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Results for “src-Family Kinases”

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PubMed1994

Specificity of protein interactions with highly related SRC homology (SH) domains of FGR and FYN protein-tyrosine kinases.

As an approach toward identification and isolation of cellular proteins that may act as substrates or effectors of the SRC-family of protein-tyrosine kinases, fusion proteins containing noncatalytic elements of two highly related SRC-family members were tested for their ability to recognize distinct molecules present in lysates of cells known to normally express both enzymes. Our results demonstrate differences of protein binding between the SH2 elements of FYN and FGR kinases, but do not discriminate proteins binding to their SH3 domains.

3T3 Cells↗

PubMed1988

Neoplastic transformation induced by an activated lymphocyte-specific protein tyrosine kinase (pp56lck).

The lck proto-oncogene encodes a lymphocyte-specific member of the src family of protein tyrosine kinases. Here we demonstrate that pp56lck is phosphorylated in vivo at a carboxy-terminal tyrosine residue (Tyr-505) analogous to Tyr-527 of pp60c-src. Substitution of phenylalanine for tyrosine at this position resulted in increased phosphorylation of a second tyrosine residue (Tyr-394) and was associated with an increase in apparent kinase activity. In addition, this single point mutation unmasked the oncogenic potential of pp56lck in NIH 3T3 cell transformation assays. Viewed in the context of similar results obtained with pp60c-src, it is likely that the enzymatic activity and transforming ability of all src-family protein tyrosine kinases can be regulated by carboxy-terminal tyrosine phosphorylation. We further demonstrate that overexpression of pp56lck in the murine T-cell lymphoma LSTRA as a result of a retroviral insertion event produces a kinase protein that despite wild-type primary structure is nevertheless hypophosphorylated at Tyr-505. Thus, control of normal growth in this lymphoid cell line may have been abrogated through acquisition of a posttranslationally activated version of pp56lck.

Animals↗

PubMed1989

Transformation of NIH 3T3 fibroblasts by an activated form of p59hck.

Phosphorylation of a tyrosine residue near the carboxy terminus of src-family protein tyrosine kinases is believed to regulate the biological activity of these gene products. Conversion of this tyrosine in p59hck (Tyr-501) to a phenylalanine residue by using oligonucleotide-directed mutagenesis yielded a product (p59hckF501) with very potent transforming activity. Quantitative analysis by a soft-agar cloning assay revealed that p59hckF501 was more than 100-fold more effective than a closely related transforming element, p56lckF505, in colony formation. Cells bearing p59hckF501 had increased levels of protein phosphotyrosine. The ability of p59hckF501 to transform NIH 3T3 cells was abolished by a second mutation believed to destroy the ATP-binding domain.

Amino Acid Sequence↗

PubMed1989

A second type of rat phosphoinositide-specific phospholipase C containing a src-related sequence not essential for phosphoinositide-hydrolyzing activity.

A fourth type of rat phosphoinositide-specific phospholipase C (PLC IV) has been cloned for cDNA and sequenced. PLC IV is distinct from the other three types of rat PLC (PLC I, II, and III) with respect to primary structure and tissue distribution of its mRNAs. PLC IV contains two homologous regions included commonly in PLC I, II, and III and is most similar to PLC II (identity: 50.2%). PLC IV, in common with PLC II, has a sequence homologous to the N-terminal regulatory domains of nonreceptor tyrosine kinases of the src-family of oncogenes. Using an Escherichia coli expression system, we succeeded in producing active PLC IV in E. coli crude extracts. Various truncation experiments of the PLC IV cDNA revealed that the src-related domain is not necessary for catalytic activity while both domains homologous among PLC I-IV are essential. PLC IV is expressed in various rat tissues and abundant in spleen, suggesting that PLC IV plays a fundamental role in cellular functions such as growth and secretion.

Amino Acid Sequence↗

PubMed1994

The protein tyrosine kinase pp60c-src is activated upon platelet stimulation.

