The protein kinase domains of v‐kit, the oncogene of the acute transforming feline retrovirus HZ4‐FeSV (HZ4‐feline sarcoma virus), CSF‐1R (macrophage colony stimulating factor receptor) and PDGFR (platelet derived growth factor receptor) display extensive homology. Because of the close structural relationship of v‐kit, CSF‐1R and PDGFR we predicted that c‐kit would encode a protein kinase transmembrane receptor (Besmer et al., 1986a; Yarden et al., 1986). We have now determined the primary structure of murine c‐kit from a DNA clone isolated from a brain cDNA library. The nucleotide sequence of the c‐kit cDNA predicts a 975 amino acid protein product with a calculated mol. wt of 109.001 kd. It contains an N‐terminal signal peptide, a transmembrane domain (residues 519‐543) and in the C‐terminal half the v‐kit homologous sequences (residues 558‐925). c‐kit therefore contains the features which are characteristic of a transmembrane receptor kinase. Comparison of c‐kit, CSF‐1R and PDGFR revealed a unique structural relationship of these receptor kinases suggesting a common evolutionary origin. The outer cellular domain of c‐kit was shown to be related to the immunoglobulin superfamily. The sites of expression of c‐kit in normal tissue predict a function in the brain and in hematopoietic cells. N‐terminal sequences which include the extracellular domain and the transmembrane domain as well as 50 amino acids from the C‐terminus of c‐kit are deleted in v‐kit. These structural alterations are likely determinants of the oncogenic activation of v‐kit.(ABSTRACT TRUNCATED AT 250 WORDS)

A new acute transforming feline retrovirus, the Hardy-Zuckerman 4 feline sarcoma virus (HZ4-FeSV), has been isolated from a feline fibrosarcoma. The viral genome of HZ4-FeSV contains a new oncogene designated v-kit, has the structure 5' delta gag-kit-delta pol-delta env 3' and specifies a gag-kit polyprotein of relative molecular mass 80,000. The predicted kit amino-acid sequence displays partial homology with tyrosine-specific protein kinase oncogenes. HZ4-FeSV appears to have been generated by transduction of feline c-kit sequences with feline leukaemia virus.

The proto-oncogene c-kit encodes a transmembrane kinase which is related to the receptors for colony-stimulating factor type 1 and platelet-derived growth factor, as well as to the immunoglobulin superfamily. Antibodies specific for the kinase domain of the P80 gag-kit protein of the Hardy-Zuckerman 4 feline sarcoma virus were prepared. These kit-specific antibodies were used to identify and characterize the c-kit protein in cat brain tissue. The c-kit protein product displays an autophosphorylating activity in immune complex kinase assays, and, in turn, this activity was used to identify the c-kit protein in different tissues. In cat brain, a single 145-kilodalton (kDa) glycoprotein was detected. Its N-linked carbohydrates were found to be sensitive to digestion with the endoglycosidases (neuraminidase, endoglycosidase F, and endoglycosidase H), indicating hybrid and/or complex and high-mannose structures. A partial purification of the c-kit protein was achieved by wheat germ agglutinin affinity chromatography, and the autophosphorylating activity of the partially purified c-kit protein was characterized and found to be specific for tyrosine. The kit antibodies cross-react with the murine c-kit protein product, and variant c-kit proteins in different mouse tissues were identified, with sizes of about 145 kDa (brain), 160 kDa (spleen), and 150 kDa (testis).

We examined gene regulation in murine lungs after hind-limb vessel occlusion and reperfusion. A rapid increase of transcript for the AMP deaminase 3 gene (AMPD3) and its enzymatic activity (EC 3.5.4.6) generating inosine monophosphate (IMP) were identified with transcripts located in bronchial and alveolar epithelium. AMP deaminase inhibitor decreased IMP levels and significantly enhanced neutrophil recruitment within lung tissue during reperfusion. In addition, IMP inhibited cytokine-initiated neutrophil infiltration in vivo and selectively attenuated neutrophil rolling by 90% in microvessels. We prepared labeled IMP and demonstrated that IMP specifically binds to neutrophils. IMP also stimulated binding of ␥-[ 35 S]thio-GTP, suggesting that IMP is a potent regulator of neutrophils. Taken together, these results elucidate a previously unrecognized mechanism that protects tissues from the potentially deleterious consequences of aberrant neutrophil accumulation. Moreover, they are relevant for new therapeutic approaches to regulate neutrophil responses in inflammation and vascular disease.

