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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Src and Yes protein-tyrosine kinase activities are elevated in malignant and premalignant tumors of the colon. To determine whether Src activity is elevated throughout the human colon carcinoma cell cycle as it is in polyomavirus middle T antigen- or F527 Src-transformed cells, and whether Yes activity, which is lower than that of Src in the carcinoma cells, is regulated differently, we measured their activities in cycling cells. We observed that the activities of both kinases were higher throughout all phases of the HT-29 colon carcinoma cell cycle than in corresponding phases of the fibroblast cycle. In addition, during mitosis of HT-29 cells, Src specific activity increased two- to threefold more, while Yes activity and abundance decreased threefold. The decreased steady-state protein levels of Yes during mitosis appeared to be due to both decreased synthesis and increased degradation of the protein. Inhibition of tyrosine but not serine/threonine phosphatases abolished the mitotic activation of Src. Mitotic Src was phosphorylated at novel serine and threonine sites and dephosphorylated at Tyr-527. Two cellular proteins (p160 and p180) were phosphorylated on tyrosine only during mitosis. Tyrosine phosphorylation of several other proteins decreased during mitosis. Thus, Src in HT-29 colon carcinoma cells, similar to Src complexed to polyomavirus middle T antigen or activated by mutation at Tyr-527, is highly active in all phases of the cell cycle. Moreover, Src activity further increases during mitosis, whereas Yes activity and abundance decrease. Thus, Src and Yes appear to be regulated differently during mitosis of HT-29 colon carcinoma cells.
Mol Cell Biol 1995 May
PMID:Src activity increases and Yes activity decreases during mitosis of human colon carcinoma cells. 773 21

Tyrosine phosphorylation of proteins is involved in several sperm functions, including capacitation, motility, and acrosome reaction of spermatozoa. This study was undertaken to determine changes of tyrosine phosphorylation during 'in vitro' capacitation as well as the ability of platelet-activating factor (PAF) and progesterone (P), two known activators of sperm functions, to stimulate tyrosine phosphorylation of human sperm proteins. Spermatozoa were capacitated in BSA-containing medium and incubated with PAF (10-1000 nM) and progesterone (0.1-1 microgram/ml). After SDS-PAGE, sperm proteins were transferred to nitrocellulose and tyrosine phosphorylated proteins immunodetected by reacting with anti-phosphotyrosine antibody. The antibody mainly reacted with two proteins of approximately 97 and 75 kDa. The level of phosphorylation increased in these two proteins as a function of capacitation time, with a maximum between 120 and 180 min. In addition, phosphorylation in these two proteins was increased in capacitated spermatozoa by treatment with progesterone and PAF and was greatly reduced by pre-incubation with the tryosine kinase inhibitor erbstatin. Furthermore, pre-incubation with the two tyrosine kinase inhibitors erbstatin and genistein inhibited the induction of acrosome reaction by progesterone and, partially, by PAF. Our results suggest a role for tyrosine kinase(s) in the mechanism of capacitation and activation of human spermatozoa by PAF and progesterone.
Mol Cell Endocrinol 1995 Feb 27
PMID:Stimulation of protein tyrosine phosphorylation by platelet-activating factor and progesterone in human spermatozoa. 775 38

ZAP-70 is a protein tyrosine kinase thought to play a critical role in T-cell receptor (TCR) signal transduction. During T-cell activation, ZAP-70 binds to a conserved signalling motif known as the immune receptor tyrosine activating motif (ITAM) and becomes tyrosine phosphorylated. To determine whether binding of ZAP-70 to the phosphorylated ITAM was able to activate its kinase activity, we measured the kinase activity of ZAP-70 both when it was bound and when it was unbound to phosphorylated TCR subunits. The ability of ZAP-70 to phosphorylate itself, but not exogenous substrates, was enhanced when it was bound to the tyrosine-phosphorylated TCR zeta and eta chains or to a construct that contained duplicated epsilon ITAMs. No enhanced ZAP-70 autophosphorylation was noted when it was bound to tyrosine-phosphorylated CD3 gamma or epsilon. In addition, autophosphorylation of ZAP-70 when bound to zeta or eta resulted in the generation of multiple distinct ZAP-70 phosphorylated tyrosine residues which had the capacity to bind the SH2 domains of fyn, lck, GAP, and abl. As the effect was noted only when ZAP-70 was bound to TCR subunits containing multiple ITAMs, we propose that one of the roles of the tandem ITAMs is to facilitate the autophosphorylation of ZAP-70. Tyrosine-phosphorylated ZAP-70 then mediates downstream signalling by recruiting SH2 domain-containing signalling proteins.
Mol Cell Biol 1995 Jun
PMID:Binding of ZAP-70 to phosphorylated T-cell receptor zeta and eta enhances its autophosphorylation and generates specific binding sites for SH2 domain-containing proteins. 776 Aug 13