Stimulation of human platelets causes a dramatic increase in phosphorylation of various proteins at tyrosine residues. The abundance of protein tyrosine kinases of the src-family in platelets, particularly pp60c-src, suggests an important role of these kinases in response to stimulation events. We have shown that pp60c-src is activated on agonist-induced platelet stimulation with respect to its substrate affinity. This was accompanied by phosphorylation of pp60c-src at Ser-12, a residue which is phosphorylated by PKC. Inhibition of PKC with a specific inhibitor, Ro-31-8220, suppressed thrombin-induced translocation of pp60c-src to the cytoskeleton. On the basis of our data, we suggest that the cytoskeletal association of pp60c-src is dependent on phosphorylation of pp60c-src at Ser-12 by PKC. Phosphorylation at Ser-12 in the membrane-binding domain might be the signal that displaces pp60c-src from the plasma membrane and, accompanied with the increased substrate affinity, facilitates phosphorylation of putative substrates.

Arginine Vasopressin↗

PubMed1991

Membrane glycoprotein IV (CD36) is physically associated with the Fyn, Lyn, and Yes protein-tyrosine kinases in human platelets.

Activation of platelets with thrombin and other agonists causes a rapid increase in the phosphorylation of multiple proteins on tyrosine. To identify candidate protein-tyrosine kinases (PTKs; EC 2.7.1.112) that may be responsible for these phosphorylation events, we analyzed the expression of seven Src-family PTKs and examined the association of these kinases with known platelet membrane glycoproteins. Five Src-related PTKs were detected in platelets: pp60SRC, pp60FYN, pp62YES, pp61HCK, and two LYN products of Mr 54,000 and 58,000. The Fgr and Lck PTKs were not detected. Although strict comparative quantification of protein levels was not possible, pp60SRC was detected at higher levels than any of the other kinases. In addition, glycoprotein IV (GPIV, CD36), one of the major platelet membrane glycoproteins, was associated in a complex with the Fyn, Yes, and Lyn proteins in platelet lysates. Similar complexes were also found in two GPIV-expressing cell lines, C32 melanoma cells and HEL cells. Since PTKs appear to be involved in stimulus-response coupling at the plasma membrane, these results suggest that ligand interaction with GPIV may activate signaling pathways that are triggered by tyrosine phosphorylation.

Antigens, CD↗

PubMed1988

Peptide antibodies to the human c-fyn gene product demonstrate pp59c-fyn is capable of complex formation with the middle-T antigen of polyomavirus.

The c-fyn proto-oncogene is a member of a family of closely related genes of which c-src is the prototype. Using peptide antibodies which had been raised against sequences predicted to be specific for the human c-fyn gene product, the c-fyn protein was identified. It is a tyrosine kinase with apparent mol. wt of 59 kd that is also phosphorylated and myristylated. Like pp60c-src and pp62c-yes, pp59c-fyn is able to form a stable complex with middle-T antigen, the transforming protein of polyomavirus. The transformation-defective middle-T mutant NG59, which is unable to associate stably with pp60c-src does not associate with pp59c-fyn. In contrast to pp60c-src, complex formation with middle-T antigen does not lead to a significant increase in the tyrosine kinase activity of pp59c-fyn. These findings lead us to suggest that middle-T mediated transformation may be a consequence of the deregulation of several members of the src-family of protein tyrosine kinases.

Animals↗

PubMed1994

Interactions of Lyn with the antigen receptor during B cell activation.

