Protein phosphatase inhibitor that specifically inhibits protein phosphatase 2A (PP2A) during mitosis. When phosphorylated at Ser-67 during mitosis, specifically interacts with PPP2R2D (PR55-delta) and inhibits its activity, leading to inactivation of PP2A, an essential condition to keep cyclin-B1-CDK1 activity high during M phase. Also acts as a stimulator of insulin secretion by interacting with sulfonylurea receptor (ABCC8), thereby preventing sulfonylurea from binding to its receptor and reducing K(ATP) channel currents (By similarity). Interacts (when phosphorylated at Ser-67) with PPP2R2D. Interacts with ABCC8. Interacts with SNCA; interaction is disrupted when phosphorylated at Ser-109 (By similarity). The N-terminus is blocked. Phosphorylation at Ser-67 by GWL during mitosis is essential for interaction with PPP2R2D (PR55-delta) and subsequent inactivation of PP2A. Phosphorylated by PKA (By similarity). Belongs to the endosulfine family.