New insights into the negative regulation of hematopoiesis by chemokine platelet factor 4 and related peptides.
Platelet factor 4 (PF4) has been recognized as an inhibitor of myeloid progenitors. However, the mechanism of action of this chemokine remains poorly understood. The present study was designed to determine its structure/function relationship. A series of peptides overlapping the C-terminal and central regions of PF4 were analyzed in vitro for their action on murine hematopoietic progenitor growth to assess the minimal sequence length required for activity. The peptides p17-58 and p34-58 possessed an increased hematopoietic inhibitory activity when compared with PF4, whereas the shorter peptides p47-58 and p47-70 were equivalent to the native molecule and the peptide p58-70 was inactive. The PF4 functional motif DLQ located in 54-56 was required for the activity of these peptides. The peptide p34-58 impaired to a similar extent the growth of colony-forming unit-megakaryocyte (CFU-MK) as well as burst-forming unit-erythroid (BFU-E) and colony-forming unit-granulocyte-macrophage (CFU-GM), whereas PF4 was more active on CFU-MK. In the experiments using purified murine CD34(+) marrow cells, statistically significant inhibition induced by p34-58 was shown at concentrations of 2.2 nmol/L or greater for progenitors of the three lineages, whereas that induced by PF4 was seen at 130 nmol/L for CFU-MK and 650 nmol/L for CFU-GM and BFU-E, indicating that the p34-58 acts directly on hematopoietic progenitors and its activity is approximately 60- to 300-fold higher than PF4. The p34-58, unlike PF4, lacked affinity for heparin and its inhibitory activity could not be abrogated by the addition of heparin. In addition, an antibody recognizing p34-58 neutralized the activity of p34-58 but not whole PF4 molecule. These results demonstrate that PF4 contains a functional domain in its central region, which is independent of the heparin binding properties, and provide evidence for a model of heparin-dependent and independent pathways of PF4 in inhibiting hematopoiesis.
Lecomte-Raclet
L
L
Institut des Vaisseaux et du Sang, Hôpital Lariboisière, Paris, France.
Alemany
M
M
Sequira-Le Grand
A
A
Amiral
J
J
Quentin
G
G
Vissac
A M
AM
Caen
J P
JP
Han
Z C
ZC
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D003029:Coagulants / Q000737:chemistry / Q000494:pharmacology*; D006410:Hematopoiesis / Q000187:drug effects*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology; D010978:Platelet Factor 4 / Q000737:chemistry / Q000494:pharmacology*; D013329:Structure-Activity Relationship
D003029:Coagulants; D010455:Peptides; D010978:Platelet Factor 4