[Platelet factor 4 acts as both inhibitor and protector of hematopoietic precursor cells: possible mechanism of action].
We have previously shown that platelet factor 4 (PF 4) is a potent inhibitor of megakaryocytopoiesis and that it may protect stem cells from 5-fluorouracil (5-FU) cytotoxicity. In the present work, the effects of human PF 4 on megakaryocyte (MK) growth from human CD34+ cord blood (CB) cells were studied in comparison with transforming growth factor beta 1 (TGF-beta 1). Development of MK from CD34+ cells in both plasma clot culture and liquid culture was significantly inhibited by PF 4 (5 micrograms/ml) and TGF beta 1 (1 ng/ml). Inhibition of cell growth by PF 4 was reversible judging from the fact that the CD34+ cells preincubated with PF 4 could regenerate colonies after washing and replating into the cultures. By contrast, TGF-beta 1 pretreated CD34+ cells gave rise to few colonies following replating. Moreover, incubation of CD34+ cells with PF 4 in liquid culture caused an increase in the number of both stem cell factor (SCF)-binding cells and CD34 antigen-bearing cells, and exhibited greater capacity to form MK colonies than control after the treatment of 5-FU. In vivo in mice, twice injections of PF 4 at 40 micrograms/kg with an interval of 6 h followed by one injection of 5-FU at 150 mg/kg resulted in a significant increase in the number of colony-forming cells with high proliferative potential (HPP-CFC) and colony-forming unit-megakaryocyte (CFU-MK) in bone marrow. In exponentially growing human erythroleukemia cells (HEL), the addition of PF 4 prolonged cell cycle progression and therefore resulted in an increased cell population in S phase, as determined by flow cytometric analysis. Different from PF 4, TGF-beta 1 blocked more cells in G 1 phase. These results demonstrate that PF 4 and TFG-beta 1 inhibit MK development from CD34+ CB cells by different mechanisms and suggest that PF 4, unlike TGF-beta 1, exerts its inhibitory effect on cell growth in a reversible and S phasespecific manner by which it protects stem cells and MK progenitor cells from 5-FU cytotoxicity.
Han
Z C
ZC
Shanghai Institute of Cell Biology, Academia Sinica.
Zhang
X J
XJ
Xi
X D
XD
Lu
M
M
Jiang
S
S
Jiang
L Z
LZ
Wang
X M
XM
Gu
G L
GL
Caen
J P
JP
D000818:Animals; D018952:Antigens, CD34; D000964:Antimetabolites, Antineoplastic / Q000009:adverse effects; D003029:Coagulants / Q000494:pharmacology*; D003114:Colony-Forming Units Assay; D005312:Fetal Blood / Q000166:cytology; D005472:Fluorouracil / Q000009:adverse effects; D006412:Hematopoietic Stem Cells / Q000187:drug effects*; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute / Q000473:pathology; D008533:Megakaryocytes / Q000187:drug effects*; D051379:Mice; D008807:Mice, Inbred BALB C; D010978:Platelet Factor 4 / Q000494:pharmacology*; D016196:S Phase; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D018952:Antigens, CD34; D000964:Antimetabolites, Antineoplastic; D003029:Coagulants; D016212:Transforming Growth Factor beta; D010978:Platelet Factor 4; D005472:Fluorouracil