ABSTRACTPolyamines promote cellular proliferation. Their levels are controlled by ornithine decarboxylase antizyme 1 (Az1, encoded byOAZ1), through the proteasome-mediated, ubiquitin-independent degradation of ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine biosynthesis. Az1-mediated degradation of other substrates such as cyclin D1 (CCND1), DNp73 (TP73) or Mps1 regulates cell growth and centrosome amplification, and the currently known six Az1substrates are all linked with tumorigenesis. To understand whether Az1-mediated protein degradation might play a role in regulating other cellular processes associated with tumorigenesis, we employed quantitative proteomics to identify novel Az1substrates. Here, we describe the identification of LIM domain and actin-binding protein 1 (LIMA1), also known as epithelial protein lost in neoplasm (EPLIN), as a new Az1target. Interestingly, between the two EPLIN isoforms (α and β), only EPLIN-β is a substrate of Az1. The interaction between EPLIN-β and Az1appears to be indirect, and EPLIN-β is degraded by Az1in a ubiquitination-independent manner. Az1absence leads to elevated EPLIN-β levels, causing enhanced cellular migration. Consistently, higherLIMA1levels correlate with poorer overall survival of colorectal cancer patients. Overall, this study identifies EPLIN-β as a novel Az1substrate regulating cellular migration.