Huang R P, Darland T, Okamura D, Mercola D, Adamson E D
La Jolla Cancer Research Foundation, California 92037.
Oncogene. 1994 May;9(5):1367-77.
The transcription factor Egr-1, stimulates the activity of a number of genes and inhibits other genes, by binding to the sequence GCGGGGGCG in 5' enhancer regions. However, the functions of Egr-1 are obscure in spite of its rather ubiquitous expression. Egr-1 may play a role in proliferation in mitogen-stimulated cells but its expression is also correlated with the differentiated state in teratocarcinoma cells. The constitutive expression of Egr-1 appears to have little effect on the growth rate of normal immortalized cell-lines. We show that in NIH3T3 cells that are conditionally transformed by the expression of v-six, the presence of Egr-1 is inhibitory to the production of transformed colonies (foci) and to growth in soft agar. In addition, the first appearance of tumors in nu/nu mice is delayed in tumorigenicity tests with cells that over-express Egr-1 and tumor growth is suppressed compared to control cells. We used a series of fragments of Egr-1 cloned into expression vectors to show that not only full length, but also truncated Egr-1 fragments inhibit colony formation. Using deletion mutants, we observed that this inhibitory activity is dependent on the presence of the DNA-binding 'zinc-finger' region. Wilm's tumor protein, WT1, (known to be a tumor suppressor gene) that exhibits the same DNA binding activity is also inhibitory. In contrast, colony formation is stimulated by an Egr-1 antisense RNA-expressing plasmid, since colonies grow rapidly and the colony-forming frequency is higher than in the presence of v-sis alone. We conclude that proteins containing the Egr-1 'zinc-finger' domain can bind to the regulatory regions of one or more genes that are required for the transformation of fibroblasts by v-sis thus inhibiting transformation. One function for Egr-1 implied by these results is the restraint of transformed growth in mitogen-stimulated cells.
转录因子Egr-1通过与5'增强子区域的GCGGGGGCG序列结合，刺激许多基因的活性并抑制其他基因。然而，尽管Egr-1表达相当普遍，但其功能仍不清楚。Egr-1可能在有丝分裂原刺激的细胞增殖中起作用，但其表达也与畸胎癌细胞的分化状态相关。Egr-1的组成型表达似乎对正常永生化细胞系的生长速率影响很小。我们发现，在通过v-sis表达进行条件转化的NIH3T3细胞中，Egr-1的存在会抑制转化菌落（集落）的产生以及在软琼脂中的生长。此外，在用过表达Egr-1的细胞进行的致瘤性试验中，裸鼠中肿瘤的首次出现延迟，并且与对照细胞相比肿瘤生长受到抑制。我们使用一系列克隆到表达载体中的Egr-1片段表明，不仅全长Egr-1，而且截短的Egr-1片段也抑制集落形成。使用缺失突变体，我们观察到这种抑制活性依赖于DNA结合“锌指”区域的存在。具有相同DNA结合活性的威尔姆斯瘤蛋白WT1（已知是一种肿瘤抑制基因）也具有抑制作用。相反，表达Egr-1反义RNA的质粒刺激集落形成，因为集落生长迅速且集落形成频率高于仅存在v-sis时。我们得出结论，含有Egr-1“锌指”结构域的蛋白质可以与v-sis转化成纤维细胞所需的一个或多个基因的调控区域结合，从而抑制转化。这些结果暗示Egr-1的一个功能是抑制有丝分裂原刺激的细胞中的转化生长。
