scholarly journals Protein phosphatase 2A associates with and regulates atypical PKC and the epithelial tight junction complex

2002 ◽  
Vol 158 (5) ◽  
pp. 967-978 ◽  
Author(s):  
Viyada Nunbhakdi-Craig ◽  
Thomas Machleidt ◽  
Egon Ogris ◽  
Dennis Bellotto ◽  
Charles L. White ◽  
...  
Keyword(s):  
Okadaic Acid ◽  
Protein Phosphatase ◽  
Paracellular Permeability ◽  
Major Protein ◽  
Calcium Dependent ◽  
Atypical Pkc ◽  
Phosphatase 2A ◽  
Epithelial Tight Junction ◽  
And Function ◽  
Darby Canine Kidney

Tight junctions (TJs) play a crucial role in the establishment of cell polarity and regulation of paracellular permeability in epithelia. Here, we show that upon calcium-induced junction biogenesis in Madin-Darby canine kidney cells, ABαC, a major protein phosphatase (PP)2A holoenzyme, is recruited to the apical membrane where it interacts with the TJ complex. Enhanced PP2A activity induces dephosphorylation of the TJ proteins, ZO-1, occludin, and claudin-1, and is associated with increased paracellular permeability. Expression of PP2A catalytic subunit severely prevents TJ assembly. Conversely, inhibition of PP2A by okadaic acid promotes the phosphorylation and recruitment of ZO-1, occludin, and claudin-1 to the TJ during junctional biogenesis. PP2A negatively regulates TJ assembly without appreciably affecting the organization of F-actin and E-cadherin. Significantly, inhibition of atypical PKC (aPKC) blocks the calcium- and serum-independent membrane redistribution of TJ proteins induced by okadaic acid. Indeed, PP2A associates with and critically regulates the activity and distribution of aPKC during TJ formation. Thus, we provide the first evidence for calcium-dependent targeting of PP2A in epithelial cells, we identify PP2A as the first serine/threonine phosphatase associated with the multiprotein TJ complex, and we unveil a novel role for PP2A in the regulation of epithelial aPKC and TJ assembly and function.

Stimulatory phosphorylation of cAMP-specific PDE4D5 by contractile agonists is mediated by PKC-dependent inactivation of protein phosphatase 2A

2008 ◽  
Vol 294 (1) ◽  
pp. G327-G335 ◽  
Author(s):  
Karnam S. Murthy ◽  
Wimolpak Sriwai
Keyword(s):  
Smooth Muscle ◽  
Muscle Contraction ◽  
Okadaic Acid ◽  
Protein Phosphatase ◽  
Dependent Inactivation ◽  
Rhythmic Cycles ◽  
Phosphatase 2A ◽  
Contraction And Relaxation ◽  
Camp Levels

Smooth muscle of the gut undergoes rhythmic cycles of contraction and relaxation. Various constituents in the pathways that mediate muscle contraction could act to cross-regulate cAMP or cGMP levels and terminate subsequent relaxation. We have previously shown that cAMP levels are regulated by PKA-mediated phosphorylation of cAMP-specific phosphodiesterase 3A (PDE3A) and PDE4D5; the latter is the only PDE4D isoform expressed in smooth muscle. In the present study we have elucidated a mechanism whereby cholecystokinin (CCK) and, presumably, other contractile agonists capable of activating PKC can cross-regulate cAMP levels. Forskolin stimulated PDE4D5 phosphorylation and PDE4D5 activity. CCK significantly increased forskolin-stimulated PDE4D5 phosphorylation and activity and attenuated forskolin-stimulated cAMP levels. The effect of CCK on forskolin-induced PDE4D5 phosphorylation and activity and on cAMP levels was blocked by the inhibitors of PLC or PKC and in cultured muscle cells by the expression of Gαq minigene. The effects of CCK on PDE4D5 phosphorylation, PDE4D5 activity, and cAMP levels were mimicked by low (1 nM) concentrations of okadaic acid, but not by a low (10 nM) concentration of tautomycin, suggesting involvement of PP2A. Purified catalytic subunit of PP2A but not PP1 dephosphorylated PDE4D5 in vitro. Coimmunoprecipitation studies demonstrated association of PDE4D5 with PP2A and the association was decreased by the activation of PKC. In conclusion, cAMP levels are cross-regulated by contractile agonists via a mechanism that involves PLC-β-dependent, PKC-mediated inhibition of PP2A activity that leads to increase in PDE4D5 phosphorylation and activity and inhibition of cAMP levels.

Propofol Inhibits Phosphorylation of N -methyl-d-aspartate Receptor NR1 Subunits in Neurons

2006 ◽  
Vol 104 (4) ◽  
pp. 763-769 ◽  
Author(s):  
Seth Kingston ◽  
Limin Mao ◽  
Lu Yang ◽  
Anish Arora ◽  
Eugene E. Fibuch ◽  
...  
Keyword(s):  
Glutamate Receptors ◽  
Okadaic Acid ◽  
Protein Phosphatase ◽  
Cortical Neurons ◽  
Protein Phosphatase 2A ◽  
Ionotropic Glutamate Receptors ◽  
Dependent Manner ◽  
Calyculin A ◽  
General Anesthetic ◽  
Phosphatase 2A

