ANALYSIS OF STEEL FACTOR (STEM-CELL FACTOR) ISOFORMS IN THE HEMATOPOIETIC MICROENVIRONMENT

Hematopoietic cell proliferation and differentiation is dependent in p art 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 microenv ironment. One mechanism to accomplish such interactions is the express ion of membrane-associated growth factors. Stem cell factor (SCF), the product of the steel gene in mice (also termed mast cell growth facto r, c-kit ligand, or Steel factor), is a hematopoietic growth factor de monstrating substantial synergistic activity with a number of other cy tokines on primitive hematopoietic stem and progenitor cells. Cloned S CF cDNA encode both a membrane-associated and a secreted growth factor . The physiologic relevance of these isoforms is unknown at present. I n order to better understand the physiologic role of these SCP isoform s in normal hematopoiesis, we have established multiple stromal cell l ines expressing each isoform. We have used these cell lines to study p rotein sequences that are required for appropriate post-translational processing of SCF protein in HM-derived stromal cell lines. These line s have also been used to study the interaction of membrane-associated and secreted SCF with murine and human hematopoietic cells. In additio n, me have generated transgenic mice expressing each isoform of murine and human SCF. These transgenic mice will be used to study the functi on of each isoform in hematopoiesis in vivo.