Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.3.16 (calcineurin)
 17,112 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Activating phosphorylation of cyclin-dependent protein kinases (CDKs) is necessary for their kinase activity and cell cycle progression. This phosphorylation is carried out by the Cdk-activating kinase (CAK); in contrast, little is known about the corresponding protein phosphatase. We show that type 2C protein phosphatases (PP2Cs) are responsible for this dephosphorylation of Cdc28p, the major budding yeast CDK. Two yeast PP2Cs, Ptc2p and Ptc3p, display Cdc28p phosphatase activity in vitro and in vivo, and account for approximately 90% of Cdc28p phosphatase activity in yeast extracts. Overexpression of PTC2 or PTC3 results in synthetic lethality in strains temperature-sensitive for yeast CAK1, and disruptions of PTC2 and PTC3 suppress the growth defect of a cak1 mutant. Furthermore, PP2C-like enzymes are the predominant phosphatases toward human Cdk2 in HeLa cell extracts, indicating that the substrate specificity of PP2Cs toward CDKs is evolutionarily conserved.
 ...
PMID:Dephosphorylation of cyclin-dependent kinases by type 2C protein phosphatases. 1058 2

pRB, the tumor suppressor product of the retinoblastoma susceptibility gene, is regarded as one of the key regulators of the cell cycle. This protein exerts its growth suppressive effect through its ability to bind and interact with a variety of cellular proteins. In turn, pRB binding and interacting ability is governed by its phosphorylation state. In recent years, this negative growth regulatory protein has captured a great deal of attention from investigators around the world due to its ability to modulate the activity of transcription regulatory proteins, enzymes which modify chromatin, and other cellular proteins which contribute to its complex role in mammalian cells. Hypophosphorylated pRB binds and sequesters transcription factors, most notably those of the E2F/DP family, inhibiting the transcription of genes required to traverse the G1 to S phase boundary. This cell cycle inhibitory function is abrogated when pRB undergoes phosphorylation mediated by cyclin/cdk complexes following cell stimulation by mitogens. Removal of these phosphates appears to be carried out by a multimeric complex of protein phosphatase type 1 (PP1) and noncatalytic regulatory subunits at the completion of mitosis. This dephosphorylation returns pRB to its active, growth suppressive state. While the mechanism of pRB phosphorylation has and continues to be extensively studied, dephosphorylation of pRB has received disproportionately less attention. The goal of this review is to revisit the role of pRB dephosphorylation in regulating the cell cycle. Emphasis will be placed on understanding the function and regulation of pRB during the cell cycle as well as our ever-expanding notions of pRB-PP1 interaction and the mechanism of pRB dephosphorylation at mitotic exit.
 ...
PMID:Role of pRB dephosphorylation in cell cycle regulation. 1070 84

Cyclin dependent kinase 4 (cdk4) activity is controlled by the binding of regulatory subunits and inhibitory factors, as well as tyrosine and serine/threonine phosphorylation. More recently the influence of calcium levels have been demonstrated. Using transient transfections in Jurkat cells, we observed specific binding between cdk4 and the calcium and calmodulin activated serine/threonine phosphatase, calcineurin. Furthermore, we demonstrated that the inhibition of the phosphatase activity of calcineurin with FK506 and cyclosporin A resulted in an overall increase in cdk4 kinase activity, suggesting that the phosphatase activity of calcineurin was inhibitory to the kinase activity of cdk4. In contrast, we were not able to observe a similar effect on the kinase activity of either cdk6 or cdk2, indicating that the phosphatase activity of calcineurin was specific for cdk4. In addition, using an in vitro phosphatase assay for calcineurin, we observed that the exogenous addition of calcineurin resulted in the dephosphorylation of cdk4, an event that downregulated the kinase activity of cdk4. Calcineurin could, therefore, play an opposing role to the action of the cyclin activating kinase complex, an enzyme that upregulates the kinase activity of cdk4, an important G0/G1 checkpoint element in mammalian cells. Oncogene (2000) 19, 2820 - 2827
 ...
PMID:Calcineurin regulation of the mammalian G0/G1 checkpoint element, cyclin dependent kinase 4. 1085 Oct 85

The Vpr protein of primate lentiviruses arrests cell cycling at the G(2)/M phase through an inactivation of cyclin B-p34(cdc2) and its upstream regulator cdc25. We provide here biochemical and functional evidence demonstrating that human immunodeficiency virus type 1 (HIV-1) Vpr mediates G(2) arrest by forming a complex with protein phosphatase 2A (PP2A), an upstream regulator of cdc25. Vpr associates with PP2A through a specific interaction with the B55 regulatory subunit. This interaction is necessary but not sufficient for G(2) arrest. Interestingly, we found that Vpr association with B55-containing PP2A targets the enzymatic complex to the nucleus and, importantly, enhances the recruitment and dephosphorylation of the cdc25 substrate. Our data suggest that Vpr mediates G(2) arrest by enhancing the nuclear import of PP2A and by positively modulating its catalytic activity towards active phosphorylated nuclear cdc25.
 ...
PMID:Human immunodeficiency virus type 1 Vpr-mediated G(2) cell cycle arrest: Vpr interferes with cell cycle signaling cascades by interacting with the B subunit of serine/threonine protein phosphatase 2A. 1211 Jun 3