Signaling through the B cell antigen receptor requires a complex set of interactions involving transmembrane components of the IgM receptor complex and cytosolic protein-tyrosine kinases. We have focused on the nature of these protein-protein interactions, the requirements for their occurrence, as well as the temporal sequence of events during the activation process. We found that cross-linking B cell antigen receptors at 0 degree C resulted in the rapid association of the Src-family protein-tyrosine kinase, Lyn, with the antigen receptor complex as judged by the presence of Lyn in anti-IgM and anti-phosphotyrosine immune complexes and the presence of MB-1 in anti-Lyn immune complexes. Receptor engagement also resulted in the rapid association of Lyn with the phosphotyrosine phosphatase, CD45. This association of Lyn with receptor components was stable in the detergent Brij 96, but was readily disrupted by Nonidet P-40, suggesting the involvement of hydrophobic interactions in stabilizing formation of the Lyn-receptor complex. The protein-tyrosine kinase, Syk, was also found associated with activated receptor complexes. This association of Syk with components of the antigen receptor complex was stable to Nonidet P-40. Antibodies directed against the carboxyl teminus of Syk, but not against the amino-terminal SH2 domain, co-immunoprecipitated MB-1 from activated cells, consistent with the binding of Syk through an SH2 domain-phosphotyrosine interaction.

Animals↗

PubMed1992

CD28-induced T cell activation. Evidence for a protein-tyrosine kinase signal transduction pathway.

CD28 is a 44-kDa homodimeric receptor expressed on the majority of T cells. Engagement of the CD28 receptor by soluble anti-CD28 mAb in conjunction with PMA causes the induction of lymphokine/cytokine production and proliferation in resting T cells via signal transduction pathways independent of the TCR. The precise nature of the biochemical events that occur after perturbation of the CD28 receptor remain unclear. We report evidence for the coupling of CD28 to a protein-tyrosine kinase pathway. Multivalent cross-linking of the CD28 receptor or stimulation by soluble CD28 mAb plus PMA, but not PMA or soluble CD28 mAb alone, reproducibly caused the rapid (within 2 min) tyrosine phosphorylation of a 100-kDa cellular substrate. In some experiments, additional cellular substrates of 110, 85, 74, 68, 56, 43, and 29 kDa were also observed. The tyrosine phosphorylation of these substrates was completely inhibited by 12 h pretreatment of T cells with herbimycin A, a selective inhibitor of src-family protein-tyrosine kinases. Pretreatment of T cells with herbimycin was without effect on CD28 surface expression but did inhibit CD28 mAb plus PMA-induced IL-2 mRNA levels, IL-2R(CD25) up-regulation, and cell proliferation. The inhibition of IL-2 mRNA levels was likely at the level of transcription, because herbimycin inhibited NF-AT, AP-1, and CD28RC but not NF-kappa B or OCT-1 binding activities to their respective IL-2 enhancer region sequences. Herbimycin did not inhibit PMA-dependent events including CD69 surface expression, NF-kappa B nuclear binding activity or the level of CD25 induced by PMA alone, supporting the notion that herbimycin is acting to inhibit a CD28 initiated or regulated protein-tyrosine kinase pathway(s).

Antigens, CD↗

PubMed1989

A function for the lck proto-oncogene.

Proto-oncogenes encode products that comprise a select group of cellular regulatory proteins whose mutation or aberrant expression can result in oncogenic transformation. With the exception of certain growth factors and their receptors, the definition of normal functions for most proto-oncogene products has been elusive. The discovery that a member of the src-family of tyrosine protein kinases (p56lck) is associated with both the CD4 and CD8 T-lymphocyte surface glycoproteins provides the first clue to understanding the potential physiological functions of this family of proto-oncogenes.

Amino Acid Sequence↗

PubMed1994

Rapid T-cell receptor-mediated tyrosine phosphorylation of p120, an Fyn/Lck Src homology 3 domain-binding protein.

