Laitinen J, Hölttä E
Department of Pathology, University of Helsinki, Finland.
J Cell Biochem. 1994 Jun;55(2):155-67. doi: 10.1002/jcb.240550202.
The early response gene ornithine decarboxylase (odc) is indispensable for normal and malignant cell growth. Although DNA methylation is generally associated with chromatin condensation and gene inactivation, the odc gene is heavily methylated at CCGG-sequences in animal cell lines. In this work we analyzed the chromatin structure and the DNA methylation status at the CpG-rich promoter sequences at the odc locus in mouse 3T3 fibroblasts. We show that the proximal promoter region of the odc locus is not hypermethylated, while the distal promoter sequences appear to have a few methylated CCGG-sites and display methylation polymorphism. Furthermore, it was found that the 5' promoter region of odc is constitutively more sensitive to micrococcal nuclease than the coding and 3' regions of the odc gene. Stimulation of the cells with serum resulted in an appearance of a DNase I sensitive site at the promoter region. The chromatin structure of the mid-coding and 3' regions of the odc gene also underwent structural changes that were accompanied by the rapid accumulation of odc mRNA. Such changes were not detected in the chromatin structure of glyceraldehyde-3-phosphate dehydrogenase (gadph) gene, whose expression remains invariant upon serum stimulation. These data suggest that the chromatin structure may play an important role in the rapid transcriptional activation of odc and other immediate early genes during serum stimulation.
早期反应基因鸟氨酸脱羧酶（odc）对于正常细胞和恶性细胞的生长不可或缺。尽管DNA甲基化通常与染色质凝聚和基因失活相关，但在动物细胞系中，odc基因在CCGG序列处高度甲基化。在本研究中，我们分析了小鼠3T3成纤维细胞中odc基因座富含CpG的启动子序列处的染色质结构和DNA甲基化状态。我们发现odc基因座的近端启动子区域并未高度甲基化，而远端启动子序列似乎有一些甲基化的CCGG位点并表现出甲基化多态性。此外，我们发现odc基因的5'启动子区域比odc基因的编码区和3'区域对微球菌核酸酶的敏感性更高。用血清刺激细胞导致启动子区域出现一个对DNase I敏感的位点。odc基因的编码区中部和3'区域的染色质结构也发生了结构变化，并伴随着odc mRNA的快速积累。在3-磷酸甘油醛脱氢酶（gadph）基因的染色质结构中未检测到此类变化，其表达在血清刺激后保持不变。这些数据表明，染色质结构可能在血清刺激期间odc和其他立即早期基因的快速转录激活中起重要作用。
