Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.1 (protein kinase)
81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thrombopoietin (Tpo) is a cytokine regulating megakaryocyte maturation and platelet formation. We studied Tpo-induced signal transduction, and found that Tpo induces phosphorylation of adapter molecules. Shc and Vav, and of serine/threonine kinases Raf-1 and mitogen-activated protein (MAP) kinases. Further, Tpo induced activation of Ras, MAP kinase kinase, MAP kinase and Pim-1. Taken together with other observations, we concluded that Tpo induces the activation of at least two distinct signaling pathways, a specific Tyk2-JAK2/STAT1-STAT3-STAT5 signaling cascade and a common Shc/Vav/Ras/Raf-1/MAP kinase kinase/MAP kinase signaling cascade.
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PMID:Thrombopoietin induces activation of at least two distinct signaling pathways. 854 84

Cytokine and growth factor receptor engagement leads to the rapid phosphorylation and activation of latent, cytosolic signal transducers and activators of transcription (STAT) proteins, which then translocate to the nucleus where they regulate transcriptional events from specific promoter sequences. STAT3 expression in particular has been associated with Abl, Src, and HTLV-1 transformation of normal cells. B-1 lymphocytes are self-renewing, CD5+ B cells that display a propensity for malignant transformation and are the normal counterpart to human chronic lymphocytic leukemias. Further, B-1 cells are characterized by aberrant intracellular signaling, including hyperresponsiveness to phorbol ester PKC agonists. Here we demonstrate that B-1 lymphocytes constitutively express nuclear activated STAT3, which is not expressed by unmanipulated conventional (B-2) lymphocytes. In contrast, STAT3 activation is induced in B-2 cells after antigen receptor engagement in a delayed fashion (after 3 h). Induction of STAT3 is inhibited by both the serine/threonine protein kinase inhibitor H-7 and the immunosuppressive drug rapamycin and requires de novo protein synthesis, demonstrating novel coupling between sIg and STAT proteins that differs from the classical paradigm for STAT induction by cytokine receptors. The inability of prolonged stimulation of conventional B-2 cells with anti-Ig, a treatment sufficient to induce CD5 expression, to result in sustained STAT3 activation suggests that STAT3 is a specific nuclear marker for B-1 cells. Thus, STAT3 may play a role in B cell antigen-specific signaling responses, and its constitutive activation is associated with a normal cell population exhibiting intrinsic proliferative behavior.
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PMID:Signal transducer and activator of transcription-3 (STAT3) is constitutively activated in normal, self-renewing B-1 cells but only inducibly expressed in conventional B lymphocytes. 909 89

Although thrombopoietin (TPO) is known to play a fundamental role in both megakaryopoiesis and thrombopoiesis, the molecular mechanism of TPO-induced megakaryocytic differentiation is not known. In a human megakaryoblastic leukemia cell line, CMK, that showed some degree of megakaryocytic differentiation after culture with TPO, the cyclin-dependent kinase (Cdk) inhibitor p21(WAF1/Cip1), but not p27(Kip1), p16(INK4A), p15(INK4B), or p18(INK4C), was found to be upregulated in an immediately early response to TPO. The expression of p21 was found to be sustained over a period of 5 days by treatment with TPO in large polyploid cells that developed in response to TPO, but not in small undifferentiated cells, indicating a close correlation between the ligand-induced differentiation and p21 induction in CMK cells. To examine potential roles of Cdk inhibitors in megakaryocytic differentiation, CMK cells were transfected with the p21, p27, or p16 gene, together with a marker gene, beta-galactosidase, and were cultured with medium alone for 5 days. The ectopic expression of p21 or p27 but not of p16 led to induction of megakaryocytic differentiation of CMK cells. Overexpression of the N-terminal domain (amino acids [aa] 1 to 75) of p21 was sufficient to induce megakaryocytic differentiation, whereas that of the C-terminal domain (aa 76 to 164) had little or no effect on morphological features. Furthermore, we found that although TPO induced tyrosine phosphorylation of both STAT3 and STAT5 in CMK cells, only STAT5 showed binding activities to potential STAT-binding sites that locate in the promoter region of p21 gene (p21-SIE sites), thereby leading to transactivation of p21. These results suggested that p21 induction, possibly mediated through activated STAT5, could play an important role in TPO-induced megakaryocytic differentiation.
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PMID:Thrombopoietin-induced differentiation of a human megakaryoblastic leukemia cell line, CMK, involves transcriptional activation of p21(WAF1/Cip1) by STAT5. 911 65

