Acts as an inhibitor of serine/threonine-protein phosphatase 2A (PP2A) activity. Potentiates ubiquitin-mediated proteasomal degradation of serine/threonine-protein phosphatase 2A catalytic subunit alpha (PPP2CA) (By similarity). Inhibits PP2A-mediated dephosphorylation of WEE1, promoting ubiquitin-mediated proteolysis of WEE1, thereby releasing G2/M checkpoint (By similarity). Interacts with PPP2CA, PPP2R2A and PPP2R1A (By similarity). The CHEK1-mediated Ser-34 phosphorylated form interacts with 14-3-3 proteins (By similarity). The CHEK1-mediated Ser-34 phosphorylated form is sequestered by 14-3-3 proteins in the cytoplasm and fails to translocate to the nucleus, where it otherwise inhibits serine/threonine-protein phosphatase 2A. CHEK1-mediated phosphorylation at Ser-34 negatively regulates its ability to inhibit serine/threonine-protein phosphatase 2A (PP2A) activity. Phosphorylation leads to its release from the PP2A complex and its sequestration by 14-3-3 proteins in the cytoplasm resulting in its inability to translocate to the nucleus, where it otherwise inhibits PP2A. Belongs to the FAM122 family.