Facilitates ubiquitin-independent proteasomal degradation of polycomb protein CBX4. Plays a role in inhibiting the activity of glucokinase GCK and both glucose-induced and basal insulin secretion. Interacts with GCK; the interaction occurs preferentially at low glucose levels. Detected in the nucleus and nucleolus with no expression in the cytoplasm (By similarity). However, a later study finds expression in the nucleus and cytoplasm with no expression in the nucleolus (PubMed:24187134).