Biological activities and potential therapeutic uses of steel factor. A new growth factor active on multiple hematopoietic lineages.

Recently, a novel growth factor has been cloned that has growth promoting activities on a wide variety of hematopoietic cell lineages. This factor has been referred to as mast cell growth factor, stem cell factor, or kit ligand, and will be referred to here as steel factor. Steel factor stimulates the growth of cells via its interaction with the c-kit proto-oncogene, which is a tyrosine kinase receptor that is expressed on the surface of a number of different cell types. In addition to its effects on hematopoiesis, this factor also plays a role in the development of melanocytes and germ cells. The discovery of this growth factor provided the final piece of the puzzle to explain the molecular defects associated with several well known genetic mutations in mice, and has opened the door to understanding the role of this factor in development. Similar genetic defects may exist in humans as well. The aim of this paper is to review the biological structure and activities of this new growth factor, and to discuss its potential applications in clinical medicine.