Abstract
One of the mechanisms by which normal hematopoietic progenitor cells remain localized within the bone marrow microenvironment is likely to involve adhesion of these cells to extracellular matrix (ECM) proteins. For example, there is evidence that uncommitted, HLA-DR-negative progenitor cells and committed erythroid precursors (BFU-E) bind to fibronectin. However, fibronectin is not known to mediate binding of committed myeloid (granulocyte-macrophage) progenitors, raising the possibility that other ECM proteins may be involved in this process. We investigated the binding of the MO7 myeloid cell line to a variety of ECM proteins and observed significant specific binding to collagen type I (56% +/- 5%), minimal binding to fibronectin (18% +/- 4%) or to laminin (19% +/- 5%), and no binding to collagen type III, IV, or V. Similarly, normal bone marrow myeloid progenitor cells (CFU-GM) demonstrated significant specific binding to collagen type I (46% +/- 8% and 47% +/- 12% for day 7 CFU-GM and day 14 CFU-GM, respectively). The ability of collagen to mediate binding of progenitor cells was not restricted to the myeloid lineage, as BFU-E also showed significant binding to this ECM protein (40% +/- 10%). The binding of MO7 cells and CFU-GM was collagen-mediated, as demonstrated by complete inhibition of adherence after treatment with collagenase type VII, which was shown to specifically degrade collagen. Binding was not affected by anti-CD29 neutralizing antibody (anti-beta-1 integrin), the RGD-containing peptide sequence GRGDTP, or divalent cation chelation, suggesting that collagen binding is not mediated by the beta-1 integrin class of adhesion proteins. Finally, mature peripheral blood neutrophils and monocytes were also found to bind to collagen type I (25% +/- 8% and 29% +/- 6%, respectively). These data suggest that collagen type I may play a role in the localization of committed myeloid and erythroid progenitors within the bone marrow microenvironment.