Activation of early response genes by interferons (IFNs) and other cytokines requires tyrosine phosphorylation of a family of transcription factors termed signal transducers and activators of transcription (Stats). The Janus family of tyrosine kinases (Jak1, Jak2, Jak3, and Tyk2) is required for cytokine-induced tyrosine phosphorylation and dimerization of the Stat proteins. In order for IFNs to stimulate maximal expression of Stat1alpha-regulated genes, phosphorylation of a serine residue in the carboxy terminus by mitogen-activated protein kinase (MAPK) is also required. In HeLa cells, both IFN-beta and oncostatin M (OSM) stimulated MAPK and Raf-1 enzyme activity, in addition to Stat1 and Stat3 tyrosine phosphorylation. OSM stimulation of Raf-1 correlated with GTP loading of Ras, whereas IFN-beta activation of Raf-1 was Ras independent. IFN-beta- and OSM-induced Raf-1 activity could be coimmunoprecipitated with either Jak1 or Tyk2. Furthermore, HeLa cells lacking Jak1 displayed no activation of STAT1alpha, STAT3, and Raf-1 by IFN-beta or OSM and also demonstrated no increase in the relative level of GTP-bound p21ras in response to OSM. The requirement for Jak1 for IFN-beta- and OSM-induced activation of Raf-1 was also seen in Jak1-deficient U4A fibrosarcoma cells. Interestingly, basal MAPK, but not Raf-1, activity was constitutively enhanced in Jak1-deficient HeLa cells. Transient expression of Jak1 in both Jak-deficient HeLa cells and U4A cells reconstituted the ability of IFN-beta and OSM to activate Raf-1 and decreased the basal activity of MAPK, while expression of a kinase-inactive form of the protein showed no effect. Moreover, U4A cells selected for stable expression of Jak1, or COS cells transiently expressing Jak1 or Tyk2 but not Jak3, exhibited enhanced Raf-1 activity. Therefore, it appears that Jak1 is required for Raf-1 activation by both IFN-beta and OSM. These results provide evidence for a link between the Jaks and the Raf/MAPK signaling pathways.
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PMID:Beta interferon and oncostatin M activate Raf-1 and mitogen-activated protein kinase through a JAK1-dependent pathway. 919 17

Thrombopoietin (Tpo) is a cytokine which stimulates megakaryocyte maturation. We found that Tpo is constitutively and ubiquitously expressed in all tissues examined, including bone marrow stromal cells, even in thrombocytopenia, thrombosis and steady-state condition in mice. Thus, platelet level in circulation is not regulated by Tpo gene expression. Furthermore, when the purified megakaryocytes were cocultured with the stromal cells, most of the megakaryocytes adhered to the stromal cells and remained unchanged, while free megakaryocytes induced proplatelet formation. Thus the stromal cells in bone marrow secrete Tpo and stimulate megakaryocytopoiesis, but the interaction of megakaryocytes with the stromal cells may suppress platelet formation. Study on signal transduction through Mp1 revealed that Tpo induces activation of JAK2 and Tyk2, which in turn activate STAT1, STAT3 and STAT5. Further, Tpo stimulates transcription factors GATA-1 and NF-E2, which induce differentiation markers, GPIIb/IIIa and Pm-1. In addition, Shc, Vav, Ras, Raf-1, MAPKK, MAPK and Pim-1 are also activated. Thus, Tpo activates a lineage-specific cascade as well as a specific JAK-STAT cascade and a common signaling cascade.
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PMID:Regulation of megakaryocytopoiesis by thrombopoietin and stromal cells. 920 16

