Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P10721 (c-kit)
 6,575 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The hematopoietic microenvironment is a complex structure in which stem cells, progenitor cells, stromal cells, growth factors, and extracellular matrix (ECM) molecules each interact to direct the coordinate regulation of blood cell development. While much is known concerning the individual components of this microenvironment, little is understood of the interactions among these various components or, in particular, the nature of those interactions responsible for the regional localization of specific developmental signals. We hypothesized that cytokines act together with ECM molecules to anchor stem cells within the microenvironment, thus modulating their function. In order to analyze matrix-cytokine-stem cell interactions, we developed an ECM model system in which purified stem cell populations and plastic-immobilized individual proteins are used to assess the role of various matrix molecules and/or cytokines in human hematopoietic cell development. Analysis of these interactions revealed that a single ECM protein, thrombospondin, in conjunction with a single cytokine (e.g., c-kit ligand), constitutes a developmental signal that synergistically modulates hematopoietic stem cell function.
 ...
PMID:Human hematopoietic stem cell adherence to cytokines and matrix molecules. 137 55

The high levels of hematopoietic growth factors required for in vitro and in vivo activity raise questions as to their role in normal hematopoietic maintenance. We hypothesize that the use of combinations of cytokines to stimulate hematopoietic progenitors might allow individual factors to exert their influence at lower, more physiologically relevant concentrations. Growth factor combinations were assessed by their ability to stimulate both total colonies and high proliferative potential colony-forming cells (HPP-CFC), an early murine hematopoietic progenitor, in double-layer agar cultures. Very-low-level combinations of colony-stimulating factor (CSF)-1, granulocyte CSF (G-CSF), granulocyte-macrophage CSF (GM-CSF), interleukin (IL)-1 alpha, and IL-3 had little or no clonogenic capacity. Plateau levels of rr stem cell factor (rrSCF), a c-kit ligand, used alone also had negligible clonogenic capacity, but when combined with the low-level combination of the other five factors produced total colony and HPP-CFC growth approaching that produced by all factors at plateau levels. Delayed addition experiments suggest that this effect may represent sequential activity of SCF and the other factors. We propose a model of the normal hematopoietic microenvironment in which SCF at locally high concentration on the stromal cell surface "anchors" the hematopoietic stem cell's response to multiple other cytokines at physiologically relevant levels.
 ...
PMID:Stem cell factor induction of in vitro murine hematopoietic colony formation by "subliminal" cytokine combinations: the role of "anchor factors". 137 85

The protooncogene c-kit encodes a tyrosine kinase receptor for the stem cell factor (SCF). Mutants of c-kit were shown to confer a pleiotropic defective phenotype and often display negative dominance in heterozygous mice. To explore the involvement of receptor dimerization in this genetic phenomenon, we employed both a human ligand, which does not recognize the murine receptor, and a rodent SCF, which binds to the human receptor with 100-fold reduced affinity as compared with human SCF. SCF binding to living cells was found to induce rapid and complete receptor dimerization that involved activation of the catalytic tyrosine kinase function. Although receptor dimerization can be attributed to the dimeric nature of the ligand, no dissociation of Kit dimers occurred at high excess of SCF, suggesting that receptor-receptor interactions are also involved in dimer stabilization. This was supported by in vitro formation of heterodimers between the human and murine Kit proteins through monovalent binding of species-specific human SCF. By coexpression of human and mouse Kit in murine fibroblasts, we found that receptor heterodimerization in living cells involved an increase in the affinity of human Kit for rat SCF and also an accelerated rate of receptor down-regulation. When a human Kit mutant lacking the kinase insert domain was coexpressed with the murine wild-type receptor, we observed a significant decrease in both the activation of the intact tyrosine kinase and its coupling to an effector protein, namely phosphatidylinositol 3'-kinase. Our results favor a receptor activation model that assumes an initial step of monovalent ligand binding, followed by an intermediate receptor dimer bound by one arm of the ligand molecule. This model predicts the existence of an intrinsic receptor dimerization site and provides a structural basis for genetic dominance of mutant SCF receptors.
 ...
PMID:Dimerization and activation of the kit receptor by monovalent and bivalent binding of the stem cell factor. 137 43

