A reappraisal of the role of insulin-like growth factor I in the regulation of human hematopoiesis.
IGF-I has been reported to increase hematopoietic progenitor cell cloning efficiency. To investigate this phenomenon, we studied the IGF-I responsiveness of human marrow cells expressing IGF-I receptor (IGF-IR), a direct strategy not used previously. IGF-IR+ and control CD34+ marrow cells were isolated using immunoaffinity methods. Then, the cells were cloned in methylcellulose containing variable amounts of serum- and lineage-appropriate growth factors supplemented with recombinant human IGF-I. In contrast to CD34+ cells, IGF-IR+ cells never gave rise to CFU-Blast, CFU-Mix, CFU-GM, BFU-E, or CFU-E. To substantiate the suggestion that CD34+ and IGF-IR+ cells were distinct populations, we used reverse transcription PCR to detect IGF-I, EpO, and KIT receptor mRNAs in these cells. The mRNA phenotype of CD34+ cells was EpO (+), KIT (+), and IGF-IR (-), while IGF-IR+ cells were IGF-IR (+), EpO (-), and KIT (-). These results suggested that IGF-IR is either not expressed or expressed at low levels on normal hematopoietic progenitor cells. Functional significance of the latter possibility was tested by exposing CD34+ cells to IGF-IR antisense oligodeoxynucleotides. Colony formation was unaffected by oligodeoxynucleotide disruption of IGF-IR, suggesting that, even if expressed at low level, the receptor's functional significance was doubtful. Nevertheless, when cultured in the presence of IGF-I, IGF-IR+ cells elaborated an activity with mild BFU-E stimulatory effects. Accordingly, if IGF-I plays a role in hematopoietic colony formation, it is probably and results from stimulation of IGF-IR-positive ancillary cells to secrete growth factors. Studies carried out with human leukemia cells yielded similar results.
Ratajczak
M Z
MZ
Department of Pathology, University of Pennsylvania School of Medicine, Philadelphia 19104.
Kuczynski
W I
WI
Onodera
K
K
Moore
J
J
Ratajczak
J
J
Kregenow
D A
DA
DeRiel
K
K
Gewirtz
A M
AM
D001483:Base Sequence; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D006410:Hematopoiesis / Q000187:drug effects*; D006412:Hematopoietic Stem Cells / Q000187:drug effects; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007938:Leukemia / Q000473:pathology; D008969:Molecular Sequence Data; D017526:Receptor, IGF Type 1 / Q000032:analysis
D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1