ERKs are inactivated by the protein phosphatase 2A (PP2A). The PP2A holoenzyme is a heterotrimer that consists of a core dimer, composed of a scaffold (A) and a catalytic (C) subunit that associates with a variety of regulatory (B) subunits. The B subunits have been divided into gene families named B (or PR55), B0 (or B56 or PR61) and B00 (or PR72). Each family comprises several members. B56 family members of PP2A in particular, increase ERK dephosphorylation, without affecting its activation by MEK.
Induction of PP2A is involved in the extracellular signal-regulated kinase (ERK) signalling pathway, in which it provides a feedback control, as well as in a broad range of other cellular processes, including transcriptional regulation and control of the cell cycle.This diversity of functions is conferred by a diversity of regulatory subunits, the combination of which can give rise to over 50 different forms of PP2A. For example, five distinct mammalian genes encode members of the B56 family, called B56a, b, g, d and e, generating at least eight isoforms. Whether a specific holoenzyme dephosphorylates ERK and whether this activity is controlled during mitogenic stimulation is unknown.