The Rho effector ARHGAP18 coordinates a Hippo pathway feedback loop through YAP and Merlin to regulate the cytoskeleton and epithelial cell polarity

The organization of the cell’s cytoskeletal filaments is coordinated through a complex network of signaling cascades activated by both internal and external cues. Two major actin regulatory pathways are signal transduction through Rho family GTPases and growth and proliferation signaling through the Hippo pathway. These two pathways define the actin cytoskeleton, controlling foundational cellular attributes such as morphology and polarity and are hijacked to promote proliferation and motility in aggressive cancers. In this study, we use human epithelial cells to investigate the interplay between the Hippo and Rho Family signaling pathways, which have predominantly been characterized as independent actin regulatory mechanisms. We identify that the RhoA effector, ARHGAP18, forms a complex with the Hippo pathway transcription factor YAP to address a long-standing enigma in the field. Using super resolution STORM microscopy, we characterize single-filament-level changes in the actin cytoskeleton that arise from CRISPR/CAS9 knockout of ARHGAP18. We report that the loss of ARHGAP18 results in cytoskeletal alterations driven by both dysregulated RhoA signaling and aberrant nuclear localization of YAP. These findings indicate that the Hippo and Rho family GTPase signaling cascades are temporally and spatially coordinated in their regulation of the actin cytoskeleton.