Background: I2PP2A/SET is  a potent inhibitor of Protein Phosphatase 2A (PP2A), a major mammalian protein serine threonine phosphatase that regulates diverse cellular processes. Purified preparations of I2PP2A/SET inhibit all forms of the phosphatase tested to date in a substrate selective manner. For example, the preparations inhibit PP2A potently (ki ~ 0.1 – 0.5 nM) with Myelin Basic Protein (MBP) and Histone H1 but not with casein as substrate.  I2PP2A/SET was identified as a fusion protein with the Nucleoporin CAN (NUP214) in a patient with acute undifferentiated leukemia. Elevated expression of I2PP2A/SET occurs in a numerous cancers.  Transient expression of I2PP2A/SET in HEK-293 cells leads to an increase in the DNA binding and AP1 activity of the proto-oncogene c-Jun.  The sphingolipid second messenger cermaide binds to I2PP2A/SET and prevents it from inhibiting PP2A. This is thought to contribute, at least in part, to the mechanism by which Ceramide promotes apoptosis. I2PP2A/SET also prevents inhibition of E-CDK-2 by p21Cip1, associates with B cyclin, regulates histone binding to DNA, transcriptional activity and chromatin condensation. I2PP2A/SET undergoes phosphorylation at Ser9 and Ser24 in intact cells. The functional significance of these phosphorylations is uncertain. Some studies indicate that Ser9 phosphorylation may causes cytoplasmic detention of I2PP2A in Alzheimer disease.

Figure: Western Blotting of purified preparations of I2PP2A/SET with Anti-I2PPA/SET polyclonal antibody.

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