Showing papers on "Receptor tyrosine kinase published in 1993"

Signaling by Receptor Tyrosine Kinases

Abstract: This is a free sample of content from Signaling by Receptor Tyrosine Kinases Click here for more information or to buy the book. This is a free sample of content from Signaling by Receptor Tyrosine Kinases Click here for more information or to buy the book. Front cover artwork: Stylized representations of the 20 different receptor tyrosine kinase (RTK) families found in humans—accounting for a total of 58 different receptors. The common intra-cellular tyrosine kinase domain (lower part of each receptor) is shown as a red rectangle. Domains in the extracellular region (upper part of each receptor) are much more variable across families and include immunoglobulin domains (blue), fibronectin type III domains (orange), and many others. The chapters in this volume describe mechanisms by which ligand binding to the extracellular region controls activity of the intracellular kinase domain, which vary substantially across the family and drive a variety of intracellular signaling pathways. All World Wide Web addresses are accurate to the best of our knowledge at the time of printing. Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by Cold Spring Harbor Laboratory Press, provided that the appropriate fee is paid directly to the Copyright Clearance Center (CCC). Write or call CCC at 222 Rosewood Drive, Danvers, MA 01923 (978-750-8400) for information about fees and regulations. Prior to photocopying items for educational classroom use, contact CCC at the above address. Additional information on CCC can be obtained at CCC Online at www.copyright.com.

Inhibition of vascular endothelial cell growth factor activity by an endogenously encoded soluble receptor

Abstract: Vascular endothelial cell growth factor, a mitogen selective for vascular endothelial cells in vitro that promotes angiogenesis in vivo, functions through distinct membrane-spanning tyrosine kinase receptors. The cDNA encoding a soluble truncated form of one such receptor, fms-like tyrosine kinase receptor, has been cloned from a human vascular endothelial cell library. The mRNA coding region distinctive to this cDNA has been confirmed to be present in vascular endothelial cells. Soluble fms-like tyrosine kinase receptor mRNA, generated by alternative splicing of the same pre-mRNA used to produce the full-length membrane-spanning receptor, encodes the six N-terminal immunoglobulin-like extracellular ligand-binding domains but does not encode the last such domain, transmembrane-spanning region, and intracellular tyrosine kinase domains. The recombinant soluble human receptor binds vascular endothelial cell growth factor with high affinity and inhibits its mitogenic activity for vascular endothelial cells; thus this soluble receptor could act as an efficient specific antagonist of vascular endothelial cell growth factor in vivo.

Structural and Functional Diversity in the FGf Receptor Multigene Family

Abstract: Publisher Summary The fibroblast growth factors (FGFs) constitute a family of closely related polypeptide mitogens There are seven members of this family, identified on the basis of amino acid sequence homologies The FGF family has distinguished itself from other growth factor families by virtue of the pleiotropic actions of its members This chapter discusses the structural and functional diversity in the FGF receptor multigene family The effects of FGFs are known to be mediated by high-affinity receptor tyrosine kinases The structurally diverse receptor molecules are also functionally different The characterization of structural and functional diversity within the FGF receptor shows the differences in the mechanisms of action among members of the FGF family The first members of the FGF family to be purified and characterized were acidic FGF (aFGF) and basic FGF (bFGF), which are purified on the basis of their mitogenicity toward fibroblasts by using bovine pituitary Functional differences among the different receptor forms are observed in the chapter at two levels The long-range goal of designing the effective agonist and antagonists of FGF action has considerable therapeutic value

Association of Sos Ras exchange protein with Grb2 is implicated in tyrosine kinase signal transduction and transformation

Abstract: The proteins Grb2–Sem-5, Shc and Sos have been implicated in the signalling pathway from tyrosine kinase receptors to Ras. Grb2–Sem-5 binds directly to murine Sos1, a Ras exchange factor, through two SH3 domains. Sos is also associated with ligand-activated tyrosine kinase receptors which bind Grb2–Sem-5, and with the Grb2–Sem-5 binding protein, Shc. Ectopic expression of Drosophila Sos stimulates morphological transformation of rodent fibroblasts. These data define a pathway by which tyrosine kinases act through Ras to control cell growth and differentiation.

