VGLL3 operates via TEAD1, TEAD3 and TEAD4 to influence myogenesis in skeletal muscle.

Henning Wackerhage,Congshan Sun,Ajaybabu V Pobbati,Martin Schönfelder,Janet Shipley,Wanjin Hong,Neil Vargesson,Edoardo Missiaglia,Abdalla D Mohamed,Johanna Pruller,Elaina Collie-Duguid,Amaya Garcia-Munoz,Oihane Jaka,Vanessa De Mello,David Matallanas,Nicolas Figeac,Stephen D R Harridge,Peter S Zammit

doi:10.1242/jcs.225946

Abstract

ABSTRACTVGLL proteins are transcriptional co-factors that bind TEAD family transcription factors to regulate events ranging from wing development in fly, to muscle fibre composition and immune function in mice. Here, we characterise Vgll3 in skeletal muscle. We found that mouse Vgll3 was expressed at low levels in healthy muscle but that its levels increased during hypertrophy or regeneration; in humans, VGLL3 was highly expressed in tissues from patients with various muscle diseases, such as in dystrophic muscle and alveolar rhabdomyosarcoma. Interaction proteomics revealed that VGLL3 bound TEAD1, TEAD3 and TEAD4 in myoblasts and/or myotubes. However, there was no interaction with proteins from major regulatory systems such as the Hippo kinase cascade, unlike what is found for the TEAD co-factors YAP (encoded by YAP1) and TAZ (encoded by WWTR1). Vgll3 overexpression reduced the activity of the Hippo negative-feedback loop, affecting expression of muscle-regulating genes including Myf5, Pitx2 and Pitx3, and genes encoding certain Wnts and IGFBPs. VGLL3 mainly repressed gene expression, regulating similar genes to those regulated by YAP and TAZ. siRNA-mediated Vgll3 knockdown suppressed myoblast proliferation, whereas Vgll3 overexpression strongly promoted myogenic differentiation. However, skeletal muscle was overtly normal in Vgll3-null mice, presumably due to feedback signalling and/or redundancy. This work identifies VGLL3 as a transcriptional co-factor operating with the Hippo signal transduction network to control myogenesis.

Highlights

The Hippo signal transduction network regulates development, stem cell identity and function, cell proliferation, and organ and body size (Hansen et al, 2015; Piccolo et al, 2014; Tremblay and Camargo, 2012)
Here, we report a comprehensive analysis of the regulation, protein binding and effect on target gene expression of the transcriptional co-regulator VGLL3 in skeletal myogenesis, and compare VGLL3 with YAP and TAZ
Whilst Vgll2 is highly expressed in skeletal muscle and involved in myogenic differentiation (Chen et al, 2004) and muscle fibre type distribution (Honda et al, 2017), far less is known about regulation and function of VGLL3 in adult skeletal muscle

Summary

Introduction

The Hippo signal transduction network regulates development, stem cell identity and function, cell proliferation, and organ and body size (Hansen et al, 2015; Piccolo et al, 2014; Tremblay and Camargo, 2012). Hippo proteins have major functions in skeletal muscle (Wackerhage et al, 2014), where the Hippo effector YAP (gene symbol YAP1), and other proteins such as the YAP paralogue TAZ (gene symbol WWTR1), vestigial-like factors (VGLL) 1–4 and the TEA domain (TEAD) 1–4 transcription factors, have been linked to both developmental and regenerative myogenesis (Chen et al, 2004; Gunther et al, 2004; Judson et al, 2012; Maeda et al, 2002; Mielcarek et al, 2002, 2009; Sun et al, 2017; Watt et al, 2010) Both YAP and TAZ are expressed in muscle stem (satellite) cells, where they promote proliferation, and while TAZ enhances subsequent myogenic differentiation into multinucleated myotubes, YAP inhibits this process (Judson et al, 2012; Sun et al, 2017). Hippo proteins are candidate regulators of adaptation to exercise training (Gabriel et al, 2016)

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