Cell-cycle transition at G2-M is controlled by MPF (M-phase-promoting factor), a complex consisting of the Cdc2 kinase and a B-type cyclin. We have shown that in mice, targeted disruption of an A-type cyclin gene, cyclin A1, results in a block of spermatogenesis prior to the entry into metaphase I. The meiotic arrest is accompanied by a defect in Cdc2 kinase activation at the G2--M transition, raising the possibility that a cyclin A1-dependent process dictates the activation of MPF. Here we show that like Cdc2, the expression of B-type cyclins is retained in cyclin A1-deficient spermatocytes, while their associated kinases are kept at inactive states. Treatment of arrested germ cells with the protein phosphatase type-1 and -2A inhibitor okadaic acid restores the MPF activity and induces entry into M phase and the formation of normally condensed chromosome bivalents, concomitant with hyperphosphorylation of Cdc25 proteins. Conversely, inhibition of tyrosine phosphatases, including Cdc25s, by vanadate suppresses the okadaic acid-induced metaphase induction. The highest levels of Cdc25A and Cdc25C expression and their subcellular localization during meiotic prophase coincide with that of cyclin A1, and when overexpressed in HeLa cells, cyclin A1 coimmunoprecipitates with Cdc25A. Furthermore, the protein kinase complexes consisting of cyclin A1 and either Cdc2 or Cdk2 phosphorylate both Cdc25A and Cdc25C in vitro. These results suggest that in normal meiotic male germ cells, cyclin A1 participates in the regulation of other protein kinases or phosphatases critical for the G2-M transition. In particular, it may be directly involved in the initial amplification of MPF through the activating phosphorylation on Cdc25 phosphatases.
 ...
PMID:A role for cyclin A1 in the activation of MPF and G2-M transition during meiosis of male germ cells in mice. 1092 75

The influence of reversible protein phosphorylation on nucleosome assembly during DNA replication was analyzed in extracts from human cells. Inhibitor studies and add-back experiments indicated requirements of cyclin A/Cdk2, cyclin E/Cdk2, and protein phosphatase type 1 (PP1) activities for nucleosome assembly during DNA synthesis by chromatin assembly factor 1 (CAF-1). The p60 subunit of CAF-1 is a molecular target for reversible phosphorylation by cyclin/Cdk complexes and PP1 during nucleosome assembly and DNA synthesis in vitro. Purified p60 can be directly phosphorylated by purified cyclin A/Cdk2, cyclin E/Cdk2, and cyclin B1/Cdk1, but not by cyclin D/Cdk4 complexes in vitro. Cyclin B1/Cdk1 triggers hyperphosphorylation of p60 in the presence of additional cytosolic factors. CAF-1 containing hyperphosphorylated p60 prepared from mitotic cells is inactive in nucleosome assembly and becomes activated by dephosphorylation in vitro. These data provide functional evidence for a requirement of the cell cycle machinery for nucleosome assembly by CAF-1 during DNA replication.
 ...
PMID:Requirement of Cyclin/Cdk2 and protein phosphatase 1 activity for chromatin assembly factor 1-dependent chromatin assembly during DNA synthesis. 1093 80

The cyclin-dependent kinase (Cdk)-associated protein phosphatase (KAP) is a human dual specificity protein phosphatase that dephosphorylates Cdk2 on threonine 160 in a cyclin-dependent manner. To investigate whether mutations of this enzyme occur in hepatocellular carcinoma (HCC), KAP mRNA was analyzed by reverse transcription-PCR (RT-PCR), followed by cloning and sequencing. Eight of 14 biopsy tissues obtained from advanced HCC, 6 of 13 surgically removed HCC tissues, and 2 of the adjacent noncancerous tissues contained aberrant KAP transcripts. Using the yeast two-hybrid system, five of seven representative KAP mutants were shown to be defective in interacting with Cdk2. These data suggest a possible role of KAP mutations in multiple-step hepatocarcinogenesis.
 ...
PMID:Aberrant transcripts of the cyclin-dependent kinase-associated protein phosphatase in hepatocellular carcinoma. 1098 70

