Drugs affecting microtubule dynamics increase alpha-tubulin mRNA accumulation via transcription in Tetrahymena thermophila.

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Abstract
In cultured mammalian cells, an increase in the amount of tubulin monomer due to treatment with a microtubule-depolymerizing agent results in a rapid decline in tubulin synthesis. This autoregulatory response is mediated through a posttranscriptional mechanism which decreases the stability of tubulin message with no change in transcriptional activity of tubulin genes. Conversely, treatment with a microtubule-polymerizing drug, such as taxol, results in a slight increase in the synthesis of tubulin. Surprisingly, we find that two microtubule-depolymerizing agents, colchicine and oryzalin, actually cause an increase in alpha-tubulin synthesis and alpha-tubulin message in starved Tetrahymena thermophila. This increase is paralleled by an increase in transcription of alpha-tubulin sequences measured by run-on transcription, while the half-life of tubulin message measured by decay in the presence of actinomycin D does not change appreciably. Treatment of starved cells with taxol also produces an increase in alpha-tubulin synthesis via an increase in message abundance due to an increase in transcription of the alpha-tubulin gene. These results indicate that tubulin synthesis in T. thermophila is regulated very differently than in cultured mammalian cells.