The c-kit proto-oncogene encodes a tyrosine kinase receptor (KIT) which is expressed on many types of human cells. Numerous studies attest to the importance of the c-kit receptor and its ligand, known variously as stem cell factor (SCF), mast cell growth factor (MGF), Steel factor (SF), or kit ligand (KL) (the nomenclature we prefer), in the development of human hematopoietic cells. KL, which is produced in membrane-bound and soluble forms by bone marrow stromal cells, acts on pre-colony forming units (pre-CFU) and CFU cells. In synergistic combination with other cytokines, KL enhances the growth of myeloid progenitor cells. However, using an antisense oligodeoxynucleotide strategy to disrupt c-kit function, we have demonstrated that the KL-KIT complex is of greatest importance for generation and/or proliferation of normal human erythropoietic progenitor cells. In malignant hematopoietic cells, the complex also appears to be important for growth of granulocyte/macrophage (GM) CFU as well.
 ...
PMID:The c-kit proto-oncogene in normal and malignant human hematopoiesis. 137 19

The ligand for the human c-kit, recombinant human stem cell factor (SCF), was administered to baboons at doses of 200, 100, 50, 25, and 10 micrograms/kg/d. SCF induced a dose-dependent expansion of hematopoietic colony-forming cells (CFC) of multiple types in both blood and marrow, including colony-forming unit (CFU) granulocyte-monocyte, burst-forming unit-erythroid, CFU-MIX, and high proliferative potential-CFC. These changes were associated with a dose-dependent leukocytosis, involving all leukocyte lineages, a reticulocytosis, and increases in marrow cellularity. At 200 micrograms/kg/d of SCF, CFC in blood were increased 10-fold to greater than 100-fold. This correlated with an increased frequency of CD34+ cells in blood. The frequency of CFC in blood approached that of marrow in some animals. These changes were reversed within 7 to 14 days of stopping SCF. The results of these studies suggest a role for the c-kit ligand in stimulating the expansion of multiple CFC types in blood and marrow for potential therapeutic purposes.
 ...
PMID:A c-kit ligand, recombinant human stem cell factor, mediates reversible expansion of multiple CD34+ colony-forming cell types in blood and marrow of baboons. 137 53

The preadipose cell line, PA6, can support long-term hemopoiesis. Frequency of the hemopoietic stem cells capable of sustaining hemopoiesis in cocultures of bone marrow cells and PA6 cells for 6 wk was 1/5.3 x 10(4) bone marrow cells. In the group of dishes into which bone marrow cells had been inoculated at 2.5 x 10(4) cells/dish, 3 of 19 dishes (16%) contained stem cells capable of reconstituting erythropoiesis of WBB6F1-W/Wv mice, indicating that PA6 cells can support the proliferation of primitive hemopoietic stem cells. When the cocultures were treated with an antagonistic anti-c-kit monoclonal antibody, ACK2, only a small number of day 12 spleen colony-forming units survived; and hemopoiesis was severely reduced. However, when the cocultures were continued with antibody-free medium, hemopoiesis dramatically recovered. To examine the proliferative properties of the ACK2-resistant stem cells, we developed a colony assay system by modifying our coculture system. Sequential observations of the development of individual colonies and their disappearance demonstrated that the stem cells having higher proliferative capacity preferentially survive the ACK2 treatment. Furthermore, cells of subclones of the PA6 clone that were incapable of supporting long-term hemopoiesis expressed mRNA for the c-kit ligand. These results suggest that a mechanism(s) other than that involving c-kit receptor and its ligand plays an important role in the survival and proliferation of primitive hemopoietic stem cells.
 ...
PMID:In vitro proliferation of primitive hemopoietic stem cells supported by stromal cells: evidence for the presence of a mechanism(s) other than that involving c-kit receptor and its ligand. 138 60

Erythropoiesis in response to erythropoietin (Epo) in myelodysplastic syndrome (MDS) in vitro and in vivo is severely impaired. We investigated the stimulative effect of c-kit ligand (KL) on the erythroid colony-forming abilities of bone marrow cells from 17 patients with MDS. The effects of normal donor-derived marrow were examined in comparison. Suppression of erythroid colony formation in MDS in response to Epo could not be restored by the addition of interleukin-3 (IL-3) to culture. In cultures dishes supplemented with KL, erythroid colony formation was dramatically enhanced, regarding both colony number and size. Colony-forming abilities by MDS progenitors were improved following costimulation with KL, particularly in refractory anemia (RA) and refractory anemia with ring sideroblasts (RARS); however, little enhancement was apparent following KL stimulation of marrow from patients with refractory anemia with excess of blasts (RAEB), refractory anemia with excess of blasts in transformation (RAEB-t), and chronic myelomonocytic leukemia (CMML). These results suggest that KL responsiveness of patients with low-risk MDS may still be intact, and that with progression to high-risk MDS, erythroid progenitors lose proliferative reactivity to both KL and Epo stimulation. KL may have a therapeutic role in restoring erythropoiesis in a subset of patients with MDS.
 ...
PMID:Kit ligand improves in vitro erythropoiesis in myelodysplastic syndrome. 138 Dec 39

