Molecular cloning, expression, and characterization of PTPA, a protein that activates the tyrosyl phosphatase activity of protein phosphatase 2A.

The transduction of signals generated by protein kinases and phosphatases are critical for the ability of integrin αIIbβ3 to support stable platelet adhesion and thrombus formation. Unlike kinases, it remains unclear how serine/threonine phosphatases engage the signaling networks that are initiated following integrin ligation. Because protein-protein interactions form the backbone of signal transduction, we searched for proteins that interact with the catalytic subunit of protein phosphatase 2A (PP2Ac). In a yeast two-hybrid study, we identified a novel interaction between PP2Ac and an adaptor protein CIN85 (Cbl-interacting protein of 85 kDa). Truncation and alanine mutagenesis studies revealed that PP2Ac binds to the P3 block (396PAIPPKKPRP405) of the proline-rich region in CIN85. The interaction of purified PP2Ac with CIN85 suppressed phosphatase activity. Human embryonal kidney 293 αIIbβ3 cells overexpressing a CIN85 P3 mutant, which cannot support PP2Ac binding, displayed decreased adhesion to immobilized fibrinogen. Platelets contain the ∼85 kDa CIN85 protein along with the PP2Ac-CIN85 complex. A myristylated cell-permeable peptide derived from residues 395–407 of CIN85 protein (P3 peptide) disrupted the platelet PP2Ac-CIN85 complex and decreased αIIbβ3 signaling dependent functions such as platelet spreading on fibrinogen and thrombin-mediated fibrin clot retraction. In a phospho-profiling study P3 peptide treated platelets also displayed decreased phosphorylation of several signaling proteins including Src and GSK3β. Taken together, these data support a role for the novel PP2Ac-CIN85 complex in supporting integrin-dependent platelet function by dampening the phosphatase activity.

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Loss of a Protein Phosphatase 2A Regulatory Subunit (Cdc55p) Elicits Improper Regulation of Swe1p Degradation

Molecular and Cellular Biology ◽

10.1128/mcb.20.21.8143-8156.2000 ◽

2000 ◽

Vol 20 (21) ◽

pp. 8143-8156 ◽

Cited By ~ 37

Author(s):

Haifeng Yang ◽

Wei Jiang ◽

Matthew Gentry ◽

Richard L. Hallberg

Keyword(s):

Phosphatase Activity ◽

Protein Phosphatase ◽

Protein Phosphatase 2A ◽

Cell Types ◽

Regulatory Subunit ◽

Cyclin Dependent Kinase ◽

Wild Type ◽

Phosphatase 2A

ABSTRACT CDC55 encodes a Saccharomyces cerevisiaeprotein phosphatase 2A (PP2A) regulatory subunit.cdc55-null cells growing at low temperature exhibit a failure of cytokinesis and produce abnormally elongated buds, butcdc55-null cells producing the cyclin-dependent kinase Cdc28-Y19F, which is unable to be inhibited by Y19 phosphorylation, show a loss of the abnormal morphology. Furthermore,cdc55-null cells exhibit a hyperphosphorylation of Y19. For these reasons, we have examined in wild-type and cdc55-null cells the levels and activities of the kinase (Swe1p) and phosphatase (Mih1p) that normally regulate the extent of Cdc28 Y19 phosphorylation. We find that Mih1p levels are comparable in the two strains, and an estimate of the in vivo and in vitro phosphatase activity of this enzyme in the two cell types indicates no marked differences. By contrast, while Swe1p levels are similar in unsynchronized and S-phase-arrested wild-type and cdc55-null cells, Swe1 kinase is found at elevated levels in mitosis-arrestedcdc55-null cells. This excess Swe1p incdc55-null cells is the result of ectopic stabilization of this protein during G2 and M, thereby accounting for the accumulation of Swe1p in mitosis-arrested cells. We also present evidence indicating that, in cdc55-null cells, misregulated PP2A phosphatase activity is the cause of both the ectopic stabilization of Swe1p and the production of the morphologically abnormal phenotype.

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Characterization of a unique aspartate-rich protein of the SET/TAF-family in the human malaria parasite, Plasmodium falciparum, which inhibits protein phosphatase 2A

Molecular and Biochemical Parasitology ◽

10.1016/s0166-6851(02)00293-1 ◽

2003 ◽

Vol 126 (2) ◽

pp. 239-250 ◽

Cited By ~ 17

Author(s):

Sean Dobson ◽

Rajinder Kumar ◽

Valerie Bracchi-Ricard ◽

Scott Freeman ◽

Samer W.K. Al-Murrani ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Protein Phosphatase ◽

Malaria Parasite ◽

Protein Phosphatase 2A ◽

Human Malaria Parasite ◽

Human Malaria ◽

Parasite Plasmodium ◽

Parasite Plasmodium Falciparum ◽

Phosphatase 2A

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An inactive protein phosphatase 2A population is associated with methylesterase and can be re-activated by the phosphotyrosyl phosphatase activator

Biochemical Journal ◽

10.1042/bj20031643 ◽

2004 ◽

Vol 380 (1) ◽

pp. 111-119 ◽

Cited By ~ 72

Author(s):

Sari LONGIN ◽

Jan JORDENS ◽

Ellen MARTENS ◽

Ilse STEVENS ◽

Veerle JANSSENS ◽

...

Keyword(s):

Phosphatase Activity ◽

Protein Phosphatase ◽

Protein Phosphatase 2A ◽

Phosphatase 2A ◽

Inactive Protein

We have described recently the purification and cloning of PP2A (protein phosphatase 2A) leucine carboxylmethyltransferase. We studied the purification of a PP2A-specific methylesterase that co-purifies with PP2A and found that it is tightly associated with an inactive dimeric or trimeric form of PP2A. These inactive enzyme forms could be reactivated as Ser/Thr phosphatase by PTPA (phosphotyrosyl phosphatase activator of PP2A). PTPA was described previously by our group as a protein that stimulates the in vitro phosphotyrosyl phosphatase activity of PP2A; however, PP2A-specific methyltransferase could not bring about the activation. The PTPA activation could be distinguished from the Mn2+ stimulation observed with some inactive forms of PP2A, also found associated with PME-1 (phosphatase methylesterase 1). We discuss a potential new function for PME-1 as an enzyme that stabilizes an inactivated pool of PP2A.

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