Traverse S, Gomez N, Paterson H, Marshall C, Cohen P
Department of Biochemistry, University of Dundee, Scotland, U.K.
Biochem J. 1992 Dec 1;288 ( Pt 2)(Pt 2):351-5. doi: 10.1042/bj2880351.
Stimulation of PC12 cells with nerve growth factor (NGF) increased mitogen-activated protein kinase kinase (MAPKK) activity > 20-fold after 5 min to a level that was largely sustained for at least 90 min. MAPKK activity was stimulated to a similar level by epidermal growth factor (EGF), but peaked at 2 min, declining thereafter and returning to basal levels after 60-90 min. Activation of MAPKK by either growth factor occurred prior to the activation of MAP kinase, consistent with MAPKK being the physiological activator of MAP kinase. The results demonstrate that the transient activation of MAPKK by EGF and its sustained activation by NGF underlies the transient and sustained activation of MAP kinase induced by EGF and NGF respectively. NGF or EGF induced the same two forms of MAPKK that were resolved on a Mono Q column. The Peak-1 MAPKK was activated initially and partially converted into the more acidic peak-2 MAPKK after prolonged growth-factor stimulation. The Peak-2 MAPKK was 20-fold more sensitive to inactivation by the catalytic subunit of protein phosphatase 2A. Stimulation with NGF caused a striking translocation of MAP kinase from the cytosol to the nucleus after 30 min, but not nuclear translocation of MAP kinase occurred after stimulation with EGF. The results suggest that sustained activation of the MAP kinase cascade may be required for MAP kinase to enter the nucleus, where it may initiate the gene transcription events required for neuronal differentiation of PC12 cells.
用神经生长因子（NGF）刺激PC12细胞5分钟后，丝裂原活化蛋白激酶激酶（MAPKK）的活性增加了20倍以上，并在很大程度上至少维持90分钟。表皮生长因子（EGF）可将MAPKK的活性刺激到类似水平，但在2分钟时达到峰值，此后下降，并在60 - 90分钟后恢复到基础水平。两种生长因子对MAPKK的激活均发生在MAP激酶激活之前，这与MAPKK作为MAP激酶的生理激活剂相一致。结果表明，EGF对MAPKK的瞬时激活及其被NGF的持续激活分别是EGF和NGF诱导的MAP激酶瞬时和持续激活的基础。NGF或EGF诱导出在Mono Q柱上分离出的两种相同形式的MAPKK。峰1 MAPKK最初被激活，在长时间生长因子刺激后部分转化为酸性更强的峰2 MAPKK。峰2 MAPKK对蛋白磷酸酶2A催化亚基失活的敏感性高20倍。用NGF刺激30分钟后，MAP激酶从细胞质显著转位至细胞核，但用EGF刺激后未发生MAP激酶的核转位。结果表明，MAP激酶级联的持续激活可能是MAP激酶进入细胞核所必需的，在细胞核中它可能启动PC12细胞神经元分化所需的基因转录事件。
