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

Evidence suggests that cellular adhesion is critical for eosinophil effector functions. Here, we tested the hypothesis that an adhesion molecule, specifically beta2 integrin, participates in intracellular signaling events of eosinophils. Eosinophils stimulated with interleukin (IL)-5 and adherent to protein-coated tissue culture plates via beta2 integrin (CD18) showed tyrosine phosphorylation of a number of proteins. Among these proteins, tyrosine phosphorylation of the 105 kD and 115 kD proteins and the product of the c-cbl protooncogene, Cbl, was specifically inhibited using soluble anti-CD18 monoclonal antibody (mAb) to block eosinophil cell adhesion. Furthermore, phosphoinositide turnover of IL-5-stimulated adherent eosinophils was also inhibited by anti-CD18 mAb, suggesting that cellular adhesion plays important roles in eosinophil signal transduction. alphaM beta2 (Mac-1, CD11b/18) was one of the beta2 integrins involved in eosinophil adhesion to protein-coated plates. We found that direct ligation of eosinophil alphaM beta2 with anti-CD11b mAb coupled to polystyrene microbeads induced tyrosine phosphorylation of a 115 kD protein and Cbl. Furthermore, anti-CD11b mAb microbeads induced increases in both phosphoinositide hydrolysis and the eosinophil degranulation response. Control antibodies, such as mouse myeloma IgG1 and anti-HLA class I antigen mAb, did not induce these cellular responses. These results suggest that engagement of beta2 integrin either by cell adhesion or by anti-CD11b mAb triggers activation of an intracellular signaling cascade, including protein tyrosine phosphorylation and phosphoinositide turnover, and subsequent cellular degranulation in human eosinophils. Tyrosine phosphorylation of a 115 kD protein and Cbl may play important roles in adhesion-dependent cellular functions of eosinophils.
Am J Respir Cell Mol Biol 1998 May
PMID:Ligation of the beta2 integrin triggers activation and degranulation of human eosinophils. 956 38

To isolate and characterize proteins that interact with the unique domain and SH3 and SH2 domains of Src and potentially regulate Src activity, we used the yeast two-hybrid assay to screen a human lung fibroblast cDNA library. We identified RACK1, a receptor for activated C kinase and a homolog of the beta subunit of G proteins, as a Src-binding protein. Using GST-Src fusion proteins, we determined that RACK1 binds to the SH2 domain of Src. Coimmunoprecipitation of Src and RACK1 was demonstrated with NIH 3T3 cells. Purified GST-RACK1 inhibited the in vitro kinase activity of Src in a concentration-dependent manner. GST-RACK1 (2 microM) inhibited the activities of purified Src and Lck tyrosine kinases by 40 to 50% but did not inhibit the activities of three serine/threonine kinases that we tested. Tyrosine phosphorylation on many cellular proteins decreased in 293T cells that transiently overexpressed RACK1. Src activity and cell growth rates decreased by 40 to 50% in NIH 3T3 cells that stably overexpressed RACK1. Flow cytometric analyses revealed that RACK1-overexpressing cells do not show an increased rate of necrosis or apoptosis but do spend significantly more time in G0/G1 than do wild-type cells. Prolongation of G0/G1 could account for the increased doubling time of RACK1-overexpressing cells. We suggest that RACK1 exerts its effect on the NIH 3T3 cell cycle in part by inhibiting Src activity.
Mol Cell Biol 1998 Jun
PMID:RACK1, a receptor for activated C kinase and a homolog of the beta subunit of G proteins, inhibits activity of src tyrosine kinases and growth of NIH 3T3 cells. 958 65

