B regulatory subunit of protein phosphatase 2A (PP2A) that plays a key role in cell cycle by controlling mitosis entry and exit. The activity of PP2A complexes containing PPP2R2D (PR55-delta) fluctuate during the cell cycle: the activity is high in interphase and low in mitosis. During mitosis, activity of PP2A is inhibited via interaction with phosphorylated ENSA and ARPP19 inhibitors. Within the PP2A complexes, the B regulatory subunits modulate substrate selectivity and catalytic activity, and also may direct the localization of the catalytic enzyme to a particular subcellular compartment (By similarity). PP2A consists of a common heterodimeric core enzyme, composed of a 36 kDa catalytic subunit (subunit C) and a 65 kDa constant regulatory subunit (PR65 or subunit A), that associates with a variety of regulatory subunits. Proteins that associate with the core dimer include three families of regulatory subunits B (the R2/B/PR55/B55, R3/B''/PR72/PR130/PR59 and R5/B'/B56 families), the 48 kDa variable regulatory subunit, viral proteins, and cell signaling molecules. Interacts with ENSA (when phosphorylated at 'Ser-67') and ARPP19 (when phosphorylated at 'Ser-62'), leading to inhibit PP2A activity (By similarity). Interacts with IER5 (By similarity). Widely expressed with high levels in brain, heart, placenta, skeletal muscle, testis, thymus and spleen. Belongs to the phosphatase 2A regulatory subunit B family.