WNK1 kinase and the termination factor PCF11 connect nuclear mRNA export with transcription.

Nick J. Proudfoot,Margarita Schlackow,Kinga Kamieniarz-Gdula,Adam Volanakis

doi:10.1101/gad.303677.117

Abstract

Nuclear gene transcription is coordinated with transcript release from the chromatin template and messenger RNA (mRNA) export to the cytoplasm. Here we describe the role of nuclear-localized kinase WNK1 (with no lysine [K] 1) in the mammalian mRNA export pathway even though it was previously established as a critical regulator of ion homeostasis in the cytoplasm. Our data reveal that WNK1 phosphorylates the termination factor PCF11 on its RNA polymerase II (Pol II) C-terminal domain (CTD)-interacting domain (CID). Furthermore, phosphorylation of the PCF11 CID weakens its interaction with Pol II. We predict that WNK1 and the associated phosphorylation of the PCF11 CID act to promote transcript release from chromatin-associated Pol II. This in turn facilitates mRNA export to the cytoplasm.

Highlights

Gene expression is a multistep and highly regulated process
Since our co-IP experiments were performed with nuclear extracts, this suggests the nuclear presence of WNK1 even though it was previously described as a cytoplasmic protein
Our results indicate that both WNK1 presence and kinase activity are required for messenger RNA (mRNA) export, as its knockdown and treatment with the WNK463 inhibitor lead to mRNA retention in the nucleus (Figs. 1C, 2, 5A)

Summary

Introduction

Gene expression is a multistep and highly regulated process. It begins with transcription of a gene in the nucleus and ends with translation of the messenger RNA (mRNA) in the cytoplasm (Moore and Proudfoot 2009). In metazoans and Saccharomyces cerevisiae (yeast), the export factors UAP56/SUB2 and ALY/YRA1 are cotranscriptionally recruited to the elongation complex through interactions with splicing and transcription factors (Johnson et al 2009, 2011; Viphakone et al 2012) This leads to assembly of the transcription export (TREX) complex (Chi et al 2013), which marks the mRNP as export-competent following its release from Pol II (for review, see Bjork and Wieslander 2014). This suggests that mRNA export and the release of mRNPs from the transcription locus require the coordinated action of export factors such as ALY with 3′ processing factors (Rougemaille et al 2008) It has been suggested from studies in yeast that recruitment of the export factor YRA1 to genes through its interaction with PCF11 can modulate transcription termination, possibly by competition with the PCF11 cofactor CLP1 (Johnson et al 2011). WNK1 and the associated PCF11 modification facilitate the release of mRNP from transcription loci and in turn promote the nuclear export of mRNA

Methods

Results

Conclusion