SCGF (stem cell growth factor) was originally detected as a
novel hematopoietic growth factor in mitogen-stimulated peripheral
blood MNCs-conditioned medium (1). Differential protein fractions
purified from the conditioned medium possessed erythroid burst-promoting activity in the presence of erythropoietin and GM-promoting activity in the presence of GM-CSF but no colony-stimulating activity for human bone marrow cells.
Culture supernatants of various hematopoietic cell lines were
screened for the hematopoietic activity (2) using an antibody raised
against purified SCGF fraction (3,4), and a human myeloid leukemia
cell line, KPB-M15 (5), established from a patient with chronic
myeloid leukemia in blast crisis, was disclosed to constitutively
produce a large amount of SCGF (2).
cDNA for SCGF, pSHDM(116-10C), was successfully cloned from
cDNA library prepared from KPB-M15 cells using λSHDM cloning
vector (6). The cDNA clone had 1,196 nucleotides with an open
reading frame of 738 nucleotides, encoding 245 aa protein. RT-PCR
with a template of single strand cDNA prepared from human bone
marrow poly(A) RNA presented another transcripts of SCGF
encoding 323 aa protein, which was longer by 78 aa than pSHDM(116-10C) clone. The longer clone was named as hSCGF-α, and the
shorter one as hSCGF-β (7). The term "SCGF" is sometimes used
synonymous to SCGF-α. Culture supernatants of COS-1 cells
transfected with pSHDM(116-10C) cDNA exhibited the
hematopoietic activity described above. Murine and rat SCGF cDNA
was serially cloned from a cDNA library prepared from preadipocyte
cell line, MC3T3-G2/PA6, and osteosarcoma cell line, ROS-17/2.8-5, respectively (7). The homology search revealed that SCGF was a
member of C-type lectin family since SCGF had the conserved
carbohydrate-recognition domain motif sequence at the carboxyl
terminal. Among the members of C-type lectin family, SCGF showed
the highest homology with tetranectin, a plasminogen kringle 4-binding protein.
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