Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Arsenic, strongly associated with increased risks of human cancers, is a potent clastogen in a variety of mammalian cell systems. The effect of sodium arsenite (a trivalent arsenic compound) on chromatid separation was studied in human skin fibroblasts (HFW). Human fibroblasts were arrested in S phase by the aid of serum starvation and aphidicolin blocking and then these cells were allowed to synchronously progress into G2 phase. Treatment of the G2-enriched HFW cells with sodium arsenite (0-200 microM) resulted in arrest of cells in the G2 phase, interference with mitotic division, inhibition of spindle assembly, and induction of chromosome endoreduplication in their second mitosis. Sodium arsenite treatment also inhibited the activities of serine/threonine protein phosphatases and enhanced phosphorylation levels of a small heat shock protein (HSP27). These results suggest that sodium arsenite may mimic okadaic acid to induce chromosome endoreduplication through its inhibitory effect on protein phosphatase activity.
Environ Mol Mutagen 1995
PMID:Sodium arsenite induces chromosome endoreduplication and inhibits protein phosphatase activity in human fibroblasts. 773 36

The catalytic activity of p56lck is repressed by phosphorylation of a conserved carboxy-terminal tyrosine residue (tyrosine 505). Accumulating data show that this phosphorylation is mediated by the tyrosine protein kinase p50csk and that it is reversed by the transmembrane tyrosine protein phosphatase CD45. Recent studies have indicated that dephosphorylation of tyrosine 505 in resting T cells is necessary for the initiation of antigen-induced T-cell activation. To better understand this phenomenon, we have characterized the factors regulating tyrosine 505 phosphorylation in an antigen-specific T-cell line (BI-141). As is the case for other T-cell lines, Lck molecules from unstimulated BI-141 cells exhibited a pronounced dephosphorylation of the inhibitory carboxyl-terminal tyrosine. This state could be corrected by incubation of cells with the tyrosine protein phosphatase inhibitor pervanadate, suggesting that it reflected the unrestricted action of tyrosine protein phosphatases. In structure-function analyses, mutation of the site of Lck myristylation (glycine 2) partially restored phosphorylation at tyrosine 505 in BI-141 cells. Since the myristylation-defective mutant also failed to stably associate with cellular membranes, this effect was most probably the consequence of removal of p56lck from the vicinity of membrane phosphatases like CD45. Deletion of the unique domain of Lck, or its replacement by the equivalent sequence from p59fyn, also increased the extent of tyrosine 505 phosphorylation in vivo. This effect was unrelated to changes in Lck membrane association and therefore was potentially related to defects in crucial protein-protein interactions at the membrane. In contrast, deletion of the SH3 or SH2 domain, or mutation of the phosphotransfer motif (lysine 273) or the site of autophosphorylation (tyrosine 394), had no impact on phosphate occupancy at tyrosine 505. In combination, these results indicated that the hypophosphorylation of the inhibitory tyrosine of p56(lck) in T lymphocytes is likely the result of the predominant action of tyrosine protein phosphatases. Moreover, they showed that both the amino-terminal myristylation signal and the unique domain of p56(lck) play critical roles in this process.
Mol Cell Biol 1995 May
PMID:The unique amino-terminal domain of p56lck regulates interactions with tyrosine protein phosphatases in T lymphocytes. 773 23

