Leukemia-Associated Nup214 Fusion Proteins Disturb the XPO1-Mediated Nuclear-Cytoplasmic Transport Pathway and Thereby the NF-κB Signaling Pathway

Abstract

c Nuclear-cytoplasmic transport through nuclear pore complexes is mediated by nuclear transport receptors. Previous reports have suggested that aberrant nuclear-cytoplasmic transport due to mutations or overexpression of nuclear pore complexes and nuclear transport receptors is closely linked to diseases. Nup214, a component of nuclear pore complexes, has been found as chimeric fusion proteins in leukemia. Among various Nup214 fusion proteins, SET-Nup214 and DEKNup214 have been shown to be engaged in tumorigenesis, but their oncogenic mechanisms remain unclear. In this study, we examined the functions of the Nup214 fusion proteins by focusing on their effects on nuclear-cytoplasmic transport. We found that SET-Nup214 and DEK-Nup214 interact with exportin-1 (XPO1)/CRM1 and nuclear RNA export factor 1 (NXF1)/TAP, which mediate leucine-rich nuclear export signal (NES)-dependent protein export and mRNA export, respectively. SET-Nup214 and DEK-Nup214 decreased the XPO1-mediated nuclear export of NES proteins such as cyclin B and proteins involved in the NF-B signaling pathway by tethering XPO1 onto nuclear dots where Nup214 fusion proteins are localized. We also demonstrated that SET-Nup214 and DEK-Nup214 expression inhibited NF-B-mediated transcription by abnormal tethering of the complex containing p65 and its inhibitor, IB, in the nucleus. These results suggest that SETNup214 and DEK-Nup214 perturb the regulation of gene expression through alteration of the nuclear-cytoplasmic transport system. Biological macromolecules are transported between the nucleus and the cytoplasm in response to extracellular signals. Transport of molecules with a molecular mass greater than 40 kDa does not occur by simple diffusion but is generally facilitated by nuclear transport receptors (NTRs) through nuclear pore complexes (NPCs) embedded in the nuclear envelope (1-3). Controlled nuclear-cytoplasmic transport plays important roles in maintaining cellular integrity in eukaryotic cells. It is reported that aberrant subcellular localization of some proteins is associated with various cancer cases (4). p53 has nuclear localization signals (NLSs) and nuclear export signals (NESs), and the accumulation of p53 in the cytoplasm has been reported to be a prognostic indicator in cancer (5). The nuclear factor B (NF-B) transcription factor is observed mainly in the cytoplasm in normal cells, whereas in many cancer cells, it is localized largely in the nucleus (6).In addition to aberrant subcellular localization of proteins in cancer, mutations of genes encoding NTRs and NPC components are found in various types of cancer (7). Mutations of exportin-5 (XPO5) and exportin-1 (XPO1)/CRM1, members of export receptors (8-10), are found in solid cancer and leukemia, respectively. Four nucleoporins-Nup98, Nup214/CAN, Nup358/ RanBP2, and Tpr-have been reported to form chimeric proteins by chromosomal translocations mainly in leukemia (11-15). Nup214, located at the cytoplasmic filament of the NPC, interacts with NTRs to control macromolecular transport....

Hitting a moving target: inhibition of the nuclear export receptor XPO1/CRM1 as a therapeutic approach in cancer

“…Examples of genetic alterations targeting the nuclear transport machinery include chromosome rearrangements involving nucleoporin genes (e.g., NUP98 and NUP214) in hematologic malignancies [71] . The abnormal fusion proteins resulting from these translocations have been reported to disrupt XPO1mediated export [72,73] . Examples of nuclear transport factors abnormally expressed in tumors include the nuclear import receptors Importin β (see Dickmanns et al [64] and references therein) and Importina1 (see Christiansen and Dyrskjøt [74] , and references therein).…”

Targeted CRM1-inhibition perturbs leukemogenic NUP214 fusion proteins and exerts anti-cancer effects in leukemia cell lines withNUP214rearrangements

“…Additionally, we observed that the fusion proteins sequestered endogenous NPC components: NUP88 ( Figure 2D) and NUP62 ( Figure 2E NUP214 fusion proteins are sensitive to nuclear export inhibition CRM1 inhibition by LMB leads to the dissolution of nuclear bodies containing NUP214 fusion proteins, in LOUCY and in transfected cells 17,18 . We confirmed these previous results for SET-NUP214 in LOUCY cells here (Figure 3 A-…”

“…The C-terminal phenylalanine-glycine (FG) repeat domain of NUP214 exhibits multiple CRM1-binding sites, which are preserved in SET-NUP214 and DEK-NUP214 [16][17][18][19] . In fact, both fusion proteins can bind CRM1 and its co-factor, the small GTPase Ran, and inhibit the nuclear export of NES-containing proteins and RNPs 17,18 .…”

“…The C-terminal phenylalanine-glycine (FG) repeat domain of NUP214 exhibits multiple CRM1-binding sites, which are preserved in SET-NUP214 and DEK-NUP214 [16][17][18][19] . In fact, both fusion proteins can bind CRM1 and its co-factor, the small GTPase Ran, and inhibit the nuclear export of NES-containing proteins and RNPs 17,18 . Targeted CRM1 inhibition by small molecule antagonists has become an appealing anti-cancer strategy, for both solid and hematologic malignancies [20][21][22][23][24] .…”

The roles of the nuclear pore complex in cellular dysfunction, aging and disease

“…Although they are less well characterized than the Nup98 fusions described later, some mechanisms have been demonstrated for Nup214 fusion proteins. Recently, the Set and Dek fusions to Nup214 have been shown to alter gene expression regulation by inhibiting nuclear export of mRNA and transcription factors by tethering the export factors Crm1 and Nxf1 to nucleoplasmic aggregates [126]. In various cancers another cytoplasmic filament nucleoporin, Nup358, is fused to Alk, Abl, and Fgfr.…”