Epidermal growth factor (EGF) usually stimulates the proliferation of a variety of normal and malignant cells. In contrast, MDA468, a human breast cancer cell line with a very high number of EGF receptors, is growth inhibited in response to concentrations of EGF that stimulate most other cells. The purpose of this study was to elucidate the cellular mechanisms involved in EGF-induced growth inhibition. EGF treatment stimulated the sustained expression of the cyclin-dependent kinase (CDK) inhibitor p21WAF1. The p21WAF1 induction in EGF-treated MDA468 cells is probably p53-independent since these cells contain no active p53. The promoter for p21WAF1 gene contains binding sites for signal transducer and activator of transcription (STAT) and EGF is known to activate members of this family of transcription factors. Using electrophoretic mobility shift assays (EMSA), we found that EGF activates STAT1 and STAT3 in the MDA468 cells. These activated STATs specifically recognized the three conserved STAT-responsive elements in the p21WAF1 gene promoter, suggesting that STATs may be responsible for the p21WAF1 induction by EGF in MDA468 cells. The sustained rise in p21WAF1 in response to EGF is proposed to be a means of growth inhibition in these cells.
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PMID:MDA468 growth inhibition by EGF is associated with the induction of the cyclin-dependent kinase inhibitor p21WAF1. 925 92

STAT transcription factors are induced by a number of growth factors and cytokines. Within minutes of induction, the STAT proteins are phosphorylated on tyrosine and serine residues and translocated to the nucleus, where they bind to their DNA targets. The leukemia inhibitory factor (LIF) mediates pleiotropic and sometimes opposite effects both in vivo and in cultured cells. It is known, for example, to prevent differentiation of embryonic stem (ES) cells in vitro. To get insights into LIF-regulated signaling in ES cells, we have analyzed protein-binding and transcriptional properties of STAT recognition sites in ES cells cultivated in the presence and in the absence of LIF. We have detected a specific LIF-regulated DNA-binding activity implicating the STAT3 protein. We show that STAT3 phosphorylation is essential for this LIF-dependent DNA-binding activity. The possibility that ERK2 or a closely related protein kinase, whose activity is modulated in a LIF-dependent manner, contributes to this phosphorylation is discussed. Finally, we show that the multimerized STAT3-binding DNA element confers LIF responsiveness to a minimal thymidine kinase promoter. This, together with our observation that overexpression of STAT3 dominant-negative mutants abrogates this LIF responsiveness, clearly indicates that STAT3 is involved in LIF-regulated transcriptional events in ES cells. Finally, stable expression of such a dominant negative mutant of STAT3 induces morphological differentiation of ES cells despite continuous LIF supply. Our results suggest that STAT3 is a critical target of the LIF signaling pathway, which maintains pluripotent cell proliferation.
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PMID:Leukemia inhibitory factor-dependent transcriptional activation in embryonic stem cells. 929 77

