AMER1 regulates the distribution of the tumor suppressor APC between microtubules and the plasma membrane

APC is a multifunctional tumor suppressor protein that negatively controls Wnt signaling, but also regulates cell adhesion and migration by interacting with the plasma membrane and the microtubule cytoskeleton. Although the molecular basis for the microtubule association of APC is well understood, molecular mechanisms that underlie its plasma membrane localization have remained elusive. We show here that APC is recruited to the plasma membrane by binding to APC membrane recruitment 1 (AMER1), a novel membrane-associated protein that interacts with the ARM repeat domain of APC. The N-terminus of AMER1 contains two distinct phosphatidylinositol(4,5)-bisphosphate [PtdIns(4,5)P₂]-binding domains, which mediate its localization to the plasma membrane. Overexpression of AMER1 increases APC levels and redirects APC from microtubule ends to the plasma membrane of epithelial cells. Conversely, siRNA-mediated knockdown of AMER1 reduces the overall levels of APC, promotes its association with microtubule ends in cellular protrusions and disturbs intercellular junctions. These data indicate that AMER1 controls the subcellular distribution of APC between membrane- and microtubule-associated pools, and might thereby regulate APC-dependent cellular morphogenesis, cell migration and cell-cell adhesion.