Inhibits phosphatase activities of protein phosphatase 1 (PP1) and protein phosphatase 2A (PP2A) complexes. Expressed in Purkinje cells of the cerebellum, hippocampus, pons, medulla and eye. Substrate for cGMP-dependent protein kinase (By similarity). Phosphorylation of Thr-72 and Thr-123 is required for its phosphatase activity. Phosphorylated by PRKG1 isoform alpha.