Axin1 (Axis inhibition protein 1) and Axin2 are multidomain scaffold proteins that negatively regulate Wnt signaling. Axin1 interacts with APC, GSK-3β, Dvl, and β-catenin and promotes the GSK-3β-mediated phosphorylation and subsequent degradation of β-catenin (1,2). Upon stimulation of cells with Wnt, Axin1 is recruited to the membrane by phosphorylated LRP5/6, a process that is believed to be crucial for activation of Wnt signaling (3,4). In addition to its role in the Wnt signaling pathway, Axin1 forms a complex with MEKK1 and activates c-Jun amino-terminal kinase (JNK/SAPK) (5). Axin2 (also known as Conductin or Axil) can functionally substitute for Axin1 in mice (6). Axin2 itself is a direct target of the Wnt signaling pathway and therefore serves to control the duration and/or intensity of Wnt signaling through a negative feedback loop (7-9). |