Protein phosphatase inhibitor that specifically inhibits protein phosphatase 2A (PP2A) during mitosis. When phosphorylated at Ser-62 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. May indirectly enhance GAP-43 expression (By similarity). Interacts (when phosphorylated at Ser-62) with PPP2R2D. Interacts with SNCA (By similarity). Isoform ARPP-19 is found in all brain regions and also present in non-neuronal tissues. Isoform ARPP-16 is enriched in the caudate nucleus, found in low levels in cerebral cortex. Phosphorylation at Ser-62 by GWL during mitosis is essential for interaction with PPP2R2D (PR55-delta) and subsequent inactivation of PP2A (By similarity). Phosphorylated by PKA. Belongs to the endosulfine family.