Protein Phosphatase 2A

Protein phosphatase 2 A (PP2A) is a ubiquitously expressed member of the PPP gene family that accounts for a substantial portion of the total serine/threonine phosphatase activity in many cell types. PP2A is an essential enzyme that functions in fundamental cellular processes, including metabolism and the cell cycle. Regulatory subunits play a primary role in specifying the proximity interactions of PP2A. The R2 family comprises a set of proteins present in a form of PP2A originally designated PP2A1. This family currently contains four known isoforms that are 79–87 percent identical. R2α mRNA is ubiquitously expressed and is the most abundant PP2A regulatory subunit in many cells and tissues. The R2β and R2γ isoforms are only expressed at high levels in brain and testis. The R2 subunit targets PP2A to pathways that regulate MAP kinase activity. Overexpression of the small-t antigen of SV40 virus disrupts endogenous PP2A complexes containing the R2 subunit. This leads to enhanced activation of MAP kinase in response to growth factors in some but not all cell types. The association of PP2A with microtubules in brain is specific for R2α- and R2β-containing isoforms, and can be enhanced by a heat-labile anchoring factor. The R5 regulatory subunits are a complex family of proteins that are components of a PP2A holoenzyme originally termed PP2A0. There are at least five isoforms that have distinct patterns of expression. The α and γ isoforms are expressed predominantly in muscle, the β and δ isoforms in brain, and the ɛ isoform in brain and testis.