Mitogen-activated protein kinases p42mapk and p44mapk are required for fibroblast proliferation

Abstract: The mitogen-activated protein kinases (MAP kinases) p42mapk and p44mapk are serine/threonine kinases rapidly activated in cells stimulated with various extracellular signals by dual phosphorylation of tyrosine and threonine residues. They are thought to play a pivotal role in integrating and transmitting transmembrane signals required for growth and differentiation. Here we demonstrate that activation of these ubiquitously expressed MAP kinases is essential for growth. To specifically suppress MAP kinase activation in fibroblasts, we transiently expressed either the entire p44mapk antisense RNA or p44mapk kinase-deficient mutants (T192A or Y194F). As expected, and through independent mechanisms, both approaches strongly inhibited MAP kinase activation. The antisense reduced the expression of endogenous p42mapk and p44mapk by 90%, whereas overexpression of the T192A mutant inhibited growth factor activation of both endogenous MAP kinases by up to 70%. As a consequence, we found that the antisense as well as the T192A mutant of p44mapk inhibited growth factor-stimulated gene transcription (collagenase promoter assay with chloramphenicol acetyltransferase reporter) and cell growth. These effects were proportional to the extent of MAP kinase inhibition and reversed by coexpression of the wild-type p44mapk. Therefore we conclude that growth factor activation of p42mapk and p44mapk is an absolute requirement for triggering the proliferative response.

Guanine-nucleotide-releasing factor hSos1 binds to Grb2 and links receptor tyrosine kinases to Ras signalling.

Abstract: Many of the actions of receptor tyrosine kinases are mediated by the protein Ras, including the activation of various downstream serine/threonine kinases and the stimulation of growth and differentiation. The human protein Grb2 binds to ligand-activated growth factor receptors and downstream effector proteins through its Src-homology (SH) domains SH2 and SH3, respectively, and like its homologue from Caenorhabditis elegans, Sem-5, apparently forms part of a highly conserved pathway by which these receptors can control Ras activity. Here we show that the SH3 domains of Grb2 bind to the carboxy-terminal part of hSos1, the human homologue of the Drosophila guanine-nucleotide-releasing factor for Ras, which is essential for control of Ras activity by epidermal growth factor receptor and sevenless. Moreover, a synthetic 10-amino-acid peptide containing the sequence PPVPPR specifically blocks the interaction. These results indicate that the Grb2/hSos1 complex couples activated EGF receptor to Ras signalling.

Inhibition by cAMP of Ras-dependent activation of Raf

Abstract: Activation of the Raf and extracellular signal-regulated kinases (ERKs) (or mitogen-activated protein kinases) are key events in mitogenic signalling, but little is known about interactions with other signaling pathways. Agents that raise levels of intracellular cyclic adenosine 3',5'-monophosphate (cAMP) blocked DNA synthesis and signal transduction in Rat1 cells exposed to epidermal growth factor (EGF) or lysophosphatidic acid. In the case of EGF, receptor tyrosine kinase activity and association with the signaling molecules Grb2 and Shc were unaffected by cAMP. Likewise, EGF-dependent accumulation of the guanosine 5'-triphosphate-bound form of Ras was unaffected. In contrast, activation of Raf-1 and ERK kinases was inhibited. Thus, cAMP appears to inhibit signal transmission from Ras by preventing Ras-dependent activation of Raf-1.

Identification of mutations in the coding sequence of the proto-oncogene c-kit in a human mast cell leukemia cell line causing ligand-independent activation of c-kit product.

Abstract: The c-kit proto-oncogene encodes a receptor tyrosine kinase. Binding of c-kit ligand, stem cell factor (SCF) to c-kit receptor (c-kitR) is known to activate c-kitR tyrosine kinase, thereby leading to autophosphorylation of c-kitR on tyrosine and to association of c-kitR with substrates such as phosphatidylinositol 3-kinase (PI3K). In a human mast cell leukemia cell line HMC-1, c-kitR was found to be constitutively phosphorylated on tyrosine, activated, and associated with PI3K without the addition of SCF. The expression of SCF mRNA transcript in HMC-1 cells was not detectable by means of PCR after reverse transcription (RT-PCR) analysis, suggesting that the constitutive activation of c-kitR was ligand independent. Sequencing of whole coding region of c-kit cDNA revealed that c-kit genes of HMC-1 cells were composed of a normal, wild-type allele and a mutant allele with two point mutations resulting in intracellular amino acid substitutions of Gly-560 for Val and Val-816 for Asp. Amino acid sequences in the regions of the two mutations are completely conserved in all of mouse, rat, and human c-kit. In order to determine the causal role of these mutations in the constitutive activation, murine c-kit mutants encoding Gly-559 and/or Val-814, corresponding to human Gly-560 and/or Val-816, were constructed by site-directed mutagenesis and expressed in a human embryonic kidney cell line, 293T cells. In the transfected cells, both c-kitR (Gly-559, Val-814) and c-kitR (Val-814) were abundantly phosphorylated on tyrosine and activated in immune complex kinase reaction in the absence of SCF, whereas tyrosine phosphorylation and activation of c-kitR (Gly-559) or wild-type c-kitR was modest or little, respectively. These results suggest that conversion of Asp-816 to Val in human c-kitR may be an activating mutation and responsible for the constitutive activation of c-kitR in HMC-1 cells.

