PP2A is a major serine/threonine phosphatase that is implicated in the negative control of cell cycle progression. PP2A encodes the beta isoform of the catalytic subunit (PP2CB). Chk2 has been shown to be negatively regulated and dephosphorylated by PP2A. Several proteins have been shown to associate with PP2A and regulate its activity such as eRF1, Hox11, CK2, and Igbp1/alpha4. Rapamycin has been shown to dissociate PP2A from alpha-4 and inhibit proliferation. This result suggests an alternative positive regulatory role of PP2A in cell proliferation.