Although steroid hormone receptor activation has been known to be dependent on ligand binding, we report here ligand-independent transcriptional activation of the vitamin D receptor and retinoid receptors. In these studies, CV1 cells were transiently transfected with a human vitamin D receptor (VDR) expression vector and a reporter plasmid that contains multiple copies of the rat osteocalcin vitamin D response element up-stream of the bacterial chloramphenicol acetyltransferase (CAT) gene [osteocalcin (OC)VDREtkCAT]. Treatment of cells with 10(-8) M 1,25-dihydroxyvitamin D3 resulted in a 25-fold induction of CAT activity. When cells were treated with 5-50 nM okadaic acid (OA), an inhibitor of protein phosphatase-1 and -2A, significant inductions of CAT activity (18- to 57-fold) were observed. As VDR and dopamine receptors are colocalized in certain brain regions, we also examined whether VDR-mediated transcription can be activated by dopamine. VDR was found to activate CAT gene expression in cells treated with 200-500 microM dopamine (3- to 11-fold induction) or the selective D1 agonist SKF38393 (20-fold induction). Cells were also transfected with retinoic acid receptor (RAR) or retinoid-X receptor (RXR) expression vectors and reporter plasmids that contain either a retinoic acid response element or an RXR-specific response element. OA alone induced chloramphenicol acetyltransferase (CAT) activity in cells transfected with RAR alpha, RAR beta, RXR alpha, RXR beta, or RXR gamma (3- to 18-fold induction). However, OA did not affect transcription by RAR gamma, suggesting specificity of activation by OA among the retinoid receptors. Although the retinoid receptors have been detected in brain, maximum stimulation of transcription was not greater than 1.6-fold in the presence of 100-500 microM dopamine or 100 microM SKF38393 treatment. These data suggest specificity for dopamine activation among steroid hormone receptors and that phosphorylation alone, in the absence of ligand, can activate VDR- and retinoid receptor-mediated transcription.
Mol Endocrinol 1995 Feb
PMID:Ligand occupancy is not required for vitamin D receptor and retinoid receptor-mediated transcriptional activation. 777 73

1. Nicotine stimulated two Ca(2+)-dependent processes in rat frontal cortex synaptosomes: the phosphorylation of an 80-kDa protein band and the release of endogenous ACh.3 Both effects were mediated by neuronal nAChRs and coincided with depolarization of the synaptosomal plasma membrane induced by the drug. Changes in the state of phosphorylation of the 80-kDa band (presumed to contain synapsin I) were correlated with changes in the release of ACh as follows, from 2 to 4. 2. Blockade of predominant, nerve terminal P-type Ca2+ channels with omega-agatoxin-IVA, did not prevent nicotine from stimulating ACh release. In contrast, exposure to the toxin partially inhibited the release promoted by the depolarizing agent veratridine and attenuated protein phosphorylation induced by either nicotine or veratridine. Taken together, these data suggest that, upon nicotine stimulation. Ca2+ enters nerve terminals through two distinct pathways. The first, via Ca2+ channels, is necessary (but not sufficient) for both nicotine-induced phosphorylation and ACh release. The second, both necessary and sufficient for nicotine-induced phosphorylation and release, is the neuronal nAChR itself. 3. Preincubation of the synaptosomes with a subeffective concentration of nicotine inactivated both nicotine-induced ACh liberation and phosphorylation. This shows that diminished release is associated to decreased phosphorylation of the 80-kDa protein band, most likely as a consequence of nicotine-promoted nAChR desensitization. 4. Augmented ACh release and phosphorylation of the 80-kDa protein band were achieved by using the protein phosphatase inhibitor okadaic acid. However, okadaic acid did not summate with either nicotine or veratridine to increase ACh release further. This is probably because okadaic acid, as in other neurons, increases intracellular Ca2+ (Cholewinski et al., 1993), thus promoting desensitization of ACh release.
Cell Mol Neurobiol 1994 Aug
PMID:Concomitant protein phosphorylation and endogenous acetylcholine release induced by nicotine: dependency on neuronal nicotinic receptors and desensitization. 778 41

