Secretion of insulinlike growth factor I and insulinlike growth factor-binding proteins by murine bone marrow stromal cells.
Insulin-like growth factor I (IGF-I) stimulates hematopoiesis. We examined whether bone marrow stromal cells synthesize IGF-I. Secretion of IGF-I immunoreactivity by cells from TC-1 murine bone marrow stromal cells was time-dependent and inhibited by cycloheximide. Gel filtration chromatography under denaturing conditions of TC-1 conditioned medium demonstrated two major peaks of apparent IGF-I immunoreactivity with molecular weights of approximately 7.5-8.0 kD, the size of native IGF-I, and greater than 25 kD. Expression of IGF-I mRNA was identified by both RNase protection assay and reverse transcription/polymerase chain reaction. To determine whether the greater than 25-kD species identified by RIA possessed IGF-binding activity, a potential cause of artifactual IGF-I immunoreactivity, charcoal adsorption assay of these gel filtration fractions was performed. The peak of IGF-binding activity coeluted with apparent IGF-I immunoreactivity suggesting that TC-1 cells secrete IGF-binding protein(s). Unfractionated conditioned medium exhibited linear dose-dependent increase in specific binding of [125I]-IGF-I with a pattern of displacement (IGF-I and IGF-II much greater than insulin) characteristic of IGF-binding proteins. Western ligand analysis of conditioned medium showed three IGF-I binding species of approximately 31, 38, and 40 kD. These data indicate that TC-1 bone marrow stromal cells synthesize and secrete IGF-I and IGF-binding proteins and constitute a useful model system to study their regulation and role in hematopoiesis.
Abboud
S L
SL
Department of Medicine, University of Texas Health Science Center, San Antonio 78284.
Bethel
C R
CR
Aron
D C
DC
D000595:Amino Acid Sequence; D000818:Animals; D001853:Bone Marrow / Q000378:metabolism*; D002352:Carrier Proteins / Q000032:analysis / Q000378:metabolism* / Q000502:physiology; D002478:Cells, Cultured; D006410:Hematopoiesis; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000378:metabolism
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I