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

Abstract

VGLL 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 <i>Vgll3</i> in skeletal muscle. We found that mouse <i>Vgll3</i> was expressed at low levels in healthy muscle but that its levels increased during hypertrophy or regeneration; in humans, <i>VGLL3</i> 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 <i>YAP1</i>) and TAZ (encoded by <i>WWTR1</i>). <i>Vgll3</i> overexpression reduced the activity of the Hippo negative-feedback loop, affecting expression of muscle-regulating genes including <i>Myf5</i>, <i>Pitx2</i> and <i>Pitx3</i>, and genes encoding certain Wnts and IGFBPs. VGLL3 mainly repressed gene expression, regulating similar genes to those regulated by YAP and TAZ. siRNA-mediated <i>Vgll3</i> knockdown suppressed myoblast proliferation, whereas <i>Vgll3</i> overexpression strongly promoted myogenic differentiation. However, skeletal muscle was overtly normal in <i>Vgll3</i>-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.