Exportin 4 (XPO4)

XPO4 belongs to a large family of karyopherins that mediate the transport of proteins and other cargo between the nuclear and cytoplasmic compartments.

The 3-prime UTR contains a repetitive sequence, and the 1,150-amino acid protein shares 99% amino acid identity with mouse Xpo4. RT-PCR ELISA detected high to moderate expression in all human tissues and specific brain regions examined. human XPO4 interacted with Smad3 via the Smad3 MH2 domain. RNAi knockdown of XPO4 blocked Smad3 export, as did addition of competing short peptides representing the Smad3-XPO4 interaction domain. In vivo and in vitro assays showed that XPO4 mediated nuclear export of Smad3 in a RanGTPase-dependent manner.