Flynn James M, Lannigan Deborah A, Clark David E, Garner Margaret H, Cammarata Patrick R
Dept. of Cell Biology and Genetics, Univ. of North Texas Health Science Center, 3500 Camp Bowie Blvd., Fort Worth, TX 76107, USA.
Am J Physiol Endocrinol Metab. 2008 Mar;294(3):E589-99. doi: 10.1152/ajpendo.00705.2007. Epub 2008 Jan 2.
17beta-Estradiol (E(2)) reduces oxidative stress-induced depolarization of mitochondrial membrane potential (MMP) in cultured human lens epithelial cells (HLE-B3). The mechanism by which the nongenomic effects of E(2) contributed to the protection against mitochondrial membrane depolarization was investigated. Mitochondrial membrane integrity is regulated by phosphorylation of BAD, and it is known that phosphorylation of Ser(112) inactivates BAD and prevents its participation in the mitochondrial death pathway. We found that E(2) rapidly increased both the phosphorylation of ERK2 and Ser(112) in BAD. Ser(112) is phosphorylated by p90 ribosomal S6 kinase (RSK), a Ser/Thr kinase, which is a downstream effector of ERK1/2. Inhibition of RSK by the RSK-specific inhibitor SL0101 did not reduce the level of E(2)-induced phosphorylation of Ser(112). Silencing BAD using small interfering RNA did not alter mitochondrial membrane depolarization elicited by peroxide insult. However, under the same conditions, silencing ERK2 dramatically increased membrane depolarization compared with the control small interfering RNA. Therefore, ERK2, functioning through a BAD-independent mechanism regulates MMP in humans lens epithelial cells. We propose that estrogen-induced activation of ERK2 acts to protect cells from acute oxidative stress. Moreover, despite the fact that ERK2 plays a regulatory role in mitochondrial membrane potential, estrogen was found to block mitochondrial membrane depolarization via an ERK-independent mechanism.
17β-雌二醇（E₂）可减轻氧化应激诱导的培养人晶状体上皮细胞（HLE-B3）线粒体膜电位（MMP）去极化。本研究探讨了E₂的非基因组效应有助于保护线粒体膜去极化的机制。线粒体膜完整性受BAD磷酸化调节，已知Ser¹¹²位点的磷酸化可使BAD失活并阻止其参与线粒体死亡途径。我们发现E₂可迅速增加ERK2和BAD中Ser¹¹²的磷酸化。Ser¹¹²由p90核糖体S6激酶（RSK）磷酸化，RSK是一种丝氨酸/苏氨酸激酶，是ERK1/2的下游效应器。RSK特异性抑制剂SL0101对RSK的抑制并未降低E₂诱导的Ser¹¹²磷酸化水平。使用小干扰RNA沉默BAD并未改变过氧化物损伤引起的线粒体膜去极化。然而，在相同条件下，与对照小干扰RNA相比，沉默ERK2显著增加了膜去极化。因此，ERK2通过不依赖BAD的机制调节人晶状体上皮细胞中的MMP。我们认为雌激素诱导的ERK2激活可保护细胞免受急性氧化应激。此外，尽管ERK2在线粒体膜电位中起调节作用，但发现雌激素通过不依赖ERK的机制阻止线粒体膜去极化。