Background Anesthetics may interact with ionotropic glutamate receptors to produce some of their biologic actions. Cellular studies reveal that the ionotropic glutamate receptors, N-methyl-D-aspartate receptors (NMDARs), can be phosphorylated on their NR1 subunits at the C-terminal serine residues, which is a major mechanism for the regulation of NMDAR functions. It is currently unknown whether anesthetics have any modulatory effects on NMDAR NR1 subunit phosphorylation. Methods The possible effect of a general anesthetic propofol on phosphorylation of NR1 subunits at serine 897 (pNR1S897) and 896 (pNR1S896) was detected in cultured rat cortical neurons. Results Propofol consistently reduced basal levels of pNR1S897 and pNR1S896 in a concentration-dependent manner. This reduction was rapid as the reliable reduction of pNR1S896 developed 1 min after propofol administration. Pretreatment of cultures with the protein phosphatase 2A inhibitors okadaic acid or calyculin A blocked the effect of propofol on the NR1 phosphorylation, whereas okadaic acid or calyculin A alone did not alter basal pNR1S897 and pNR1S896 levels. In addition, propofol decreased tyrosine phosphorylation of protein phosphatase 2A at tyrosine 307, resulting in an increase in protein phosphatase 2A activity. In the presence of propofol, the NMDAR agonist-induced intracellular Ca2+ increase was impaired in neurons with dephosphorylated NR1 subunits. Conclusions Together, these data indicate an inhibitory effect of a general anesthetic propofol on NMDAR NR1 subunit phosphorylation in neurons. This inhibition was mediated through a signaling mechanism involving activation of protein phosphatase 2A.

Protein Phosphatase 2A Inactivates Bcl2’s Antiapoptotic Function by Dephosphorylation and Up-Regulation of Bcl2-p53 Binding.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1436-1436
Author(s):  
Xingming Deng ◽  
Fengqin Gao ◽  
Tammy Flagg ◽  
W. Stratford May
Keyword(s):  
Cell Death ◽  
Cell Survival ◽  
Okadaic Acid ◽  
Protein Phosphatase ◽  
Apoptotic Cell ◽  
Protein Phosphatase 2A ◽  
Survival Function ◽  
Phosphorylation Site ◽  
Apoptotic Cell Death ◽  
Phosphatase 2A

Abstract DNA damage-induced p53/Bcl2 interaction at the outer mitochondrial membranes results in a Bcl2 conformational change and loss of its antiapoptotic function. Our data now indicate that either treatment of cells with the protein phosphatase 2A (PP2A) inhibitor, okadaic acid (10 nM), or specific disruption of PP2A activity by the expression of SV40 small tumor antigen enhances Bcl2 phosphorylation and suppresses the cisplatin-stimulated Bcl2-p53 interaction in association with prolonged cell survival. By contrast, C2-ceramide, a potent PP2A activator, reduces Bcl2 phosphorylation and increases Bcl2-p53 binding and promotes apoptotic cell death, suggesting that PP2A may function as a physiological regulator of Bcl2 by, at least in part, affecting its association with p53. Overexpression of the PP2A catalytic subunit (PP2A/C) suppresses Bcl2 phosphorylation in association with increased p53-Bcl2 binding and apoptotic cell death. By contrast, specific depletion of PP2A/C by RNA interference enhances Bcl2 phosphorylation, suppresses p53-Bcl2 interaction and prolongs cell survival. Purified PP2A can directly enhance the formation of the p53-Bcl2 complex in vitro in an okadaic acid-sensitive manner, supporting a direct mechanism. Importantly, PP2A directly interacts with Bcl2 at its BH4 domain which may function as the PP2A ‘docking site’ to potentially ‘bridge’ PP2A to the flexible loop domain which contains the physiological serine 70 phosphorylation site. Thus, PP2A may provide a double whammy to Bcl2’s survival function by both dephosphorylating and enhancing p53-Bcl2 binding. Therapeutically stimulating Bcl2 dephosphorylation and/or increasing Bcl2/p53 binding by activating PP2A may represent an efficient and novel antineoplastic approach.

scholarly journals Protein Phosphatase 2A Reactivates FOXO3a through a Dynamic Interplay with 14-3-3 and AKT

2010 ◽  
Vol 21 (6) ◽  
pp. 1140-1152 ◽  
Author(s):  
Amrik Singh ◽  
Min Ye ◽  
Octavian Bucur ◽  
Shudong Zhu ◽  
Maria Tanya Santos ◽  
...  
Keyword(s):  
Subcellular Localization ◽  
Transcriptional Activation ◽  
Protein Phosphatase ◽  
Nuclear Translocation ◽  
Akt Phosphorylation ◽  
Forkhead Box ◽  
Phosphatase 2A ◽  
And Function ◽  
Dynamic Interplay

Forkhead box transcription factor FOXO3a, a key regulator of cell survival, is regulated by reversible phosphorylation and subcellular localization. Although the kinases regulating FOXO3a activity have been characterized, the role of protein phosphatases (PP) in the control of FOXO3a subcellular localization and function is unknown. In this study, we detected a robust interaction between FOXO3a and PP2A. We further demonstrate that 14-3-3, while not impeding the interaction between PP2A and FOXO3a, restrains its activity toward AKT phosphorylation sites T32/S253. Disruption of PP2A function revealed that after AKT inhibition, PP2A-mediated dephosphorylation of T32/S253 is required for dissociation of 14-3-3, nuclear translocation, and transcriptional activation of FOXO3a. Our findings reveal that distinct phosphatases dephosphorylate conserved AKT motifs within the FOXO family and that PP2A is entwined in a dynamic interplay with AKT and 14-3-3 to directly regulate FOXO3a subcellular localization and transcriptional activation.

Sign in / Sign up

Export Citation Format

Share Document