Biochemical and genetic characterization of multiple splice variants of the Flt3 ligand.
We have performed a comprehensive analysis of cell lines and tissues to compare and contrast the expression patterns of Flt3 ligand (FL), c-Kit ligand (KL), and macrophage colony-stimulating factor as well as their receptors, Flt3, c-Kit, and c-Fms. The message for FL is unusually ubiquitous, whereas that of its receptor is quite restricted, apparently limiting the function of the ligand to fetal development and early hematopoiesis. We have also sequenced a mouse FL genomic clone, revealing how the three splice variant FL mRNAs that we have isolated arise. The chromosomal location of the FL gene has been mapped, by in situ hybridization, to chromosome 7 in mouse and chromosome 19 in human. Natural FL protein has been purified from a stromal cell line and shown to be a 65 kD nondisulfide-linked homodimeric glycoprotein comprised of 30 kD subunits, each containing 12 kD of N- and O-linked sugars. Pulse-chase experiments show that one of the splice variants (T110) is responsible for producing the bulk of soluble FL, but only after it has first been expressed at the cell surface as a membrane-bound form. The other splice-variant forms produce molecules that are either obligatorily soluble (T169) or membrane-bound but released only very slowly (T118). Finally, even though most cell lines express some amount of FL mRNA, we found that very little FL protein is actually made, with T cells and stromal cells being the major producers. The data suggests that FL plays its roles over very short distances, perhaps requiring cell-cell contact.
DNAX Research Institute of Molecular and Cellular Biology, Department of Molecular Biology, Palo Alto, CA 94304, USA.
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T
McClanahan
J
J
Culpepper
D
D
Campbell
J
J
Wagner
K
K
Franz-Bacon
J
J
Mattson
S
S
Tsai
J
J
Luh
M J
MJ
Guimaraes
M G
MG
Mattei
O
O
Rosnet
D
D
Birnbaum
C H
CH
Hannum
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D006801:Humans; D016173:Macrophage Colony-Stimulating Factor / Q000235:genetics* / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics* / Q000378:metabolism; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics*; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism; D016186:Receptor, Macrophage Colony-Stimulating Factor / Q000235:genetics* / Q000378:metabolism; D019089:Stem Cell Factor / Q000235:genetics* / Q000378:metabolism; D014162:Transfection; D051941:fms-Like Tyrosine Kinase 3
D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D019089:Stem Cell Factor; C084881:flt3 ligand protein; D016173:Macrophage Colony-Stimulating Factor; C497970:FLT3 protein, human; C497971:Flt3 protein, mouse; D019009:Proto-Oncogene Proteins c-kit; D020794:Receptor Protein-Tyrosine Kinases; D016186:Receptor, Macrophage Colony-Stimulating Factor; D051941:fms-Like Tyrosine Kinase 3