PP2A fulfills its promises as tumor suppressor: which subunits are important?

Reversible phosphorylation of proteins, catalyzed by kinases and phosphatases, is a key regulatory mechanism in the control of multiple cellular signal transduction pathways. Uncontrolled regulation by the altered phosphorylation state of the components of these pathways often leads to increased cell proliferation and cell transformation. Many viruses encode oncogenic proteins, required for their efficient viral replication, which deregulate the activity of host cell proteins. This might program cells to a malignant state, underlying the molecular mechanism of tumor formation and cancer development. Recent studies reveal a role for a specific form of protein phosphatase 2A (PP2A) in viral-induced cell transformation by interaction with the small t antigen (ST) of the DNA tumor simian virus 40 (SV40).