Ligand-specific activation of HER4/p180erbB4, a fourth member of the epidermal growth factor receptor family.

Abstract: This report describes the isolation and recombinant expression of a cDNA clone encoding HER4, the fourth member of the human epidermal growth factor receptor (EGFR) family. The HER4/erbB4 gene encodes a 180-kDa transmembrane tyrosine kinase (HER4/p180erbB4) whose extracellular domain is most similar to the orphan receptor HER3/p160erbB3, whereas its cytoplasmic kinase domain exhibits 79% and 77% identity with EGFR and HER2/p185erbB2, respectively. HER4 is most predominantly expressed in several breast carcinoma cell lines, and in normal skeletal muscle, heart, pituitary, brain, and cerebellum. In addition, we describe the partial purification of a heparin-binding HER4-stimulatory factor from HepG2 cells. This protein was found to specifically stimulate the intrinsic tyrosine kinase activity of HER4/p180erbB4 while having no direct effect on the phosphorylation of EGFR, HER2, or HER3. Furthermore, this heparin-binding protein induces phenotypic differentiation, and tyrosine phosphorylation, of a human mammary tumor cell line that overexpresses both HER4 and HER2. These findings suggest that this ligand-receptor interaction may play a role in the growth and differentiation of some normal and transformed cells.

flk-1, an flt-related receptor tyrosine kinase is an early marker for endothelial cell precursors

Abstract: We have used RT-PCR to screen pluripotent murine embryonic stem cells to identify receptor tyrosine kinases (RTKs) potentially involved in the determination or differentiation of cell lineages during early mouse development. Fourteen different tyrosine kinase sequences were identified. The expression patterns of four RTKs have been examined and all are expressed in the mouse embryo during, or shortly after, gastrulation. We report here the detailed expression pattern of one such RTK, the flt-related gene flk-1. In situ hybridization analysis of the late primitive streak stage embryo revealed that flk-1 was expressed in the proximal-lateral embryonic mesoderm; tissue fated to become heart. By headfold stages, staining was confined to the endocardial cells of the heart primordia as well as to the blood islands of the visceral yolk sac and the developing allantois. Patchy, speckled staining was detected in the endothelium of all the major embryonic and extraembryonic blood vessels as they formed. During early organogenesis, expression was detected in the blood vessels of highly vascularized tissues such as the brain, liver, lungs and placenta. Since flk-1 was expressed in early mesodermal cells prior to any morphological evidence for endothelial cell differentiation (vasculogenesis), as well as in cells that form blood vessels from preexisting ones (angiogenesis), it appears to be a very early marker of endothelial cell precursors. We have previously reported that another novel RTK, designated tek, was expressed in differentiating endothelial cells. We show here that flk-1 transcripts are expressed one full embryonic day earlier than the first tek transcripts. The expression of these two RTKs appear to correlate with the specification and early differentiation of the endothelial cell lineage respectively, and therefore may play important roles in the establishment of this lineage.

IL-6-induced homodimerization of gp130 and associated activation of a tyrosine kinase

Abstract: The biological functions of interleukin-6 (IL-6) are mediated through a signal-transducing component of the IL-6 receptor, gp130, which is associated with the ligand-occupied IL-6 receptor (IL-6R) protein. Binding of IL-6 to IL-6R induced disulfide-linked homodimerization of gp130. Tyrosine kinase activity was associated with dimerized but not monomeric gp130 protein. Substitution of serine for proline residues 656 and 658 in the cytoplasmic motif abolished tyrosine kinase activation and cellular responses but not homodimerization of gp130. The IL-6-induced gp130 homodimer appears to be similar in function to the heterodimer formed between the leukemia inhibitory factor (LIF) receptor (LIFR) and gp130 in response to the LIF or ciliary neurotrophic factor (CNTF). Thus, a general first step in IL-6-related cytokine signaling may be the dimerization of signal-transducing molecules and activation of associated tyrosine kinases.

