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PROTEIN PHOSPHATASE 2A, CATALYTIC SUBUNIT, ALPHA ISOFORM; OKDB#: 1419
 Symbols: PROTEIN PHOSPHATASE 2A, CATALYTIC SUBUNIT, ALPHA I Species: human
 Synonyms: PP2CA|  Locus: 5q23-q31 in Homo sapiens


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General Comment Protein phosphorylation, a crucial posttranslational modification step controlling many diverse cellular functions, is dependent on the opposing actions of protein kinases and protein phosphatases. The enzyme protein phosphatase 2A is 1 of 4 major protein phosphatases identified in the cytosol of eukaryotic cells which are responsible for the dephosphorylation of serine and threonine residues in proteins. Although all 4 protein phosphatases, PP1, PP2A, PP2B, and PP2C, have overlapping substrate specificities in vitro, they can be distinguished by the use of inhibitor proteins and by their dependence on metal ions. PP1 is inhibited by nanomolar concentrations of 2 thermostable proteins, inhibitor 1 and inhibitor 2, whereas the type 2 phosphatases are unaffected by these inhibitors. The type 2 phosphatases can be distinguished by how their activity is regulated: PP2A activity is independent of metal ions, PP2B is activated by Ca(2+)/calmodulin, and PP2C is activated by Mg(2+).
General function Cell death/survival, Apoptosis, Cell cycle regulation, Enzyme, Transferase, Hydrolase, Nucleic acid binding, DNA binding, Transcription factor
Comment
Cellular localization Cytoplasmic, Nuclear, Mitochondrial
Comment
Ovarian function Oogenesis, Oocyte maturation
Comment Lu Q, et al 2002 reported the regulation of Spindle Formation by Active Mitogen-Activated Protein Kinase and Protein Phosphatase 2A During Mouse Oocyte Meiosis. Mitogen-activated protein kinase (MAPK) and protein phosphatase 2A (PP2A) regulate oocyte meiosis, yet little is known regarding their mechanisms of action. This study addressed the functional importance of active MAPK and PP2A in regulating oocyte meiosis. Experiments were conducted to identify MAPK activation, PP2A activity, intracellular enzyme trafficking, and ultrastructural associations during meiosis. Questions of requisite kinase and/or phosphatase activity and chromatin condensation, microtubule polymerization, and spindle formation were addressed. At the protein level, MAPK and PP2A were present in constant amounts throughout the first meiotic division. Both MAPK and PP2A were activated following germinal vesicle breakdown (GVBD) in conjunction with metaphase I development. Immunocytochemical studies confirmed the absence of active MAPK in germinal vesicle-intact (GVI) and GVBD oocytes. At metaphase I and during the metaphase I/metaphase II transition, activated MAPK colocalized with microtubules, poles, and plates of meiotic spindles. Protein phosphatase 2A was dispersed evenly throughout the GVI oocyte cytoplasm. Throughout the metaphase I/metaphase II transition, PP2A colocalized with microtubules of meiotic spindles. Both active MAPK and PP2A associated with in vitro-polymerized microtubules, suggesting that active MAPK and PP2A locally regulate spindle formation. Inhibition of MAPK activation resulted in compromised microtubule polymerization, no spindle formation, and loosely condensed chromosomes. Treatment with okadaic acid (OA) or calyculin-A (CL-A), which inhibits oocyte cytoplasmic PP2A, caused an absence of microtubule polymerization and spindles, even though MAPK activity was increased under these treatment conditions. Thus, active MAPK is required, but is not sufficient, for normal meiotic spindle formation and chromosome condensation. In addition, the oocyte OA/CL-A-sensitive PP, presumably PP2A, is essential for microtubule polymerization and meiotic spindle formation. Gene whose expression is detected by cDNA array hybridization: GDP/GTP exchangers, GTPase stimulators and inhibitors, apoptosis Rozenn Dalbis-Tran and Pascal Mermilloda
Expression regulated by LH
Comment
Ovarian localization Oocyte
Comment
Follicle stages Antral, Preovulatory
Comment
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Mutations 0 mutations
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created: Jan. 18, 2002, 11:13 a.m. by: hsueh   email:
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last update: July 26, 2006, 11:02 a.m. by: Alex    email:



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