Protein phosphatase 2A1 is the major enzyme in vertebrate cell extracts that dephosphorylates several physiological substrates for cyclin-dependent protein kinases.

Abstract

Okadaic acid (2 nM) inhibited by 80-90% the protein phosphatase activities in diluted extracts of rat liver, human fibroblasts, and Xenopus eggs acting on three substrates (high mobility group protein-I(Y), caldesmon and histone H1) phosphorylated by a cyclin-dependent protein kinase (CDK) suggesting that a type-2A phosphatase was responsible for dephosphorylating each protein. This result was confirmed by anion exchange chromatography of rat liver and Xenopus extracts, which demonstrated that the phosphatases acting on these substrates coeluted with the two major species of protein phosphatase 2A, termed PP2A1 and PP2A2. When matched for activity toward glycogen phosphorylase, PP2A1 was five- to sevenfold more active than PP2A2 and 35-fold to 70-fold more active than the free catalytic subunit (PP2Ac) toward the three CDK-labeled substrates. Protein phosphatases 1, 2B, and 2C accounted for a negligible proportion of the activity toward each substrate under the assay conditions examined. The results suggest that PP2A1 is the phosphatase that dephosphorylates a number of CDK substrates in vivo and indicate that the A and B subunits that are associated with PP2Ac in PP2A1 accelerate the dephosphorylation of CDK substrates, while suppressing the dephosphorylation of most other proteins. The possibility that PP2A1 activity is regulated during the cell cycle is discussed.

Vimentin Dephosphorylation by Protein Phosphatase 2A Is Modulated by the Targeting Subunit B55

“…Because such hyperphosphorylated vimentin was completely insoluble, we were constrained to measure dephosphorylation on phosphovimentin adsorbed to nitrocellulose strips. In these assays recombinant B55 increased the specificity of dimeric PP2A by approximately fivefold, an increase similar to that measured with histone H1, which is a highly specific substrate for B55-containing PP2A (Ferrigno et al, 1993). Further confirmation that PP2A could act on native vimentin was derived from an in situ assay, which is based on the assumption that vimentin phosphorylation induces its disassembly and bundling, whereas dephosphorylation would induce reassembly into filaments (Inagaki et al, 1996).…”

“…The lack of functional B55 in yeast and Drosophila causes severe aberrations in mitotic transit (Healy et al, 1991;Mayer-Jaekel et al, 1993;Wang and Burke, 1997) presumably because of the lack of dephosphorylation of certain p34 cdc2 phosphorylated sites (Ferrigno et al, 1993;. It was recently also reported that B55 associates with the microtubule network (Sontag et al, 1995).…”

“…The 55-kDa regulatory subunit B55 (or PR55) was one of the first B-type regulators to be identified in skeletal muscle preparations of PP2A, and subsequent cDNA cloning revealed evolutionary conservation from yeast to human (Healy et al, 1991;Mayer et al, 1991;Pallas et al, 1992;Mayer-Jaekel et al, 1993). The lack of functional B55 in yeast and Drosophila causes severe aberrations in mitotic transit (Healy et al, 1991;Mayer-Jaekel et al, 1993;Wang and Burke, 1997) presumably because of the lack of dephosphorylation of certain p34 cdc2 phosphorylated sites (Ferrigno et al, 1993;. It was recently also reported that B55 associates with the microtubule network (Sontag et al, 1995).…”

Upregulation of miR-27a contributes to the malignant transformation of human bronchial epithelial cells induced by SV40 small T antigen

“…The alteration of the phosphorylation status of signaling molecules has been demonstrated to be the primary action of the ST antigen in cell transformation (Janssens and Goris, 2001; Moreno Sablina and Hahn, 2008). Indeed, PP2A complexes formed by various B subunits confer specificity of substrates dephosphorylation (Ferrigno et al, 1993;Cegielska et al, 1994). Among them, several members of the B56 family have been reported to have important roles in control of PP2A potential tumorsuppressive activity by dephosphorylation of its target oncogene (Arnold and Sears, 2006;Margolis et al, 2006;Grochola et al, 2009;Shouse et al, 2010).…”

Protein phosphatase 2A subunit assembly: the catalytic subunit carboxy terminus is important for binding cellular B subunit but not polyomavirus middle tumor antigen

“…For example, the B subunit greatly increases PP2A activity towards cdc2 phosphorylated histone H1 (Sola et al, 1991;Agostinis et al, 1992;Ferrigno et al, 1993;Mayer-Jaekel et al, 1994). PP2A regulation during the development in di erent tissues may therefore occur in part through di erential expression of the various subunits (for review, see Mumby and Walter, 1993).…”