Spatial Rho regulation: Molecular mechanisms controlling the GAP protein DLC3.

The spatial regulation of cellular Rho signaling by GEF and GAP proteins and the molecular mechanisms controlling the Rho regulators themselves are still incompletely understood. We previously reported that the poorly characterized RhoGAP protein DLC3 localizes to cell-cell adhesions and Rab8-positive membrane tubules. However, it was unclear how DLC3 is targeted to these subcellular sites to execute its functions. In our recent work, protein partners of DLC3 were identified by mass spectrometry, identifying the basolateral polarity protein Scribble as a scaffold for DLC3 at cell-cell contacts. We found that the PDZ-mediated interaction of DLC3 and Scribble is essential for junctional DLC3 recruitment and its role as a local regulator of RhoA-ROCK signaling controlling adherens junction integrity and Scribble localization. Furthermore, DLC3 and Scribble depletion interfered with polarized lumen formation in a 3D model of cyst morphogenesis, emphasizing the relevance of both proteins in epithelial polarity. These findings reveal a new mechanism for spatial Rho regulation at adherens junctions in polarized epithelial cells and highlight the necessity to investigate DLC3 localization and function also in cellular contexts that require cell junction remodeling.