The Raf-1 protein mediates insulin-like growth factor-induced proliferation of erythroid progenitor cells.
Previous studies from this and other laboratories have shown that insulin-like growth factor-1 (IGF-I) and insulin-like growth factor-2 (IGF-II) support erythroid colony formation in cultures supplemented with serum substitute and recombinant erythropoietin. Subpopulations of IGF-I- and IGF-II-dependent, erythropoietin-independent colony-forming unit-erythroid (CFU-E)-derived colonies and BFU-E-derived colonies were identified under serum-substituted conditions for adult bone-marrow-derived erythroid progenitors which proliferate in the absence and presence of exogenous anti-erythropoietin receptor monoclonal antibody and in serum-substituted medium that was preadsorbed with anti-erythropoietin IgG. To assess whether Raf-1 is required for the formation of IGF-dependent, erythropoietin-independent human erythroid colonies, 5-15 microM sense or antisense oligomer to raf-1 were added to serum-substituted cultures containing either 2 U/ml recombinant human erythropoietin (rHuEpo) alone or 0-1,000 ng/ml IGF-I or IGF-II with/without 2 U/ml rHuEpo. Both erythropoietin-induced and IGF-induced erythroid colony formation were completely blocked by antisense (but not sense) oligomers to raf-1. Purified human CFU-Es were examined for Raf-1 message and protein. Total RNA was extracted, and raf-1 mRNA was detected on Northern blots. Furthermore, a 74 kD protein, corresponding to Raf-1, was also detected in CFU-Es purified from human adult sources. Together, these studies support the hypothesis that the Raf-1 protein mediates both erythropoietin-induced and IGF-induced signal transduction in human erythroid progenitor cells.
Sanders
M R
MR
Department of Pediatrics, University of Connecticut School of Medicine, Farmington, USA.
Lu
H
H
Walker
F
F
Sorba
S
S
Dainiak
N
N
D000328:Adult; D001854:Bone Marrow Cells / Q000166:cytology; D002478:Cells, Cultured; D002585:Cesarean Section; D015672:Erythroid Precursor Cells / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D004921:Erythropoietin / Q000494:pharmacology; D005312:Fetal Blood / Q000166:cytology; D005333:Fetus; D006801:Humans; D007231:Infant, Newborn; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000196:embryology; D009838:Oligodeoxyribonucleotides / Q000494:pharmacology; D016376:Oligonucleotides, Antisense / Q000494:pharmacology*; D019908:Proto-Oncogene Proteins c-raf / Q000096:biosynthesis / Q000502:physiology*
D009838:Oligodeoxyribonucleotides; D016376:Oligonucleotides, Antisense; D004921:Erythropoietin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D019908:Proto-Oncogene Proteins c-raf