Tyrosine phosphorylation of cellular proteins is the earliest identifiable event following T-cell antigen receptor (TCR) stimulation and is essential for activating downstream signaling machinery. Two Src-family protein-tyrosine kinases, the TCR-associated p59fyn (Fyn) and the CD4/8-associated p56lck (Lck), have emerged as the likely mediators of early tyrosine phosphorylation in T cells. Here, we show direct binding of a 120-kDa TCR-induced phosphotyrosyl polypeptide, p120, to glutathione S-transferase fusion proteins of the Src homology 3 (SH3) domains of Fyn, Lck, and p60src (Src) but not other proteins. While binding of p120 to Fyn SH2 domain was phosphotyrosine-dependent as expected, its binding to the SH3 domain was independent of tyrosine phosphorylation, as shown by lack of competition with a phosphotyrosyl competitor peptide. In contrast, an SH3-specific proline-rich peptide completely abolished p120 binding to SH3. p120 was tyrosine-phosphorylated within 10 sec following stimulation of Jurkat cells with anti-CD3 monoclonal antibody, with maximal phosphorylation at 30 sec. Importantly, p120 was found associated with Fyn and Lck proteins in unstimulated Jurkat cells and served as an in vitro substrate for these kinases. These results provide evidence for a role of the SH3 domains of Fyn and Lck in the recruitment of early tyrosine-phosphorylation substrates to the TCR-associated tyrosine kinases.

Amino Acid Sequence↗

PubMed1992

Comparison of src-family cDNAs reveals distinct mechanisms underlying focus formation in transfected fibroblasts.

Despite the intensive study of both cellular transformation and src-family protein-tyrosine kinases, there have been no direct comparisons of transforming potency for normal members of this gene-family. In this study, the focus-forming activity of normal c-src, fyn, and lck cDNAs were compared in NIH 3T3 cell transfection assays. Focus formation was studied quantitatively, and individual foci were analyzed for phosphotyrosine content and expression of appropriate translational products. Each foci arising from c-src transfectants had a marked increase in phosphotyrosine content, and the majority of these foci expressed a c-src protein with an aberrant carboxyl terminus. Foci derived from lck transfectants also had a marked increase in phosphotyrosine content, and some foci expressed a lck protein with an aberrant carboxyl terminus. In contrast, foci from fyn-transfected cells were not distinguished from G418-selected mass cultures in terms of total phosphotyrosine content or expression of p59fyn. These studies support the previously published concept that overexpression of the normal fyn protein contributes to focus formation in transfected NIH 3T3 cells but suggest that the focus-forming activity observed after c-src or lck transfections is frequently attributable to mutational events. Because lck mutations have not been previously described in transformed foci, we characterized the lck transcript expressed in two foci and identified a novel point mutation that encodes a lck protein with increased in vivo kinase and focus-forming activity.

3T3 Cells↗

PubMed1992

Phenotypic changes induced by interleukin-2 (IL-2) and IL-3 in an immature T-lymphocytic leukemia are associated with regulated expression of IL-2 receptor beta chain and of protein tyrosine kinases LCK and LYN.

We have previously reported the establishment of an interleukin-3 (IL-3)-dependent and phenotypically myeloid cell line (TALL-103/3), obtained by culturing cells from an immature T-lymphoblastic leukemia in the presence of IL-3. These cells differentiated into a T-lymphoid cell line (TALL-103/2) upon removal of IL-3 and incubation in IL-2. Despite the different phenotype, the two cell lines remained karyotypically and genotypically identical. Here, we have analyzed the phenotypic changes and the signaling events induced by these two lymphokines in TALL-103/3 cells by switching them to temporary growth in IL-2 and returning them to IL-3. All four sublines obtained (the myeloid in IL-3 and the lymphoid in IL-2) expressed RNA for CD3, IL-2 receptor (R) alpha, and T-cell receptor (TCR)-gamma and -delta chains. However, cells cultured in IL-3 failed to express detectable levels of the IL-2R beta chain at both the protein and RNA levels, whereas cells exposed to IL-2 always expressed IL-2R beta. In parallel with the changes in IL-2R beta expression, the SRC-like protein tyrosine kinase (PTK) p56 LCK could not be detected in IL-3-dependent cells, but was abundant in the IL-2-dependent cells and underwent markedly increased autophosphorylation in response to IL-2. In contrast, p53/p56 LYN was highly expressed in IL-3-dependent cells, and greatly decreased when these cells were switched to growth in IL-2. LYN kinase autophosphorylation modestly increased in response to IL-3. None of the other kinases in the SRC family that were tested underwent increased autophosphorylation after lymphokine stimulation, indicating the specificity of IL-2 for LCK and of IL-3 for LYN. The TALL-103 cell lines provide a unique system to study the interaction between lymphokines and SRC-family PTKs in signal transduction pathways leading to hematopoietic cell differentiation.

