Protein phosphatase 2A (PP2A) is a family of
serine threonine phosphatases responsible for regulating
protein phosphorylation, thus opposing the activity of cellular
kinases. PP2A is composed of a catalytic subunit (PP2A Cα/β) and scaffolding subunit (PP2A Aα/β) and various substrate-directing B regulatory subunits. PP2A biogenesis is regulated at multiple levels. For example, the sequestration of the free catalytic subunit during the process of biogenesis avoids promiscuous
phosphatase activity. Posttranslational modifications of PP2A C direct PP2A heterotrimeric formation. Additionally, PP2A functions as a haploinsufficient
tumor suppressor, where attenuated PP2A enzymatic activity creates a permissive environment for oncogenic transformation. Recent work studying PP2A in
cancer showed that its role in
tumorigenesis is more nuanced, with some
holoenzymes being
tumor suppressive, while others are required for oncogenic transformation. In
cancer biology, PP2A function is modulated through various mechanisms including the displacement of specific B regulatory subunits by
DNA tumor viral antigens, by recurrent mutations, and through loss of carboxymethyl-sensitive heterotrimeric complexes. In aggregate, these alterations bias PP2A activity away from its
tumor suppressive functions and toward oncogenic ones. From a therapeutic perspective, molecular
glues and disruptors present opportunities for both the selective stabilization of
tumor-suppressive
holoenzymes and disruption of
holoenzymes that are pro-oncogenic. Collectively, these approaches represent an attractive
cancer therapy for a wide range of
tumor types. This review will discuss the mechanisms by which PP2A
holoenzyme formation is dysregulated in
cancer and the current
therapies that are aimed at biasing heterotrimer formation of PP2A for the treatment of
cancer.