Abstract
Nucleocytoplasmic shuttling of macromolecules is a well-controlled process involving importins and exportins. These karyopherins recognize and bind to receptor-mediated intracellular signals through specific signal sequences that are present on cargo proteins and transport into and out of the nucleus through nuclear pore complexes. Nuclear localization signals (NLS) present on cargo molecules to be imported while nuclear export signals (NES) on the molecules to be exported are recognized by importins and exportins, respectively. The classical NLS are found on many transcription factors and molecules that are involved in the pathogenesis of allergic diseases. In addition, several immune modulators, including corticosteroids and vitamin D, elicit their cellular responses by regulating the expression and activity of importin molecules. In this review article, we provide a comprehensive list of importin and exportin molecules and their specific cargo that shuttled between cytoplasm and the nucleus. We also critically review the role and regulation of specific importin and exportin involved in the transport of activated transcription factors in allergic diseases, the underlying molecular mechanisms, and the potential target sites for developing better therapeutic approaches.
Highlights
The trafficking of molecules between the cytoplasm and the nucleus in eukaryotes is regulated by nuclear pore complexes (NPCs or nucleoporins), which are cylindrical structures containing about 100 different polypeptides and embedded in the double membrane of the nuclear envelope
The regulation of bidirectional movement of molecules within a cell is critical in the exchange of molecules in and out of the nucleus and precise control of signal transduction processes as well as gene expression, cell cycle progression, and other cellular responses
Nuclear export of proteins occurs through nuclear export signals (NES) in an analogous manner by exportins, which are homologous to importin-β
Summary
The trafficking of molecules between the cytoplasm and the nucleus in eukaryotes is regulated by nuclear pore complexes (NPCs or nucleoporins), which are cylindrical structures containing about 100 different polypeptides and embedded in the double membrane of the nuclear envelope. The protein containing NLS is transported through NPC to the nucleus by importin α/β heterodimeric complex This translocation of the substrate-receptor complex through the NPC requires energy provided by a low molecular weight Ras-family GTPase, Ran, which is present in the nucleus. Nuclear export of proteins occurs through NES in an analogous manner by exportins, which are homologous to importin-β This requires the binding of Ran-GTP to protein-NES-exportin complex. The experimental evidence is provided by many studies validating the fact that different importin/exportin molecules possess distinct properties in terms of interacting with the NLS of specific cargo proteins [6, 9, 10].
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