A key feature of the copy control in the 2 micron circle plasmid of Saccharomyces cerevisiae is its ability to amplify when the copy number drops below the steady state value. The Flp protein encoded by the plasmid is an essential component of the amplification mechanism. A central regulatory event in amplification involves the phosphorylation/dephosphorylation of Tyr-343 of Flp. Tyrosine phosphorylation is achieved by a transesterification mechanism involving a specific phosphodiester within the 2 micron circle. The dephosphorylation is also a transesterification reaction that uses a specific 5'-OH (generated during tyrosine phosphorylation) as the phosphoryl acceptor. A sum of four phosphorylation/dephosphorylation reactions, coordinated in sets of two, is thought to invert the relative directions of a pair of replication forks. This allows more than one copy of the plasmid to be made from a single replication initiation event. In this paper we discuss the structural features of the Flp active site that control and coordinate the transesterification reactions required for amplification.
Cell Mol Biol Res 1994
PMID:Role of tyrosine phosphorylation-dephosphorylation in copy number control of the yeast plasmid 2 micron circle. 787 98

Effect of gamma-glutamyl transpeptidase (GGTP) inhibitor acivicin on tyrosine transport was investigated in cultured bovine adrenal chromaffin cells. Tyrosine transport into the cells was inhibited by acivicin at the low concentration range. This drug also caused the inhibition of GGTP in the cell lysates, but the concentration required for the inhibition of the enzyme was evidently different from that producing the inhibition of tyrosine transport into the cells. In addition, tyrosine transport was not affected by a GGTP activator hippurate even at the high concentration. These results seem to provide the evidence that GGTP may not be involved in the transport of tyrosine into the adrenal chromaffin cell.
Biochem Mol Biol Int 1994 May
PMID:Lack of relationship between gamma-glutamyl transpeptidase and tyrosine transport in cultured bovine adrenal chromaffin cells. 791 26

The murine myeloid progenitor cell line 32D was recently shown to undergo monocytic differentiation when protein kinase C-delta (PKC-delta) was overexpressed and activated by 12-O-tetradecanoylphorbol-13-acetate (TPA) (H. Mischak, J.H. Pierce, J. Goodnight, M.G. Kazanietz, P.M. Blumberg, and J.F. Mushinski, J. Biol. Chem. 268:20110-20115, 1993). Tyrosine phosphorylation of PKC-delta occurred when PKC-delta-transfected 32D cells were stimulated by TPA (W. Li, H. Mischak, J.-C. Yu, L.-M. Wang, J.F. Mushinski, M.A. Heidaran, and J.H. Pierce, J. Biol. Chem. 269:2349-2352, 1994). In order to elucidate the role played by PKC-delta in response to activation of a receptor tyrosine kinase, we transfected platelet-derived growth factor beta receptor (PDGF-beta R) alone (32D/PDGF-beta R) or together with PKC-delta (32D/PDGF-beta R/PKC-delta) into 32D cells. NIH 3T3 cells which endogenously express both PDGF-alpha R and PDGF-beta R were also transfected with PKC-delta (NIH 3T3/PKC-delta). Like TPA treatment, PDGF-BB stimulation caused striking phosphorylation of PKC-delta in vivo and translocation of some PKC-delta from the cytosol fraction to the membrane fraction in both cell systems. Some of the phosphorylation induced by PDGF-BB treatment was found to be on a tyrosine residue(s). Tyrosine-phosphorylated PKC-delta was observed only for the membrane fraction after stimulation with PDGF-BB or TPA. The enzymatic activity of PKC-delta in the membrane fraction also increased after stimulation with TPA or PDGF, providing a positive correlation between PKC-delta tyrosine phosphorylation and its activation. Overnight treatment of 32D/PDGF-beta R/PKC-delta cells with PDGF-BB induced monocytic differentiation as judged by an increase in expression of cell surface macrophage differentiation markers. PDGF-BB had much weaker effects on 32D/PDGF-beta R cell differentiation, suggesting that increased PKC-delta expression enhanced monocytic differentiation. These results indicate that PKC-delta is a downstream molecule in the PDGFR signaling pathway and may play a pivotal role in PDGF-beta R-mediated cell differentiation.
Mol Cell Biol 1994 Oct
PMID:Stimulation of the platelet-derived growth factor beta receptor signaling pathway activates protein kinase C-delta. 793 92

Tyrosine phosphorylation of cytoskeletal proteins occurs during integrin-mediated cell adhesion to extracellular matrix proteins. We have investigated the role of tyrosine phosphorylation in the migration and initial spreading of human umbilical vein endothelial cells (HUVEC). Elevated phosphotyrosine concentrations were noted in the focal adhesions of HUVEC migrating into wounds. Anti-phosphotyrosine Western blots of extracts of wounded HUVEC monolayers demonstrated increased phosphorylation at 120-130 kDa when compared with extracts of intact monolayers. The pp125FAK immunoprecipitated from wounded monolayers exhibited increased kinase activity as compared to pp125FAK from intact monolayers. The time to wound closure in HUVEC monolayers was doubled by tyrphostin AG 213 treatment. The same concentration of AG 213 interfered with HUVEC focal adhesion and stress fiber formation. AG 213 inhibited adhesion-associated tyrosine phosphorylation of pp125FAK in HUVEC. Tyrphostins AG 213 and AG 808 inhibited pp125FAK activity in in vitro kinase assays. pp125FAK immunoprecipitates from HUVEC treated with both of these inhibitors also had kinase activity in vitro that was below levels seen in untreated HUVEC. These findings suggest that tyrosine phosphorylation of cytoskeletal proteins may be important in HUVEC spreading and migration and that pp125FAK may mediate phosphotyrosine formation during these processes.
Mol Biol Cell 1994 Mar
PMID:Tyrosine kinase activity, cytoskeletal organization, and motility in human vascular endothelial cells. 804 26

