Li S, Wattenberg E V
School of Public Health, University of Minnesota, Minneapolis 55455, USA.
Toxicol Appl Pharmacol. 1998 Aug;151(2):377-84. doi: 10.1006/taap.1998.8471.
We previously demonstrated that the marine toxin and skin tumor promoter palytoxin activates the stress-activated protein kinase/c-Jun N-terminal kinase (JNK), but not the extracellular signal-regulated kinase (ERK), which is typically activated by mitogenic agents. JNK, ERK, and p38, another stress-activated protein kinase, are members of the mitogen-activated protein (MAP) kinase family of serine/threonine kinases, which coordinate the transmission of various signals through the cell. The Na+,K+-ATPase is the putative palytoxin receptor. Therefore, we hypothesized that the Na+,K+-ATPase inhibitor ouabain might also stimulate signaling pathways that activate MAP kinases. Using HeLa and COS7 cells, we found that, although there are similarities between the protein kinase cascades by which palytoxin and ouabain activate JNK, there are also significant differences between the activation of specific MAP kinases by palytoxin and ouabain. Transient expression of dominant negative mutants indicates that ouabain, like palytoxin, activates JNK through a protein kinase cascade that involves the JNK kinase SEK1 but does not require the GTPase Ras. Palytoxin activates JNK and p38 to a greater extent than ouabain. By contrast, ouabain activates ERK to a greater extent than palytoxin. Ouabain blocked palytoxin-stimulated activation of JNK and p38, but not anisomycin-stimulated activation of these kinases, supporting the conclusion that ouabain and palytoxin bind to the same site on the Na+,K+-ATPase. These results suggest that the Na+,K+-ATPase can differentially mediate the activation of MAP kinases by two diverse ligands, palytoxin and ouabain.
我们之前证实，海洋毒素及皮肤肿瘤启动子刺尾鱼毒素可激活应激激活蛋白激酶/c-Jun氨基末端激酶（JNK），但不会激活通常由促有丝分裂剂激活的细胞外信号调节激酶（ERK）。JNK、ERK以及另一种应激激活蛋白激酶p38均为丝氨酸/苏氨酸激酶的丝裂原激活蛋白（MAP）激酶家族成员，它们共同协调各种信号在细胞内的传递。Na⁺,K⁺-ATP酶被认为是刺尾鱼毒素的受体。因此，我们推测Na⁺,K⁺-ATP酶抑制剂哇巴因可能也会刺激激活MAP激酶的信号通路。利用HeLa细胞和COS7细胞，我们发现，尽管刺尾鱼毒素和哇巴因激活JNK的蛋白激酶级联反应存在相似之处，但刺尾鱼毒素和哇巴因对特定MAP激酶的激活也存在显著差异。显性负性突变体的瞬时表达表明，哇巴因与刺尾鱼毒素一样，通过一个涉及JNK激酶SEK1但不需要GTP酶Ras的蛋白激酶级联反应来激活JNK。刺尾鱼毒素比哇巴因更能激活JNK和p-38。相比之下，哇巴因比刺尾鱼毒素更能激活ERK。哇巴因可阻断刺尾鱼毒素刺激的JNK和p-38激活，但不能阻断茴香霉素刺激的这些激酶激活，这支持了哇巴因和刺尾鱼毒素结合到Na⁺,K⁺-ATP酶上同一部位的结论。这些结果表明，Na⁺,K⁺-ATP酶可通过两种不同配体——刺尾鱼毒素和哇巴因——差异性地介导MAP激酶的激活。
