| Abstract: |
The proto-oncogene c-kit is allelic with the white spotting locus (W) on mouse chromosome 5 and it encodes a transmembrane protein tyrosine kinase which belongs to the platelet-derived growth factor and macrophage-colony stimulating factor (CSF-1) receptor subfamily. In an effort to study the function of the c-kit receptor, specifically the physiological mechanism of controlling the signal induced by the ligand, the effect and mechanism of down-regulation of the c-kit receptor by the kit ligand (KL) was investigated in mast cells. Following preincubation with KL, the capacity of mast cells to bind kit antibody was reduced and binding of radiolabeled KL to mast cells decreased with similar kinetics, suggesting that KL stimulates the loss of c-kit receptor from the cell surface. After binding to the c-kit receptor, KL was rapidly internalized, and degradation of the receptor was accelerated. The c-kit receptor was transmodulated by the protein kinase C activator 12-O-tetradecanoylphorbol-13-acetate (TPA) and by the calcium ionophore ionomycin. TPA- and ionomycin-induced down-regulation of the c-kit receptor was accompanied by release of the extracellular domain of the receptor, presumably by proteolytic cleavage near the transmembrane domain. Release of the extracellular domain of the c-kit receptor occurred also in untreated cells but at a slow rate. In addition, ionomycin induced shedding of the intact c-kit receptor. In mast cells depleted of protein kinase C, the c-kit receptor remained sensitive to down-regulation induced by KL and ionomycin, but not by treatment with TPA. Therefore, the down-regulation of the c-kit receptor induced by KL, activated protein kinase C, and an increased level of intracellular calcium is mediated through independent mechanisms. |
| Keywords: |
signal transduction; proto-oncogene proteins; nonhuman; flow cytometry; animal cell; mouse; animal; mice; cells, cultured; stem cell factor; proto oncogene; down-regulation; calcium; dose-response relationship, drug; mice, inbred c57bl; time factors; kinetics; iodine 125; isotope labeling; recombinant proteins; immunoprecipitation; protein kinase c; molecular weight; ligand binding; methionine; calcium cell level; autoradiography; internalization; 3t3 cells; electrophoresis, polyacrylamide gel; cell surface receptor; receptors, cell surface; phorbol 13 acetate 12 myristate; tetradecanoylphorbol acetate; ionomycin; mast cell; mast cells; receptor down regulation; binding kinetics; priority journal; article; sulfur radioisotopes; support, non-u.s. gov't; support, u.s. gov't, p.h.s.; hematopoietic cell growth factors; proto-oncogene protein c-kit
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