Reduces the ATPase activity of VCP (PubMed:9824302, PubMed:9214505). Necessary for the fragmentation of Golgi stacks during mitosis and for VCP-mediated reassembly of Golgi stacks after mitosis (PubMed:12411482). May play a role in VCP-mediated formation of transitional endoplasmic reticulum (tER) (PubMed:10930451). Inhibits the activity of CTSL (in vitro) (By similarity). Together with UBXN2B/p37, regulates the centrosomal levels of kinase AURKA/Aurora A during mitotic progression by promoting AURKA removal from centrosomes in prophase (By similarity). Also, regulates spindle orientation during mitosis (By similarity).