The protein tyrosine kinase JAK1 complements defects in interferon-α/β and -γ signal transduction

Abstract: We have produced a cell line which lacks the protein tyrosine kinase JAK1 and is completely defective in interferon response. Complementation of this mutant with JAK1 restored the response, establishing the requirement for JAK1 in both the interferon-α/β and -γ signal transduction pathways. The reciprocal interdependence between JAK1 and Tyk2 activities in the interferon-α pathway, and between JAK1 and JAK2 in the interferon-γ pathway, may reflect a requirement for these kinases in the correct assembly of interferon receptor complexes.

LIFR beta and gp130 as heterodimerizing signal transducers of the tripartite CNTF receptor.

Abstract: The ciliary neurotrophic factor (CNTF) receptor complex is shown here to include the CNTF binding protein (CNTFR alpha) as well as the components of the leukemia inhibitory factor (LIF) receptor, LIFR beta (the LIF binding protein) and gp130 [the signal transducer of interleukin-6 (IL-6)]. Thus, the conversion of a bipartite LIF receptor into a tripartite CNTF receptor apparently occurs by the addition of the specificity-conferring element CNTFR alpha. Both CNTF and LIF trigger the association of initially separate receptor components, which in turn results in tyrosine phosphorylation of receptor subunits. Unlike the IL-6 receptor complex in which homodimerization of gp130 appears to be critical for signal initiation, signaling by the CNTF and LIF receptor complexes depends on the heterodimerization of gp130 with LIFR beta. Ligand-induced dimerization of signal-transducing receptor components, also seen with receptor tyrosine kinases, may provide a general mechanism for the transmission of a signal across the cell membrane.

SH2-containing phosphotyrosine phosphatase as a target of protein-tyrosine kinases

Abstract: A mouse phosphotyrosine phosphatase containing two Src homology 2 (SH2) domains, Syp, was identified. Syp bound to autophosphorylated epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) receptors through its SH2 domains and was rapidly phosphorylated on tyrosine in PDGF- and EGF-stimulated cells. Furthermore, Syp was constitutively phosphorylated on tyrosine in cells transformed by v-src. This mammalian phosphatase is most closely related, especially in its SH2 domains, to the corkscrew (csw) gene product of Drosophila, which is required for signal transduction downstream of the Torso receptor tyrosine kinase. The Syp gene is widely expressed throughout embryonic mouse development and in adult tissues. Thus, Syp may function in mammalian embryonic development and as a common target of both receptor and nonreceptor tyrosine kinases.

Modulation of the glycogen synthase kinase-3 family by tyrosine phosphorylation.

Abstract: Glycogen synthase kinase-3 (GSK-3) is a protein serine kinase implicated in the cellular response to insulin. The enzyme is the mammalian homologue of the zeste-white3 (shaggy) homeotic gene of Drosophila melanogaster and has been implicated in the regulation of the c-Jun/AP-1 transcription factor. In mammals this protein serine kinase is encoded by two related genes termed GSK-3 alpha and beta. Here, we demonstrate that these two proteins and the fruit fly protein are phosphorylated on tyrosine in vivo. Moreover, GSK-3 beta activity and function are shown to be dependent on tyrosine phosphorylation. The modified tyrosine residue is conserved in all members of the GSK-3 family and is equivalent to that required for activity by mitogen-activated protein (MAP) kinases. However, unlike MAP kinases, GSK-3 is highly phosphorylated on tyrosine and thus active in resting cells.

Differential responses of human tumor cell lines to anti-p185HER2 monoclonal antibodies.