Interleukin-11 (IL-11), a pleiotropic cytokine originally isolated from a primate bone marrow stromal cell line, has been shown to stimulate T-cell-dependent B-cell maturation, megakaryopoiesis, and various stages of myeloid differentiation, but to inhibit adipogenesis. Because stromal cells are essential for the maintenance of early hematopoietic progenitor cells in long-term culture, we investigated the effects of IL-11 on multipotent and erythroid precursors from murine bone marrow in vitro in suspension and semisolid cultures. Our results show that in the presence of IL-3 or c-kit ligand (KL), IL-11 has profound stimulatory effects on primitive multilineage hematopoietic progenitors, pre-CFC(multi), as well as on precursors representing various stages of erythroid differentiation observable in vitro, including CFC(multi), BFU-E, and CFU-E. In addition, the combination of KL with IL-11 also stimulated highly proliferative erythroid progenitors that yield remarkable macroscopic erythroblast colonies in culture. These results indicate that IL-11 is likely to play a pivotal role in early hematopoiesis and at multiple stages of erythropoiesis.
 ...
PMID:Interleukin-11 stimulates multiple phases of erythropoiesis in vitro. 138 Dec 40

The c-kit proto-oncogene encodes a transmembrane glycoprotein identical to the receptor for the recently cloned stem cell factor (SCF). The present study examines constitutive synthesis of transcripts in primary acute myelogenous leukemia (AML) blasts and the effects of recombinant human tumor necrosis factor (TNF)-alpha on c-kit mRNA expression in these cells. The c-kit transcripts were detectable at low levels in 10 of 10 different AML samples investigated. TNF treatment of AML cells was associated with enhanced c-kit mRNA expression in all specimens. Nuclear run-on transcription assays indicated that the c-kit gene was transcriptionally active in all leukemias examined and the rate of transcription was unaffected by exposure to TNF, suggesting posttranscriptional control mechanisms of c-kit mRNA accumulation. In the absence of TNF, the half-life of c-kit transcripts was 2 to 3 hours, while in TNF-treated AML cells, c-kit half-life was found to be 5 to 9 hours. Inhibition of protein synthesis reduced TNF-induced c-kit mRNA expression by Northern blot analysis, but did not affect the rate of c-kit gene transcription. In the presence of inhibition of protein synthesis, the half-life of c-kit transcripts in TNF-induced leukemia cells decreased to 2 to 4 hours. These findings indicate that levels of c-kit mRNA are controlled by a labile protein that is involved in TNF-mediated stabilization of c-kit transcripts. The effects of TNF-alpha also extended to the protein level in that TNF-alpha treatment of primary AMLs was associated with enhanced surface expression of the SCF receptor by some of these cells. While exogenous SCF induced clonogenic growth of all primary AML samples investigated, TNF-alpha failed to stimulate leukemic cells to proliferate. However, the combination of SCF and TNF-alpha resulted in synergistic growth stimulation in seven of nine different AML specimens investigated. The finding of transmodulation of the SCF receptor through posttranscriptional modifications might further contribute to our understanding of the synergistic interplay of TNF-alpha and SCF.
 ...
PMID:Functional expression of c-kit by acute myelogenous leukemia blasts is enhanced by tumor necrosis factor-alpha through posttranscriptional mRNA stabilization by a labile protein. 1101 49

Steel factor (SF) (also called stem cell factor, mast cell growth factor, or c-kit ligand) is a recently cloned hemopoietic growth factor that is produced by bone marrow stromal cells, fibroblasts, and hepatocytes. In both mouse and man it acts synergistically with several colony stimulating factors, including interleukin-3 (IL-3) and granulocyte macrophage-colony stimulating factor (GM-CSF), to induce the proliferation and differentiation of primitive hemopoietic precursor cells. In order to study its mechanism of action and to explore the molecular basis for its synergistic activity we have examined the proteins that become tyrosine phosphorylated in response to SF, IL-3, and GM-CSF. We report herein that SF, but not IL-3 or GM-CSF, dramatically stimulates the tyrosine phosphorylation of the product of the recently discovered proto-oncogene, vav, in two SF-responsive human cell lines, M07E and TF-1. Although phosphorylation is very rapid, reaching maximal levels within 2 min at 37 degrees C, co-immunoprecipitation studies suggest that c-kit may either not associate directly with p95vav or bind to it with very low affinity. Nonetheless, our data suggest that c-kit may utilize p95vav to mediate downstream signaling in hemopoietic cells.
 ...
PMID:Steel factor stimulates the tyrosine phosphorylation of the proto-oncogene product, p95vav, in human hemopoietic cells. 138 60


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>