Phosphorylation acts positively and negatively to regulate MRTF-A subcellular localisation and activity.

Richard Panayiotou,Francesc Miralles,Helen R Flynn,Jessica Diring,Rafal Pawlowski,Richard Treisman,Mark Skehel

doi:10.7554/elife.15460

Richard Panayiotou, Francesc Miralles + Show 5 more

Open Access

https://doi.org/10.7554/elife.15460

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Journal: eLife	Publication Date: Jun 15, 2016
Citations: 69	License type: CC BY 4.0

Affiliation: The Francis Crick Institute

Abstract

The myocardin-related transcription factors (MRTF-A and MRTF-B) regulate cytoskeletal genes through their partner transcription factor SRF. The MRTFs bind G-actin, and signal-regulated changes in cellular G-actin concentration control their nuclear accumulation. The MRTFs also undergo Rho- and ERK-dependent phosphorylation, but the function of MRTF phosphorylation, and the elements and signals involved in MRTF-A nuclear export are largely unexplored. We show that Rho-dependent MRTF-A phosphorylation reflects relief from an inhibitory function of nuclear actin. We map multiple sites of serum-induced phosphorylation, most of which are S/T-P motifs and show that S/T-P phosphorylation is required for transcriptional activation. ERK-mediated S98 phosphorylation inhibits assembly of G-actin complexes on the MRTF-A regulatory RPEL domain, promoting nuclear import. In contrast, S33 phosphorylation potentiates the activity of an autonomous Crm1-dependent N-terminal NES, which cooperates with five other NES elements to exclude MRTF-A from the nucleus. Phosphorylation thus plays positive and negative roles in the regulation of MRTF-A.

Highlights

The myocardin-related transcription factors (MRTFs, called MKLs), act in partnership with serum response factor (SRF) to control cytoskeletal gene expression in development, morphogenesis, and cell migration (Arsenian et al, 1998; Esnault et al, 2014; Schratt et al, 2002)
Using mouse NIH3T3 fibroblasts, we first investigated the relationship between transcriptional activation by MRTF-A and its phosphorylation, as assessed by its reduced mobility in SDS-PAGE (Miralles et al, 2003)
We characterised the role of phosphorylation and nuclear export in the regulation of mouse MRTFA, a member of the myocardin family of SRF transcriptional coactivators

Summary

Introduction

The myocardin-related transcription factors (MRTFs, called MKLs), act in partnership with serum response factor (SRF) to control cytoskeletal gene expression in development, morphogenesis, and cell migration (Arsenian et al, 1998; Esnault et al, 2014; Schratt et al, 2002). G-actin competes with importin ab for binding to an NLS within the RPEL domain (Hirano and Matsuura, 2011; Mouilleron et al, 2011; Pawłowski et al, 2010). It cooperates with the Crm exportin in MRTF nuclear export (Vartiainen et al, 2007).

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