PKA-regulated VASP phosphorylation promotes extrusion of transformed cells from the epithelium

Abstract

At the early stages of carcinogenesis, transformation occurs in single cells within tissues. In an epithelial monolayer, such mutated cells are recognized by their normal neighbors and are often apically extruded. The apical extrusion requires cytoskeletal reorganization and cell shape changes, but it is poorly understood what molecular switches are involved in regulation of these processes. Here, using SILAC-based quantitative mass spectrometry we have identified proteins that are modulated in transformed cells upon their interaction with normal cells. Phosphorylation of VASP at serine 239 is specifically upregulated in RasV12-transformed cells when they are surrounded by normal cells. VASP phosphorylation is required for the cell shape changes and apical extrusion of Ras-transformed cells. Furthermore, PKA is activated in Ras-transformed cells surrounded by normal cells, leading to VASP phosphorylation. These results indicate that the PKA/VASP pathway is a crucial regulator for tumor cell extrusion from the epithelium and shed light on the events occurring at the early stage of carcinogenesis.