NHE1是Akt真正底物的标准，包括体外直接磷酸化，使用质谱和Akt磷酸化底物抗体鉴定出Ser(648)为Akt磷酸化位点，以及在表达突变体NHE1-S648A的成纤维细胞中，胰岛素和血小板衍生生长因子导致的交换体磷酸化增加和活性增强现象消失。目前尚不清楚Akt如何诱导肌动蛋白细胞骨架重塑以促进细胞迁移和肿瘤细胞转移，但在表达NHE1-S648A的成纤维细胞中，血小板衍生生长因子和胰岛素导致的肌动蛋白应力纤维解聚以及生长培养基中细胞增殖增加受到抑制。我们预测，Akt和NHE1共有的其他功能，包括细胞生长和存活，可能受H⁺外流增加的调节。
