GROWTH-SUPPORTING ACTIVITIES OF FIBRONECTIN ON HEMATOPOIETIC STEM PROGENITOR CELLS IN-VITRO AND IN-VIVO - STRUCTURAL REQUIREMENT FOR FIBRONECTIN ACTIVITIES OF CS1 AND CELL-BINDING DOMAINS

Fibronectin (FN) is supposed to play important roles in various aspect s of hematopoiesis through binding to very late antigen 4 (VLA4) and V LA5. However, effects of FN on hematopoietic stem cells are largely un known. In an effort to determine if FN had a growth-supporting activit y on hematopoietic stem cells, human CD34(+)/VLA4(bright)/VLA5(dull) h ematopoietic stem cells and a murine stem cell factor (SCF)dependent m ultipotent cell line, EML-C1, were treated with or without FN in a ser um and growth-factor-deprived medium, and then subjected to clonogenic assay in the presence of hematopoietic growth factors. The pretreatme nt of the CD34(+) cells with FN gave rise to significantly increased n umbers of granulocyte-macrophage colony-forming units (CFU-GM), erythr oid burst colony-forming units, and mixed erythroid-myeloid colony-for ming units. In addition, the numbers of blast colony-forming units and CFU-GM that developed after culture of EML-C1 cells with SCF and the combination of SCF and interleukin-l, respectively, were augmented by the pretreatment with FN. The augmented colony formation by FN was com pletely abrogated by the addition of CS1 fragment, but not of GRGDSP p eptide, suggesting an essential role of FN-VLA4 interaction in the FN effects. Furthermore, the effects of various FN fragments consisting o f RGDS-containing cell-binding domain (CBD), heparin-binding domain (H BD), and/or CS1 portion were tested on clonogenic growth of CD34(+) ce lls. Increased colony formation was induced by CBD-CS1 and CBD-HBD-CS1 fragments, but not with other fragments lacking CBD or CS1 domains, s uggesting that both CS1 and CBD of FN were required for the augmentati on of clonogenic growth of hematopoietic stem/progenitor cells in vitr o. In addition to the in vitro effects, the in vivo administration of CBD-CS1 fragment into mice was found to increase the numbers of hemato poietic progenitor cells in bone marrow and spleen in a dose-dependent manner. Thus, FN may function on hematopoietic stem/progenitor cells as a growth-supporting factor in vitro and in vivo. (C) 1998 by The Am erican Society of Hematology.