The RET proto-oncogene encodes a tyrosine kinase receptor expressed in neuroectoderm-derived cells. Mutations in specific regions of the gene are responsible for the tumor syndromes multiple endocrine neoplasia types 2A and 2B (MEN 2A and 2B), while mutations along the entire gene are involved in a developmental disorder of the gastrointestinal tract, Hirschsprung's disease (HSCR disease). Two mutants in the extracellular domain of RET, one associated with HSCR disease and one carrying a flag epitope, were analyzed to investigate the impact of the mutations on RET function. Both mutants were impeded in their maturation, resulting in the lack of the 170-kDa mature form and the accumulation of the 150-kDa immature form in the endoplasmic reticulum. Although not exposed on the cell surface, the 150-kDa species formed dimers and aggregates; this was more pronounced in a double mutant bearing a MEN 2A mutation. Tyrosine phosphorylation and the transactivation potential were drastically reduced in single and double mutants. Finally, in cotransfection experiments both mutants exerted a dominant negative effect over protoRET and RET2A through the formation of a heteromeric complex that prevents their maturation and function. These results suggest that HSCR mutations in the extracellular region cause RET loss of function through a dominant negative mechanism.
Mol Cell Biol 1998 Jun
PMID:Mutations in the extracellular domain cause RET loss of function by a dominant negative mechanism. 958 72

To improve our understanding of structure-function relationships for neurotransmitter transporters, we performed site-directed mutagenesis of the rat dopamine transporter (DAT) and assessed the functions of the mutants in transiently-expressing COS cells. Tyrosine-533 of rat DAT lies in the 11th transmembrane region, where the corresponding amino acid of human DAT is phenylalanine. Alanine substitution of tyrosine-533 (Y533A) conferred an increased affinity for 1-methyl-4-phenylpyridinium (MPP+). Phenylalanine substitution of tyrosine-533 (Y533F) increased the velocity of MPP+ uptake but decreased DAT's affinity for MPP+. Cocaine's potency in inhibiting dopamine uptake was unchanged with Y533A, but increased with Y533F. Differences in the uptake kinetics and inhibitory potency of cocaine between rat and human DATs were similar to the differences observed between the wild-type and Y533F mutants DATs. Tyrosine-533 may be important for the DAT function and for species differences in transporter functions, including differential sensitivities to cocaine and 1-methyl-1,2,3,6-tetrahydropyridine (MPTP) in humans and rats.
Brain Res Mol Brain Res 1998 May
PMID:Tyrosine-533 of rat dopamine transporter: involvement in interactions with 1-methyl-4-phenylpyridinium and cocaine. 960 72

Although arsenite is an established carcinogen, the mechanisms underlying its tumor-promoting properties are poorly understood. Previously, we reported that arsenite treatment leads to the activation of the extracellular signal-regulated kinase (ERK) in rat PC12 cells through a Ras-dependent pathway. To identify potential mediators of the upstream signaling cascade, we examined the tyrosine phosphorylation profile in cells exposed to arsenite. Arsenite treatment rapidly stimulated tyrosine phosphorylation of several proteins in a Ras-independent manner, with a pattern similar to that seen in response to epidermal growth factor (EGF) treatment. Among these phosphorylated proteins were three isoforms of the proto-oncoprotein Shc as well as the EGF receptor (EGFR). Tyrosine phosphorylation of Shc allowed for enhanced interactions between Shc and Grb2 as identified by coimmunoprecipitation experiments. The arsenite-induced tyrosine phosphorylation of Shc, enhancement of Shc and Grb2 interactions, and activation of ERK were all drastically reduced by treatment of cells with either the general growth factor receptor poison suramin or the EGFR-selective inhibitor tyrphostin AG1478. Down-regulation of EGFR expression through pretreatment of cells with EGF also attenuated ERK activation and Shc tyrosine phosphorylation in response to arsenite treatment. These results demonstrate that the EGFR and Shc are critical mediators in the activation of the Ras/ERK signaling cascade by arsenite and suggest that arsenite acts as a tumor promoter largely by usurping this growth factor signaling pathway.
Mol Cell Biol 1998 Sep
PMID:Tumor promoter arsenite activates extracellular signal-regulated kinase through a signaling pathway mediated by epidermal growth factor receptor and Shc. 971 Jun 2

