Aziz N, Cherwinski H, McMahon M
Department of Cell Signaling, DNAX Research Institute, Palo Alto, California 94304-1104, USA.
Mol Cell Biol. 1999 Feb;19(2):1101-15. doi: 10.1128/MCB.19.2.1101.
Ras-activated signal transduction pathways are implicated in the control of cell proliferation, differentiation, apoptosis, and tumorigenesis, but the molecular mechanisms mediating these diverse functions have yet to be fully elucidated. Conditionally active forms of Raf, v-Src, and MEK1 were used to identify changes in gene expression that participate in oncogenic transformation, as well as in normal growth control. Activation of Raf, v-Src, and MEK1 led to induced expression of c-Myc and cyclin D1. Induction of c-Myc mRNA by Raf was an immediate-early response, whereas the induction of cyclin D1 mRNA was delayed and inhibited by cycloheximide. Raf activation also resulted in the induction of an established c-Myc target gene, ornithine decarboxylase (ODC). ODC induction by Raf was mediated, in part, by tandem E-boxes contained in the first intron of the gene. Activation of the human colony-stimulating factor 1 (CSF-1) receptor in NIH 3T3 cells leads to activation of the mitogen-activated protein (MAP) kinase pathway and induced expression of c-Fos, c-Myc, and cyclin D1, leading to a potent mitogenic response. By contrast, a mutated form of this receptor fails to activate the MAP kinases or induce c-Myc and cyclin D1 expression and fails to elicit a mitogenic response. The biological significance of c-Myc and cyclin D1 induction by Raf and v-Src was confirmed by the demonstration that both of these protein kinases complemented the signaling and mitogenic defects of cells expressing this mutated form of the human CSF-1 receptor. Furthermore, the induction of c-Myc and cyclin D1 by oncogenes and growth factors was inhibited by PD098059, a specific MAP kinase kinase (MEK) inhibitor. These data suggest that the Raf/MEK/MAP kinase pathway plays an important role in the regulation of c-Myc and cyclin D1 expression in NIH 3T3 cells. The ability of oncogenes such as Raf and v-Src to regulate the expression of these proteins reveals new lines of communication between cytosolic signal transducers and the cell cycle machinery.
Ras激活的信号转导通路与细胞增殖、分化、凋亡及肿瘤发生的调控有关，但介导这些多样功能的分子机制尚未完全阐明。使用Raf、v-Src和MEK1的条件活性形式来鉴定参与致癌转化以及正常生长控制的基因表达变化。Raf、v-Src和MEK1的激活导致c-Myc和细胞周期蛋白D1的诱导表达。Raf诱导c-Myc mRNA是一种早期快速反应，而细胞周期蛋白D1 mRNA的诱导则延迟且受环己酰亚胺抑制。Raf激活还导致一个已确定的c-Myc靶基因鸟氨酸脱羧酶（ODC）的诱导。Raf对ODC的诱导部分由该基因第一个内含子中包含的串联E盒介导。NIH 3T3细胞中人集落刺激因子1（CSF-1）受体的激活导致丝裂原活化蛋白（MAP）激酶通路的激活以及c-Fos、c-Myc和细胞周期蛋白D1的诱导表达，从而产生强烈的促有丝分裂反应。相比之下，该受体的突变形式无法激活MAP激酶或诱导c-Myc和细胞周期蛋白D1的表达，也无法引发促有丝分裂反应。通过证明这两种蛋白激酶都能弥补表达这种人CSF-1受体突变形式的细胞的信号传导和促有丝分裂缺陷，证实了Raf和v-Src诱导c-Myc和细胞周期蛋白D1的生物学意义。此外，原癌基因和生长因子对c-Myc和细胞周期蛋白D1的诱导受到特异性MAP激酶激酶（MEK）抑制剂PD098059的抑制。这些数据表明，Raf/MEK/MAP激酶通路在NIH 3T3细胞中c-Myc和细胞周期蛋白D1表达的调控中起重要作用。Raf和v-Src等原癌基因调节这些蛋白质表达的能力揭示了胞质信号转导器与细胞周期机制之间新的通信线路。
