Mechanism of Rac and Cdc42 Synchronization at the Cell Edge by ARHGAP39-Dependent Signaling and the Impact on Protrusion Dynamics

Compartmentalization of GTPase regulators into signaling nodules dictates specific GTPase signaling pathway selection. Rac and Cdc42 are synchronized at the cell edge for effective protrusion in motile cells, but how their activity is coordinated remains elusive. Here, we report that ARHGAP39, a Rac and Cdc42 GTPase-activating protein, sequentially interacts with WAVE and mDia2 to control lamellipodia and filopodia protrusions, respectively. Mechanistically, ARHGAP39 binds WAVE, whereupon phosphorylation by Src promotes Rac inactivation and leads to Cdc42-induced filopodia formation. Using an optimized FRET biosensor, we detected active Cdc42 at the filopodia tips that controls filopodia extension. ARHGAP39 is transported to filopodia tips by Myosin-X where it binds mDia2 and inactivates Cdc42, leading to filopodia retraction. Failure in lamellipodia-to-filopodia switch by defective ARHGAP39 impairs cell invasion and metastasis. Our study reveals that compartmentalization of ARHGAP39 within Rac/Cdc42 signaling nodules orchestrates the synchronization of lamellipodia and filopodia and highlights the intricate regulation of leading edge dynamics in migrating cells.