T-lymphocyte activation consists of multiple intracellular signaling events, eventually leading to cellular proliferation by the control of cytokine gene expression and the acquisition of diverse effector function. To investigate the functional specificity of ITAM (Immunoreceptor Tyrosine-based Activation Motif), chimeric molecules CD8-zeta, CD8-Igalpha, CD8-Igbeta, which contain the extracellular and transmembrane domains of the human CD8alpha molecule and the cytoplasmic tail of T-cell receptor (TcR) chain, Igalpha or Igbeta subunit of B-cell receptor, respectively, were stably expressed in a Jurkat cell line. Upon stimulation with anti-CD8 mAb OKT8, CD8-zeta and CD8-Igalpha chimeric proteins induced tyrosine phosphorylation of various cytoplasmic substrates as seen in TcR stimulation. They were also capable of stimulating IL-2 gene expression in a NF-AT dependent manner and inducing CD69 expression on the surface. However, stimulation of CD8-Igbeta can induce activation of CD69 surface expression and IL-2 gene expression equivalent to the level by CD8-Igalpha and CD8-zeta without induction of the tyrosine phosphorylation of intracellular signaling molecules. These results suggested that some of signaling chains containing ITAM may utilize a signal pathway without substrate tyrosine phosphorylation during T-cell activation leading to the IL-2 secretion.
Mol Cells 1998 Aug 31
PMID:Induction of late activation events by Igbeta signaling subunit of B-cell receptor in Jurkat T-cell without tyrosine phosphorylation. 974 27

Tyrosine phosphorylation is thought to play a critical role in the clustering of acetylcholine receptors (AChR) at the developing neuromuscular junction. Yet, in vitro approaches have led to conflicting conclusions regarding the function of tyrosine phosphorylation of AChR beta subunit in AChR clustering. In this work, we followed in situ the time course of tyrosine phosphorylation of AChR in developing Torpedo electrocyte. We observed that tyrosine phosphorylation of the AChR beta and delta subunits occurs at a late stage of embryonic development after the accumulation of AChRs and rapsyn in the membrane and the onset of innervation. Interestingly, in the mature postsynaptic membrane, we observed two populations of AChR differing both in their phosphotyrosine content and distribution. Our data are consistent with the notion that tyrosine phosphorylation of the AChR is related to downstream events in the pathway regulating AChR accumulation rather than to initial clustering events.
Mol Cell Neurosci 1999 Jan
PMID:Developmental regulation of tyrosine phosphorylation of the nicotinic acetylcholine receptor in Torpedo electrocyte. 1004 32

The enteropathogenic Escherichia coli (EPEC) Tir protein becomes tyrosine phosphorylated in host cells and displays an increase in apparent molecular mass. The interaction of Tir with the EPEC outer membrane protein, intimin, triggers actin nucleation beneath the adherent bacteria. The enterohaemorrhagic E. coli O157:H7 (EHEC) Tir molecule is not tyrosine phosphorylated. In this paper, Tir tyrosine phosphorylation is shown to be essential for actin nucleation activity, but not for the increase in apparent molecular mass observed in target cells. Tyrosine phosphorylation had no role in Tir molecular mass shift, indicating additional host modifications. Analysis of Tir intermediates indicates that tyrosine-independent modification functions to direct Tir's correct insertion from the cytoplasm into the host membrane. Deletion analysis identified Tir domains participating in translocation, association with the host membrane, modification and antibody recognition. Intimin was found to bind a 55-amino-acid region (TIBA) within Tir that topological and sequence analysis suggests is located in an extracellular loop. Homologous TIBA sequences exist in integrins, which also bind intimin. Collectively, this study provides definitive evidence for the importance of tyrosine phosphorylation for EPEC Tir function and reveals differences in the pathogenicity of EPEC and EHEC. The data also suggest a mechanism for Tir insertion into the host membrane, as well as providing clues to the mode of intimin-integrin interaction.
Mol Microbiol 1999 Feb
PMID:Phosphorylation of tyrosine 474 of the enteropathogenic Escherichia coli (EPEC) Tir receptor molecule is essential for actin nucleating activity and is preceded by additional host modifications. 1009 89