Gamma interferon (IFN-gamma), a macrophage-activating cytokine, modulates gene expression through the activity of a transcription factor designated IFN-gamma activation factor (GAF). GAF is formed after phosphorylation on tyrosine and dimerization of the 91-kDa protein STAT1. We have recently reported that differentiation of the promonocytic cell line U937 into monocytes increases the amount of cellular GAF after IFN-gamma treatment and at the same time increases the phosphorylation of STAT1. Here we show that activation of the JAK family kinases, which are instrumental in mediating STAT1 phosphorylation on tyrosine, did not increase upon monocytic U937 differentiation. Consistent with this finding, levels of STAT1 tyrosine phosphorylation were virtually identical in promonocytic and monocytic U937 cells. Analysis of STAT1 phosphoamino acids and mapping of phosphopeptides showed an IFN-gamma-dependent increase in Ser phosphorylation in differentiated cells. Analyses of STAT1 isoforms by two-dimensional gel electrophoresis demonstrated a differentiation-induced shift toward more acidic isoforms. All isoforms were equally sensitive to subsequent tyrosine phosphorylation, as indicated by a sodium dodecyl sulfate-polyacrylamide gel electrophoresis mobility shift typical for tyrosine-phosphorylated STAT1. Consistent with the importance of Ser phosphorylation for high-affinity binding to the IFN-gamma activation site sequence, phosphatase 2A treatment strongly reduced the formation of IFN-gamma activation site-GAF complexes in an electrophoretic mobility shift assay. Our data indicate that the activity of GAF is modulated by STAT1 serine kinases/phosphatases and suggest that this mechanism is employed in the developmental control of macrophage responsiveness to IFN-gamma.
Mol Cell Biol 1995 Jul
PMID:Differentiation-regulated serine phosphorylation of STAT1 promotes GAF activation in macrophages. 779 65

The calmodulin-stimulated phosphatase calcineurin plays a critical role in calcium-dependent T-lymphocyte activation pathways. Here, we report the identification of a missense mutation in the calcineurin A alpha gene expressed by EL4 T-lymphoma cells. This mutation changes an evolutionarily conserved aspartic acid to asparagine within the autoinhibitory domain of the calcineurin A alpha protein. A comparison of wild-type and mutant autoinhibitory peptides indicates that this amino acid substitution greatly reduces inhibition of calcineurin phosphatase activity. Additional peptide inhibition studies support a pseudosubstrate model of autoinhibitory function, in which the conserved aspartic acid residue may serve as a molecular mimic of either phosphoserine or phosphothreonine. Expression of the mutant calcineurin appears to affect cellular signal transduction pathways, as EL4 cells can be activated by suboptimal concentrations of calcium ionophore in the presence of phorbol esters. Moreover, this phenotype can be transferred to Jurkat T cells by transfection of the mutated calcineurin gene. These findings implicate a conserved aspartic acid in the mechanism of calcineurin autoinhibition and suggest that mutation of this residue is associated with aberrant calcium-dependent signaling in vivo.
Mol Cell Biol 1995 Jul
PMID:Characterization of a mutant calcineurin A alpha gene expressed by EL4 lymphoma cells. 779 92

Two cDNA species encoding sequences homologous to the 65 kDa regulatory subunit (PR 65) of protein phosphatase 2A (PP2A) have been isolated from an Arabidopsis thaliana cDNA library. These were designated pDF1 and pDF2. pDF1 is 1795 bp long and by comparison with the human and porcine PP2A regulatory subunit sequences represents a full-length clone. It encodes a predicted polypeptide of 587 amino acid residues. pDF2 is truncated at the 5' end by 237 bp. The complete nucleotide sequences have been determined for both cDNA species. Comparison of the nucleotide and the deduced amino acid sequences showed that the two sequences were homologous but not identical and therefore must be derived from two different genes. Northern blot analysis was performed on total RNA and poly(A)+ RNA isolated from seed at various stages of development and from young leaf material of Brassica napus L. (oilseed rape). Both cDNA probes hybridised to a single major mRNA species of ca. 2.2 kb. The highest level of expression was observed in the total RNA from developing rape seed at about 33 days after flowering, and the transcript level in the poly(A)+ RNA of the seed was higher than in young leaf of oilseed rape. Southern blot analysis was performed on two varieties of A. thaliana and B. napus genomic DNA; this identified a small family of genes in A. thaliana consisting of at least 2 or 3 members and a larger multigene family in B. napus of at least 5 or 6 members. Two independent genomic clones were isolated from an A. thaliana genomic library. Sequencing of a fragment common to both revealed that the sequence was identical in both clones and, therefore, they were assumed to contain the same genomic sequence. The genomic sequence selected, designated regA, is 3639 bp long and the coding sequence contains eleven introns. The gene encodes a predicted polypeptide of 590 amino acid residues. The sequence comparison with both cDNA sequences showed that it is homologous but not identical to the two, confirming that at least three different genes exist in A. thaliana which encode PR65 of PP2A.
Plant Mol Biol 1994 Nov
PMID:Characterisation of cDNA and genomic clones encoding homologues of the 65 kDa regulatory subunit of protein phosphatase 2A in Arabidopsis thaliana. 781 71

