GPCRs are regulators of MRTF‐A and YAP mediated CCN1 expression (1066.4)

Abstract

Cysteine‐rich 61 (Cyr61/CCN1) is a multifunctional matricellular, secreted protein involved in myriad cellular processes including tumor cell growth, inflammation, and wound healing. It is part of a family of three immediate early genes all largely subserving regulatory rather than structural roles in signaling. CCN1 functions in the extracellular matrix through binding to integrins on the cell surface. The role of G‐protein coupled receptors (GPCRs) in CCN1 regulation has remained largely unexplored. However, recent evidence from our laboratory indicates that CCN1 is highly and rapidly induced via a subset of GPCRs, in particular the protease activated receptor (PAR1) thrombin receptor and the receptors for lysophospholipids, LPA and S1P through Rho activation. Myocardin‐related transcription factor A (MRTF‐A), a transcription coactivator has been shown to regulate CCN1 expression, as has Yes‐associated protein (YAP). Whether these transcriptional co‐activators work in parallel or in synergy to induce CCN1 expression is not known, nor are the distinct signals that activate these pathways defined. Here we report that stimulation of GPCRs that activate Rho leads to YAP dephosphorylation and MRTF‐A dissociation from the actin cytoskeleton, both of which result in nuclear translocation and gene activation. Whereas both responses are Rho‐dependent and inhibited with C3 exoenzyme, inhibiton of Rho kinase blocks MRTF‐A but not YAP activation. Studies using reporter genes confirm these findings. Knockdown of either MRTF‐A or YAP significantly reduces agonist induced CCN1 expression and we are currently examining other genes to determine whether regulation of multiple genes requires activation by these two signals. Our observations establish that MRTF‐A and YAP are activated through different signals downstream of RhoA, but CCN1 serves as a downstream effector where these two important transcriptional hubs converge.