Members of the recently discovered SOCS/CIS/SSI family have been proposed as regulators of cytokine signaling, and while targets and mechanisms have been suggested for some family members, the precise role of these proteins remains to be defined. To date no SOCS proteins have been specifically implicated in interleukin-2 (IL-2) signaling in T cells. Here we report SOCS-3 expression in response to IL-2 in both T-cell lines and human peripheral blood lymphocytes. SOCS-3 protein was detectable as early as 30 min following IL-2 stimulation, while CIS was seen only at low levels after 2 h. Unlike CIS, SOCS-3 was rapidly tyrosine phosphorylated in response to IL-2. Tyrosine phosphorylation of SOCS-3 was observed upon coexpression with Jak1 and Jak2 but only weakly with Jak3. In these experiments, SOCS-3 associated with Jak1 and inhibited Jak1 phosphorylation, and this inhibition was markedly enhanced by the presence of IL-2 receptor beta chain (IL-2Rbeta). Moreover, following IL-2 stimulation of T cells, SOCS-3 was able to interact with the IL-2 receptor complex, and in particular tyrosine phosphorylated Jak1 and IL-2Rbeta. Additionally, in lymphocytes expressing SOCS-3 but not CIS, IL-2-induced tyrosine phosphorylation of STAT5b was markedly reduced, while there was only a weak effect on IL-3-mediated STAT5b tyrosine phosphorylation. Finally, proliferation induced by both IL-2- and IL-3 was significantly inhibited in the presence of SOCS-3. The findings suggest that when SOCS-3 is rapidly induced by IL-2 in T cells, it acts to inhibit IL-2 responses in a classical negative feedback loop.
Mol Cell Biol 1999 Jul
PMID:SOCS-3 is tyrosine phosphorylated in response to interleukin-2 and suppresses STAT5 phosphorylation and lymphocyte proliferation. 1037 48

Tyrosine/dihydroxyphenylalanine decarboxylase (TYDC) and the berberine bridge enzyme (BBE) represent the entry point and a key branch point, respectively, in the biosynthesis of benzylisoquinoline alkaloids in select species of the Papaveraceae and Fumariaceae. Genomic clones for tydc7 and bbe1 from opium poppy (Papaver somniferum L.) were isolated. Deletion analysis of tydc7 and bbe1 5'-flanking regions revealed the location of putative regulatory domains necessary for expression of the beta-glucuronidase (gus) reporter gene in a transient assay system based on the microprojectile bombardment of cultured opium poppy cells. A 105-nucleotide region between -393 and -287 of the tydc7 5'-flanking region, and a 155-nucleotide region between -355 and -200 of the bbe1 5'-flanking region, were found to be essential for promoter activity. RNA gel blot analysis showed that tydc7 and bbe1 expression is induced in cultured opium poppy cells in response to wounding or treatment with a pathogen-derived elicitor. Time-courses for the induction of tydc7 and bbe1 mRNAs in wounded cells were nearly identical to those for GUS activity in cells bombarded with select promoter-gus constructs when the -393 to -287 region of tydc7, or the -355 to -200 region of bbe1, was present. Our data suggest that the wound signal caused by the entry of DNA-coated microcarriers into opium poppy cells was sufficient to induce tydc7 and bbe1 promoter activity, and that wound-responsive regulatory elements are located within domains identified by deletion analysis.
Plant Mol Biol 1999 May
PMID:Analysis of promoters from tyrosine/dihydroxyphenylalanine decarboxylase and berberine bridge enzyme genes involved in benzylisoquinoline alkaloid biosynthesis in opium poppy. 1039 51


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