Abstract: The HER2 protooncogene encodes a receptor tyrosine kinase, p185HER2. The overexpression of p185HER2 has been associated with a worsened prognosis in certain human cancers. In the present work we have screened a variety of different tumor cell lines for p185HER2 expression using both enzyme-linked immunosorbent and fluorescence-activated cell sorting assays employing murine monoclonal antibodies directed against the extracellular domain of the receptor. Increased levels of p185HER2 were found in breast (5/9), ovarian (1/6), stomach (2/3) and colorectal (5/16) carcinomas, whereas all kidney and submaxillary adenocarcinoma cell lines tested were negative. Some monoclonal antibodies directed against the extracellular domain of p185HER2 inhibited growth in monolayer culture of breast and ovarian tumor cell lines overexpressing p185HER2, but had no effect on the growth of colon or gastric adenocarcinomas expressing increased levels of this receptor. The most potent growth-inhibitory anti-p185HER2 monoclonal antibody in monolayer culture, designated mumAb 4D5 (a murine IgG1κ antibody), was also tested in soft-agar growth assays for activity against p185HER2-overexpressing tumor cell lines of each type, with similar results. In order to increase the spectrum of tumor types potentially susceptible to monoclonal antibody-mediated anti-p185HER2 therapies, to decrease potential immunogenicity issues with the use of murine monoclonal antibodies for human therapy, and to provide the potential for antibody-mediated cytotoxic activity, a mouse/human chimeric 4D5 (chmAb 4D5) and a “humanized” 4D5 (rhu)mAb 4D5 HER2 antibody were constructed. Both engineered antibodies, in combination with human peripheral blood mononuclear cells, elicited antibody-dependent cytotoxic responses in accordance with the level of p185HER2 expression. Since this cytotoxic activity is independent of sensitivity to mumAb 4D5, the engineered monoclonal antibodies expand the potential target population for antibody-mediated therapy of human cancers characterized by the overexpression of p185HER2.

Grb2 mediates the EGF-dependent activation of guanine nucleotide exchange on Ras

Abstract: Activation of receptor tyrosine kinases such as those for epidermal growth factor (EGF), platelet-derived growth factor, or nerve growth factor converts the inactive, GDP-bound form of Ras to the active, GTP-bound form, and a dominant negative mutant of Ras interferes with signalling from such receptors. The mechanisms by which receptor tyrosine kinases and Ras are coupled, however, are not well understood. Many cytoplasmic proteins regulated by such receptors contain Src-homology (SH) 2 and 3 domains, and the SH2- and SH3-containing protein Grb2, like its homologue from Caenorhabditis elegans, Sem-5, appears to play an important role in the control of Ras by receptor tyrosine kinases. Here we show that overexpression of Grb2 potentiates the EGF-induced activation of Ras and mitogen-activated protein kinase by enhancing the rate of guanine nucleotide exchange on Ras. Cellular Grb2 appears to form a complex with a guanine-nucleotide-exchange factor for Ras, which binds to the ligand-activated EGF receptor, allowing the tyrosine kinase to modulate Ras activity.

Activation of a phosphotyrosine phosphatase by tyrosine phosphorylation.

Abstract: Regulation of cell proliferation, differentiation, and metabolic homeostasis is associated with the phosphorylation and dephosphorylation of specific tyrosine residues of key regulatory proteins. The phosphotyrosine phosphatase 1D (PTP 1D) contains two amino terminally located Src homology 2 (SH2) domains and is similar to the Drosophila corkscrew gene product, which positively regulates the torso tyrosine kinase signal transduction pathway. PTP activity was found to be regulated by physical interaction with a protein tyrosine kinase. PTP 1D did not dephosphorylate receptor tyrosine kinases, despite the fact that it associated with the epidermal growth factor receptor and chimeric receptors containing the extracellular domain of the epidermal growth factor receptor and the cytoplasmic domain of either the HER2-neu, kit-SCF, or platelet-derived growth factor beta (beta PDGF) receptors. PTP 1D was phosphorylated on tyrosine in cells overexpressing the beta PDGF receptor kinase and this tyrosine phosphorylation correlated with an enhancement of its catalytic activity. Thus, protein tyrosine kinases and phosphatases do not simply oppose each other's action; rather, they may work in concert to maintain a fine balance of effector activation needed for the regulation of cell growth and differentiation.

Complementation by the protein tyrosine kinase JAK2 of a mutant cell line defective in the interferon-& gamma; signal transduction pathway

Abstract: Interferons (IFNs) alpha/beta (type I) and gamma (type II) bind to distinct cell surface receptors, inducing transcription of overlapping sets of genes by intracellular pathways that have recently attracted much attention. Previous studies using cell lines selected for their inability to respond to IFN-alpha (ref. 4) have shown that the protein kinase Tyk2 plays a central role in the IFN alpha/beta response. Here we report the isolation of the cell line gamma 1A, selected for its inability to express IFN-gamma-inducible cell-surface markers, that is deficient in all aspects of the IFN-gamma response tested, but responds normally to IFNs alpha and beta. The mutant cells can be complemented by the expression of another member of the JAK family of protein tyrosine kinases, JAK2 (refs 6-9). Unlike IFNs alpha and beta, IFN-gamma induces rapid tyrosine phosphorylation of JAK2 in wild-type cells, and JAK2 immunoprecipitates from these cells show tyrosine kinase activity. These responses are absent in gamma 1A cells. JAK2 is therefore required for the response to IFN-gamma but not to IFNs alpha and beta.