Cell Division↗

PubMed1992

Interleukin-3 regulates the activity of the LYN protein-tyrosine kinase in myeloid-committed leukemic cell lines.

The lymphokine interleukin-3 (IL-3) promotes the growth and survival of immature hematopoietic cells. Previous studies have shown that IL-3 induces rapid increases in protein-tyrosine kinase (PTK) activity in IL-3--dependent cells. Unlike some other hematopoietic growth factor receptors (eg, c-fms and c-kit), however, the known subunits of the IL-3 receptor (IL-3R) lack intrinsic kinase activity. Recently, it was reported that the IL-2R (whose p75 beta-subunit shares sequence homology with a known murine IL-3R subunit and a common beta-subunit of the human IL-3R and granulocyte-macrophage colony-stimulating factor [GM-CSF] receptors) can physically associate with and regulate the activity of the SRC-family PTK, p56-LCK. Because most IL-3--dependent cells contain p53/56-LYN, but not p56-LCK, we explored the effects of IL-3 on the activities of LYN and other SRC-like PTKs in two human leukemic cell lines, AML-193 and TALL-101, which are phenotypically myeloid, and whose in vitro growth is dependent on IL-3. These cells expressed four of the eight known SRC-family proto-oncogenes: lyn, fyn, yes, and hck. When these factor-dependent leukemic cell lines were deprived of lymphokine to achieve cellular quiescence and then restimulated with IL-3, rapid increases (detectable within 1 minute and maximal by 10 minutes) were observed in the activity of the p53/56-LYN kinase, as assessed by in vitro kinase assays. In contrast, no alteration in the activities of other SRC-family PTKs present in these cells was detected after restimulation with IL-3 under the same conditions. This effect of IL-3 reflected an increase in the specific activity of the LYN kinase, because levels of the 53-Kd and 56-Kd LYN proteins were unaltered by IL-3 stimulation, as assessed by immunoblotting. Furthermore, the magnitude of these inducible increases in LYN kinase activity was dependent on the concentration of IL-3, and correlated with IL-3--induced proliferation. The IL-3--induced upregulation of LYN kinase activity may be mediated by the 120-Kd common subunit of the human IL-3 and GM-CSF receptors, because GM-CSF also stimulated marked increases in the activity of the LYN kinase, whereas granulocyte-CSF (G-CSF) did not, despite inducing cellular proliferation. These observations provide the first example of an IL-3--regulable PTK, and strongly suggest that the p53/56-LYN kinase participates in early IL-3--initiated signalling events, at least in some human leukemic cell lines.

Cell Line↗

PubMedDate not supplied

A Drosophila genomic sequence with homology to human epidermal growth factor receptor.

Vertebrate genomes contain an extensive family of genes possessing varying degrees of homology to the v-src oncogene. Most src-related proteins identified to date are intracellular and membrane-associated, although some are transmembrane proteins and function as receptors for peptide growth factors. Three Drosophila gene sequences related to the v-src gene have been identified, each exhibiting a high degree of homology to one or more of the src-family members encoding an intracellular protein. We have isolated a panel of cloned Drosophila sequences exhibiting weak v-src hybridization and were interested to determine whether any members of this group represented homologues of additional known src-family genes, especially those functioning as growth factor receptors. As we report here, four of these clones, representing overlapping portions of the same genomic segment, hybridized preferentially with the v-erb-B oncogene and were further characterized. The deduced amino-acid sequence from a portion of this Drosophila genomic segment is 77% homologous to the kinase domain of human epidermal growth factor (EGF) receptor, a substantially greater degree of homology than was observed with any other known src-family member. By hybridization with a human EGF receptor complementary DNA clone probe, we demonstrate that the same genomic segment showing homology with the kinase domain also contains sequences related to the extracellular domain of the EGF receptor gene.

