Epidermal Growth Factor Activates the Rho GTPase-activating Protein (GAP) Deleted in Liver Cancer 1 via Focal Adhesion Kinase and Protein Phosphatase 2A

Abstract

Deleted in Liver Cancer 1 (DLC1) is a RHO GTPase-activating protein (GAP) that negatively regulates RHO. Through its GAP activity, it modulates the actin cytoskeleton network and focal adhesion dynamics, ultimately leading to suppression of cell invasion and metastasis. Despite its presence in various structural and signaling components, little is known about how the activity of DLC1 is regulated at focal adhesions. Here we show that EGF stimulation activates the GAP activity of DLC1 through a concerted mechanism involving DLC1 phosphorylation by MEK/ERK and its subsequent dephosphorylation by protein phosphatase 2A (PP2A) and inhibition of focal adhesion kinase by MEK/ERK to allow the binding between DLC1 and PP2A. Phosphoproteomics and mutation studies revealed that threonine 301 and serine 308 on DLC1, known previously to be mutated in certain cancers, are required for DLC1-PP2A interaction and the subsequent activation of DLC1 upon their dephosphorylation. The intricate interplay of this "MEK/ERK-focal adhesion kinase-DLC1-PP2A" quartet provides a novel checkpoint in the spatiotemporal control of cell spreading and cell motility.