ACTIVATION DOMAINS OF L-MYC AND C-MYC DETERMINE THEIR TRANSFORMING POTENCIES IN RAT EMBRYO CELLS
ACTIVATION DOMAINS OF L-MYC AND C-MYC DETERMINE THEIR TRANSFORMING POTENCIES IN RAT EMBRYO CELLS
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DOI：
10.1128/mcb.12.7.3130
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发表时间：
1992-07-01
影响因子：
5.3
通讯作者：
DANG, CV
中科院分区：
文献类型：
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作者：
BARRETT, J;BIRRER, MJ;DANG, CV
Myc 蛋白质家族的成员共享许多在基因转录调节因子中发现的蛋白质基序。 c-Myc N 端转录激活结构域中的保守氨基酸片段是共转化活性所必需的。大多数 Myc 蛋白含有基本的螺旋-环-螺旋拉链 (bHLH-Zip) DNA 结合基序，这也是 c-Myc 共转化活性所必需的。 L-Myc 是 myc 家族基因的产物，在许多人类肺癌中高度扩增，被发现可以与激活的 ras 基因共同转化原代大鼠胚胎细胞。然而，L-Myc 共转化活性仅为 c-Myc 的 1 至 10% (M. J. Birrer, S. Segal, J. S. DeGreve, F. Kaye, E. A. Sausville, and J. D. Minna, Mol. Cell. Biol. 8:2668-2673, 1988)。我们试图确定 c-Myc 和 L-Myc 在 N 端或 C 端结构域中的功能差异是否可以解释 L-Myc 共转化活性相对减弱。虽然 L-Myc 的 N 末端结构域与酵母 GAL4 DNA 结合结构域融合时可以激活转录，但其活性仅为相当的 c-Myc 结构域的 5%。接下来我们确定 L-Myc 或 c-Myc 的 C 端 bHLH-Zip 区域与 Myc 伴侣蛋白 Max 的相互作用在转染细胞中是等效的。发现 Max 表达载体可增强 L-Myc 和 c-Myc 的共转化活性。此外，L-Myc 的细菌合成 DNA 结合结构域（如 c-Myc 的 DNA 结合结构域）与纯化的 Max 蛋白异二聚化，以结合核心 DNA 序列 CACGTG。为了确定 L-Myc 负责其相对减弱的共转化活性的区域，我们构建了含有与 L-Myc 外显子融合的 c-Myc 外显子 2（构成激活结构域）和 3（构成 DNA 结合结构域）的嵌合体。将这些嵌合体的共转化效力与大鼠胚胎细胞中的全长 L-Myc 或 c-Myc 进行比较。相对共转化活性表明激活域的效力决定了 c-Myc 和 L-Myc 的共转化效率。这种相关性支持了 Myc 蛋白在肿瘤共转化中作为转录因子起作用的假设。
Members of the Myc family of proteins share a number of protein motifs that are found in regulators of gene transcription. Conserved stretches of amino acids found in the N-terminal transcriptional activation domain of c-Myc are required for cotransforming activity. Most of the Myc proteins contain the basic helix-loop-helix zipper (bHLH-Zip) DNA-binding motif which is also required for the cotransforming activity of c-Myc. L-Myc, the product of a myc family gene that is highly amplified in many human lung carcinomas, was found to cotransform primary rat embryo cells with an activated ras gene. However, L-Myc cotransforming activity was only 1 to 10% of that of c-Myc (M. J. Birrer, S. Segal, J. S. DeGreve, F. Kaye, E. A. Sausville, and J. D. Minna, Mol. Cell. Biol. 8:2668-2673, 1988). We sought to determine whether functional differences between c-Myc and L-Myc in either the N-terminal or the C-terminal domain could account for the relatively diminished L-Myc cotransforming activity. Although the N-terminal domain of L-Myc could activate transcription when fused to the yeast GAL4 DNA-binding domain, the activity was only 5% of that of a comparable c-Myc domain. We next determined that the interaction of the C-terminal bHLH-Zip region of L-Myc or c-Myc with that of a Myc partner protein, Max, was equivalent in transfected cells. A Max expression vector was found to augment the cotransforming activity of L-Myc as well as that of c-Myc. In addition, a bacterially synthesized DNA-binding domain of L-Myc, like that of c-Myc, heterodimerizes with purified Max protein to bind the core DNA sequence CACGTG. To determine the region of L-Myc responsible for its relatively diminished cotransforming activity, we constructed chimeras containing exons 2 (constituting activation domains) and 3 (constituting DNA-binding domains) of c-Myc fused to those of L-Myc. The cotransforming potencies of these chimeras were compared with those of full-length L-Myc or c-Myc in rat embryo cells. The relative cotransforming activities suggest that the potencies of the activation domains determine the cotransforming efficiencies for c-Myc and L-Myc. This correlation supports the hypothesis that the Myc proteins function in neoplastic cotransformation as transcription factors.