Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10802942 | Biochimica et Biophysica Acta (BBA) - Molecular Cell Research | 2009 | 8 Pages |
Abstract
TIF-IA is a basal transcription factor of RNA polymerase I (Pol I) that is a major target of the JNK2 signaling pathway in response to ribotoxic stress. Using advanced fluorescence microscopy and kinetic modeling we elucidated the subcellular localization of TIF-IA and its exchange dynamics between the nucleolus, nucleoplasm and cytoplasm upon ribotoxic stress. In steady state, the majority of (GFP-tagged) TIF-IA was in the cytoplasm and the nucleus, a minor portion (7%) localizing to the nucleoli. We observed a rapid shuttling of GFP-TIF-IA between the different cellular compartments with a mean residence time of â¼Â 130 s in the nucleus and only â¼Â 30 s in the nucleoli. The import rate from the cytoplasm to the nucleus was â¼Â 3-fold larger than the export rate, suggesting an importin/exportin-mediated transport rather than a passive diffusion. Upon ribotoxic stress, GFP-TIF-IA was released from the nucleoli with a half-time of â¼Â 24 min. Oxidative stress and inhibition of protein synthesis led to a relocation of GFP-TIF-IA with slower kinetics while osmotic stress had no effect. The observed relocation was much slower than the nucleo-cytoplasmic and nucleus-nucleolus exchange rates of GFP-TIF-IA, indicating a time-limiting step upstream of the JNK2 pathway. In support of this, time-course experiments on the activity of JNK2 revealed the activation of the JNK kinase as the rate-limiting step.
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Authors
JÄdrzej SzymaÅski, Christine Mayer, Urs Hoffmann-Rohrer, Claudia Kalla, Ingrid Grummt, Matthias Weiss,