Atherosclerosis is a focal inflammatory disease and preferentially occurs in areas of low fluid shear stress and oscillatory flow, whereas the risk of atherosclerosis is decreased in regions of high fluid shear stress and steady laminar flow. Sphingosine kinase-1 (SphK1) catalyzes the conversion of sphingosine to sphingosine-1 phosphate (S1P), a sphingolipid metabolite that plays important roles in angiogenesis, inflammation, and cell growth. In the present study, we demonstrated that exposure of human aortic endothelial cells to oscillatory flow (shear stress, Ϯ5 dyn/cm 2 for 48 h) resulted in a marked increase in SphK1 mRNA levels compared with endothelial cells kept in static culture. In contrast, laminar flow (shear stress, 20 dyn/cm 2 for 48 h) decreased SphK1 mRNA levels. We further investigated the role of SphK1 in TNF-␣-induced expression of inflammatory genes, such as monocyte chemoattractant protein-1 (MCP-1) and VCAM-1 by using small interfering RNA (siRNA) specifically for SphK1. Treatment of endothelial cells with SphK1 siRNA suppressed TNF-␣-induced increase in MCP-1 mRNA levels, MCP-1 protein secretion, and activation of p38 MAPK. SphK1 siRNA also inhibited TNF-␣-induced cell surface expression of VCAM-1, but not ICAM-1, protein. Exposure of endothelial cells to S1P led to an increase in MCP-1 protein secretion and MCP-1 mRNA levels and activation of NF-B-mediated transcriptional activity. Treatment of endothelial cells with the p38 MAPK inhibitor SB-203580 suppressed S1P-induced MCP-1 protein secretion. These data suggest that SphK1 mediates TNF-␣-induced MCP-1 gene expression through a p38 MAPK-dependent pathway and may participate in oscillatory flow-mediated proinflammatory signaling pathway in the vasculature. p38 MAPK ATHEROSCLEROSIS IS A FOCAL inflammatory disease and preferentially occurs in areas of low fluid shear stress and nonlaminar flow within the vasculature. Conversely, the risk of atherosclerosis is decreased in regions of high fluid shear stress and steady laminar flow (3,8,22). Recent studies show that hemodynamic forces play a significant role in determining the functional phenotype of the vascular endothelium. For example, extended exposure of endothelial cells to laminar flow activates expression of antioxidant and cytoprotective genes including heme oxygenase-1, ferritin, manganese, copper-zinc superoxide dismutase, and endothelial nitric oxide synthase (7,9,32). In contrast, extended exposure of endothelial cells to oscillatory flow leads to upregulation of VCAM-1, ICAM-1, and E-selectin gene expression (6), suggesting that oscillatory flow may contribute to the pathogenesis of atherosclerosis by stimulating the expression of proinflammatory genes. Overall, results from these studies suggest that hemodynamic stress modulates the expression of genes that regulate vascular inflammation.Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite that regulates diverse biological processes (25, 31). Recently, it was reported (35) that sphingosine kinase (SphK), the enz...

