Department of Physiology, University of Tennessee Health Science Center, 894 Union Avenue, Memphis, TN, 38163, USA.
Apoptosis. 2014 Mar;19(3):467-79. doi: 10.1007/s10495-013-0944-1.
Polyamine-depletion inhibited apoptosis by activating ERK1/2, while, preventing JNK1/2 activation. MKP-1 knockdown by SiRNA increased ERK1/2, JNK1/2, and p38 phosphorylation and apoptosis. Therefore, we predicted that polyamines might regulate MKP1 via MEK/ERK and thereby apoptosis. We examined the role of MEK/ERK in the regulation of MKP1 and JNK, and p38 activities and apoptosis. Inhibition of MKP-1 activity with a pharmacological inhibitor, sanguinarine (SA), increased JNK1/2, p38, and ERK1/2 activities without causing apoptosis. However, pre-activation of these kinases by SA significantly increased camptothecin (CPT)-induced apoptosis suggesting different roles for MAPKs during survival and apoptosis. Inhibition of MEK1 activity prevented the expression of MKP-1 protein and augmented CPT-induced apoptosis, which correlated with increased activities of JNK1/2, caspases, and DNA fragmentation. Polyamine depleted cells had higher levels of MKP-1 protein and decreased JNK1/2 activity and apoptosis. Inhibition of MEK1 prevented MKP-1 expression and increased JNK1/2 and apoptosis. Phospho-JNK1/2, phospho-ERK2, MKP-1, and the catalytic subunit of PP2Ac formed a complex in response to TNF/CPT. Inactivation of PP2Ac had no effect on the association of MKP-1 and JNK1. However, inhibition of MKP-1 activity decreased the formation of the MKP-1, PP2Ac and JNK complex. Following inhibition by SA, MKP-1 localized in the cytoplasm, while basal and CPT-induced MKP-1 remained in the nuclear fraction. These results suggest that nuclear MKP-1 translocates to the cytoplasm, binds phosphorylated JNK and p38 resulting in dephosphorylation and decreased activity. Thus, MEK/ERK activity controls the levels of MKP-1 and, thereby, regulates JNK activity in polyamine-depleted cells.
多胺耗竭通过激活 ERK1/2 抑制细胞凋亡，同时抑制 JNK1/2 的激活。通过 siRNA 敲低 MKP-1 可增加 ERK1/2、JNK1/2 和 p38 的磷酸化和细胞凋亡。因此，我们预测多胺可能通过 MEK/ERK 调节 MKP1，从而调节细胞凋亡。我们研究了 MEK/ERK 在调节 MKP1 和 JNK、p38 的活性以及细胞凋亡中的作用。用药理学抑制剂血根碱（SA）抑制 MKP-1 的活性会增加 JNK1/2、p38 和 ERK1/2 的活性，但不会引起细胞凋亡。然而，SA 预先激活这些激酶会显著增加喜树碱（CPT）诱导的细胞凋亡，这表明 MAPK 在存活和凋亡过程中具有不同的作用。抑制 MEK1 的活性可防止 MKP-1 蛋白的表达，并增强 CPT 诱导的细胞凋亡，这与 JNK1/2、半胱天冬酶和 DNA 片段化活性的增加相关。多胺耗竭细胞具有更高水平的 MKP-1 蛋白和降低的 JNK1/2 活性和细胞凋亡。抑制 MEK1 可防止 MKP-1 的表达并增加 JNK1/2 和细胞凋亡。磷酸化 JNK1/2、磷酸化 ERK2、MKP-1 和 PP2Ac 的催化亚基在 TNF/CPT 作用下形成复合物。抑制 PP2Ac 对 MKP-1 和 JNK1 的结合没有影响。然而，抑制 MKP-1 的活性会降低 MKP-1、PP2Ac 和 JNK 复合物的形成。在用 SA 抑制后，MKP-1 定位于细胞质中，而基础和 CPT 诱导的 MKP-1 仍存在于核部分。这些结果表明，核 MKP-1 易位到细胞质中，与磷酸化的 JNK 和 p38 结合，导致去磷酸化和活性降低。因此，MEK/ERK 活性控制 MKP-1 的水平，从而调节多胺耗竭细胞中 JNK 的活性。
