Sakurai T, Abe Y, Kasuya Y, Takuwa N, Shiba R, Yamashita T, Endo T, Goto K
Department of Pharmacology, University of Tsukuba, Ibaraki, Japan.
J Biol Chem. 1994 May 13;269(19):14118-22.
Activin A stimulated DNA synthesis and transient c-fos expression in quiescent Swiss 3T3 fibroblasts. The activin A-induced DNA synthesis was dose-dependent with a half-maximal effect obtained at 0.3 nM. The maximal response obtained at 10 nM was comparable with that induced by 5 ng/ml basic fibroblast growth factor. Swiss 3T3 fibroblasts expressed abundant high affinity binding sites for 125I-labeled activin A with a Kd value of 0.63 nM and the number of binding sites at 24,000/cell. Northern blot analysis revealed that Swiss 3T3 fibroblasts express a high level of type II activin receptor mRNA. In an attempt to elucidate the mechanism of mitogenic action of activin A, we examined the effect of activin A on mitogen-activated protein kinase activation. Unexpectedly, however, activin A did not induce kinase activation under conditions in which basic fibroblast growth factor and endothelin-1 at similar or even less potent mitogenic concentrations did. Furthermore, activin A did not induce phosphorylation of the Erk2 species of mitogen-activated protein kinase. These observations strongly suggest that the activation of mitogen-activated protein kinase is not a necessary step for activin A-induced DNA synthesis in Swiss 3T3 fibroblasts.
激活素A可刺激静止的瑞士3T3成纤维细胞中的DNA合成及瞬时c-fos表达。激活素A诱导的DNA合成呈剂量依赖性，在0.3 nM时可达到半数最大效应。在10 nM时获得的最大反应与5 ng/ml碱性成纤维细胞生长因子诱导的反应相当。瑞士3T3成纤维细胞表达大量高亲和力的125I标记激活素A结合位点，解离常数（Kd）值为0.63 nM，每个细胞的结合位点数为24,000个。Northern印迹分析显示，瑞士3T3成纤维细胞表达高水平的II型激活素受体mRNA。为了阐明激活素A的促有丝分裂作用机制，我们研究了激活素A对丝裂原活化蛋白激酶激活的影响。然而，出乎意料的是，在碱性成纤维细胞生长因子和内皮素-1处于相似甚至更低促有丝分裂浓度的条件下，激活素A并未诱导激酶激活。此外，激活素A并未诱导丝裂原活化蛋白激酶的Erk2亚型发生磷酸化。这些观察结果强烈表明，丝裂原活化蛋白激酶的激活并非激活素A诱导瑞士3T3成纤维细胞DNA合成的必要步骤。
