Formin mDia2 is a cytoskeleton-regulatory protein that switches reversibly between a closed, auto-inhibited and an open, active conformation. Although the open conformation of mDia2 induces actin assembly thereby controlling many cellular processes, mDia2 possesses also actin-independent and conformation-insensitive scaffolding roles related to microtubules and p53, respectively. Thus, we hypothesise that mDia2 may have other unappreciated functions and regulatory modes. Here we identify and validate proteasome and Ubiquitin as genuine mDia2-interacting partners using quantitative proteomics and a multi-disciplinary approach, respectively.