Analysis of steel factor (stem cell factor) isoforms in the hematopoietic microenvironment.

Hematopoietic cell proliferation and differentiation is dependent in part on the interaction of hematopoietic stem and progenitor cells with cells making up the hematopoietic microenvironment (HM). Direct cell-cell interactions appear to be important in the hematopoietic microenvironment. One mechanism to accomplish such interactions is the expression of membrane-associated growth factors. Stem cell factor (SCF), the product of the steel gene in mice (also termed mast cell growth factor, c-kit ligand, or Steel factor), is a hematopoietic growth factor demonstrating substantial synergistic activity with a number of other cytokines on primitive hematopoietic stem and progenitor cells. Cloned SCF cDNA encode both a membrane-associated and a secreted growth factor. The physiologic relevance of these isoforms is unknown at present. In order to better understand the physiologic role of these SCF isoforms in normal hematopoiesis, we have established multiple stromal cell lines expressing each isoform. We have used these cell lines to study protein sequences that are required for appropriate post-translational processing of SCF protein in HM-derived stromal cell lines. These lines have also been used to study the interaction of membrane-associated and secreted SCF with murine and human hematopoietic cells. In addition, we have generated transgenic mice expressing each isoform of murine and human SCF. These transgenic mice will be used to study the function of each isoform in hematopoiesis in vivo.