RAP2 Mediates Mechanotransduction to Hippo pathway

Mammalian cells are surrounded by the extracellular matrix (ECM), which regulates intercellular signal transduction and provides structural support to cells. Mechanical forces generated by ECM play a key role in regulating cell behaviors including survival, growth, mobility, and differentiation. However, it is unclear how mechanical forces are sensed by cells and transmit biochemical signals to cell fate-determining transcription factors such as YAP (Yes-associated protein) and TAZ (transcriptional coactivator with PDZ-binding motif). Here we show the identification of Ras-associated protein 2 (RAP2) as an intracellular signal transducer that senses ECM rigidity and modulates cell survival and growth by negatively regulating YAP/TAZ. Activation of RAP2 by low ECM stiffness or contact inhibition triggers YAP/TAZ phosphorylation. Deletion of RAP2 leads to sustained YAP/TAZ activation in cells that grow on soft matrix or undergo contact inhibition, alters transcription programs initiated by low matrix stiffness, and results in cell transformation and malignant growth. Mechanistically, RAP2 can directly bind to Mitogen-activated protein kinase kinase kinase kinase 4/6/7 (MAP4K4/6/7) or Rho GTPase activating protein 29 (ARHGAP29), both of which lead to LATS1/2 activation and YAP/TAZ inhibition. These findings define a new molecular pathway that transmits mechanical cues to their effectors in the nucleus. The overall goal is to examine expression changes in response to ECM stiffness. mRNA profiles of wild type (WT), RAP2A/B/C-tKO, LATS1/2-dKO, and YAP/TAZ-dKO HEK293A cells were generated using deep sequencing with three biological replicates.