mRNA Export from Mammalian Cell Nuclei Is Dependent on GANP

Abstract

SummaryBulk nuclear export of messenger ribonucleoproteins (mRNPs) through nuclear pore complexes (NPCs) is mediated by NXF1. It binds mRNPs through adaptor proteins such as ALY [1, 2] and SR splicing factors [3] and mediates translocation through the central NPC transport channel via transient interactions with FG nucleoporins [4–10]. Here, we show that mammalian cells require GANP (germinal center-associated nuclear protein) for efficient mRNP nuclear export and for efficient recruitment of NXF1 to NPCs. Separate regions of GANP show local homology to FG nucleoporins, the yeast mRNA export factor Sac3p, and the mammalian MCM3 acetyltransferase. GANP interacts with both NXF1 and NPCs and partitions between NPCs and the nuclear interior. GANP depletion inhibits mRNA export, with retention of mRNPs and NXF1 in punctate foci within the nucleus. The GANP N-terminal region that contains FG motifs interacts with the NXF1 FG-binding domain. Overexpression of this GANP fragment leads to nuclear accumulation of both poly(A)+RNA and NXF1. Treatment with transcription inhibitors redistributes GANP from NPCs into foci throughout the nucleus. These results establish GANP as an integral component of the mammalian mRNA export machinery and suggest a model whereby GANP facilitates the transfer of NXF1-containing mRNPs to NPCs.

The human TREX-2 complex is stably associated with the nuclear pore basket

“…In agreement with a former study showing that GANP interacts with the mRNA export receptor NXF1 (Wickramasinghe et al, 2010), we could show that NXF1 colocalizes with EGFP-ENY2 and EGFP-PCID2 at the nuclear periphery ( Fig. 2A; supplementary material Fig.…”

“…In human, depletion of most TREX-2 subunits results in mRNA nuclear accumulation. Some subunits such as GANP, ENY2 and CETN2 were shown to associate with the nuclear envelope where GANP is required for ENY2 localization (Wickramasinghe et al, 2010;Jani et al, 2012). Conversely, ENY2 depletion did not affect GANP localization.…”

Lyn Signaling To Upregulate GANP Is Critical for the Survival of High-Affinity B Cells in Germinal Centers of Lymphoid Organs

“…GANP is involved in mRNA export in mammalian cells (30) and particularly in the selective export of Shugoshin-1 mRNA required for cell cycle progression through the M phase (20). The lack of GANP results in embryonic lethality at embryonic day 12.5 in mice and induces homology-mediated DNA hyperrecombination in cells, similar to that observed in suppressor of actin 3-deficient yeast cells (31,32).…”

GANP Regulates the Choice of DNA Repair Pathway by DNA-PKcs Interaction in AID-Dependent IgV Region Diversification

“…region of GANP is homologous to the Saccharomyces cerevisiae SAC3 protein, a component of the SAC3/THO complex involved in RNA export following transcription in yeast, and therefore GANP is proposed as a component of the mammalian transcription/ export-2 complex (31,32). Recently, we demonstrated that GANP interacts with cytoplasmic AID and assists its nuclear localization to augment its transport to the transcribed IgV region segment in B cells (33).…”