Aspirin-triggered 15-epi-lipoxin A4 (ATL) is an endogenous lipid mediator that mimics the actions of native lipoxin A4, a putative "stop signal" involved in regulating resolution of inflammation. A metabolically more stable analog of ATL, 15-epi-16-(para-fluoro)-phenoxy-lipoxin A4 analog (ATLa), inhibits neutrophil recruitment in vitro and in vivo and displays potent anti-inflammatory actions. ATLa binds with high affinity to the lipoxin A4 receptor, a G protein-coupled receptor on the surface of leukocytes. In this study, we used freshly isolated human neutrophils to examine ATLa's potential for initiating rapid nuclear responses. Using differential display reverse transcription polymerase chain reaction, we identified a subset of genes that was selectively up-regulated upon short exposure of polymorphonuclear leukocytes to ATLa but not to the chemoattractant leukotriene B4 or vehicle alone. We further investigated ATLa regulation of one of the genes, NAB1, a transcriptional corepressor identified previously as a glucocorticoid-responsive gene in hamster smooth muscle cells. Treatment of human neutrophils with pertussis toxin blocked ATLa up-regulation of NAB1. In addition, ATLa stimulated NAB1 gene expression in murine lung vascular smooth muscle in vivo. These findings provide evidence for rapid transcriptional induction of a cassette of genes via an ATLa-stimulated G protein-coupled receptor pathway that is potentially protective and overlaps with the anti-inflammatory glucocorticoid regulatory circuit.

The c-kit proto-oncogene encodes a 145- to 160-Kd transmembrane tyrosine kinase, which is a member of the platelet-derived growth factor receptor family and is allelic with the murine white spotting locus (W). W mutations affect several aspects of hematopoiesis, most notably erythroid progenitors and mast cells. A monoclonal antibody, YB5.B8, had been raised against the leukemic blasts of a patient with M1-type acute myelocytic leukemia (AML) and it precipitates a 150-Kd cell surface glycoprotein from leukemic cells. The YB5.B8 epitope is expressed on mast cells, on up to 3% of normal mononuclear bone marrow cells, and it identifies a sub-group of AML patients with a poor prognosis. In view of similarities noted between the cell surface antigen identified by YB5.B8 and the c-kit protein product, we performed experiments to determine whether they are identical. c-kit RNA expression in the cell lines HEL (human erythroleukemia) and A172 (glioblastoma) was shown to parallel the expression of the YB5.B8 epitope in these lines as measured by flow cytometry. Immunoprecipitation analysis with anti-kit serum and YB5.B8 antibody indicated that the two antibodies identified proteins of identical size in HEL (155 Kd) and A172 (145 Kd) cells, and sequential immunoprecipitations with the kit and the YB5.B8 antibodies demonstrated that the two antibodies recognize the same molecule. The proteins identified by both the anti-kit and YB5.B8 antibodies displayed in vitro autophosphorylation activity in immune complex kinase assays. In addition, YB5.B8 was able to inhibit the binding of the kit ligand to HEL cells. These studies provide evidence that the YB5.B8 antigen and the c-kit protein product are identical and raise certain hypotheses regarding the role of c-kit in AML.

Regulation of neutrophil (PMN) trafficking by soluble mediators is a critical component in the outcome of host defense, inflammation resolution, and neutrophil-mediated tissue injury. Elucidation of the endogenous mediators that protect tissues from excess leukocyte traffic and aberrant PMN activation that can lead to tissue damage and chronic inflammation is of considerable interest, especially the endogenous mechanisms of anti-inflammation. To this end, we recently uncovered two new classes of mediators: inosine monophosphate (IMP) and aspirin-triggered 15(R)-epimers of native lipoxin A(4). Here, we examined the combined actions of both classes of compounds in regulating key events in neutrophil trafficking. Neutrophil rolling in mouse microvessels was inhibited by both IMP or 5S,6R,15R-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid (15-epi-LXA(4)) in a concentration-dependent fashion. When combined, IMP (300 nM) and 15-epi-LX (10 nM) demonstrated additive inhibition of neutrophil rolling in microvessels. IMP and 15-epi-LX also significantly inhibited tumor necrosis factor-alpha (TNF-alpha)-induced neutrophil accumulation into the mouse air pouch in a dose-dependent manner. Again, the combination of low dose IMP (10 microg) and LX analog (5 microg) gave additive inhibition of neutrophil accumulation in this model. These results demonstrate the inhibition of neutrophil trafficking in two separate models by two different classes of small endogenous molecules. The additive inhibition by IMP and aspirin-triggered LX may represent key pathways that protect and resolve inflammatory responses that could be harnessed for treatment.