Acts as a cofactor for XPO1/CRM1-mediated nuclear export, perhaps as export complex scaffolding protein. Bound to XPO1/CRM1, stabilizes the XPO1/CRM1-cargo interaction. In the absence of Ran-bound GTP prevents binding of XPO1/CRM1 to the nuclear pore complex. Binds to CHC1/RCC1 and increases the guanine nucleotide exchange activity of CHC1/RCC1. Recruits XPO1/CRM1 to CHC1/RCC1 in a Ran-dependent manner. Negative regulator of TGF- beta signaling through interaction with the R-SMAD proteins, SMAD2 and SMAD3, and mediating their nuclear export. Interacts with CHC1 in a Ran-stimulated manner. Interacts with XPO1. Interacts (via its C-terminal R domain) with SMAD2 (dephosphorylated form via its MH1 and MH2 domains); the interaction results in the nuclear export of SMAD2 and termination of the TGF-beta signaling. Interacts (via its C-terminal R domain) with SMAD3 (dephosphorylated form via its MH1 domain); the interaction results in the nuclear export of SMAD3 and termination of the TGF-beta signaling. Widely expressed with high levels in testis and heart. 3 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.