Exportrezeptor

Exportrezeptor is a class of transport receptors in eukaryotic cells that mediate the export of proteins and RNA from the nucleus to the cytoplasm. They belong mainly to the karyopherin family and recognize cargo that contains a nuclear export signal (NES). The exportin binds the NES-containing cargo together with Ran-GTP in the nucleus to form a trimeric complex. This complex is transported through the nuclear pore complex to the cytoplasm, where GTP hydrolysis converts Ran-GTP to Ran-GDP, triggering dissociation and release of the cargo. Ran-GDP is then recycled back into the nucleus to maintain the Ran gradient that drives directional export.

Multiple exportins exist in cells, each with preference for different cargo classes. The best characterized is Exportin 1 (XPO1, also known as CRM1), which exports a range of regulatory proteins including various transcription factors and cell-cycle regulators. Other exportins, such as Exportin 5 (XPO5), export RNA species like pre-microRNA, and additional exportins contribute to the export of specific RNAs and ribonucleoprotein particles. The exact cargo repertoire depends on cell type and physiological context.

Clinical and research relevance: dysregulation of exportin pathways can influence cell growth and stress responses, and export receptors are targets for therapeutic intervention. Inhibitors of XPO1, such as selinexor, can retain tumor suppressor proteins in the nucleus and are being investigated as anticancer agents. Understanding Exportrezeptoren is essential for broader concepts of nucleocytoplasmic transport and its role in development, physiology, and disease.