The 663 amino acid Mu transposase protein is absolutely required for Mu DNA transposition. Mutant proteins were constructed in vitro in order to locate regions of transposase that may be important for the catalysis of DNA transposition. Deletions in the A gene, which encodes the transposase, yielded two stable mutant proteins that aid in defining the end-specific DNA-binding domain. Linker insertion mutagenesis at eight sites in the Mu A gene generated two proteins, FF6 and FF14 (resulting from two and four amino acid insertions, respectively, at position 408), which were thermolabile for DNA binding in vitro at 43 degrees C. However, transposition activity in vivo was severely reduced for all mutant proteins at 37 degrees C, except those with insertions at positions 328 and 624. In addition, site-specific mutagenesis was performed to alter tyrosine 414, which is situated in a region that displays amino acid homology to the active sites of a number of nicking/closing enzymes. Tyrosine 414 may reside within an important, yet non-essential, site of transposase, as an aspartate-substituted protein had a drastically reduced frequency of transposition, while the remaining mutants yielded reduced, but substantial, frequencies of microMu transposition in vivo.
Mol Gen Genet 1994 Feb
PMID:Characterization of functionally important sites in the bacteriophage Mu transposase protein. 810 74

Huperzine A (HUP), a natural, potent, 'slow,' reversible inhibitor of antiacetylcholinesterase (AChE), has been suggested to be superior to antiacetylcholinesterase drugs now being used for management of Alzheimer's disease. To delineate the binding site of human AChE (HuAChE) for HUP, the biochemical constants kon, koff, and Ki were determined for complexes formed between HUP and single-site (Y337F, Y337A, F295A, W286A, and E202Q) or double-site (F295L/F297V) mutants of recombinant HuAChE (rHuAChE). The kinetic and dissociation constants were compared with those obtained for wild-type rHuAChE and AChE from Torpedo californica. Results demonstrate that the inhibition of AChE by HUP occurs through association with residues located inside the active site 'gorge,' rather than at the rim of the gorge. Tyrosine at position 337 (Y337) is essential for inhibition of rHuAChE by HUP (Ki = 26 nM). An aromatic array constituted from residues Y337, F295, and probably W86 is likely to offer a multicontact subsite that interacts with the ammonium group and with both the exo-and endocyclic double bond moieties of HUP. Lack of the aromatic side chain in the position homologous to Y337 explains the poor inhibitory potency of HUP toward human butyrylcholinesterase (Ki > 20,000 nM). Replacement of the carboxylate-containing E202 by glutamine had only marginal effect on the stability of the complex formed between HUP and rHuAChE. The pH-rate profiles suggest that destabilization of the complex after proton gain cannot be attributed solely to protonation of E202. These findings are expected to establish HUP as a lead compound for the design of new anti-AChE drugs.
Mol Pharmacol 1994 Mar
PMID:Role of tyrosine 337 in the binding of huperzine A to the active site of human acetylcholinesterase. 814 39

Mitogen-activated protein kinase (MAPK) and its direct activator, MAPK kinase (MAPKK), have been suggested to play a pivotal role in a variety of signal transduction pathways in higher eukaryotes. The fission yeast Schizosaccharomyces pombe carries a gene, named spk1, whose product is structurally related to vertebrate MAPK. Here we show that Spk1 is functionally related to Xenopus MAPK. (i) Xenopus MAPK partially complemented a defect in the spk1- mutant. An spk1- diploid strain could not sporulate, but one carrying Xenopus MAPK could. (ii) Both Spk1 and Xenopus MAPK interfered with sporulation if overexpressed in S. pombe cells. (iii) Spk1 underwent tyrosine phosphorylation as does Xenopus MAPK. Tyrosine phosphorylation of Spk1 appeared to be dependent upon mating signals because it occurred in homothallic cells but not in heterothallic cells. Furthermore, this phosphorylation was diminished in a byr1 disruptant strain, suggesting that spk1 lies downstream of byr1, which encodes a MAPKK homolog in S. pombe. Taken together, the MAPKK-MAPK cascade may be evolutionarily conserved in signaling pathways in yeasts and vertebrates.
Mol Cell Biol 1993 Oct
PMID:Schizosaccharomyces pombe Spk1 is a tyrosine-phosphorylated protein functionally related to Xenopus mitogen-activated protein kinase. 841 41


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