Microtubule-dependent subcellular redistribution of the transcriptional coactivator p/CIP.
The transcriptional coactivator p/CIP is a member of a family of nuclear receptor coactivator/steroid receptor coactivator (NCoA/SRC) proteins that mediate the transcriptional activities of nuclear hormone receptors. We have found that p/CIP is predominantly cytoplasmic in a large proportion of cells in various tissues of the developing mouse and in a number of established cell lines. In mouse embryonic fibroblasts, serum deprivation results in the redistribution of p/CIP to the cytoplasmic compartment and stimulation with growth factors or tumor-promoting phorbol esters promotes p/CIP shuttling into the nucleus. Cytoplasmic accumulation of p/CIP is also cell cycle dependent, occurring predominantly during the S and late M phases. Leptomycin B (LMB) treatment results in a marked nuclear accumulation, suggesting that p/CIP undergoes dynamic nuclear export as well as import. We have identified a strong nuclear import signal in the N terminus of p/CIP and two leucine-rich motifs in the C terminus that resemble CRM-1-dependent nuclear export sequences. When fused to green fluorescent protein, the nuclear export sequence region is cytoplasmic and is retained in the nucleus in an LMB-dependent manner. Disruption of the leucine-rich motifs prevents cytoplasmic accumulation. Furthermore, we demonstrate that cytoplasmic p/CIP associates with tubulin and that an intact microtubule network is required for intracellular shuttling of p/CIP. Immunoaffinity purification of p/CIP from nuclear and cytosolic extracts revealed that only nuclear p/CIP complexes possess histone acetyltransferase activity. Collectively, these results suggest that cellular compartmentalization of NCoA/SRC proteins could potentially regulate nuclear hormone receptor-mediated events as well as integrating signals in response to different environmental cues.
Cancer Research Laboratories, London Regional Cancer Centre, Ontario, Canada.
Majdi S
MS
Qutob
Rabindra N
RN
Bhattacharjee
Elisa
E
Pollari
Siu Pok
SP
Yee
Joseph
J
Torchia
D016475:3T3 Cells; D000123:Acetyltransferases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002453:Cell Cycle; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D006367:HeLa Cells; D051548:Histone Acetyltransferases; D006801:Humans; D007150:Immunohistochemistry; D007930:Leucine / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D008870:Microtubules / Q000378:metabolism*; D008969:Molecular Sequence Data; D056921:Nuclear Receptor Coactivator 3; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000378:metabolism* / Q000502:physiology*; D015533:Transcriptional Activation
D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D000123:Acetyltransferases; D051548:Histone Acetyltransferases; C538866:NCOA3 protein, human; C538867:Ncoa3 protein, mouse; D056921:Nuclear Receptor Coactivator 3; D007930:Leucine