Animals↗

PubMed1989

Characterization and functional allotment of proto-oncogenes belonging to the src family.

Eight proto-oncogenes encode cytoplasmic protein tyrosine kinases whose primary structures are closely related to that of p60proto-src. This group of related genes is called the src-family. Their products share common structures: namely, a glycine residue at position 2 from the N terminus, a unique domain, a modulatory domain (SH2, SH3), a kinase (catalytic) domain, and a regulatory domain. Oncogenic activation of these genes may occur by various mutations such as 1) deletion or substitution of the tyrosine at the C-terminal position, 2) mutation at a defined position in the kinase domain or 3) deletion or mutation in the modulatory domain. The expressions of the proto-oncogenes of this family are tissue specific and are unique for each gene, suggesting functional allotment of these gene products. In the hematopoietic system, the genes appear to be expressed in specific cell lineages. In this paper, the functional allotments of these genes in the hematopoietic system are considered with special reference to the functions of lck, lyn, and fyn in cells of T and B lymphocyte lineages.

Amino Acid Sequence↗

PubMed1994

Inhibition of phospholipase D of human platelets by protein tyrosine kinase inhibitors.

Protein tyrosine kinases (PTKs) of the src family are thought to play an important role in platelet signal transduction, but little is known about the targets of these enzymes in platelets. We determined that exposure of human platelets to pervanadate, an inhibitor of protein tyrosine phosphatases, caused an increase in the activity of phospholipase D (PLD), an enzyme that might be involved in signaling events leading to aggregation or secretion. To further investigate whether tyrosine phosphorylation is a step in the pathway of activation of PLD in response to thrombin, we tested the effects of a series of PTK inhibitors on the activity of platelet PLD. PLD was activated in response to 0.3 U/ml thrombin, and this activation was reduced by several of the PTK inhibitors, especially genistein, methyl 2,5-dihydroxycinnamate (MDHC), ST271, and the tyrphostins A25 and A47. In saponin-permeabilized platelets, we observed a marked inhibition of GTP-gamma S-stimulated PLD by many of the PTK inhibitors, consistent with the possibility that PTKs are involved in the regulation of PLD activity by a G-protein or small GTP-binding protein. MDHC did not affect PLD activity in permeabilized cells, which suggests that this compound might inhibit PLD in intact platelets via another pathway. The inhibitors were also tested for their effects on the phosphorylation of a peptide substrate of src-family PTKs in a platelet membrane preparation and in permeabilized platelets. Several of the compounds partially inhibited peptide phosphorylation in the membrane preparation and in permeabilized platelets, most notably ST271, ST638, and tyrphostin A25.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1990

Translational regulation of the lymphocyte-specific protein tyrosine kinase p56lck.

The lck gene encodes a lymphocyte-specific membrane-associated protein tyrosine kinase that is implicated in signal transduction processes that regulate T-cell growth. Previous studies demonstrate that lck transcripts, unlike most other vertebrate mRNAs, contain 5' proximal AUG sequences upstream relative to the major open reading frame (5' AUGs) that serve as satisfactory targets for recognition by 40S ribosomal subunits. There exist two distinct lck transcripts, generated through alternative promoter utilization, that differ only in their 5' untranslated region sequences. Both transcripts are present in murine and human lymphocytes, and the structures of the two distinct 5' untranslated regions have been closely conserved since the divergence of these species. Moreover, both transcripts contain 5'-AUG elements. Intriguingly, inspection of primary sequence data for other src-family transcripts reveals that virtually all contain 5'AUG triplets, and many contain a large number of these potential initiators. By analogy with the well-studied translational regulation of the yeast GCN4 gene, I propose that control of ribosomal reinitiation permits tight regulation of expression of the lck gene product and of other src-like protein tyrosine kinases.

Animals↗