NF-κB transcription factors are retained in the cytoplasm in an inactive form until they are
activated and rapidly imported into the nucleus. We identified importin α3 and importin α4 as
the main importin α isoforms mediating TNF-α-stimulated NF-κB p50/p65 heterodimer
translocation into the nucleus. Importin α3 and α4 are close relatives in the human importin α
family. We show that importin α3 isoform also mediates nuclear import of NF-κB p50
homodimer in nonstimulated cells. Importin α3 is shown to directly bind to previously …