Identification and characterization of a soluble c-kit receptor produced by human hematopoietic cell lines.
Stem cell factor (SCF) triggers cell growth by binding to cell surface c-kit receptors. Soluble forms of several cytokine receptors have been described and may play a role in the modulation of cytokine activity in vivo. For these reasons, we investigated whether human hematopoietic cells produce soluble c-kit receptors. The human leukemia cell lines OCIM1 and MO7e display approximately 80,000 and approximately 35,000 high-affinity cell surface c-kit receptors, respectively. Soluble c-kit receptors were detected by enzyme immunoassay in OCIM1 and MO7e culture supernatants. We determined the molecular weight and binding affinity of soluble c-kit receptor produced by OCIM1 cells, soluble c-kit receptor purified from human serum, and recombinant soluble c-kit receptor expressed in CHO cells. The three soluble c-kit receptors each have a molecular weight of 98 kD. Quantitative binding experiments with 125I-SCF indicate that the soluble c-kit receptors obtained from human serum or OCIM1 cells have binding affinities for SCF of approximately 200 to 300 pmol/L, in contrast to the recombinant form, which has a binding affinity of approximately 1.5 nmol/L. All three forms of the soluble c-kit receptor were able to compete with c-kit receptors on OCIM1 cells for 125I-SCF binding. Thus human hematopoietic cells can produce a soluble form of the c-kit receptor that retains high-affinity SCF binding activity. We speculate that the soluble c-kit receptor may bind SCF and function as a receptor antagonist in vivo.
Turner
A M
AM
Division of Hematology, University of Washington, Seattle 98195, USA.
Bennett
L G
LG
Lin
N L
NL
Wypych
J
J
Bartley
T D
TD
Hunt
R W
RW
Atkins
H L
HL
Langley
K E
KE
Parker
V
V
Martin
F
F
D000595:Amino Acid Sequence; D001483:Base Sequence; D001667:Binding, Competitive; D002051:Burkitt Lymphoma / Q000473:pathology; D016298:Hematopoietic Cell Growth Factors / Q000378:metabolism; D006412:Hematopoietic Stem Cells / Q000378:metabolism*; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute / Q000473:pathology; D007947:Leukemia, Megakaryoblastic, Acute / Q000473:pathology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D014411:Neoplastic Stem Cells / Q000378:metabolism; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification*; D019009:Proto-Oncogene Proteins c-kit; D020794:Receptor Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification*; D016184:Receptors, Colony-Stimulating Factor / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification*; D011994:Recombinant Proteins / Q000378:metabolism; D012995:Solubility; D019089:Stem Cell Factor; D014407:Tumor Cells, Cultured
D016298:Hematopoietic Cell Growth Factors; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D016184:Receptors, Colony-Stimulating Factor; D011994:Recombinant Proteins; D019089:Stem Cell Factor; D019009:Proto-Oncogene Proteins c-kit; D020794:Receptor Protein-Tyrosine Kinases