Protein phosphatase 2A (PP2A) is a major form of serine/threonine phosphatase in many cell types. The purified enzyme is a heterotrimer composed of a catalytic subunit (C) and two regulatory subunits (A and B). While the A and C subunits appear to be relatively homogeneous, there are multiple distinct families of regulatory proteins (generally classified as B subunits) that create a diversity of enzyme forms with distinct enzymatic activities and substrate specificities. Biochemical and genetic evidence have shown that PP2A is involved in a number of cellular signalling pathways, including those controlling cell growth and proliferation. Alteration of PP2A activity by protein-protein interaction plays an important role in modulating signalling through these pathways. For example, interaction of polyomavirus middle tumor antigen with the AC complex is necessary but not sufficient for transformation by this protein. Our goal is to determine the molecular basis for the interaction of regulatory proteins with PP2A, the effects of these interactions on enzyme activity and specificity, and how these interactions control the phosphorylation states of cellular proteins. The A subunit plays a central role in bringing together the catalytic subunit with an array of regulatory proteins (B subunits and tumor antigens). We plan to determine the molecular basis for the interaction of the A subunit with the catalytic subunit and with previously characterized regulatory subunits. The binding domains and relevant amino acids involved in these interactions will be identified by biochemical methods, by deletional and site-directed mutagenesis of the cloned cDNA, and by structural analysis of the A subunit using circular dichroism and X-ray crystallography. New proteins that interact with and regulate the activity of PP2A will be identified by the polymerase chain reaction and cDNA cloning, by functional analysis, and by A subunit affinity chromatography. The molecular basis for the regulation of the activity and specificity of PP2A will be determined by identifying how previously characterized and newly identified regulatory proteins interact with the catalytic subunit in the heterotrimeric complexes. C subunit domains required for interaction with the A subunit will be identified by chemical crosslinking and deletional and site-directed mutagenesis.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
2R01HL031107-14
Application #
2028138
Study Section
Medical Biochemistry Study Section (MEDB)
Project Start
1983-07-01
Project End
2002-03-31
Budget Start
1997-04-01
Budget End
1998-03-31
Support Year
14
Fiscal Year
1997
Total Cost
Indirect Cost
Name
University of Texas Sw Medical Center Dallas
Department
Pharmacology
Type
Schools of Medicine
DUNS #
City
Dallas
State
TX
Country
United States
Zip Code
75390
Mumby, Marc (2007) PP2A: unveiling a reluctant tumor suppressor. Cell 130:21-4
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Price, N E; Mumby, M C (2000) Effects of regulatory subunits on the kinetics of protein phosphatase 2A. Biochemistry 39:11312-8
Price, N E; Wadzinski, B; Mumby, M C (1999) An anchoring factor targets protein phosphatase 2A to brain microtubules. Brain Res Mol Brain Res 73:68-77
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Yan, Y; Mumby, M C (1999) Distinct roles for PP1 and PP2A in phosphorylation of the retinoblastoma protein. PP2a regulates the activities of G(1) cyclin-dependent kinases. J Biol Chem 274:31917-24
Sontag, E; Nunbhakdi-Craig, V; Lee, G et al. (1999) Molecular interactions among protein phosphatase 2A, tau, and microtubules. Implications for the regulation of tau phosphorylation and the development of tauopathies. J Biol Chem 274:25490-8
Deng, X; Ito, T; Carr, B et al. (1998) Reversible phosphorylation of Bcl2 following interleukin 3 or bryostatin 1 is mediated by direct interaction with protein phosphatase 2A. J Biol Chem 273:34157-63
Yan, Y; Shay, J W; Wright, W E et al. (1997) Inhibition of protein phosphatase activity induces p53-dependent apoptosis in the absence of p53 transactivation. J Biol Chem 272:15220-6
Sontag, E; Nunbhakdi-Craig, V; Lee, G et al. (1996) Regulation of the phosphorylation state and microtubule-binding activity of Tau by protein phosphatase 2A. Neuron 17:1201-7

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