THE EFFECT OF ALPHA(4)BETA(1)-INTEGRIN BINDING SEQUENCES OF FIBRONECTIN ON GROWTH OF CELLS FROM HUMAN HEMATOPOIETIC PROGENITORS

Highly regulated interactions between adhesion receptors on progenitor cells and their extracellular matrix ligands are essential for the co ntrol of hematopoiesis in bone marrow stroma, We have examined the rel ationship between alpha(4) beta(1)-integrin-mediated adhesion and grow th of CD34(+) cells by assessing their adhesive and migratory patterns of proliferation in a mixture of hematopoietic growth factors in the presence of different recombinant fragments of the HepII/IIICS region of fibronectin, CD34(+) cells were isolated from cord blood and placed in culture wells containing serum-free medium and growth factors, Wel ls were precoated with either the H120 fragment of fibronectin, which contains three alpha(4) beta(1)-integrin binding sites, or the H0 frag ment, which lacks the two highest affinity alpha(4) beta(1) binding se quences, Proliferation of single cells of CD34(+)38(+)DR(+) and CD34()38(-)DR(+) phenotypes occurred in contact with the H120 substrate and was associated with migration, Larger numbers of cells were used to q uantitate proliferative responses. Cells growing in wells coated with H120 formed attachments to the base of the wells throughout the cultur e period. Higher total cell counts were consistently found in wells co ated with H120 compared with HO and bovine serum albumin controls. The difference was first apparent at day 8 of culture and reached a maxim um at days 11 through 13, when expansion with H120 was a mean of 1.8-f old higher than that seen with HO (P less than or equal to.0001), The greatest expansion (2.25-fold) with H120 compared with HO was seen whe n the growth factor concentrations were reduced to 1/16 of the standar d levels (P less than or equal to .001), The increase in total cell nu mbers was not at the expense of CD34(+) cells as numbers of these were similar in H120 and control cultures. These results provide evidence for synergy between growth factors and integrins that may be relevant to understanding hematopoiesis in marrow stroma. (C) 1998 by The Ameri can Society of Hematology.