Gu L, Gaertig J, Stargell L A, Gorovsky M A
Department of Biology, University of Rochester, New York 14627, USA.
Mol Cell Biol. 1995 Sep;15(9):5173-9. doi: 10.1128/MCB.15.9.5173.
Mammalian cells regulate tubulin mRNA abundance by a posttranscriptional mechanism dependent on the concentration of tubulin monomer. Treatment of mammalian cells with microtubule-depolymerizing drugs and microtubule-polymerizing drugs causes decreases and increases in tubulin mRNA, respectively (D. W. Cleveland, Curr. Opin. Cell Biol. 1:10-14, 1989). In striking contrast to the case with mammalian cells, perturbation of microtubules in Tetrahymena thermophila by microtubule-depolymerizing or -polymerizing drugs increases the level of the single alpha-tubulin gene message by increasing transcription (L. A. Stargell, D. P. Heruth, J. Gaertig, and M. A. Gorovsky, Mol. Cell. Biol. 12:1443-1450, 1992). In this report we show that antimicrotubule drugs preferentially induce the expression of one of two beta-tubulin genes (BTU1) in T. thermophila. In contrast, deciliation induces expression of both beta-tubulin genes. Tubulin gene expression was examined in a mutant strain created by transformation with an in vitro-mutagenized beta-tubulin gene that conferred resistance to microtubule-depolymerizing drugs and sensitivity to the polymerizing drug taxol and in a strain containing a nitrosoguanidine-induced mutation in the single alpha-tubulin gene that conferred the same pattern of drug sensitivities. In both cases the levels of tubulin mRNA expression from the drug-inducible BTU1 gene in the mutant cells paralleled the altered growth sensitivities to microtubule drugs. These studies demonstrate that T. thermophila has distinct, gene-specific mechanisms for modulating tubulin gene expression depending on whether ciliary or cytoplasmic microtubules are involved. They also show that the cytoplasmic microtubule cytoskeleton itself participates in a signal transduction pathway that regulates specific tubulin gene transcription in T. thermophila.
哺乳动物细胞通过一种依赖于微管蛋白单体浓度的转录后机制来调节微管蛋白mRNA丰度。用微管解聚药物和微管聚合药物处理哺乳动物细胞，分别会导致微管蛋白mRNA减少和增加（D. W. 克利夫兰，《细胞生物学当前观点》1:10 - 14，1989年）。与哺乳动物细胞的情况形成显著对比的是，用微管解聚或聚合药物扰动嗜热四膜虫中的微管，会通过增加转录来提高单个α-微管蛋白基因信息的水平（L. A. 斯塔格尔、D. P. 赫鲁斯、J. 盖尔蒂格和M. A. 戈罗夫斯基，《分子与细胞生物学》12:1443 - 1450，1992年）。在本报告中，我们表明抗微管药物优先诱导嗜热四膜虫中两个β-微管蛋白基因之一（BTU1）的表达。相比之下，去纤毛作用会诱导两个β-微管蛋白基因的表达。在一个通过用体外诱变的β-微管蛋白基因转化而产生的突变菌株中检测了微管蛋白基因表达，该突变菌株对微管解聚药物具有抗性，对聚合药物紫杉醇敏感，并且在一个单个α-微管蛋白基因中含有亚硝基胍诱导突变的菌株中也检测了微管蛋白基因表达，该菌株具有相同的药物敏感性模式。在这两种情况下，突变细胞中药物诱导的BTU1基因的微管蛋白mRNA表达水平与对微管药物改变的生长敏感性平行。这些研究表明，嗜热四膜虫具有不同的、基因特异性的机制来调节微管蛋白基因表达，这取决于涉及的是纤毛微管还是细胞质微管。它们还表明，细胞质微管细胞骨架本身参与了一条信号转导途径，该途径调节嗜热四膜虫中特定微管蛋白基因的转录。
