RASSF1A uncouples Wnt from Hippo signalling and promotes YAP mediated differentiation via p73

Angelos Papaspyropoulos ,Anastasia Samsonova ,Ludovico Buti ,Cláudia P Grou ,David Matallanas ,Dafni-Eleftheria Pefani ,Anna M Grawenda ,Konstantinos Toskas ,Alexander Kanapin ,Syed Haider ,Alex Von Kriegsheim ,Chuen Yan Leung ,Nikola Vlahov ,Leanne Bradley ,Magdalena Zernicka‐Goetz ,Jagat Chauhan ,Asmita Thapa ,Cinzia Raso ,Garth Hamilton ,Delia Koennig ,Francesca M Buffa ,Grigory L Dianov ,Xin Lü ,Eric O’neill

doi:10.1038/s41467-017-02786-5

Abstract

Transition from pluripotency to differentiation is a pivotal yet poorly understood developmental step. Here, we show that the tumour suppressor RASSF1A is a key player driving the early specification of cell fate. RASSF1A acts as a natural barrier to stem cell self-renewal and iPS cell generation, by switching YAP from an integral component in the β-catenin-TCF pluripotency network to a key factor that promotes differentiation. We demonstrate that epigenetic regulation of the Rassf1A promoter maintains stemness by allowing a quaternary association of YAP–TEAD and β-catenin–TCF3 complexes on the Oct4 distal enhancer. However, during differentiation, promoter demethylation allows GATA1-mediated RASSF1A expression which prevents YAP from contributing to the TEAD/β-catenin–TCF3 complex. Simultaneously, we find that RASSF1A promotes a YAP–p73 transcriptional programme that enables differentiation. Together, our findings demonstrate that RASSF1A mediates transcription factor selection of YAP in stem cells, thereby acting as a functional “switch” between pluripotency and initiation of differentiation.

Highlights

Transition from pluripotency to differentiation is a pivotal yet poorly understood developmental step
To determine whether RASSF1A played a role in stem cell differentiation we first examined levels of RASSF1A in human (H1 and H9) and mouse (J1 and V6.5) embryonic stem cells (ESC) lines allowed to differentiate over a period of 7–14 days. hRASSF1A and mRassf1A mRNA expression increased upon differentiation of both human and mouse ESCs (Fig. 1a, b)
WNT/β−catenin signalling drives maintenance of pluripotency by switching the WNT effector TCF3 from a repressor to an activator of Oct[4] transcription in ESCs57. We demonstrate that these two events are mutually dependant and that both YAP–TEAD and β-catenin–TCF3 cooperate to promote transcription of Oct[4] from its distal enhancer to sustain pluripotency in ESCs

Summary

Introduction

Transition from pluripotency to differentiation is a pivotal yet poorly understood developmental step. The transcriptional co-factors of the Hippo pathway, YAP and TAZ (Wwtr1) promote stem cell self-renewal and pluripotency by mediating TEA-domain (TEAD1-4) transcription. The WNT pathway effector TCF1/LEF can actively repress or activate expression of Oct[4], depending on β-catenin association In this manner, β-catenin plays a major role as a mediator of WNT signaling in maintaining stem cell selfrenewal[11, 12] but requires YAP to drive dedifferentiation of cardiac progenitors[13], indicating that WNT and Hippo converge to regulate pluripotency. The earliest specification of stem cell fate upon exiting pluripotency has recently been reported to be dependent on p7315, a transcriptional partner of the Hippo pathway mediator YAP, that is required during terminal differentiation[16,17,18]. Methylation of RASSF1A is proposed to induce dedifferentiation of tumour cells, which may account for poor prognosis of patients whose cancers are associated with high levels of epigenetic silencing[29, 30]

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Conclusion