In vascular smooth muscle cells, the induction of early growth response genes involves the Janus kinase (JAK)/signal transducer and activators of transcription (STAT) and the Ras/Raf-1/mitogen-activated protein kinase cascades. In the present study, we found that electroporation of antibodies against MEK1 or ERK1 abolished vascular smooth muscle cell proliferation in response to either platelet-derived growth factor or angiotensin II. However, anti-STAT1 or -STAT3 antibody electroporation abolished proliferative responses only to angiotensin II and not to platelet-derived growth factor. AG-490, a specific inhibitor of the JAK2 tyrosine kinase, prevented proliferation of vascular smooth muscle cells, complex formation between JAK2 and Raf-1, the tyrosine phosphorylation of Raf-1, and the activation of ERK1 in response to either angiotensin II or platelet-derived growth factor. However, AG-490 had no effect on angiotensin II- or platelet-derived growth factor-induced Ras/Raf-1 complex formation. Our results indicate that: 1) STAT proteins play an essential role in angiotensin II-induced vascular smooth muscle cell proliferation, 2) JAK2 plays an essential role in the tyrosine phosphorylation of Raf-1, and 3) convergent mitogenic signaling cascades involving the cytosolic kinases JAK2, MEK1, and ERK1 mediate vascular smooth muscle cell proliferation in response to both growth factor and G protein-coupled receptors.
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PMID:Role of Janus kinase/signal transducer and activator of transcription and mitogen-activated protein kinase cascades in angiotensin II- and platelet-derived growth factor-induced vascular smooth muscle cell proliferation. 930 39

Estrogen biosynthesis in adipose tissue increases with age and obesity, and has been implicated in the development of endometrial cancer and breast cancer. In normal human adipose tissue, expression of the CYP19 gene which encodes aromatase P450, the enzyme responsible for estrogen biosynthesis, is regulated by a distal promoter, namely promoter I.4. Stimulation of expression in adipose stromal cells by members of the type 1 cytokine family, i.e. interleukin (IL)-6, IL-11, leukemia inhibitory factor (LIF) and oncostatin M (OSM), is mediated via a Jak-STAT3 signaling pathway and a GAS element upstream of promoter I.4. In contrast, aromatase expression in breast adipose tissue proximal to tumor is increased three- to four-fold to the utilization of another promoter, namely promoter II, proximal to the translation initiation site. In the present report, we show that prostaglandin (PG) E2 is the most potent factor which stimulates aromatase expression via cyclic AMP and promoter II. PGE2 acts via EP1 and EP2 receptor subtypes to stimulate both the PKC and PKA pathways. The combined stimulation of both of these pathways results in the maximal expression of promoter II-specific CYP19 transcripts. Because PGE2 is a major secretory product both of breast tumor epithelial cells and fibroblasts, as well as of macrophages infiltrating the tumor site, then this could be the mechanism whereby estrogen biosynthesis is stimulated in breast sites adjacent to a tumor, leading in turn to increased growth and development of the tumor itself.
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PMID:Transcriptional regulation of CYP19 gene (aromatase) expression in adipose stromal cells in primary culture. 936 91

To explore the pathogenesis of chronic lymphocytic leukemia (CLL), we examined whether phosphorylation of one or more signal transducer and activator of transcription (STAT) factors was abnormal in cells from CLL patients. No constitutive tyrosine phosphorylation was detected on any STAT in CLL cells. To assess the phosphorylation of serine residues of STAT1 and STAT3 in CLL cells, we raised antibodies that specifically recognize the form of STAT1 phosphorylated on ser-727 and the form of STAT3 phosphorylated on ser-727. We found that in 100% of patients with CLL (n = 32), STAT1 and STAT3 were constitutively phosphorylated on serine. This was in contrast to normal peripheral blood B lymphocytes or CD5+) B cells isolated from tonsils, in which this phosphorylation was absent. Serine phosphorylation of STAT1 and STAT3 was seen occasionally in other leukemias, but it was a universal finding only in CLL. The serine phosphorylation of these STATs was a continuous process, as incubation of CLL cells with the kinase inhibitor H7 led to the dephosphorylation of these serine residues. The STAT serine kinase in CLL cells has not been identified, and appears to be neither mitogen-activated protein kinase nor pp70(s6k). In summary, the constitutive serine phosphorylation of STAT1 and STAT3 is present in all CLL samples tested to date, although the physiologic significance of this modification remains to be determined.
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PMID:B lymphocytes from patients with chronic lymphocytic leukemia contain signal transducer and activator of transcription (STAT) 1 and STAT3 constitutively phosphorylated on serine residues. 939 61


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