Harrison Rene E, Sikorski Barbara A, Jongstra Jan
Cell Biology Programme, The Hospital for Sick Children Research Institute, Toronto, Ontario, M5G 1X8, Canada.
J Cell Sci. 2004 Apr 15;117(Pt 10):2151-7. doi: 10.1242/jcs.00955.
The identification and characterization of scaffold and targeting proteins of the ERK/MAP kinase pathway is important to understand the function and intracellular organization of this pathway. The F-actin binding protein leukocyte-specific protein 1 (LSP1) binds to PKCbetaI and expression of B-LSP1, an LSP1 truncate containing the PKCbetaI binding residues, inhibits anti-IgM-induced translocation of PKCbetaI to the plasma membrane and anti-IgM-induced activation of ERK2. To understand the role of LSP1 in the regulation of PKCbetaI-dependent ERK2 activation, we investigated whether LSP1 interacts with ERK/MAP kinase pathway components and targets these proteins to the actin cytoskeleton. We show that LSP1 associates with the ERK scaffold protein KSR and with MEK1 and ERK2. LSP1-associated MEK1 is activated by anti-IgM treatment and this activation is inhibited by expression of B-LSP1, suggesting that the activation of LSP1-associated MEK1 is PKCbetaI dependent. Confocal microscopy showed that LSP1 targets KSR, MEK1 and ERK2 to peripheral actin filaments. Thus our data show that LSP1 is a cytoskeletal targeting protein for the ERK/MAP kinase pathway and support a model in which MEK1 and ERK2 are organized in a cytoskeletal signaling complex together with KSR, PKCbetaI and LSP1 and are activated by anti-IgM in a PKCbetaI-dependent manner.
识别和鉴定细胞外信号调节激酶/丝裂原活化蛋白激酶（ERK/MAP激酶）信号通路的支架蛋白和靶向蛋白，对于理解该信号通路的功能和细胞内组织至关重要。F-肌动蛋白结合蛋白白细胞特异性蛋白1（LSP1）与蛋白激酶CβI（PKCβI）结合，而B-LSP1（一种包含PKCβI结合残基的LSP1截短体）的表达会抑制抗IgM诱导的PKCβI向质膜的转位以及抗IgM诱导的ERK2激活。为了了解LSP1在PKCβI依赖性ERK2激活调节中的作用，我们研究了LSP1是否与ERK/MAP激酶信号通路的组分相互作用，并将这些蛋白靶向到肌动蛋白细胞骨架。我们发现LSP1与ERK支架蛋白激酶抑制蛋白（KSR）、MEK1和ERK2相关联。抗IgM处理可激活与LSP1相关的MEK1，而B-LSP1的表达可抑制这种激活，这表明与LSP1相关的MEK1的激活依赖于PKCβI。共聚焦显微镜显示LSP1将KSR、MEK1和ERK2靶向到外周肌动蛋白丝。因此，我们的数据表明LSP1是ERK/MAP激酶信号通路的细胞骨架靶向蛋白，并支持一种模型，即MEK1和ERK2与KSR、PKCβI和LSP1一起组织成细胞骨架信号复合物，并以PKCβI依赖性方式被抗IgM激活。
