The regulation of the activity of transcription factors by controlling their distribution between cytoplasm and nucleus is well known. Qutob et al. extend this observation to a member of the steroid receptor coactivator (SRC) family, p300/CBP-interacting protein (p/CIP). They found that, in mouse tissues and in cell lines, p/CIP was present in both the cytoplasm and nucleus. The distribution of p/CIP changed during the cell cycle (being exclusively cytoplasmic during S phase and M phase), and stimulation of cells with growth factors or phorbol esters promoted nuclear accumulation. One surprising result was that the cytoplasmic distribution was coincident with that of the microtubule network, and cytoplasmic p/CIP was found in a large-molecular-mass complex (700 kD) that also contained tubulin. If the microtubule network was disrupted with colchicine, p/CIP did not redistribute to the nucleus in response to the phorbol ester PMA. Thus, the interaction of P/CIP with microtubules may serve both a passive sequestering role in keeping this transcription factor in the cytoplasm and a more active role in controlling transport into the nucleus.
M. S. Qutob, R. N. Bharracharjee, E. Pollari, S. P. Yee, J. Torchia, Microtubule-dependent subcellular redistribution of the transcription coactivator p/CIP, Mol. Cell. Biol. 22, 6611-6626 (2002). [Abstract] [Full Text]