RAP2 Mediates Mechano-responses of Hippo Pathway

Mammalian cells are surrounded by neighboring cells and extracellular matrix (ECM), which provide cells with structural support and mechanical cues that influence diverse biological processes(1). The Hippo pathway effectors YAP and TAZ are regulated by mechanical cues and mediate cellular responses to ECM stiffness(2,3). Here we identified Ras-related GTPase RAP2 as a critical intracellular signal transducer that relays ECM rigidity signals to control mechano-sensitive cellular activities through YAP/TAZ. RAP2 is activated by low ECM stiffness, and RAP2 deletion blocks YAP/TAZ regulation by stiffness signals and promotes aberrant cell growth. Mechanistically, matrix stiffness acts through phospholipase Cγ1 (PLCγ1) to influence levels of phosphatidylinositol 4,5-bisphosphate (PIP2) and its product phosphatidic acid (PA), which activates RAP2 through PDZGEF1/2. At low stiffness, active RAP2 binds to and stimulates mitogen-activated protein kinase kinase kinase kinase 4/6/7 (MAP4K4/6/7) and Rho GTPase activating protein 29 (ARHGAP29), resulting in LATS1/2 activation and YAP/TAZ inhibition. RAP2 and YAP/TAZ play pivotal roles in mechano-regulated transcription, as YAP/TAZ deletion abolishes the ECM stiffness-responsive transcriptome. Our findings reveal RAP2 as a molecular switch in mechanotransduction, thereby defining a mechanosignaling pathway from ECM stiffness to the nucleus.