GROWTH ARREST AND DNA DAMAGE INDUCIBLE GENE GADD153-- REGULATION BY DNA DAMAGE

gadd 153是一种哺乳动物基因，其表达响应于 各种 包括DNA损伤和生长停滞。 它 编码与CCAAT/增强子结合蛋白同源的19 kd蛋白 蛋白质（C/EBP）家族的转录因子。 这个家庭由 至少5个成员含有保守的bZIP羧基末端 域 bZIP结构域由参与DNA的碱性区域组成 识别和结合，和相邻的亮氨酸拉链区， 介导亚基二聚化。 gadd 153在C/EBP相关的 蛋白质不能与DNA结合。 但是，它可以形成稳定的 异源二聚体与C/EBP蛋白，并阻止其DNA结合，这表明 GADD 153作为这些转录激活因子的抑制剂。的 这些相互作用的功能意义及其与 应激后gadd 153表达的升高尚不清楚，但我们已经证实， 最近显示，另外两种C/EBP相关蛋白，C/EBP α和C/EBP 6， 也是由DNA损伤引起的。 我们已经研究了钙作为第二信使在调节 GADD 153表达，并且已经发现用钙处理细胞 离子载体A23187导致gadd 153 mRNA的快速诱导。 升高 mRNA水平的增加是由于gadd 153 转录和增强的稳定性gadd 153 mRNA。 缓冲 用BAPTA-AM处理细胞内钙可防止gadd 153 A23187和DNA烷化剂MMS的诱导。 照经上所 可能细胞内钙在控制GAD 153中起作用 DNA损伤后的表达。 各种蛋白激酶和磷酸酶的抑制剂也已被广泛应用。 测试了它们在DNA转染后影响gadd 153表达的能力， 损害 蛋白激酶C抑制剂不能抑制gadd 153 mRNA 诱导以及gadd 153启动子激活。 酪氨酸激酶 抑制剂（染料木黄酮和钒酸盐）也没有效果。 然而，在这方面， 两种常用的激酶抑制剂2-氨基嘌呤和H7均阻断gadd 153， mRNA表达。 冈田酸和calyculin，特异性抑制剂 磷酸酶1和2A，诱导gadd 153 mRNA表达，并增强 gadd 153启动子活性。 因此，gadd 153似乎是在 蛋白激酶和磷酸酶，尽管特定的酶 仍有待确认。

gadd153 is a mammalian gene whose expression is increased in response to a variety of stresses including DNA damage and growth arrest. It encodes a 19 kd protein with homology to the CCAAT/enhancer-binding protein (C/EBP) family of transcription factors. This family consists of at least 5 members which contain a conserved bZIP carboxyl-terminal domain. The bZIP domain consists of a basic region involved in DNA recognition and binding, and an adjacent leucine zipper region, that mediates subunit dimerization. gadd153 is unique among C/EBP-related proteins in that it cannot bind to DNA. However, it can form stable heterodimers with C/EBP proteins and prevent their DNA-binding, suggesting that gadd153 acts as an inhibitor of these transcriptional activators. The functional significance of these interactions and their relationship to elevated gadd153 expression following stress is unclear, but we have recently shown that two other C/EBP-related proteins, C/EBPa, and C/EBP6, are also induced by DNA damage. We have examined the role of calcium as a second messenger in regulating gadd153 expression and have found that treatment of cells with the calcium ionophore A23187 leads to the rapid induction of gadd153 mRNA. Elevated mRNA levels result from both an increase in the rate of gadd153 transcription and an enhanced stability of gadd153 mRNA. Buffering intracellular calcium by treatment with BAPTA-AM prevents gadd153 induction by both A23187 and the DNA alkylating agent MMS. Thus, it is likely that intracellular calcium plays a role in controlling gadd153 expression following DNA damage. Inhibitors of various protein kinase and phosphatases have also been tested for their ability to influence gadd153 expression following DNA damage. Protein kinase C inhibitors failed to inhibit gadd153 mRNA induction as well as gadd153 promoter activation by MMS. Tyrosine kinase inhibitors (genestein and vanadate) were also without effect. However, two general kinase inhibitors, 2-aminopurine and H7, both blocked gadd153 mRNA expression. Okadaic acid and calyculin, specific inhibitors of phosphatases 1 and 2A, induced gadd153 mRNA expression and enhanced gadd153 promoter activity. Thus, gadd153 appears to be under control of both protein kinase(s) and phosphatase(s), although the specific enzymes remain to be identified.