An essential heparin-binding domain in the fibroblast growth factor receptor kinase

Abstract: Heparin or heparin-like heparan sulfate proteoglycans are obligatory for activity of the heparin-binding fibroblast growth factor (FGF) family. Heparin interacts independently of FGF ligand with a specific sequence (K18K) in one of the immunoglobulin-like loops in the extracellular domain of the FGF receptor tyrosine kinase transmembrane glycoprotein. A synthetic peptide corresponding to K18K inhibited heparin and heparin-dependent FGF binding to the receptor. K18K and an antibody to K18K were antagonists of FGF-stimulated cell growth. Point mutations of lysine residues in the K18K sequence abrogated both heparin- and ligand-binding activities of the receptor kinase. The results indicate that the FGF receptor is a ternary complex of heparan sulfate proteoglycan, tyrosine kinase transmembrane glycoprotein, and ligand.

Tie-1 and tie-2 define another class of putative receptor tyrosine kinase genes expressed in early embryonic vascular system.

Abstract: We report the molecular cloning and characterization of two structurally related putative receptor tyrosine kinases, encoded by distinct genes (tie-1 and tie-2) on mouse chromosome 4. Both tie-1 and tie-2 encode receptor proteins possessing unique multiple extracellular domains: two immunoglobulin-like loop domains flanking three epidermal growth factor repeats followed by three fibronectin-type III repeats. Both genes are expressed in early embryonic vascular system and in maternal decidual vascular endothelial cells, where the vasculature undergoes an active angiogenesis. tie-2, but not tie-1, expression was also detected in extraembryonic mesoderm of the amnion. tie-1, but not tie-2, is expressed in an acute myelogenic cell line in vitro. tie-1 and tie-2 may form another class within the receptor tyrosine kinase gene family, and further characterization of these genes and identification of their putative ligands should define the nature of the signal-transduction cascades underlying early vascular system development, as well as their differential roles in mesodermal cells of the amniotic and myeloid lineages.

Polypeptide signalling to the nucleus through tyrosine phosphorylation of Jak and Stat proteins

Abstract: Binding of interferons IFN-alpha and IFN-gamma to their cell surface receptors promptly induces tyrosine phosphorylation of latent cytoplasmic transcriptional activators (or Stat proteins, for signal transducers and activators of transcription). Interferon-alpha activates both Stat91 (M(r) 91,000; ref. 1) and Stat113 (M(r) 113,000; ref. 2) whereas IFN-gamma activates only Stat91 (refs 3, 4). The activated proteins then move into the nucleus and directly activate genes induced by IFN-alpha and IFN-gamma. Somatic cell genetics experiments have demonstrated a requirement for tyrosine kinase-2 (Tyk2) in the IFN-alpha response pathway and for Jak2 (ref. 6), a kinase with similar sequence, in the IFN-gamma response pathway. Here we investigate the tyrosine phosphorylation events on Stat and Jak proteins after treatment of cells with IFNs alpha and gamma and with epidermal growth factor (EGF). Stat91 is phosphorylated on Tyr701 after cells are treated with IFN-alpha and EGF, as it was after treatment with IFN-gamma (ref. 8). We find that Jak1 also becomes phosphorylated on tyrosine after cells are treated with these same three ligands, although each ligand is shown to activate at least one other different kinase. Jak1 may therefore be the enzyme that phosphorylates Tyr 701 in Stat91.

Structure of the murine Jak2 protein-tyrosine kinase and its role in interleukin 3 signal transduction.

Abstract: Interleukin 3 (IL-3) regulates the proliferation and differentiation of hematopoietic cells. Although the IL-3 receptor chains lack kinase catalytic domains, IL-3 induces tyrosine phosphorylation of cellular proteins. To investigate the potential role of the JAK family of protein-tyrosine kinases in IL-3 signal transduction, we have obtained full-length cDNA clones for murine Jak1 and Jak2 protein-tyrosine kinases and prepared antiserum against the predicted proteins. Using antisera against Jak2, we demonstrate that IL-3 stimulation results in the rapid and specific tyrosine phosphorylation of Jak2 and activates its in vitro kinase activity.