Effects of surface-immobilized stem cell factor on the differentiation and proliferation of hematopoietic cells

Stem cell factor (SCF), in combination with other cytokines, supports the growth and maintains the viability of primitive hematopoietic stem cells. Membrane-associated and soluble SCF have been shown to be functionally different. We hypothesized that reduced internalization of the soluble extracellular domain of SCF would be sufficient to generate the distinct physiological differences caused by stromal-cell lines expressing membrane-bound SCF. In order to develop a well-defined presentation of bound SCF, we immobilized SCF through the biotin-neutravidin interaction and evaluated its impact on the M07e hematopoietic cell line and human CD34-selected primary cells. Parameters controlling SCF biotinylation and immobilization were examined in order to optimize the bioactivity of surface-immobilized SCF. We show that chemically immobilized SCF can mimic the effects on signal transduction in M07e cells induced by membrane-bound-SCF expressing stromal cells. SCF receptor dimerization, c-kit tyrosine autophosphorylation, and MAP kinase activation of M07e cells cultured with immobilized SCF are prolonged, while soluble SCF induces a transient activation of these signaling molecules. Correlation of cell proliferation with cell attachment indicates that these effects are specific to surface-immobilized SCF. Surface-immobilized SCF also induces a greater expansion of human mobilized peripheral-blood CD34+ cells. Using a previously developed SCF receptor trafficking model, we made an effort to quantitatively understand the effects induced by surface-immobilized SCR The manipulation of SCF presentation may provide a means to modulate the fate of hematopoietic cells and a well-characterized system to study the SCF to c-kit interactions in juxtacrine signaling.