Dynamic Control of Gene Expression during mRNA Export and Translation

Abstract

Messenger (m)RNA‐binding proteins (RBPs) are key arbiters in coordinating gene expression from transcription through translation. The specific RBP complement is repeatedly remodeled across the mRNA lifecycle through the activation of distinct RNA‐dependent DEAD‐box ATPases (Dbps in yeast/DDXs in humans). In this manner, the dynamic interactions of mRNA‐RBP complexes (mRNPs) with cellular machinery are controlled in a spatial and temporal manner to direct an mRNA's progression and ultimate fate. For mRNA export through the nuclear pore complex (NPC), an mRNP at the nuclear face must contain the proper complement of adaptor proteins and export receptor to initiate and mediate export, and the removal of key proteins by remodeling at the cytoplasmic NPC face is critical for export directionality. This mRNP remodeling is achieved through localized activation of human DDX19B (S. cerevisiae Dbp5) by Gle1, a multifunctional regulator of distinct Dbps/DDXs, and inositol hexakisphosphate (IP6). At least two Gle1 isoforms are expressed in human cells, with Gle1B required at the NPC and Gle1A in the cytoplasm. We recently uncovered the role for the Nup42 carboxy‐terminal domain (CTD) in mRNA export during the stress response. Altering the minimal Nup42 binding site on Gle1B revealed that mRNA export in HeLa cells requires the Nup42‐Gle1B interaction. In vitro assays with purified, recombinant proteins for both yeast and human systems demonstrated that the Nup42 CTD enhanced the Gle1/Gle1B‐stimulated, RNA‐dependent Dbp5/DDX19B ATPase activity independently of IP6. Of note, the Gle1B‐IP6 stimulatory effect also required purification of DDX19B from a baculovirus insect cell expression system. In contrast to Gle1B at the NPC, Gle1A lacks the Nup42 binding domain, is primarily cytoplasm at steady state, and is not capable of supporting mRNA export. We found that Gle1A is required for translation activity and stress granule dynamics. Furthermore, ERK1/2, JNK and GSK3 targeted Gle1A for stress‐induced sequential phosphorylation. Analysis of gle1A mutants mimicking phospho‐deficient or hyperphosphorylated states revealed roles for its phosphorylation in stress granule dynamics, Gle1 oligomerization, and Gle1‐mediated stimulation of DDX3 activity. Overall, multifactorial control of Gle1 functions by Nup42, IP6, and phosphorylation allows for regulation of gene expression from mRNA export through translation, and provides potential new insights into gle1 dysfunction underlying disease pathologies.Support or Funding InformationNIH 5R37 GM051219This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.