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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)
 
 
 

Platelet factor 4 promotes adhesion of hematopoietic progenitor cells and binds IL-8: novel mechanisms for modulation of hematopoiesis.

Platelet factor 4 (PF4) is an abundant platelet alpha-granule C-X-C chemokine that has weak chemotactic potency but strongly inhibits hematopoiesis through an unknown mechanism. We find that PF4 binds to human CD34+ hematopoietic progenitor cells (HPCs) with a median effective concentration of 1 microg/mL but not after exposure to chondroitinase ABC. PF4 enhances adhesion of HPCs to intact stroma. Committed progenitors also adhere avidly to immobilized PF4. This adhesion is time-dependent, requires metabolic activity, causes cytoskeletal rearrangement, and induces cell-cycle inhibition. Using extracellular acidification rate to indicate transmembrane signaling, we find that interleukin-8 (IL-8), but not PF4, activates CD34+ progenitors, and PF4 blocks IL-8-mediated activation. Surface plasmon resonance analysis shows that PF4 binds IL-8 with high (dissociation constant [Kd] = 42 nM) affinity. Nuclear magnetic resonance analysis of IL-8 and PF4 in solution confirms this interaction. We conclude that PF4 has the capacity to influence hematopoiesis through mechanisms not mediated by a classical high-affinity, 7-transmembrane domain chemokine receptor. Instead, PF4 may modulate the hematopoietic milieu both directly, by promoting progenitor adhesion and quiescence through interaction with an HPC chondroitin sulfate-containing moiety, and indirectly, by binding to or interfering with signaling caused by other, hematopoietically active chemokines, such as IL-8.[1]

References

  1. Platelet factor 4 promotes adhesion of hematopoietic progenitor cells and binds IL-8: novel mechanisms for modulation of hematopoiesis. Dudek, A.Z., Nesmelova, I., Mayo, K., Verfaillie, C.M., Pitchford, S., Slungaard, A. Blood (2003) [Pubmed]
 
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