Comprehensive isolation and functional analysis of the genes whose expressions are specifically induced upon entry into the Go phase of cell cycle

当培养液中胎牛血清浓度从10%降至0.5%时，哺乳动物细胞停止生长，进入静止期或G0期。认为G0期细胞所在的培养液中存在一定的增殖抑制因子，以维持细胞的静止状态。然而，关于G_0期的基因及其基因产物的研究报道甚少。因此，如果对其表达被诱导的基因进行大规模分离，就有可能分离出通过生长抑制功能维持静止阶段所需的基因。为了全面分离这些基因，我们使用了一种改进的cdna文库消减p，如前所述。利用这种方法，我们到目前为止已经能够分离到60多个在生长停滞条件下诱导表达的基因，并将其称为生长停滞诱导转录本，TIGA基因。一些TIGA基因的转录也是在接触抑制细胞生长时被诱导的。TIGA基因之一TIGA1编码一个带有单一跨膜基序的小蛋白。共表达的TIGA1对细胞生长有明显的抑制作用。对这些TIGA基因的功能分析可能有助于理解诱导和维持细胞周期G_0状态的分子机制。

Mammalian cells stops growth and enter into the static phase or G_0 phase when the concentration of fetal calf serum in the culture medium was reduced from 10% to 0.5%. It was believed that a certain proliferation inhibitory factors exist in the medium harboring the cells in the G_0 phase to maintain the static condition. However, very few studies have been reported on the genes and their gene products that define the G_0 phase. Thus, if a large scale isolation of the genes whose expression was induced is performed, it would be possible to isolate the gene that is required to maintain the static phase by growth-inhibitory function. To isolate such genes comprehensively, we used an improved cDNA library subtraction p as we described previously. Using this method, we have so far been able to isolate more than 60 genes whose expression is induced in growth arrest condition and termed the transcript induced in growth arrest, TIGA, genes. Transcription of some of the TIGA genes are also induced upon contact inhibition of the cell growth. One of the TIGA genes, TIGA1, encodes a small protein with a single transmembrane motif. Ecopically expressed Tiga1 potently inhibited cell growth. Functional analyses of these TIGA genes might shed light to understanding the molecular mechanisms of induction and maintenance of G_0 state of the cell cycle.