A Genetic Defect in Exportin-5 Traps Precursor MicroRNAs in the Nucleus of Cancer Cells

SummaryThe global impairment of mature microRNAs (miRNAs) is emerging as a common feature of human tumors. One interesting scenario is that defects in the nuclear export of precursor miRNAs (pre-miRNAs) might occur in transformed cells. Exportin 5 (XPO5) mediates pre-miRNA nuclear export and herein we demonstrate the presence of XPO5-inactivating mutations in a subset of human tumors with microsatellite instability. The XPO5 genetic defect traps pre-miRNAs in the nucleus, reduces miRNA processing, and diminishes miRNA-target inhibition. The XPO5 mutant form lacks a C-terminal region that contributes to the formation of the pre-miRNA/XPO5/Ran-GTP ternary complex and pre-miRNAs accumulate in the nucleus. Most importantly, the restoration of XPO5 functions reverses the impaired export of pre-miRNAs and has tumor-suppressor features.

► Exportin-5 inactivating mutations occur in tumors with microsatellite instability ► Exportin-5 mutant form traps precursor microRNAs in the nucleus ► Exportin-5 mutations decrease miRNA processing efficiency and target inhibition ► Exportin-5 shows tumor-suppressor features in vitro and in vivo