At the end of the cell cycle, cyclin-dependent kinase (CDK) activity is inactivated to allow mitotic exit [1]. A protein phosphatase, Cdc14, plays a key role during mitotic exit in budding yeast by activating the Cdh1 component of the anaphase-promoting complex to degrade cyclin B (Clb) and inducing the CDK inhibitor Sic1 to inactivate Cdk1 [2]. To prevent mitotic exit when the cell cycle is arrested at G2/M, cells must prevent CDK inactivation. In the spindle checkpoint pathway, this is accomplished through Bfa1/Bub2, a heteromeric GTPase-activating protein (GAP) that inhibits Clb degradation by keeping the G protein Tem1 inactive [3-5]. Tem1 is required for Cdc14 activation. Here we show that in budding yeast, BUB2 and BFA1 are also required for the maintenance of G2/M arrest in response to DNA damage and to spindle misorientation. cdc13-1 bub2 and cdc13-1 bfa1 but not cdc13-1 mad2 double mutants rebud and reduplicate their DNA at the restrictive temperature. We also found that the delay in mitotic exit in mutants with misoriented spindles depended on BUB2 and BFA1, but not on MAD2. We propose that Bfa1/Bub2 checkpoint pathway functions as a universal checkpoint in G2/M that prevents CDK inactivation in response to cell-cycle delay in G2/M.
 ...
PMID:The Bfa1/Bub2 GAP complex comprises a universal checkpoint required to prevent mitotic exit. 1108 39

In Alzheimer disease brain the activities of protein phosphatase (PP)-2A and PP-1 are decreased and the microtubule-associated protein tau is abnormally hyperphosphorylated at several sites at serine/threonine. Employing rat forebrain slices kept metabolically active in oxygenated artificial CSF as a model system, we investigated the role of PP-2A/PP-1 in the regulation of some of the major abnormally hyperphosphorylated sites of tau and the protein kinases involved. Treatment of the brain slices with 1.0 microM okadaic acid inhibited approximately 65% of PP-2A and produced hyperphosphorylation of tau at Ser 198/199/202, Ser 396/404 and Ser 422. No significant changes in the activities of glycogen synthase kinase-3 (GSK-3) and cyclin dependent protein kinases cdk5 and cdc2 were observed. Calyculin A (0.1 microM) inhibited approximately 50% PP-1, approximately 20% PP-2A, 50% GSK-3 and approximately 30% cdk5 but neither inhibited the activity of cyclin AMP dependent protein kinase A (PKA) nor resulted in the hyperphosphorylation of tau at any of the above sites. Treatment of brain slices with 1 microM okadaic acid plus 0.1 microM calyculin A inhibited approximately 100% of both PP-2A and PP-1, approximately 80% of GSK-3, approximately 50% of cdk5 and approximately 30% of cdc2 but neither inhibited PKA nor resulted in the hyperphosphorylation of tau at any of the above sites. These studies suggest (i) that PP-1 upregulates the phosphorylation of tau at Ser 198/199/202 and Ser 396/404 indirectly by regulating the activities of GSK-3, cdk5 and cdc2 whereas PP-2A regulates the phosphorylation of tau directly by dephosphorylation at the above sites, and (ii) that a decrease in the PP-2A activity leads to abnormal hyperphosphorylation of tau at Ser 198/199/202, Ser 396/404 and Ser 422.
 ...
PMID:Role of protein phosphatase-2A and -1 in the regulation of GSK-3, cdk5 and cdc2 and the phosphorylation of tau in rat forebrain. 1108 71

Cdc25A is a dual-specific protein phosphatase involved in the regulation of the kinase activity of Cdk-cyclin complexes in the eukaryotic cell cycle. To understand the mechanism of this important regulator, we have generated highly purified biochemical reagents to determine the kinetic constants for human Cdc25A with respect to a set of peptidic, artificial, and natural substrates. Cdc25A and its catalytic domain (dN25A) demonstrate very similar kinetics toward the artificial substrates p-nitrophenyl phosphate (k(cat)/K(m) = 15-25 M(-1) s(-1)) and 3-O-methylfluorescein phosphate (k(cat)/K(m) = 1.1-1.3 x 10(4) M(-1) s(-1)). Phospho-peptide substrates exhibit extremely low second-order rate constants and a flat specificity profile toward Cdc25A and dN25A (k(cat)/K(m) = 1 to 10 M(-1) s(-1)). In contrast to peptidic substrates, Cdc25A and dN25A are highly active phosphatases toward the natural substrate, T14- and Y15-bis-phosphorylated Cdk2/CycA complex (Cdk2-pTpY/CycA) with k(cat)/K(m) values of 1.0-1.1 x 10(6) M(-1) s(-1). In the context of the Cdk2-pTpY/CycA complex, phospho-threonine is preferred over phospho-tyrosine by more than 10-fold. The highly homologous catalytic domain of Cdc25c is essentially inactive toward Cdk2-pTpY/CycA. Taken together these data indicate that a significant degree of the specificity of Cdc25 toward its Cdk substrate resides within the catalytic domain itself and yet is in a region(s) that is outside the phosphate binding site of the enzyme.
 ...
PMID:Specificity of natural and artificial substrates for human Cdc25A. 1116 Dec 93


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>