title: Platelet factor 4 promotes adhesion of hematopoietic progenitor cells and binds IL-8: novel mechanisms for modulation of hematopoiesis.
abstract: 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.
authors.affiliation: Department of Medicine, Division of Hematology, Oncology, and Transplantation, Stem Cell Institute, Minneapolis, MN, USA. dudek002@umn.edu
authors.forename: Arkadiusz Z
authors.initials: AZ
authors.lastname: Dudek
authors.forename: Irina
authors.initials: I
authors.lastname: Nesmelova
authors.forename: Kevin
authors.initials: K
authors.lastname: Mayo
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Verfaillie
authors.forename: Simon
authors.initials: S
authors.lastname: Pitchford
authors.forename: Arne
authors.initials: A
authors.lastname: Slungaard
mesh_terms: D018952:Antigens, CD34 / Q000032:analysis; D019921:Biotinylation; D001854:Bone Marrow Cells / Q000166:cytology; D002448:Cell Adhesion / Q000187:drug effects*; D002455:Cell Division; D002478:Cells, Cultured; D019765:Chondroitin ABC Lyase / Q000494:pharmacology; D003080:Cold Temperature; D003114:Colony-Forming Units Assay; D017077:Culture Media, Conditioned; D006410:Hematopoiesis / Q000187:drug effects*; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism* / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D010978:Platelet Factor 4 / Q000378:metabolism* / Q000494:pharmacology*; D015398:Signal Transduction; D017154:Stromal Cells / Q000166:cytology; D020349:Surface Plasmon Resonance
chemical_list: D018952:Antigens, CD34; D017077:Culture Media, Conditioned; D016209:Interleukin-8; D010978:Platelet Factor 4; D019765:Chondroitin ABC Lyase