Phosphatidylinositol 3-kinase and mTOR signaling pathways regulate RNA polymerase I transcription in response to IGF-1 and nutrients

Martyn J. James, Joost C. B. M. Zomerdijk

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    Regulation of ribosomal RNA gene transcription by RNA polymerase I (Pol I) is fundamental to ribosome biogenesis and therefore protein translation capacity and cell growth, yet little is known of the key signaling cascades involved. We show here that insulin-like growth factor-1 (IGF-1)-induced Pol I transcription in HEK293 cells is entirely dependent on phosphatidylinositol 3-kinase (PI3K) activity and, additionally, is modulated by the mammalian target of rapamycin ( mTOR), which coordinates Pol I transcription with the availability of amino acids. The mitogen-activated protein kinase ( MAPK) pathway is weakly stimulated by IGF-1 in these cells and partly contributes to Pol I transcription regulation. Activation of Pol I transcription by IGF-1 results from enhancement of the activity of the Pol I transcription machinery and increased occupancy by SL1 of the endogenous tandemly repeated ribosomal promoters in vivo. The inputs from PI3K, mTOR, and MAPK pathways converge to direct appropriate rRNA gene expression by Pol I in the nucleolus of mammalian cells in response to environmental cues, such as growth factors and nutrients.

    Original languageEnglish
    Pages (from-to)8911-8918
    Number of pages8
    JournalJournal of Biological Chemistry
    Issue number10
    Publication statusPublished - 2004

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