Intracellular signaling by the second messenger Ca2+ through its receptor calmodulin (CaM) regulates cell function via the activation of CaM-dependent enzymes. Previous studies have shown that cell cycle progression at G1/S and G2/M is sensitive to intracellular CaM levels. However, little is known about the CaM-regulated enzymes involved. Protein phosphorylation has been shown to be important for cell-cycle regulation. Because CaM regulates several protein kinases, and at least one protein phosphatase, our studies are focusing on the roles of these enzymes within the cell cycle. As an initial approach to this problem, cDNAs encoding either normal or mutant calcium/calmodulin kinase II (CaMKII) have been expressed in Schizosaccharomyces pombe. The results show that overexpression of a constitutively active mutant CaMKII caused cell-cycle arrest in G2. Arrest was associated with a failure to activate the p34/cdc2 protein kinase. Expression of the mutant CaMKII in strains of S. pombe with altered timing of mitosis revealed that this effect is not mediated either by cdc25+ or wee1+, suggesting that CaMKII may regulate G2/M progression by another mechanism.
Mol Biol Cell 1994 Jul
PMID:Inhibition of G2/M progression in Schizosaccharomyces pombe by a mutant calmodulin kinase II with constitutive activity. 781 47

The expression of the three catalytic subunits of protein phosphatase (PP) type 1 and 2A, PP1 alpha, PP1 gamma 1, and PP2AC, was examined in 8 cases of lipoma as a benign tumor and 4 cases of liposarcoma as a malignant tumor using immunohistochemical analysis. Both types of of tumor cells stained positively with antisera against PP1 catalytic subunit isoforms PP1 alpha and PP1 gamma 1 were significantly higher in liposarcoma than in lipoma. Furthermore, liposarcoma showed a markedly high S-phase fraction in the cell cycle of tumor cells, as compared with lipoma. These results suggest that PP1 is involved in the accelerated growth of malignant cells in liposarcoma.
Res Commun Mol Pathol Pharmacol 1994 Sep
PMID:Enhanced expression of catalytic subunits of protein phosphatase type 1 and high S-phase fraction in liposarcoma. 782 12

The expression of the three catalytic subunits of protein phosphatase (PP) type 1 and 2A, PP1 alpha, PP1 gamma 1, and PP2AC, was examined in malignant fibrous histiocytoma using immunohistochemical analysis. The percentage of cells stained positively with antiserum against PP1 catalytic subunit isoform PP1 gamma 1 was significantly higher in tumorous region than in non-tumorous region of malignant fibrous histiocytoma. Furthermore, tumorous region showed markedly high S-phase fraction in the cell cycle, as compared to non-tumorous region. These results suggest that PP1 gamma 1 is involved in the accelerated growth of tumor cells in malignant fibrous histiocytoma.
Res Commun Mol Pathol Pharmacol 1994 Oct
PMID:Enhanced expression of catalytic subunit isoform PP1 gamma 1 of protein phosphatase type 1 in malignant fibrous histiocytoma. 785 Feb 51


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