Sato N, Sakamaki K, Terada N, Arai K, Miyajima A
DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, CA 94304.
EMBO J. 1993 Nov;12(11):4181-9. doi: 10.1002/j.1460-2075.1993.tb06102.x.
The high-affinity receptors for granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin 3 (IL-3) and IL-5 consist of two subunits, alpha and beta. The alpha subunits are specific to each cytokine and the same beta subunit (beta c) is shared by these three receptors. Although none of these receptor subunits has intrinsic kinase activity, these cytokines induce protein tyrosine phosphorylation, activation of Ras, Raf-1 and MAP kinase, and transcriptional activation of nuclear proto-oncogenes such as c-myc, c-fos and c-jun. In this paper, we describe a detailed analysis of the signaling potential of the beta c subunit by using a series of cytoplasmic deletion mutants. The human beta c consists of 881 amino acid residues. A C-terminal deletion mutant of beta c at amino acid 763 (beta 763) induced phosphorylation of Shc and activation of Ras, Raf-1, MAP kinase and p70 S6 kinase, whereas a deletion at amino acid 626 (beta 626) induced none of these effects. The beta 763 mutant, as well as the full-length beta c, induced transcription of c-myc, c-fos and c-jun. Deletions at amino acid 517 (beta 517) and 626 (beta 626) induced c-myc and pim-1, but no induction of c-fos and c-jun was observed. GM-CSF increased phosphatidylinositol 3 kinase (PI3-K) activity in anti-phosphotyrosine immunoprecipitates from cells expressing beta 763 as well as beta c, whereas it was only marginally increased from cells expressing beta 517 or beta 626. Thus, there are at least two distinct regions within the cytoplasmic domain of beta c that are responsible for different signals, i.e. a membrane proximal region of approximately 60 amino acid residues upstream of Glu517 is essential for induction of c-myc and pim-1, and a distal region of approximately 140 amino acid residues (between Leu626 and Ser763) is required for activation of Ras, Raf-1, MAP kinase and p70 S6 kinase, as well as induction of c-fos and c-jun.
粒细胞-巨噬细胞集落刺激因子（GM-CSF）、白细胞介素3（IL-3）和IL-5的高亲和力受体由α和β两个亚基组成。α亚基对每种细胞因子具有特异性，这三种受体共享相同的β亚基（βc）。尽管这些受体亚基均无内在激酶活性，但这些细胞因子可诱导蛋白酪氨酸磷酸化、Ras、Raf-1和丝裂原活化蛋白激酶（MAP激酶）的激活，以及核原癌基因如c-myc、c-fos和c-jun的转录激活。在本文中，我们通过使用一系列胞质缺失突变体详细分析了βc亚基的信号转导潜能。人βc由881个氨基酸残基组成。βc在氨基酸763处的C末端缺失突变体（β763）可诱导Shc磷酸化以及Ras、Raf-1、MAP激酶和p70 S6激酶的激活，而在氨基酸626处的缺失突变体（β626）则未诱导这些效应。β763突变体以及全长βc均可诱导c-myc、c-fos和c-jun的转录。在氨基酸517（β517）和626（β626）处的缺失可诱导c-myc和pim-1，但未观察到c-fos和c-jun的诱导。GM-CSF可增加表达β763以及βc的细胞中抗磷酸酪氨酸免疫沉淀物中的磷脂酰肌醇3激酶（PI3-K）活性，而表达β517或β626的细胞中该活性仅略有增加。因此，βc胞质结构域内至少有两个不同区域负责不同信号，即Glu517上游约60个氨基酸残基的膜近端区域对于c-myc和pim-1的诱导至关重要，而约140个氨基酸残基的远端区域（位于Leu626和Ser763之间）对于Ras、Raf-1、MAP激酶和p70 S6激酶的激活以及c-fos和c-jun的诱导是必需的。
