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Mol Cell. 2002 Aug;10(2):271-82.

Smad2 nucleocytoplasmic shuttling by nucleoporins CAN/Nup214 and Nup153 feeds TGFbeta signaling complexes in the cytoplasm and nucleus.

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Cell Biology Program and Howard Hughes Medical Institute, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.


The transcription factor Smad2 is released from cytoplasmic retention by TGFbeta receptor-mediated phosphorylation, accumulating in the nucleus where it associates with cofactors to regulate transcription. We uncovered direct interactions of Smad2 with the nucleoporins CAN/Nup214 and Nup153. These interactions mediate constitutive nucleocytoplasmic shuttling of Smad2. CAN/Nup214 and Nup153 compete with the cytoplasmic retention factor SARA and the nuclear Smad2 partner FAST-1 for binding to a hydrophobic corridor on the MH2 surface of Smad2. TGFbeta receptor-mediated phosphorylation stimulates nuclear accumulation of Smad2 by modifying its affinity for SARA and Smad4 but not for CAN/Nup214 or Nup153. Thus, by directly contacting the nuclear pore complex, Smad2 undergoes constant shuttling, providing a dynamic pool that is competitively drawn by cytoplasmic and nuclear signal transduction partners.

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