The B regulatory subunit might modulate substrate selectivity and catalytic activity, and also might direct the localization of the catalytic enzyme to a particular subcellular compartment. Within the PP2A holoenzyme complex, isoform 2 is required to promote proapoptotic activity. Isoform 2 regulates neuronal survival through the mitochondrial fission and fusion balance. 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 (By similarity). Interacts with TOMM22 (By similarity). Interacts with IER5 (via N- and C-terminal regions) (By similarity). Under basal conditions, localizes to both cytosolic and mitochondrial compartments. Relocalizes from the cytosolic to the mitochondrial compartment during apoptosis. Its targeting to the outer mitochondrial membrane (OMM) involves an association with import receptors of the TOM complex and is required to promote proapoptotic activity (By similarity). Expressed in brain, testis, lung and spleen. In the brain, expressed in the cortex, hippocampus and cerebellum (at protein level). Expressed in embryo at 14 and 17 dpc. The N-terminal 26 residues of isoform 2 constitute a cryptic mitochondrial matrix import signal with critical basic and hydrophobic residues, that is necessary and sufficient for targeting the PP2A holoenzyme to the outer mitochondrial membrane (OMM) and does not affect holoenzyme formation or catalytic activity. The last WD repeat of isoform 2 constitutes a mitochondrial stop-transfer domain that confers resistance to the unfolding step process required for import and therefore prevents PPP2R2B matrix translocation and signal sequence cleavage. Contains a cryptic mitochondrial transit peptide at positions 1-26. Belongs to the phosphatase 2A regulatory subunit B family. Aberrant splicing.